# Aqua Regia 1 - Intro & Fume Hoods



## goldsilverpro (Apr 9, 2007)

Aqua Regia is about the only method, for the small refiner, to purify gold to 999.9 Fine - no matter what anyone says. Not only does this method work on most karat golds, it is also the final re-fining step that is used to purify the gold collected from all types of scrap. Once you learn the steps for karat gold, which is the most difficult, you can easily adapt to gold from most other sources. 

It's not easy to get 999.9 fine gold. In that purity, there is only one part of impurities to every 9,999 parts of gold. Not much. Everybody learns to do it a little differently. Many small refiners never learn to do it. Since reaching this goal is foremost in my mind, I have begged, borrowed, stolen, and invented tricks, in order to achieve this purity. It's sort of a pride thing, with me, to be able to to produce beautiful 999.9 bars. Also, I get more money for the very pure gold. It's not that hard to do. The most important things are: (1) Keep excess nitric out of the aqua regia. I have a good way to do this. (2) Rinse the final gold very well. Have a plan.

To do aqua regia, you almost have to have a fume hood. You can do things outside but, you then must deal with the weather and other problems. When it comes to automobiles, metal buildings, lungs, etc., aqua regia fumes are one of the most corrosive things around. Also, aqua regia fumes are heavy and tend to cling to the ground in inverse weather conditions. It's best to not have any neighbors nearby. When you are very small, you can probably get away with exhausting the fumes into the air. When you get big, you'll have to get a fume scrubber. Besides the corrosive nature of the fumes, one other problem is the high visibility of the red/brown nitric oxide fumes that are produced.

Commercial fume hoods are expensive. I usually build my own. I briefly discussed fume hoods on this thread:
http://goldrefiningforum.com/phpBB3/viewtopic.php?t=10

The last fume hood I built, a 10 footer, was made as follows. I first built a bench 10 feet long with a 2" X 4" framework, 4" X 4" legs, and a 3/4", 3 feet wide plywood top. The top was about 36" high, a height that is good for siphoning the solutions out of buckets. The room I installed it in was in a metal building with 10' ceilings. I then built a frontless plywood box to enclose the bench with full sides, a full back, and a full top. I built it about a foot, or so, short of the ceiling, in order to mount the blower motor on top of the box and keep it away from the fumes. I ran a piece of plywood across the top front of the hood. I made the bottom edge of this strip of plywood about 6' off the floor, to keep from bumping my head on it. I then got 2 blowers, mounted in tandem, out of the junk yard. I think they were of 10" size. I mounted them at the top, back, center, inside of the hood and ran them to the motor above with a belt. I exhausted the fumes from the blowers through large fiberglass ducting to the outside of the building.

I didn't have a complete front on the hood or, sliding doors. You can add a series of 3 or 4 sliding, overlapping, plywood doors, on wooden tracks, that you can close when the blowers are shut down at night. They get in the way and I worked around the shutting down problem in other ways. I kept all acids under the hood in containers with lids, such as buckets, that I sealed before leaving at night. I never left open containers when the blowers were off. If I had a dissolving reaction going on that would work overnight, I left the blowers on. Also, I had the hood in a fairly small room, in which the walls and ceiling had been covered with low grade 1/2" plywood. I also had a couple of light bulbs, in PVC receptacles, covered with fume proof globes, mounted inside of the hood.

This is hard to explain. If anything is unclear, please ask questions. Constructing the hood only took a day, or two. It's really pretty simple. For a smaller hood, you can use the same basics.

Next: Dissolving the Gold


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## lazersteve (Apr 9, 2007)

Chris,



goldsilverpro said:


> Aqua Regia is about the only method, for the small refiner, to purify gold to 999.9 Fine - no matter what anyone says.



How does AR puriify gold this well?

What makes it better?

I always thought that the impurities mostly arise from the percipitation stage (i.e.: Dropping additional metals besides gold with nonspecific percipitant and/or poor rinsing of the mud). I know that other parts of the processing can introduce impurities, but what makes the auric chloride formed by AR somehow more pure than auric chlorides formed by other methods? Please clarify this if possible.

Thank you,

Steve


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## Harold_V (Apr 10, 2007)

I would suggest using caution when dealing with nitric acid. Wood, once contaminated with nitric, is very eager to burn. Think nitrocellulose. The problem is exacerbated if you process palladium, using sodium chlorate. 

Considering that incineration is very much a part of refining, a fume hood that is fire resistant and non-absorbent is the best choice. 

Having had a fire from using a fiber glass hood, I strongly advise against anything combustible. I was lucky, only my garage got involved in the fire. My next two fume hoods were made of asbestos products. 

