# 99.5%? Is it possible?



## Montecristo (Jun 16, 2010)

Is it possible for a refiner on lots of 4,000 grams or more of clean karat scrap already melted into a bar to pay 99.5% and still make money, while still giving an accurate assay?

(What I mean by clean is the bar will contain nothing else besides Au, Ag, Cu, Ni and Zn.)


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## Montecristo (Jun 16, 2010)

I don't think it is possible for a refiner to give a true payout of 99.5% and still make enough money to stay in business without fudging on the assay.

I only bring it up because someone was telling me that xxxxxx Refiner is paying 99.5% and that I should be sending my materiel there. Obviously, I don't get that kind of return now, so I started thinking. And the more I thought about it, the more I came to the conclusion that it's not very likely that the refiner could actually pay out that much on an honest assay. They probably are banking on people not actually knowing exactly what they are shipping off to be refined and picking up the extra profit on a lower assay.

I thought I would run it by you guys to see if you all came to the same conclusion.


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## goldsilverpro (Jun 16, 2010)

I remember a cartoon in an ad, about 20 years, in a recycling magazine where a refiner had his arm around the customer's shoulder and he winked and said, "You're such a great guy, we'll refine your scrap at no charge"


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## 4metals (Jun 16, 2010)

It comes down to a question of scale, aqua regia refining in large enough lot sizes, costs a medium sized refiner about 1/4 of 1% for labor chemicals treatment of waste etc. Assuming your process yields 99.875 accountability on lot by lot basis and the balance is retrieved from residues, slags, baghouse dust, etc. This says nothing of insurance, security and overhead. 

So if you process a Pfaudler full of karat you can still make a profit at 1/2%. But there is no room for error. Those rates are for the big refiners and only given on larger lots. So if you're not dealing with JM Branford, Metalor' Republic, or Ohio precious metals, watch your back.


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## Montecristo (Jun 17, 2010)

4metals and nickvc,

Thanks for the replies. So, both of you are saying that it is possible, but not likely, unless we're dealing with 100+ oz. lots of recoverable metal and the refiner can sell his bars directly to the bank who sells them to the COMEX?


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## nickvc (Jun 17, 2010)

To be honest unless that was a weekly amount they probably wouldn't offer those sorts of terms, as I said they need to have the plant running 24/7 to make it pay and I dread to think of the volumes the big boys can handle and need to keep the plant near capacity. When you have access to the markets you can sell volumes you don't have but delivery in full is usually required within 28 days, fortunes can be made or lost but no manipulation of the markets ever takes place :roll:


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## 4metals (Jun 17, 2010)

Monte,

The attractive rates are the kind given to those who ship upwards of 5000 ounces fine gold content weekly. With the quantities you're talking you could get rates around 1% if you shop around in NYC and if you can produce it week after week. Make sure you are there to witness or the quoted rate means nothing.


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## Montecristo (Jun 18, 2010)

I'm not going to chase the extra 1/2% by switching refiners, I sincerely doubt they would deliver that kind of return on a fair assay. I'm pretty comfortable and fairly confident with the refiner I'm using now, but you guys have given me something to think about.

Thanks for the replies.


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## HAuCl4 (Jun 18, 2010)

You can Miller process your stuff in a few hours for a lot less than 0.5% costs and keep the silver. You'd be delivering 995+ or better material to the refiner/buyer, which would probably pay you very near spot price.

On the other hand, 0.5% is about $6 per ounce...so really all this cost savings, etc. are dwarfed by price risk. If you are already incurring price risk, and only sell and settle when you want, then consider refining yourself with Miller process.

Forget about Wohlwill and 9999, etc., etc. That's extremely expensive to setup and operate properly. But Miller is cheaper and simpler than acid methods for lots above 100 OZ, produces Good Delivery grade (995+), and the silver is yours to keep or sell separately.

If all you have is a one-off batch and/or your time is better spent sourcing material, then ignore everything I typed and go with a refiner you trust and negotiate your terms. It's very hard to operate successfully anything gold related with anyone other than yourself involved, due to fidelity/honesty issues. Even with someone else that is honest, the suspicions will drain your mental resources. Gold brings out the best and the worst in people, if you see what I mean.


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## nickvc (Jun 19, 2010)

I really can't agree with you on the cost of setting up the Miller process , the largest problem is having the proper extraction and fume treatment which is really expensive and will have the Environment Agencies crawling over you to check on the fumes released into the atmosphere, not to mention the toxic chloride waste left over which contains precious metals which will need further treatment to recover them and render the material safe to dispose of. One of our leading lights 4metals was involved in setting up a version of this and I hope he can give us an idea as to cost and the issue of total reclamation of all the precious metals from the process. The wet process can be very effective for large volumes as GSP, Harold and others will bear witness and in the right hands very quick with reasonable accountability and is well documented which the Miller process certainly isn't.


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## Oz (Jun 19, 2010)

I have been seeing a lot of talk recently about the Miller Chlorine Process on the forum. I have to question whether that those that are recommending it to others have practical experience in using this process themselves. The process is not all that complicated from a technical viewpoint but I have yet to see it as a low cost process for small quantities of gold. With all this talk I would like to see someone come forward with how they are setting up and using it for processing lots of 5 ounces and up and how they can justify the capital investment to do it on that scale. 

Theoretical thought processes are fine for discussion but it is a hard sell to advise someone to use a process that they have not used successively themselves. Beyond that one must look at if it is cost effective on the volume they run in a typical week. I would like to hear from someone that is currently doing this for a cost that is less than traditional refining on lots of 5 ounces Au. I chose the 5 ounce mark since it fits with a moderate refiner as a per week through-put (I do not see how one can pay their bills on less than 5 ounces per week). That is also more gold than 95% of our typical forum members will process in a year.


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## HAuCl4 (Jun 19, 2010)

You can't bubble neither air nor chlorine through a 5 Oz melt. I have done it/seen it done in 3 Kg/15 Kg (around 100/400 Oz) of material.

This process is not cost effective for 1-off batches, and I would not use it unless a minimum steady 100 Oz per week of material could be sourced.

I do not professionally refine gold/silver these days.

Properly setup this has less fumes than the equivalent size acid operation. Especially if you use an electric furnace. All the "fumes problem" has been blown out of proportion in the literature, but it is understandable if you use a gas-fired furnace and just start blowing chlorine in an open crucible...all the fumes mix with the flue from the furnace and then you have a huge "fumes problem".

And you are right, I do not currently process even 5 Oz of material per year, and all this is just a hobby/mental exercise to avoid Alzheimer's for me and keep myself busy somehow.

But since I visited the Royal Canadian Mint and also met/spent several hours with Mr. Robert Trepanier (ex Refinery Manager of same) in Caracas in 1988, and setup a small refinery using same process back then, maybe I have a clue or two, but then maybe not. I remember at the time discussing how they were changing all parting furnaces to induction from gas. And how he was very impressed at what we had achieved locally with a normal electric (non-induction) furnace.

Since I was screwed in business from that deal, for one reason or another, I never re-entered the "gold business", till I joined this forum, first as JohnW, but since I lost my password to my email account, I decided to create another without making any noise.

I have read passionately the info in this forum, where I learned a lot, especially from Steve and his ideas of chemical loops, where little/no chemicals are wasted, and the per-sulfuric cell process which was completely new to me.

I have been "advised" to blow myself up once, to shut up because I'm a newbie that knows nothing, and that I am always asking the wrong questions... just for being creative.

Now even my credibility is attacked/questioned/whatever. I have no desire, time or inclination to defend my views or knowledge anymore.

From now on I will just shut up, read, learn whatever is there to learn, and wish you all a happy refining experience using whatever methods you like.


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## nickvc (Jun 19, 2010)

This is an open forum and ideas and discussion of ideas is part of what makes it work. The comments I made are based on what little I could glean from the literature on the Miller process and from some one I know who is at present trying to install it into his new refinery, if I'm wrong please enlighten me, I don't claim to be an expert in any field so I would love to hear how you or anyone else set up and ran the Miller process and at what cost what equipment you used and what problems you encountered and how you over came them .The same I'm sure goes for Oz, we just don't see how you can set up and use this process at reasonable cost and safely so again please tell us your story I'm sure the whole forum will be reading your posts with rapt attention but do expect questions and no doubt some cynicism until the whole story is told. Get typing you have me fascinated already even though I'll never do it now


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## Oz (Jun 20, 2010)

HAuCl4,

I have seen the Miller process brought up here and in other threads. Perhaps my choice of threads to reply in was poor but it was the most recent I read. I had gathered the impression from these different threads that some might have felt that this might be viable for smaller lots. It is possible that someone here may have experience that shows smaller scale as viable, I am doubtful. You were clear that you were recommending this for 100 ounces and up. 

I would think it was reasonable to ask if any that were recommending the process were actually using it, as well as if they are using it if they are able to do so on small lots. To be clear I have no practical experience with it so I was asking for clarification from those that do. I would enjoy any discussion of it but find it helpful to know whether what is being presented is theoretical or from personal experience. 

Since you have clarified by saying that you set up and ran the Miller Chlorine Process successfully in a small refinery of your own I would be particularly interested in what you have to say of it. You are the first that I know of on the forum that has instituted this process into their refinery.


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## nickvc (Jun 20, 2010)

Oz I believe there are several but their lips seem sealed, actual hands on experience is really hard to uncover and I'm really looking forward to having a tour round my friends refinery when its up and running, I know that his costs in setting up his refinery is over $750,000, admittedly it covers a furnace that can melt around 100 kilos a time but the cost of the extraction equipment is horrendous apparently due to the fact that the gold chloride is happy to be follow the extracted fumes into the system so recovery is a must to collect the values. I hope our friend HAuCl4 will give us all an insight into what he did and how employing the Miller process, it might well be out of nearly all of our reach on the forum but I for one will be reading every word that he hopefully posts recalling his experiences.


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## HAuCl4 (Jun 20, 2010)

Considering that my equipment setup costs were less than $7,500 complete and that I never lost more than 1/1000th of the gold processed, you probably don't want to hear my story, because it is already unbelievable for most.

$750,000...whew...what a waste. I'm hoping that he spent 95% of that in the vault, the building and other security mechanisms...

I'll type 1 or 2 pages with tips and will try to answer questions to the best of my ability...

My "fumes problem" processing equipment was a state of the art $300.00 vacuum cleaner and 2 drums filled with soda ash and water. We got some silver out of the sludge and insignificant amounts of gold, and no fumes on the exhaust only dry air. I carefully processed this sludge once only to establish the what is what, and then it was just mixed with the low grade slags, sweeps, etc. and smelted once a year.

The gold stayed 97-99% in the crucible charge, in the copper/silver chloride slags 1-3% (recovered as a silver dore cullot inmediately with a sprinkle of soda ash, and re-melt), and maybe a 0.2% as metal in the cracks of the crucible, fully/mostly recovered every 4-5 melts when the crucible was taken out of commission and crushed. The bigger the charge the smaller % that stayed "in transit".

We used AP Green #14 crucibles (Same as the Royal Canadian Mint at the time, why reinvent the wheel right?) at a cost around $15 a piece at the time, and crucible covers for same, in which we drilled a hole for the clay tube used for injecting. If I had to do it again today, I'd try to use state of the art nonporous sintered zirconia crucibles at slightly higher cost, but much higher number of melts per crucible, and a cheap induction furnace.

We built and optimized an electric furnace around that crucible setup. A simple but not trivial cheap furnace setup was reached after a little trial and error.

All the fumes came out from around the injecting clay tube and were promptly sucked in by the vacuum cleaner, and soda ash drum. The biggest amount of fumes occurred when pouring the chlorides slags into another crucible, the vacuum cleaner took care of it, but we also used masks for safety. A couple good electric fans kept the air circulating.

The batches were mainly mine dore at around 90% gold, but sometimes a batch of scrap karat here and there. We injected a little pure air first instead of chlorine to scorify instead of chloridize. The difference in costs was negligible, but I believe it helped on the total removal of copper and other base metals before starting with the chlorine.

9985 was the best we achieved even with extended exposure to chlorine. (And no we did not lose any significant amount of gold as chloride. This is a myth. I can see how one could lose a lot of gold in the flue in a gas fired, open crucible, chlorine splashing operation, but not with this setup.)

Maybe the crucible cover and the mix of glass and borax I used for the flux was a factor in the negligible losses of gold as chloride. There was also a very clear transition when reaching the end of operation, and where chlorine injection had to be slowed down in the elimination of the last remaining silver. If you were paying attention this posed no problems. The purple stain on the clay tube was very distinctive, and marked the near-end of the process. We pushed this point often at a slow chlorine rate in the hopes of ever increasing the fineness of the final product, but after a while it was just a waste of time and chlorine, and negligible gold chloride. Remember all these losses get smaller as a % as the charge gets bigger, and even 1 gram of gold makes A LOT of gold chloride fumes to be detected. And we always had the $300 vacuum cleaner!. :roll: 

The silver chloride we recovered using sulphuric and iron, like explained in the literature. We did not refine silver except for a small amount in a thum cell, to be used in the fire assays. This is another story and fully documented in the literature.

Everyone that I have ever met that used Miller to this date (a handful maybe), still regards this process as "secret" and few if any are forthcoming with details. Mr. Trepanier was a notable exception 20+ years ago, and now you are stuck with me, as far as I know... :lol:, but maybe others that have been quiet till now, will share their experience.

There were no platinum group metals present.


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## nickvc (Jun 20, 2010)

Now I love this and you're right the process is clouded in mystery and rumour and hard facts and figures are non existent to anyone outside of the companies using it. I'm shocked that there was so little fume after been led to believe that was the main concern but not surprised as it helps keep the process supposedly beyond the educated amateur. I'm going to read your post over again and try not to be so shocked at the simplicity. Fantastic information, I bet you will not be popular with the big boys in the refining world for sharing this with the forum. I think my friend is installing other refining equipment but until I get a look round I won't know but I do remember him saying he was having trouble getting the clay pipes to use?


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## HAuCl4 (Jun 20, 2010)

Morgan crucible makes and sells clay pipes. Nowadays I know how to make my own, but I don't need to!. Back in that day (there was no internet I remind you!), we obtained tubes made of zirconia that were used in the manufacture of thermocouples for harsh environments. (We got them free at first from the discards!). Each tube would last forever with certain care. There are many internet sources now, just google "clay tubes". So easy now. The hard part is getting the material to refine!. At $1,200 an ounce this is no mystery. Too little gold going around, and too many "refiners".

Re. the "fumes" and the "chlorine": Any pool boy that maintains a medium sized swimming pool at a country club, handles more chlorine per year than most refiners...  . He keeps it dilute in water though!. :shock:


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## nickvc (Jun 20, 2010)

Well I have re read your post twice and all I can say is FANTASTIC..... :lol: I never would have believed that a process that is over a century old could still be so little documented until I tried to find out how it worked and what dangerous fumes and by products :roll: were likely to be encountered, now I know why. Thank you for sharing that and for once the information really is gold....I'm pleased you came back onto the forum as an active member, let's see if anyone can fault this who has actually done it!


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## qst42know (Jun 20, 2010)

If clay pipes are hard to find, isn't fused quartz tubing capable of doing this job?


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## HAuCl4 (Jun 20, 2010)

Here are 3 photos taken this afternoon by a friend. Quality is not the best.

One is of a new/untreated crucible with the injection tube in position. Missing (don't have them them), are the slotted crucible cover, the furnace, and the vacuum cleaner "fume processing" device. Maybe I'll make a diagram later this week.

Then you have the tube with characteristic purple stain (this tube bottom part was broken). And another of same tube with the latest new all time high price of last Friday for the August delivery of COMEX gold.

That ceramic tube is about the only "evidence" I still have that I once processed gold using Miller chlorination. An expert connoisseur will recognize it inmediately as authentic.


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## HAuCl4 (Jun 21, 2010)

nickvc said:


> I'm shocked that there was so little fume after been led to believe that was the main concern



Oh no. There are enough fumes to be dangerous, but no fumes problem if you control them at the source before they get mixed with more air.