Harold


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## goldsilverpro (Apr 10, 2007)

Steve,

I know what you're getting at. Let me qualify my statement. Actually, aqua regia has nothing to do the purity. It is only the dissolving medium. The purity comes from the precipitation and the other steps. Any method of forming gold chloride is OK.

However, these other methods, such as HCl + Cl2 and HCl + sodium nitrate, don't work well, if at all, on bulky solid items, such as karat golds. They will work on fine materials with large surface areas, such as gold powder and gold foil. Even with these items, aqua regia goes faster. I guess I would rather use and master one powerful universal solvent than use a bunch of wimpy ones.


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## lazersteve (Apr 10, 2007)

Chris,

No one will argue with you on that. Hands down AR is the heavyweight champion of the world when it comes to gold dissolution rates in this day and age. 

The *purity* of gold produced by other solvents can equal that produced by AR, they are just slower to dissolve for bulky items. I'm not sure I would call them 'wimpy', just not as agressive. After all gold is one tough character and any substance that can dissolve it deserves some merit. 

http://www.goldrecovery.us/goldrecovery/documents/EtchantRatios.pdf

AR has a dissolution rate of 10 times that of HCl-Cl. In contrast HCl-Cl has a dissolution rate of 45 times that of Acid Peroxide. Some people may want to use the slower acting formulas due to the easily available ingredients. Most of us will never reach the level of gold production that you and Harold have attained. It is a given that for the full scale professional refinery the use of AR is a requirement.

Steve.


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## goldsilverpro (Apr 10, 2007)

In 40 years, I have never seen a fire in a fume hood. I have probably been using wooden hoods for 30 of those years. You are right about the combination of nitric and cellulose becoming more flammable. When using these hoods, I was aware of this possibility and, thinking back, I always did things to prevent a fire from from happening.

I never, ever, used an open flame under the hood. The hot plates were electric and were always sitting on a piece of Transite or sheet metal. If you don't feel comfortable with acids soaking into the bench top, coat the top with polyester boat resin. You can also use a premade kitchen Formica counter top. The Formica will soon stain but, who cares? It you don't mind the expense, you can have any type plastic coating you want chopped onto the entire hood.

The absolute best fume hoods are the industrial ones but, they cost from $5000, for a small one, to about $20,000. A stainless hood soon gets ugly and starts corroding away. A Transite hood would be great but, asbestos products are nearly impossible to get. A sheet plastic hood would be OK if you used plastic at least 1/4" thick, to keep it from buckling - not cheap. I think they have non-flammable fiberglass. All in all, if I ever build another hood, it will be from plywood.


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## goldsilverpro (Apr 10, 2007)

Steve,

It's often very hard for me to think of an amateur's needs. I've always had the same problem on these type forums. I guess my attitude is, if you're going to do it, do it right. Also, I always have large quantities and the profit aspect jingling around in my head. To me, in this field, the word hobbyist is a foreign word, no matter how much I try to identify with it.

I think you occupy a very much needed position on this forum, as a buffer between us with professional experience and the newbies. You have a decent chemical background and a lot of common sense and, are able to identify with those who are starting out. Keep up the good work.


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## Anonymous (Apr 10, 2007)

Hey there, Steve. 
No modern refinery worth its salt predominately uses acidic refining, aka Aqua Regia. We certainly don't. If they are, I would avoid them like the plague because the costs as reflected in their refining charges would price them out of the competitive refining environment. If you want to talk just on the acidic side of the pH scale, then I suppose you could claim A/R is a heavy weight.

But trust me all three of you, -you, Chris and Harold --are thinking just acidic based refining. I have to go with more cost effective refining, and that most assuredly is NOT acidic. Not at all! 

Cheers.
Sue


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## lazersteve (Apr 10, 2007)

Sue,

I'm glad you've commented on this one, what processes are they using and what are the dissolution rates relative to AR?

Steve


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## goldsilverpro (Apr 10, 2007)

Sue,

You are probably using the Miller Chlorine method and a Wohlwill cell. I agree that these are much more cost effective for the large refiner. Can you afford to set up for these processes if you're only producing an occassional ounce? How many thousands of dollars does it cost to set up a 1/2 gallon Wohlwill cell. Even a medium sized refiner can't afford to set these things up. Also, the copper chloride that comes off in the Miller method is very toxic. Or, do you have a nifty small setup that you can tell us about?

The big refiners obtain most of their karat gold for somewhere in the 90+% area. They're not hustling their gold off of the street and paying only 50-80%, like the small refiners do. Even with electronic scrap, the big refiner's margins are very tight, unless they are good thieves. The big refiners have to look closer at costs. The small guys have a lot more flexibility in their operating costs. The big refiners compete with the big refiners. The small refiners compete with the small refiners.