This was easily controlled with the vacuum cleaner during the process. When pouring the slags, the chlorine injection was stopped and the tube removed, so no more chlorine, and a fume hood was connected to the vacuum cleaner and brought close to the pouring spout, and we wore masks at this point. This was the point of "maximum amount of fumes".

Also this pouring of chloride slags (into another cold crucible) had to be done carefully, because silver chloride at that temperature looked like chicken soup, only more fluid, and it was fuming. Gold stayed in the crucible, and we added more borax and glass at that point after most of the slags were out. Fumes after that were a lot less.

My guess is that with a comparable acid system for the same volume of material, the volume of fumes to control would have been bigger, although of a different nature, and not necessarily easier to process.


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## 4metals (Jun 25, 2010)

The corrosivity of the chlorine gas is an issue, the piping to the furnace and the storage of the bottles of gas were a major concern to local firemen. I never had much issue with the gas coming out of the reaction either. I never used an expensive Cottrell electrostatic exhaust either. I exhausted into a 6" quartz glass tube which switched over to CPVC when it was cooler at a distance of 10 feet from the furnace. The chloride fume is water soluble so it actually scrubbed easier than a NOx fume. The base metals were easily dropped from the scrubber water for waste treatment using caustic.

Not pushing the reaction to get three nines is also smart. If you stop when the clay tube turns purple all of the gold is in the pot. I melted 700 ounce lots of karat (fine gold content) and used French Clay parting crucibles which were used for 1 melt. When the clay tube indicated the reaction was complete I pulled the tube and removed the crucible to let it cool. I never bailed chlorides off the top. In the morning the cold crucible was smacked with a hammer and the 99% fine gold was on the bottom and the silver chlorides had solidified to look like the top of a lemon meringue pie. These chlorides contain between 1/2 and 1 percent by weight fine gold beads which were trapped in the thick foamy chloride. They were crushed and reduced to metal and processed in a silver cell to recover the gold as a slime. 

There have been many authors who have detailed the process used at large refineries, these reports combined with a knowledge of chemistry and the ability to experiment helped detail the process. 

I still wouldn't take the chlorine gas lightly, it will kill you if there is an accident and it will be a painful choking death. For this reason I advise people to stay away, it requires meticulous maintenance of the delivery system and safety systems for the one time when it goes bad. Continued success makes us complacent, then it happens. Look at what happened in the Gulf.

Considering the non chemical backgrounds of some members I would never recommend the process.


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## HAuCl4 (Jun 26, 2010)

Nice idea of using the crucible just once and crushing it. I bet you had hardly any "fumes problem". We recovered most of the gold inside the slags by sprinkling soda ash in the molten slags (in another crucible).

The chlorine cylinder (we had one at a time only) was kept inside a large water tank outside the room (in case of leaks), and a plastic hose inside a hard plastic tube was ran into the furnace room. We never had any incidents, so probably I was taking more risks than I knew at the time.


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## 4metals (Jun 26, 2010)

I chose CPVC because of the temperature. Something about exhausting over a furnace with plastic made me nervous, that's why I fed the fume directly over the furnace into a quartz glass pipe for 10 feet before transitioning to CPVC. (Did you ever see a PVC fueled fire? I did once in a plating shop it was like someone threw kerosene on it.) I suppose the physical scrubber could have been PVC but the deal I got at the time had it all in schedule 80 CPVC. The scrubber could have also been fiberglass, I like the vinyl ester resin as it withstands the corrosivity well. 

Using a single cylinder and having it in a water tank is a good approach but we were doing 6 to 10 melts per day so we needed a bank of 8 tanks. Because of the way they were delivered and the distance, we purchased chlorine 4 tanks at a time. They were outside, 100 feet away from any building and enclosed by fire department rules. All of the delivery piping was double walled and we even ran it inside a dedicated 6" exhaust duct constantly pulling air out of the shop. That duct ended about 5 feet from the point of use. A pressure gauge told us the line pressure and in case of a leak in the feed the air was already going out. Fortunately the exhaust ducting on feed piping was never put to the test. When I design something I always make it like I have to be the guy over the furnace, sometimes I was, so I'm kind of anal about the safety I build into a process. 

We never processed the crucibles separately from the regular melting room crucibles and stir rods, so I don't know how much metal was in the crucibles but I do know that our accountability of the gold between the melting and the slimes from the silver cell ran inside the margin of error for fire assays so it was negligible.

My point again about Chlorine gas is you can make it safe, even super safe, but I don't believe you can make it backyard safe!


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## HAuCl4 (Jun 27, 2010)

Maybe a little paranoid about the chlorine? :lol: Although 8 tanks in a fire could easily get out of hand...

It looks very safe and simple and not too costly. I think you did good.

Can you describe further your furnace/crucible setup?. Electric, induction or gas-fired?. Tilting furnaces?. Crucible covers?. You already said that you didn't slag the melts. 

Did you further flux the pure gold afterwards with nitre/other?. What was your average fineness stopping at just the "purple stain" point without pushing further?.


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## 4metals (Jun 27, 2010)

The melting was done in an induction furnace, I prefer the push up type. I never covered the crucible because the ability to see the melt and control the chlorine feed rate was important to me.

The purity averaged 99.2% with silver being the remaining impurity. For that reason toughening with niter wouldn't help much. 

Our goal for purity was .9995 back in the day so upgrade was necessary. For reasons of speed, and so no metal was ever out of the vault overnight, the 99 fine gold was shotted and digested in aqua regia. The acid stayed a beautiful red color as there were no base metals and due to careful nitric additions we were gassing by lunchtime. This process produced .9995 metal or better every time and acid use was half that of putting up karat gold directly. An added benefit was waste treatment was easy due to the lack of significant base metals. 

If I had to do it over, I would consider solvent extraction to get to .9999 but in the early '80s I was happy with removing the bulk of the impurities quickly with chlorine followed by an aqua regia cleanup.


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## HAuCl4 (Jun 28, 2010)

Wow. 1 day refining with AR!. What vessels did you use to digest those big amounts in AR?. Glass or something else?. I bet you had a "fumes problem" bigger than with Miller.

How/to whom did you sell your refined products?. Mint or something?. Did they pay full price?.

I have avoided AR like the plague, except for a few experiments and batches containing palladium and platinum. Call me paranoid but never liked the idea of a broken vessel full of gold in solution, even with safety measures, it could get expensive very fast.

I still cringe when I see videos of people with a glass flask on top of an electric heater, nothing underneath, and dissolving gold.

After the failed Miller refinery "experience", all I did was inquarting 23-77 with silver and nitric digesting, whenever I had accumulated enough from small batches and running low on fine. It has been a hobby more than a business (or never a business, but didn't cost me money, but could never live off it??. Maybe that's better put.). I routinely got 997-998 with inquarting, and that was good enough to exchange with the jewelers. In the very rare cases where my gold didn't roll like butter, fluxing with nitre and/or ammonium chloride fixed the problem.

I always kept the best pieces that I bought directly (not from jewelers) and cleaned them and attempted to resell them at a premium instead of melting them and refine them.

Haven't refined anything in years, but maybe soon. Will have to borrow a torch here, and a crucible there...and steal some cookware from my wife. :roll: 

Most of all what I liked best was to learn about human nature, if you get my drift...


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## 4metals (Jun 28, 2010)

250 gallon steam heated Pfaudlers will handle 6000 ounces per digestion, considering the gold was in at 99% that's 5900 plus ounces out per batch, it went up quickly and scrubbing with caustic in one scrubber and peroxide in the other there was good fume control.

The gold was shipped overseas and Brinks was there every night for bars fine going out and karat coming in. They paid a few cents under per ounce, like $.20, if I remember. 

Made a lot of money but worked a lot of hours, I like the consulting business much more and the hours are better.


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## HAuCl4 (Jun 29, 2010)

Very nice. Excuse my ignorance: What is a "Pfaudler"?.

I once helped "improve" an AR digesting setup made of double walled PVC, but I was never happy with the original design, and how they handled the filtering, etc afterwards, etc. I collected my small consulting fees, left them a list of recommendations, and moved on. They didn't/wouldn't want to change much, just to take care of the fumes, and some safety aspects. It looked very unprofessional setup and handling. Afterwards, I heard they broke a 5 gallon pyrex full of dissolved gold and had to "mop it", etc, etc.

I stopped giving free/unsolicited advice to people not long after, and started charging more for my services!.

Edit: Found in google: http://www.pfaudler.com/


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## HAuCl4 (Jun 29, 2010)

Do those glass lined reactors/vessels wear inside?. How did you go about that?. 

How did you filter afterwards, before precipitation?. Dropping with SO2 I presume or other?.

I'm fascinated!. You are/were the largest commercial refiner-person I have ever met, asides of Mr. Trepanier from the Canadian Mint!.

Thanks for the answers!.


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## goldsilverpro (Jun 29, 2010)

Pfaudler is probably the primary manufacturer of glass-lined kettles/reaction vessels. The type I always used was made of steel and had a thick (I would guess about 1/4"-1/2") blue glass lining on the inside which was impervious to acids. There was a steam jacket around it for heating the solution inside. I usually used a 50 gallon one but they are available in any size, starting with 5 - 10 gallons. They cost many thousands of dollars new but there are tons of used ones available. For dissolving large quantities of metal, like karat gold, they can't be beat. Never buy a used one if any part of the glass lining has been damaged or patched. They have patch kits but they're not worth a damn. About the only way to properly repair the glass is to send it back to Pfaudler for re-lining - terribly expensive. When putting material into the kettle, don't drop heavy parts into it. I always placed the material in it carefully before adding the solution, to avoid chipping the glass. The glass is actually quite tough and durable but, you have to still be very careful.

I tried to find a photo of just the kettle but couldn't find one. Most have stirrer and pressure assemblies on top but all you need is the kettle (the vessel), itself. In this photo, for most dissolving, all you need is the bottom part, the kettle. Most people cover the kettle with a sheet of heavy inert plastic or fiberglass. About 2/3 to 3/4 of the cover is hinged and is raised in order to add or remove material. Usually, an inert exhaust pipe (usually high temp plastic) is mounted vertically to the back stationary part of the cover, in order to suck out the fumes and transport them to a scrubber. The shape of the kettle in the photo is fairly typical, but they come in various shapes. At one place I worked, we had several new dish-shaped kettles, 5 or 6 feet in diameter and a foot or two deep.
http://www.alibaba.com/product-gs/213307266/Glass_lined_reactor/showimage.html

I just found a photo of the inside (and, outside) of a small 10 gallon one. The ones I used were solid on the bottom, without the drain hole as in this photo. Click on View 2 more Photos and then click on Next or the small photo on the left.
http://www.aaronequipment.com/UsedEquipment/Tanks/Glass+Lined/77183.html


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## HAuCl4 (Jun 29, 2010)

Thanks GSP. Hanging a basket made of fiberglass inside the PVC reactor was the way the folks did it in the setup I inspected (max 200 Oz at a time, so small reactor). That way the metal never touched or wore the lining of the reactor. Still this Pfaudler looks like A LOT better piece of equipment. 

How did you ladle or siphon the stuff out, solid and liquid, for filtration, etc.?


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## HAuCl4 (Jun 29, 2010)

I made a quick draw (sorry for the quality) for the PVC design that I mentioned before. I added another PVC valve at the bottom to the original design that I encountered and bettered somewhat.

The removable basket sits inside the reactor with the gold shot, it has a bottom with several large holes (like a colander), and a fiberglass filter.

The cover has a tube to plug the fume scrubber sucking air.

Basket was loaded with the shot and put in place, then hot HCl added, then nitric. After reaction complete, the basket was removed with most of the AgCl. The rest of AgCl settled on the bottom and was "brushed" towards the drain hole, with first valve open and bottom valve closed. Then closed the top valve and drained into a bucket with a little gold chloride/HCL by opening the bottom valve. Most of the chloride was out at this point. Then the main solution was filtered with a Buchner funnel made also of PVC. The Chloride washings, etc, also filtered.

Then precipitation with SMB in the funnel vessel.

It seems efficient in writing, but it was quite messy in practice, in my opinion. Too much man-handling of liquids, and rolling in, rolling out vessels, funnels, etc.


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## 4metals (Jun 29, 2010)

I found that digestion was both quicker and more complete under a little pressure, our reactor was an open topped, and no outlet on the bottom of the reactor. To create pressure I had a very heavy lid which was also coated with the blue glass, the top had a tab connected to a chain hoist to lift the reactor top off. The seal was made with a heavy flat viton gasket which sealed well under the full weight of the lid.

The top also had a 2" hole which I connected to a 24 inch diameter by 48" deep cylindrical tank. There was also a 1" hole for chemical feed. The 2" hose went in the bottom of the tank. On top of the tank was an exhaust to a scrubber. I had sight glasses so I could see how much water was in the tank. If I kept the tank empty, the reactor operated at atmospheric pressure, but if I added water to the tank the pressure inside increased to displace the weight of the water. 

It was an easy cheap way to pressurize the reactor. 

The top was lifted off after disconnecting the hoses and the steam lines (all quick disconnect) and the solution was siphoned into a filter and by using a vacuum filtration setup drawn directly into a gassing tank which was fiberglass reinforced to withstand the vacuum so the solution was pulled directly into the tank where it was to be gassed. Less handling less losses. The final bit of solution and any chlorides were removed by dumping the reactor into buckets. The reactor was mounted to pivot about its center of gravity when empty. So emptying was easy. 

I've seen the wok shaped glass lined reactors GSP mentioned, they were used to concentrate gold potassium cyanide to make salts at a Lea Ronal refinery in Freeport. I went to an auction last winter at that plant, which had changed hands to Rhom & Haas and the reactor was there for bidding. The glass was in rough shape though so I passed. GSP is right to have them re-lined is very pricey.


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## goldsilverpro (Jun 29, 2010)

4metals,

Excellent suggestions for creating some pressure. A little pressure always helps. 

We siphoned what we could and dipped the rest out. I always fashioned dippers by cutting a round plastic gallon jug in a certain manner.


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## 4metals (Jun 29, 2010)

GSP Wrote;


> We siphoned what we could and dipped the rest out. I always fashioned dippers by cutting a round plastic gallon jug in a certain manner



So you were the master of purple fingers in your day! 8)


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## goldsilverpro (Jun 29, 2010)

> So you were the master of purple fingers in your day!



True. The purple always came off with cyanide, though.


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## Harold_V (Jun 30, 2010)

goldsilverpro said:


> > So you were the master of purple fingers in your day!
> 
> 
> 
> True. The purple always came off with cyanide, though.


That worked for me. (Sure did leave your fingers feeling slimy, though!)

Harold


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## HAuCl4 (Jun 30, 2010)

Thanks for the detailed description 4metals. A few questions:

Did you get rid of fumes/vapors at the end before lifting the top off?.

Was there an HCl stink at all during the operation?.

How did you load the shot inside the tank at the beginning?. 180 Kg of material to load is not trivial.

What about the acid pumps to load the reactor?.

Also: Were there any bits of undigested metal trapped in the chloride slimes?.

Thanks also GSP.


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## 4metals (Jun 30, 2010)

To eliminate the fumes above the solution we first drained the tank which created pressure, now the scrubber could actually suck out of the reactor. Then we cooled the reactor by running chilled water through the steam jacket, this served 2 purposes, the cooler acid didn't smell as much and the cool acid drops most of its silver so it can be filtered much more effectively.

There was never any strong acid small in the refinery, the room did have a good air turnover though.

The shot was loaded in by tilting the reactor and pouring the shotted material so it slid down the wall. After a few years of doing this we could see where the shot had scratched the shiny surface of the glass along its path but not enough damage to cause concern. 

The acid was added with double diaphragm drum pumps, a 316 stainless one for nitric and a composite one for hydrochloric.

The chlorides were pure white and fluffy never trapped any gold, probably because the silver percentage going in was so low.


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## HAuCl4 (Jun 30, 2010)

Thanks again 4metals.

Now, after the filtration and SO2 drop (I assume you used SO2 because of costs?), did you re-cycle the HCl from the barren liquids or else what did you do with the liquid waste?.

Also, would you describe the filtration membrane and setup?. I assume it was a Buchner type with vacuum, but for that amount of liquid I can't think of a proper membrane material/setup.