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## Harold_V (Apr 10, 2007)

goldsilverpro said:


> Sue,
> You are probably using the Miller's Chlorine method and a Wohlwill cell. I agree that these are much more cost effective for the large refiner.



Having chemically refined gold on a daily basis for many years, I can state that the AR process was, and is, the method of choice for the small refiner. It lends itself well to reasonably sized batches, anything from a grain of gold upwards. How it compares to refining in large volume, where the Miller chlorine process might be the better choice, isn't really one of the options open to the home refiner. It is pretty well beyond the reach of most home operations, and for multiple reasons. For one, I have yet to read of anyone here using a furnace-----for the most part, melting appears to be accomplished with a torch. Nothing wrong with that, but it excludes any chance of the Miller process. Second----and this one is extremely important-------I hear or read of no one using a fume hood. Without a method to isolate the operator from the hazards of refining with chlorine, truly, that is a place where only a fool would tread.

Regards a Wohwill cell, I had a miniature one completed except for assembly. I had the built to order fiber glass container, heater, and titanium buss bars made. I even had anode molds machined and anodes cast. I never finished the project. When you consider the ease by which AR can be used, the tiny benefit of running the cell to guarantee that last 9, when the level of quality being produced already exceeded the industry standard, made little sense. My only regret in never having used the cell was not having the experience. I produced gold that melted with no trace of oxide coating, and cooled without any signs of frosting, all by the AR process. The quality didn't warrant further treatment. 

I've tried to encourage those that are recovering gold from waste materials to think like a refiner------simply recovering gold is not enough. How they accomplish the task, as long as it doesn't endanger the operator unnecessarily, isn't a concern as long as it accomplishes the task at hand. There may be more than one way to arrive at the same destination. I chose the route I took because I am not a chemist, nor do I pretend to be one. I am also not a metallurgist, so I avoided trying to be too creative. I explored books written by leading authorities on given subjects and relied heavily on their advice. I chose Hoke's book as my bible. I was successful. I was competitive----and had more work to accomplish than I had time to perform the tasks at hand. What more can one ask?

Harold


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## Harold_V (Apr 10, 2007)

Sue said:


> But trust me all three of you, -you, Chris and Harold --are thinking just acidic based refining. I have to go with more cost effective refining, and that most assuredly is NOT acidic. Not at all!
> 
> Cheers.
> Sue



Your contrary comments serve no useful purpose unless you are willing to offer an alternative method. If your chosen method of operation is proprietary in nature, and can't be shared with the readers, it is disingenuous of you to toss a wet blanket on others that may be using good and accepted practices for extracting and refining their metals, but they are not the methods being employed by you. I think I can speak for the vast majority when I say that none of this is a contest, it is, hopefully, a place where those of us that have had success can and will share what we know with others. 

May I suggest to you that you either become a helpful contributor to this forum, or stop commenting? The task of learning good procedures is complicated enough without having someone constantly creating doubt. 

Harold


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## Anonymous (Apr 10, 2007)

Steve,

There are SO VERY MANY variables when doing a comparison in dissolution rates even within the perameters of just a specific metal, there are no easy answers to the thrust of your question.

So, to talk dissolution rates in an apples and apples comparison, the topic of origin plus current form and rate of dispersion determinations *must be* defined before a cogent comparison can even be attempted.

There is a recent interesting 2003 peer reviewed article published in an SME monthly magazine, on the pros and cons of Na2S2O3, as an alternative to NaCN in the leaching phase. That, too, is a 1950s revisitation of an old and mostly universally rejected protocol. For us, it has unacceptable dispersion rates. 

I'd like to suggest if you'd consider tackling for the forum participants, Na2S2O3 (thiosulfate) gold harvesting angle in one of your video tutorials. It is touted as the safest, and is certainly (I guarantee you) the slowest. You might be doing this group a real service by turning them onto thiosulfate methodology, since it is so easily available, right in their local hardware stores.

Cheers
Sue


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## goldsilverpro (Apr 10, 2007)

Right on, Harold (referring to your post of 2:02 pm and not the 2:11 post)

Sue, it's obvious that you have a ton of technical knowledge about these subjects. And, you're probably a very nice guy. But, most of these people are hands on. It would benefit us all if you provided a little more meat and a little less theory. 

I feel a little kinship towards you since I had a job that sounds similar to yours in the late '60's, early '70's. I was senior chemist (metallurgist) for the largest, at that time, refinery west of the Mississippi, in Chatsworth, CA. I even used to talk like you. I'm sure you're doing a great job for your company.