The setup I left the PVC folks with used a Buchner type made of PVC with layered coffee filters in the middle of two fiberglass cloths. It was gravity filtered without vacuum, because...the vacuum pump had broken and they said they would replace it "sometime".

They never had any gold in the AgCl either, because the shot was layered out horizontally to offer maximum surface to the acids, and was pretty much all digested simultaneously.


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## 4metals (Jun 30, 2010)

After gassing with SO2 the PGMs were cemented with copper. Back in the '80s during the last gold scrap rush, there was considerable platinum and palladium and iridium in the waste. To recover these metals cementing was necessary. The solution was treated with MagOx to raise the pH to drop out any remaining metals and the solids were filter pressed and the liquids discharged as they met the sewage discharge criterion. 

Filtration was by a 50 cm table top buchner funnel. The filter media was actually in the form of pads which were rigid and about 1/4 inch thick. They fit tightly into the funnel bottom and swelled when wet. These pads filtered the material both quickly and to a small micron porosity.
Back then the pads were about $2 each. When we first used these pads we saved them and burned them to recover any gold but between the strong suction and the fact that the chlorides were rinsed from the pads to process separately, there was never any values in the burnt residues so we stopped burning them.


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## HAuCl4 (Jun 30, 2010)

Thanks again 4metals for the thorough descriptions. 

You may step down from the expert witness stand!. I'm sure if anyone wants to cross examine you they'll post the questions!.

Seriously, thanks a lot for openly sharing your knowledge. I learned a lot.

You too GSP.


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## HAuCl4 (Jul 10, 2010)

I thought I would ask one last question to 4metals:

What would you change in your processes if you had to do it over again today?


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## 4metals (Jul 10, 2010)

I would change a lot! The real reason for the chlorine (Miller process) is the speed of getting the product into a high purity. The next step, whether it is aqua regia or electrolytic is still necessary. Aqua regia is faster than electrolytic, one has waste the other ties up gold longer. 

In my mind the fix is chemical refining but with a twist. First the karat material needs to be in the proper form physically. Big changes in the refining process can be had by processing a fine 100 to 200 mesh powder. To do that the molten gold has to be atomized. A water atomizer is the most cost effective way to go here. It takes the proper balance of high pressure water hitting a thin stream of gold to get it right but the payoff is big.

If your fine powdered gold scrap is suspended in warm hydrochloric acid and agitated the gold will dissolve with the addition of chlorine. But chlorine is a chore to work with to say the least. A handy substitute is sodium chlorate. Warm hydrochloric, sodium chlorate plus gold (finely divided) will give you Aurochloric acid. From there on out it's simple.

Actually much simpler than you would imagine at first. Since there was no nitric used in the process, there is no nitric to eliminate before precipitation begins, second you can add ammonium chloride after cooling and filtering to recover any platinum. Palladium will come down as well because there is an excess of sodium chlorate in solution. Filter out the Pt and Pd and go for the gold. Fast and easy, no chlorine, no NOx scrubbing. Happy days, isn't chemistry a wonderful thing?


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## HAuCl4 (Jul 10, 2010)

Wow. That was really creative!.

You'd actually choose sodium chlorate over NaClO?. Faster, cheaper or both?.

100 mesh is really thin. Have you done it or seen it done?

Would you recycle the HCl at the end?.


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## Lou (Jul 10, 2010)

I would say that I'd only use sodium chlorate or sodium hypochlorite (or chlorine for that matter) if and only if it were substantially silver free gold I was dissolving. It's nice to not have to fret about removing nitrogen oxides and residual nitric acid, especially nice considering you're not producing lots of NOx to go out into the environment. Bear in mind though, adding only just enough nitric is quite easily accomplished with a large equal pressure addition funnel or a diaphragm pump. Cover your gold in conc. HCl, and add in nitric as needed. Some people prefer not to heat while doing gold, but heat is a requirement for platinum.


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## 4metals (Jul 10, 2010)

I've never tried to recycle HCl as it is saturated with SO2 after the gold is dropped. Maybe I'm not as green as others. I went for speed of recovering product over recycling.

Actually 200 mesh is attainable with a minimal % oversize and yes I've seen it done and it is done in production levels. This method is used in production methods although it's not talked about. 

I used sodium chlorate because it has a higher percentage of chlorine available. It is a strong oxidizer and there are precautions involved in its use and storage.

I'd tell you more but then I'd have to hunt you down. :lol:


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## 4metals (Jul 10, 2010)

Lou,

I have worked this process successfully with silver as high as 10%. The silver chloride makes an easier job of collecting the undissolved particles which are reduced with the silver chlorides and processed in a cell to recover any slimes. 

The encrustation by silver chloride is an issue at 200 mesh but the fine mesh does allow good penetration and the resulting entrapped gold in the silver bar after reduction is similar in concentration to the gold entrapped in aqua regia refining of cornflake karat scrap. Which is usually 1% or less of the assay of the silver bar. 

Unless you spend a ton of money on an atomizer (like $250,000) where you can be assured your over-sized is minimal, I assume the over-sized particles are too large for the Cl-HCl reaction to go to completion so they end up in the insolubles and get processed with the chlorides. 

I have never sieved the powder and tested this procedure on dust I know to be 200 mesh or smaller to test this theory. It is a pain to dry the powder to sieve it (I suppose I could sieve it wet) and as the gold levels in the insolubles aren't too high I haven't taken the time to do a proper test. (Something for my to do list) 

The biggest problem is waiting for the fine mesh powders to settle in the atomizing tank, currently it is filtered but I'm up for suggestions.


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## HAuCl4 (Jul 10, 2010)

4metals said:


> Lou,
> 
> The biggest problem is waiting for the fine mesh powders to settle in the atomizing tank, currently it is filtered but I'm up for suggestions.



A vibrating tank perhaps will help settle faster?.

Not planning anything, as this is just an intellectual pursuit for me. Great ideas and variations nonetheless!.


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## 4metals (Aug 30, 2010)

Was able to sift some atomized powders last week to quantify the sizes before digestion, the HCl sodium chlorate reaction goes to completion on particles as large as -50 mesh. This process is also effective on material containing up to 20% silver. The small particle size allows the acid to penetrate completely and the resultant chlorides contain only traces of gold, not the typical 1% found by digesting typical karat (8%Ag) which has been corn-flaked and digested in aqua regia.


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## HAuCl4 (Aug 30, 2010)

Digestion must be very fast too. They are going to call you the flash refiner!. 8)

I bet the atomizer is not too easy to build.


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## nickvc (Aug 30, 2010)

This is fascinating if I remember we had a member that was using water jets to do the same process on his dental scraps, this will speed up the time that the high values are left lying around exponentially and produce high grade gold if the processing is done properly, it almost makes the Miller Process redundant. Keep the research going it's got great potential for large scale refining.


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## Barren Realms 007 (Aug 30, 2010)

HAuCl4 said:


> Irons said:
> 
> 
> > HAuCl4 said:
> ...



I don't think he was, there was a thread on here about atomizing gold to digest it faster. The pressure of the water was around 2,500-3,000 PSI or higher that was used.


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## 4metals (Aug 30, 2010)

The pressure does come from a pressure washer, it's the modifications to make the pressure consistent that's the hard part. The basic atomizer, which can process 500 pounds per hour (that's 7,291 ounces) costs $150,000 without the melter.


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## HAuCl4 (Aug 30, 2010)

That digestion must take ... 30 minutes tops?.

One could make the pressure consistent with an hydraulic capacitor. Basically a high pressure air and water tank. The exact design of the (heated ceramic? ) metal nozzle is likely the most high-tech part.

El CheapO would stick with inquartation first and avoid atomizers, with a good nitric-recycle plan. Still would get the job done within an 8 hour shift, and maybe better accounting for all 4 metals and insolubles. I think. :?: :idea:


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## 4metals (Aug 30, 2010)

> and maybe better accounting for all 4 metals and insolubles. I think.



And you think this because........?


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## HAuCl4 (Aug 30, 2010)

4metals said:


> > and maybe better accounting for all 4 metals and insolubles. I think.
> 
> 
> 
> And you think this because........?



Mainly because the big AgCl volume traps all the insolubles and still some gold/platinum/palladium in the atomizer process, whereas the AgCl (if you go that way) is much cleaner in the inquartation first process. Notice that after inquartation+nitric leach, the recovery of the Ag, most Pd, Pt can go in parallel (time) with the AR or HCL-NaCLO3 leach of the gold+other, NH4Cl recovery of whatever Pt,Pd is left, and finally the gold. The insolubles would be very easy to isolate too.

That's just my opinion without actual hands on experience.


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## Fournines (Aug 30, 2010)

HAuCl4 said:


> Digestion must be very fast too. They are going to call you the flash refiner!. 8)
> 
> I bet the atomizer is not too easy to build.




I've watched 5,000 oz get turned into wet mud in just a few minutes. It's pretty cool the first time you see one of those things in action.


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## Irons (Aug 30, 2010)

HAuCl4 said:


> Irons said:
> 
> 
> > HAuCl4 said:
> ...



I'm being perfectly serious. I bought a power washer a while back and the manual says it will generate over 2000 psi, depending on which nozzle you use. I bet it would break up the Gold quite well. There would probably have to be more than one nozzle. I don't know how many nozzles one power washer would handle, but they are not that expensive and two or more would be a reasonable expense.


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## 4metals (Aug 30, 2010)

If you get the particles small enough, and that is what the atomizer is there for, the acid penetrates and the digestion is complete. Yes there are silver chlorides but the coating over undissolved metal to trap values is minimal if it exists at all due to the fine particle size. The ability of the acid to penetrate a silver chloride coating is apparently greater than the size of the particles. 

And Fournines is right, seeing a bar one minute, molten metal the next and then fine mud is a sight to see.


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## HAuCl4 (Aug 30, 2010)

If you can wash the AgCl very well of me (HAuCl4 :lol: ) and there are no other nasty PGMs at all present, then I agree with you 100%. 8)

I perfectly believe fournines. I understand he runs a large operation in NYC. I was just joking, because I have only seen 5,000 OZ in pictures and films, like mostly everybody else.


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## HAuCl4 (Aug 30, 2010)

Irons said:


> HAuCl4 said:
> 
> 
> > Irons said:
> ...



OK...so we got the pressure source, water nozzles, hydraulic capacitor, anyone got a picture of the heated metal nozzle, melter?.


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## Barren Realms 007 (Aug 30, 2010)

You don't use a heated metal nozzle to inject the gold to be atomized. You can take a crucible drill 1/8" holes in the bottom. This is the crucible you are going to pour your molten gold into. You heat the crucible with the holes in it and then you pour your gold into that and it run out the holes thru the atomizer and you are complete.


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## HAuCl4 (Aug 30, 2010)

Cool. Simpler than I thought.

What angle, pressure and volume per second of water through the nozzles (3 nozzles?) to produce sub 100 mesh powder?. 

At what temperature do you pour the metal?.


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## HAuCl4 (Aug 30, 2010)

I was thinking that inquarting and then atomizing would be even better. Even with a less than perfect atomizer, and a less than perfect 1:3 inquart.

Get the best of both worlds: Flash digestion, no values at all trapped in the AgCl, and 9999 Ag possible in 1 pass without re-processing AgCl. Insolubles like Rh, etc. available immediately. Still would probably need to re-cycle the nitric. :shock:


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## HAuCl4 (Aug 30, 2010)

4metals said:


> Think again dude, it works..........well.



I take your word for it 4metals!. Cheaper than $150 K too!. :lol:


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## HAuCl4 (Aug 31, 2010)

So using one of these atomizers, the "new standard" is something like:

400 Lb of 4 metals refined in 4 hours to 4 nines?. :lol: 

I can see gold could be done in 1-2 hours, silver 2-3 hours, Pd 2-3 hours, and a stretch to do 9999 Pt in 4 hours, but perhaps possible?.

Less than 1 per 1000 in "losses" too.

Unthinkable stuff 20 years ago!. 8)

edit: Probably not cost effective to refine small amounts of Pt, Pd on a daily basis, yet technically possible.


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## Irons (Aug 31, 2010)

I have a question about settling time and any losses from colloidal gold suspended in the water. One time bottleneck I see, is the Gold settling time. If it takes a day or more for the fines to settle out, that would be a significant bottleneck in the process. You can filter the water with a sub-micron filter but if you do it too soon, the filter will clog and the process will slow to a crawl again. It could take weeks or months for the finest particles to settle out. I've found that a few drops of acid in 4 liters of water speeds things up a lot, but it still takes time, and time is money.


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## HAuCl4 (Aug 31, 2010)

Hi Irons: I thought about that and the best solution I could come up with was using a COARSE filter and passing the liquid twice, the second time through, the larger particles acting like a filter for the small particles.

Like a bed of rocks on the bottom, then of pebbles, then of sand, then of mud.

I think with good vacuum that would work. I've used that trick before in a water treatment application, but not on those very fine particles of precious metals.

Maybe the guys doing it will speak on how they actually do it.


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## HAuCl4 (Aug 31, 2010)

Maybe I didn't put my idea across correctly Barren:

A fiberglass cloth filter (that can be leached). Pass the liquid once, and the coarse particles stay, the fines some stay some get through. Pass it again, and the previously trapped particles act like a filter now, etc. 

Maybe waiting is better. I do not know. What's the typical waiting time?.

A vibrating tank is another alternative, a centrifugal filter yet another, but trying to keep it simple.


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## HAuCl4 (Aug 31, 2010)

If one could manage to use little enough water for the atomization (recirculate it?), there would be no need to filter at all, just put in the reactor as is, add the hot HCl, start to stir and feed the NaClO3 as solid. :idea:

Or just atomize into the cold HCl and heat it up at the same time!. I.e.: Use the HCl instead of water, to atomize :idea: :idea:


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## 4metals (Aug 31, 2010)

Most of the metal settles within 15 minutes, in a 3000 ounce pour about 2 ounce of fine are adrift in the water. For tight production schedules, process the 2998 ounces which have settled and the balance has settled within 24 hours so it can go in the next lot.

As far as letting the HCl heat up from the reaction, bad move. The sodium chlorate would gas off the Cl2 and not do as much work as if the acid was warm. Remember the molecules are dancin' and jigglin' when they are warm so they're more reactive.


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## Irons (Aug 31, 2010)

The Cl2 may be dancin' right out of the leach if it gets too warm. :mrgreen:


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## 4metals (Aug 31, 2010)

There is a world of difference between being warm when the metal is being digested and being warm when it is being dropped. I always drop gold from cold acid, the colder the better, the cold acid drops all of its silver so it can be filtered out before dropping. 

The only digestion I can think of that is better with cold acid is to separate gold from platinum, the gold will digest but the platinum will be much less soluble.

The settling I spoke of above is strictly due to the small size of the atomized karat material which is in water, not even digested yet.


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## Oz (Sep 1, 2010)

I put my gold chloride solutions in the freezer to precipitate my silver chloride, as the double dilution with water creates so much unnecessary waste. The added benefit is that if I filter quickly the solution is still cold when I go to precipitate, greatly increasing the solubility of SO2. This may be more important to me than some as I add my SMB dry. If you are lacking dedicated freezer space or are just in a hurry, ice cubes do wonders.

Empirically it seems that 32F or lower is every bit as effective as dilution with water X2 at room temperature. Does anyone have access to solubility charts for silver chloride that could confirm my observations?

For those that have never chilled auric chloride, when your solution is cold, dry SMB just drops to the bottom of your beaker before it reacts and gives off no wasted SO2 bubbles for you to breathe until near the endpoint of the reaction. If you keep it cool (the reaction is exothermic) you can reach the endpoint without dispelling noxious SO2 gas and still have complete precipitations as long as you do not add SMB/SO2 gas too rapidly.


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## HAuCl4 (Sep 1, 2010)

People would be better served if they heed the words of 4metals as the guy actually DOING it, as opposed to my wild speculative ideas POSTING on how it COULD be done differently. 8)

I keep thinking that properly washing and filtering the AgCl is the lengthiest and hardest part. How long does it actually take 4metals?.