Please don't get PO'ed and stop posting. I, for one, study your posts and have learned a lot from you or, at least, relearned stuff that I had forgotten. Have you ever owned your own refinery?

I've been reading about using thiosulfate for many years but, haven't really messed with it. Do you have any solid, hands on Na2S2O3 schemes that you could share?


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## Anonymous (Apr 10, 2007)

Hey there, Harold,

If you don't like what I have to offer, hit the next button. Sounds like a plan to me.

Cheers,
Sue


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## Anonymous (Apr 10, 2007)

edit: 

Looks like you want a piece of me, too, Chris? Why are you insecure?

Can't any of you think outside the box of your own experience except for Steve who is willing to ask and learn?

You guys have a brand on Steve I don't know about? Am I messing with your personal property? 

This is crap.


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## Harold_V (Apr 10, 2007)

goldsilverpro said:


> In 40 years, I have never seen a fire in a fume hood.



You may not have seen a fume hood fire in your many years, but I managed to have one, which could have easily cost me my home had I not reacted as I did. Ignoring the possibility of hazard isn't a viable solution. 

Just a cautionary note to those that may get involved with refining for jewelers, which was my specialty. For me, it was the source of a tremendous amount of gold, far greater than that which comes from recycling electronic scrap, and certainly more fruitful for one's time. I might agree, if one is to ignore jewelry waste as a source, could be a fume hood isn't necessary, but incineration before extraction is always a good policy----for it eliminates traces of oils and other substances that can be problematic. 

For those that may process jewelry waste in the future, incineration is a constant companion. Filings, filters and polishing lint must be incinerated prior to processing. That task is best accomplished in a fume hood----using a gas hot plate. Unless a person has a fume hood that won't burn, a second hood that is fire resistant would be required. If the home refiner has no chemical hood, I see little hope that there would be a fire hood. It is for that reason that I suggest that a fire resistant hood be built, hopefully to serve both purposes. 

The last fume hood I built was used for incineration without fear of fire, and to deal with fumes from processing. It also had proper filtration to capture traces of values that are lost when refining. I have included a picture (very poor quality, but it's all I have) of the hood in question. Picture was taken just before the operation was sold, and was used as exhibit evidence for the sale, which was accomplished with the aid of an attorney. The general appearance is the result of ten years of refining----with gold and silver stains on almost everything. 

Harold


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## Anonymous (Apr 10, 2007)

Hey there, Harold, 

Directly venting to the outside???

Good thing you sold your business when you did. 

The EPA wouldn't allow you to stay in biz with your huge reputation according to you and learning you vented directly to the outside without any fume scrubbers at all.

I would have been most pleased to have reported you and put you out of business. Chew on that, little boy.

a man named Sue


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## goldsilverpro (Apr 10, 2007)

C'mon guys, this isn't a pissing contest.


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## Anonymous (Apr 10, 2007)

Then quit pissing on me, Chris. Real simple.


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## goldsilverpro (Apr 10, 2007)

Cool down and reread my post of 2:13 pm, the one you are hot about. In it, you will find mostly complements.

Added later: I really didn't rewrite it. Someone posted in between, just like it happened to you. It was truly a misunderstanding. Sorry.

My final comment

Peace


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## Anonymous (Apr 10, 2007)

Editing the reply to Harold where you took your cheap shot at me, without leaving in the original support for Harold's pot shots at me post immediately after he wrote them before mine got posted is an rank amateur stunt.

I saw your first post, and *yes, it was anything but complimentary. * I'm not fooled for a minute by your re-write which is currently posted.

You're damn straight I'm hot. Peace my ass. Man up and just say, my bad, Chris. You'll get more respect if you do. 

If you want to respond, go ahead...after all, you just proved you are the last liar refiner in here.


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## lazersteve (Apr 10, 2007)

I just arrived at the house form my 35 mile commute home and all h*ll has broke loose. What did I miss? I thought we were all discussing gold dissolution processes like adults when I left work !

I want to remind everyone that we are all on the same team.

This is about the community sharing ideas and experiences not who's smarter or who's the best refiner. Obviuosly all of you guys take great pride in your work and that's a good thing, but there's no reason to go at each other over any topic. A healthy debate is one thing, but to behave without regard for the other members is foolish.

I'm not anyone's property except maybe my wife's :lol: 

I'll learn what I can from anyone more experienced or not, without prejudice or bias. Good information is good information regardless of the source. It's when you close your mind that you can learn no more. Remember the other forum members will be reading this as well and the way you each of you present yourselves here will be seen by them. Let's not give them any reasons to take sides. That would definitely undermine the entire idea of this forum.

If you get ticked off at what someone has said, take a minute and breathe before jumping in and firing back. It takes a bigger man to turn the other cheek.

Steve


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