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## 4metals (Sep 1, 2010)

Silver chlorides from a 3000 oz batch, about 240 ounces of silver expected, do not slow things down much. The chlorides settle quickly in the acid and the liquid is siphoned into a filter with strong vacuum, the chlorides / insolubles are the last to hit the filter as they have settled to the bottom. They are soft white fluffy chlorides and rinse easily with cold water. 

Later they are removed from the filter and washed / soaked in hot water to remove any lead chloride. Overall they do not slow down the procedure other than requiring filtration to remove them. But that's normal with aqua regia as well if there is no nitric pre-treat of an inquart.


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## HAuCl4 (Sep 1, 2010)

So, for the record: 

How long does it take to get all the bars/fine shot of 9999 fine gold from the moment you put the 3,000 Oz of scrap in the induction furnace?.

Melt- 5 minutes?
Gold mud atomized - 5 minutes?
*Mud settled - 15 minutes.*
Digestion in hot HCl-NaClO3 - 20 minutes ?.
AgCl filtering and washing - 20 minutes ?.
NH4Cl drop of Pt, Pd salts and filtering- 15 minutes ?
Gold drop and wash- 35 minutes?
Melt and pour of fine gold- 15 minutes ?.


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## 4metals (Sep 1, 2010)

melt time to get from bars to molten 5 - 10 minutes
atomizing 2 t.o/second
settling, majority 15 minutes, balance 24 hours
digestion 30 minutes
filtering chlorides (about 85 gallons acid) 30 - 45 minutes
PGM Drop 5 minutes*
filtering again same as before
gold gassing 45 minutes
filtering again
washing gold 15 minutes
melt and pour 400 oz bars 30 minutes


total time around 6 hours


* if Pt , Pd is low in concentration it takes longer to re-settle and filter than it's worth, most want to ship their gold and be paid for it within 24 hours so cementation and collecting when it accumulates is a better use of time.


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## HAuCl4 (Sep 18, 2010)

During my trip, and due to the introduction of "the atomizer", the obvious question kept popping in my head:

Can gold of sufficient purity be quickly produced using only "the atomizer" followed by some carefully designed fluxing and/or salt cementation method?.

Have you done any experiments in this direction 4metals, anyone?. 

I think it could work well if there are no PGMs in the feed, maybe with more than 1 atomization in the sequence. No aqueous treatments has a nice appeal. 

I wonder what Vanoccio Biringuccio could have achieved in terms of fineness, had he had access to an atomizer... :shock:


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## 4metals (Sep 18, 2010)

Interestingly enough, I am working with atomization on sterling silver for that same purpose. My logic is that by adequately fluxing the sterling and taking advantage of the huge surface area, and the ability of the fluxing materials to contact the majority of the material, the copper can be oxidized out of the alloy. I doubt you could ever get it all so that's why I never considered karat material. 

Once the material melts most of the fluxing action is at the surface of the metal pool that is why the contact between the atomized metal and the flux is so important. If the metallic copper doesn't oxidize early on it may not go, so determining flux to atomized karat ratios are paramount to success. That is what I'm working on now. 

With proper fluxing, enough copper can be removed to produce an alloy that has low enough copper to run in silver cells easily without the "copper buildup blues."


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## HAuCl4 (Sep 18, 2010)

Very nice. I think "the time spent at a high temperature but below melting point" is likely a very important parameter. As you say, as soon as the material melts, the flux action is greatly diminished and confined to the surface of the melt.

These middle age guys were bringing gold from 37% to 90%+ in one pass using table salt, urine, and crushed brick...and no atomizer...so I think the idea has some merit.

You, yourself have used scavenger fluxes on leached inquarts to bring 99% gold to 9995 with great success, so there is only that band from 90% to 99% to bridge the gap.

In my head it is possible. Just need to do the experiments...sometime.


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## HAuCl4 (Sep 19, 2010)

I see. It makes sense. Definitely hard to beat the atomizer for exposed surface area and speed of reaction. 

Have you timed the time for a leach of an atomized gold-silver inquart in hot nitric?. It must be almost explosive-fast. It is probably very fast too with sulfuric acid. Different application. Sorry to digress.


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## 4metals (Sep 19, 2010)

Atomized inquart would be too violent and too fast in Nitric. When I do inquarting I use a scrubber designed to regenerate nitric in an O2 rich atmosphere, since retention time is critical in the design of a scrubber the reaction rate has to be considered. The inquarted silver is usually digested in coarsely grained shot for that reason.

I'm afraid atomized inquarted alloy would break some glass!


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## HAuCl4 (Sep 19, 2010)

Atomized inquarted alloy digested in sulfuric acid in a heated cast iron kettle sounds like a very expedite, simple and economical solution for material without PGMs. Only issue is that the price of silver is not what it used to be, and large lots need much metal, larger furnaces, etc.

Your HCL-Chlorate process with atomizer is very hard to beat for an all-in-one economical and fast solution. Maybe only if the fluxing experiments work out and only if no PGMs.

I'd say that the atomizer is the biggest innovation in a very long time.


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## 4metals (Oct 9, 2010)

Water atomizing is surprisingly uncomplicated.


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## qst42know (Oct 10, 2010)

Several methods are described in this book with many diagrams and charts.


http://books.google.com/books?id=6aP3te2hGuQC&pg=PA102&lpg=PA102&dq=atomizing+precious&source=bl&ots=wO2MEMO__b&sig=XZC7n4C50XGAtf3H5f-1b70FN9o&hl=en&ei=LqexTIUXi_6cB-j5oJsG&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBIQ6AEwAA#v=onepage&q=atomizing%20precious&f=false


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## 4metals (Oct 10, 2010)

Excellent book, and worth the $280 price tag if you are considering building your own atomizer. It took a month for my copy to arrive, I doubt it's because everyone's reading it, more like they had to dust it off to find it.


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## qst42know (Oct 10, 2010)

I had no idea this was in your library. 8) 

I take it atomizer tanks are included in the refineries you consult for. There is one thing I wasn't clear on. 

Is the water recirculated through the high pressure pump, or the tank sized to accommodate the additional water.

If the water is recirculated what sort of filter is used to keep the pms out and how much material is tied up in the filter?


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## 4metals (Oct 10, 2010)

Generally the water is not recirculated, although with a large enough holding tank it could be. The processing lot size determines everything, smaller units will atomize 2 oz of karat per second using 4 nozzles pushing 1.4 gpm each at 5000 psi. So to atomize 1000 oz, you will generate about 50 gallons of water, that requires a tank holding about 75 gallons because if you don't allow a few inches of water in your receiver to start, you will be spending time scraping gold off the bottom! 

The tanks I like to use will accommodate the full volume water needed, then it can settle overnight and be pumped down in the morning. The water could be re-used for the next lot if you use a shallow well pump to feed the pressure pump. If you need to process immediately all but 2 ounces of a 1000 ounce lot settle within 5 minutes. Within 24 hours it's all down. 

I prefer not to filter it because the super fine particles work their way into the fiber of the filter media requiring incineration and all the associated processing and accounting.


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## qst42know (Oct 10, 2010)

Thinking small scale, is an atomizer rig efficient enough in cooling a pour you could do so in a poly drum?


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## 4metals (Oct 10, 2010)

No firsthand experience, I like stainless. I guess with enough depth before you start you will be OK.


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## HAuCl4 (Oct 11, 2010)

4metals: I understand you melt with an induction furnace. How do you heat the ceramic nozzle/crucible with a hole for the trickling molten metal or did you put a ceramic tap on the bottom of the induction crucible?.

Thanks for posting the exact specs of the atomizer.


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## 4metals (Oct 11, 2010)

The orifice (tundish) is mounted in an induction heated head. Small melts op to 1000 oz can be melted in the tundish which is plugged with a removable rod to start the flow, larger melts are accommodated by pouring at a controlled rate into the heated tundish. 

I suppose a small unit could be fabricated from an electric kiln, with a hole in the bottom to drain into the spray and a top that opened to feed it. This would suffice for karat gold and smaller melts, feeding from the top would be possible I guess.


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## HAuCl4 (Oct 11, 2010)

http://en.wikipedia.org/wiki/Tundish

In modern use, a tundish is a broad, open container *with one or more holes* in the bottom, used in various industrial processes. In metal casting, the tundish is used to feed molten metal into an ingot mould so as to avoid splashing and give a smoother flow.

The tundish allows a reservoir of metal to feed the casting machine while ladles are switched, thus acting as a buffer of hot metal, as well as smoothing out flow, regulating metal feed to the moulds and cleaning the metal.

Metallic remains left inside a tundish are known as tundish skulls[1] and need to be removed, typically by mechanical means (scraping, cutting).


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## 4metals (Oct 11, 2010)

A properly heated tundish leaves no skulls!!!


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## HAuCl4 (Oct 12, 2010)

What is the material the "tundish" you use made of and what do you use as a rod/plunger to close the drip hole?. Any chance of a quick hand drawn diagram or a picture?. 

Can Platinum scrap be "nuked" with this type of atomizer in your opinion, or melting point is too high?. :shock:


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## 4metals (Oct 12, 2010)

The tundish is a continuous casting crucible which have the hole and the plunger. Off the shelf stuff, all sizes available. 




Platinum is difficult and I haven't worked with it as a high grade metal with this application, however I have "inquarted" platinum in karat scrap 3:1 and atomized it effectively. The chemistry used after atomizing lends itself to PGM recovery nicely.

The long standing issue with platinum is its difficulty in digestion for high grade material, the above inquarting scenario addresses that nicely.


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## HAuCl4 (Oct 12, 2010)

Thanks 4metals as usual. 8)


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## qst42know (Nov 22, 2010)

The spray nozzles used for atomizing must create a considerable draft of air. Does this process require any sort of shroud?


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## 4metals (Nov 23, 2010)

There is some spray and the top of the receiving tank is sealed with a lid leaving the only opening, which is where the stream of gold is delivered to the high pressure stream.


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## HAuCl4 (Nov 25, 2010)

I believe a relatively cheap atomizer can be built using a second-hand SCUBA air compressor attached to a cascade, attached to an air-water tank, attached to the water cleaner nozzles, delivering the spray into the receiving tank. The air cascade would keep the pressure constant for a steady spray.

http://www.northshorecompressor.com/cascade-systems/cascade-systems.html

Instead of tundish (to make it simpler), an electric kiln at around 1200 C, with a graphite crucible with a small hole (or several for a larger multiple nozzle system) in the bottom, fed molten metal from the top, would provide a relatively steady metal drip into the atomizing nozzles.

A little trial and error would be expected for a first time builder however, and a safety warning about the high pressures used and the pipes, tanks, valves, etc to handle the pressures safely. This isn't something to toy with. :shock:


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## 4metals (Nov 25, 2010)

The crucible with the hole in it is exactly what a tundish is. It's pretty simple already. I happen to know a bit about scuba diving, I've been doing it for 40 years, and there is no way a cascade system will be cheaper than a 5000 psi power washer.

However 4, 1250 psi washers will be cheaper than 1 bigger one and the plumbing will not need to withstand the same 5000 psi so it can be threaded pipe. Just run the pipes so they form the same 4 jet configuration and make sure all the 4 washer can be turned on at the same time.


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## HAuCl4 (Nov 25, 2010)

Obviously we have a confusion. I understood the system operated at 5,000 psi. Now you say that it operates at 1,250 psi?. That would be certainly cheaper. 4 water cleaner systems at 1,250 psi would deliver higher *flowrate*, but they wouldn't take 5,000 psi of *pressure*. I'm confused about the specs you quoted above in one of the earlier posts.  

In my head I was building a 5,000 - 6,000 psi atomizer, not a 1,250 psi one. :shock:

Here's a link for several 5,000+ psi pressure water washers. Probably a used one is cheaper.

http://www.ultimatewasher.com/5000psi-gas-powered-pressure-washers.htm


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## 4metals (Nov 25, 2010)

A 5000 psi pressure source will supply 4 nozzles which each have 1250 psi of pressure and 1.4 gpm of flow (each) The 5000 psi is what is delivered to the manifold before it is broken down to the individual spray nozzles. I suppose you could use 5000 psi per nozzle but you may make powder so fine it will never settle.


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## HAuCl4 (Nov 25, 2010)

I see. So the system operates at 1,250 psi of maximum *pressure* and 1.4 GPM of *flowrate* per nozzle. Thanks. 8)

I used to teach fluid mechanics at a university 25 years ago, and design protection for pipe systems against water hammer events, but there you go, I still managed to get confused about pressure and flowrate. :lol:

IMHO a 5,000 psi pressure source would destroy equipment designed for 1,250 psi unless the designer used a very generous safety factor. Pressure at the manifold is likely a little over 1,250 psi and the manifold simply distributes *flowrate*. A technicality over which I'm not ready to start world war III with you!.


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## 4metals (Nov 25, 2010)

Well I never taught fluid mechanics so I'll defer to your wisdom. I do know that I've personally seen manifolds supplied with 5000 psi of pressure with 4 individual 1250 psi nozzles at 1.4 gpm coming off to form the 4 nozzle arrangement to atomize the metals. 

It used butt welded schedule 80 pipe fittings for a manifold. I was told that these fittings are in excess of the requisite 5000 psi and the welds were x-rayed to assure they could take the pressure. 

I assume, and while assuming can get one into trouble in this case I feel relatively safe, that the maximum pressure the manifold sees is the output of the pressure washer. That pressure is vented in 4 places with the nozzles each rated for 1250 psi. So the manifold can take 5000 psi but I doubt it ever sees close to that.


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## HAuCl4 (Nov 25, 2010)

I see. The pressure inside the manifold depends on the pump and the flowrate. The pump (probably a reciprocating pump), if one attaches a wide hose to it (with no backup resistance to flow), the pressure delivered is basically zero (the reading of a gage at the manifold at atmospheric pressure). If one restricts the flow with nozzles, or a valve, or whatever, then the pressure rises to the maximum limit the pump is capable of (most have a bleed off safety valve to prevent self-destruction, or a shut down mechanism). 

If what you saw was a max 5,000 psi machine attached to the manifold, then the pressure in the manifold (and each nozzle) could get close to that. If however a 1,250 psi machine (or four of them in parallel) were attached, then the pressure in the manifold could be close to 1,250 psi.

The way nozzles work is that, for a certain flowrate, a certain pressure drop across is needed. This is the 1,250 psi drop at 1.4 GPM that you quote. The pressure at the discharge point of the nozzle is zero (atmospheric pressure), all the energy has been converted to fluid kinetic energy. This speed is what cuts the metal. In the inside of the nozzle, and towards the manifold, the pressure is 1,250 psi only if the flowrate is 1.4 (for that quoted nozzle). If one forces more flowrate through the nozzle, the pressure drop is bigger. If you put a 6gpm nozzle, the pressure drop would be smaller.

It's not clear to me just yet what the atomizing pressure is. Was there a pressure gage at the manifold?. What was the pump used 5,000 psi pump or 4 pumps of 1,250 psi?. :?: Of course the lower the pressure, the cheaper the system. Also the less dangerous.

If the flow rate at 1.4 GPM measurement is accurate, then the most likely pressure in the manifold is 1,250 psi. If you put 5,000 psi to that same nozzle, then the measured flowrate will be bigger.


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## Lou (Dec 29, 2010)

The chlorine reacts with everything but the gold (and PGMs present). Gold chloride is not stable thermodynamically at that temperature. The silver, copper, and other base metal chlorides are either volatile, or float to the top as a slag that is bailed off. The resultant gold usually clocks in around 3N. Bear in mind that the AgCl so produced must still be smelted to silver and then the slimes processed for accountability on the gold.


Lou


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## qst42know (Dec 29, 2010)

From this link the pressure should be closer to 13.7 MPa, 40L/min (1987 psi, 10 gal/min). 

http://books.google.com/books?id=6aP3te2hGuQC&lpg=PA102&ots=wO3JDSW_Vc&dq=water%20atomizing%20precious&pg=PA105#v=onepage&q=water%20atomizing%20precious&f=false


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## FrugalRefiner (Apr 13, 2015)

The moderators would like to thank all of the members who contributed to the original thread that this post was based on, as well as those who asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above, consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, 99.5%? Is it possible?.

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

For those who prefer a printed copy, a pdf file of this thread is provided below.


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