# Is this Precipitating?



## Richard TJ (Jun 4, 2010)

Okay, I've read just about everything I can on Gold refining through chem pocesses. Got a pretty good idea of the various processes and run an e-waste recycling company that processes tons of computers every week. Chopped off and collected a couple of boxes full of plated connectors (some really old stuff as well, with heavier plating), IC's, CPU's, memory sticks (fingers only) etc etc. 

Started 2 processes last week. 

The first was with fingers only. Washed in Nitric (70%) and filtered to remove copper. Washed the remainder to remove solution, heated till dry, added AR, left for 24 hours, added prills (urea) till fizzing stopped and them some more to ensure reaction had finished. Diluted solution 1-1 with H2O and then dumped in a lump of copper and lump of Aluminium along with Ferrous Sulphate. Reaction took 48 hours and precipitant, when filtered off was washed in 5% Ammonia solution and H2O. Dark Blue solution was filtered and filtered material was washed again in weak Ammonia. The precipitant was extremely fine grained and like a caramel coloured material. Would not react with ammonia. Then stupidly added the pyrex beaker with this H20/ Ammonia/ Gold? solution to a burner to dry it out. Whole lot sort of exploded- forgot that ammonia and glass on hot stove does not go down too well!- Question: Was this Gold that had precipitated out?

Batch 2: 1st stage as above, washed in Nitric acid, before being added to AR. V Good reaction. Gold pins completely dissolved after 24 hours. Left to stand for further 24 hours to ensure all gold in solution. Filtered last night to remove solids. Added Urea (prills) in sufficient quantities for it to form a salt on the bottom of beaker. Filtered to remove salt from AR/ Gold solution after 1 hour. Solution was noted as having a luminescent green colour to it. Added SMB+ Distilled water to solution and left overnight. Solution now has large crystals precipitating to base of beaker of a white colour (looked like stars floating on surface of solution this morning). Bugger of it is that last night, a black precipitate had started forming on the base of the beaker. Question: Have I overdone it with the SMB? Should I add more H2O to put remaining SMB into Solution? Interestingly, the solution itself has taken on a much darker (almost black) appearance, with what looks very much like a layer starting to form where the top 20% of the beaker is a clear green colour. Has this done the trick? How long does it take for the gold to precipitate out of solution? Am I being impatient here?


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## Harold_V (Jun 4, 2010)

Richard TJ said:


> Diluted solution 1-1 with H2O and then dumped in a lump of copper and lump of Aluminium along with Ferrous Sulphate.


Blink. Blink. 

Huh?

I'm a little bit curious. What prompted you to use copper, aluminum and ferrous sulfate? 

I've commented on a regular basis that readers should read Hoke's book. The reason I do is because she provides methods that work, and work well. 

She does not discuss the use of urea. It is also not a requirement for refining---just one of the cheats that can be used to circumvent acceptable procedures. 

You were on the right track until you introduced copper and/or aluminum. That is not an acceptable way to recover gold when you are attempting to refine. It is an acceptable method if your objective is to recover values from a dirty solution, when other options may have failed. In this case, had you not introduced either of the two, the ferrous sulfate would have precipitated your gold very nicely. The only thing left for you to have done would be to wash the recovered gold well, using HCl, then drying. Do not despair. We learn even from mistakes. Consider this a good learning experience. 

Please, please, please, read Hoke, and follow her instructions. There is no need for you, or anyone, to re-invent the wheel. 

If your objective is to do research, hoping to discover shortcuts, or to develop a different method for refining, I have no problem with the idea, but it would be in your best interest to have a firm understanding of what works, and why, before you venture forward with any experiments. Follow this advice for more than one reason. If you get too creative with gold chloride, you run the risk of creating explosive compounds, some of which are so unstable that they are known to exist in theory, only. Said another way, one of the clever things you try may kill you. 

Harold


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## Richard TJ (Jun 4, 2010)

Harold_V,

Thanks for your reply- have read a large number of your posts. The first batch test was to put it bluntly, an experiment and did produce results, but the sample was lost. It was the second batch that I was looking for feedback on. I have read "Refining Precious Metal Wastes" by C.M. Hoke and it makes sense of the whole process, but materials, resources and techniques have evolved since she wrote it. There's been a lot of posts in this forum about the use of SMB, but what I was looking for was feedback about how long it takes to precipitate gold from AR and if anyone else had seen the formation of crystals from the addition of SMB (probably in excess) into AR with neutralised excess Nitric Acid via Urea. However, I'll check it over this evening and if no further precip has developed, will dilute with Dist H2O to remove excess salts, which will most probably kick start the reaction/ precipitation.


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## qst42know (Jun 4, 2010)

> I have read "Refining Precious Metal Wastes" by C.M. Hoke and it makes sense of the whole process, but materials, resources and techniques have evolved since she wrote it.



Things haven't changed that much. I see none of Hoke in either of your processes. It sure doesnt seem you have read near enough.


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## Richard TJ (Jun 4, 2010)

This is from an other board: Another method for precipitating the gold from aqua regia which doesn't involve boiling away the nitric acid and generating toxic nitrogen oxides is as follows:

After dissolving your gold or base metal/gold into the aqua regia, add granulated or prilled urea to the acid/gold complex until the fizzing stops. This will destroy the nitric acid without boiling. The fizzing isn't violent nor are any disagreeable fumes released. A slight excess of urea at this point is ok. Next, slowly add a solution of sodium bisulfite (sodium metabisulfite in water) to the HCL/gold/urea mixture. When you start to smell sulfur dioxide being released, that is a good indication that all of the gold is reduced. Any further addition of sodium bisulfite will begin to reduce copper chloride to cupric chloride, which will precipitate along with your gold. This can discolor the gold, release clouds of noxious fumes when the gold is melted and generally screw up your assay. The gold will precipitate over the course of several hours as a chocolate brown powder which melts to the yellow color we all know and love. Add a few ml of Isopropyl Alcohol [link is to product info at Amazon] of other ! non-acid labile surfactant to free the finer particles which are floating atop the surface tension. After the solution becomes a transparent green, decant off the remaining HCl/copper chloride solution, cover the gold with concentrated HCl and swirl. This will dissolve out any precipitated cupric chloride. Wash the gold several times in distilled water until the water shows neutral to litmus. You can substitute concentrated ammonium hydroxide solution for the HCL wash since it too will dissolve cupric chloride with the added feature that cupric chloride will turn aqua ammonia blue. Repeat the ammonia rinse until no more blue is seen, and then do it once more. One caution here: If there is any possibility that silver salts have been precipitated along with the gold, do not use ammonia. Ammonia will form explosive acetylides such as silver fulminate, especially with insoluble silver chloride or silver oxide. When these dry, they will violently detonate if you even look a! t them too hard. This hazard can be completely avoided if you filter your acid after the urea step since this would trap any insoluble silver chloride and keep it out of your gold. I know this post is long, but the beauty of this process is in the details. I will post a second, even easier method in a followup post so that I won't choke the server with this one.


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## Richard TJ (Jun 4, 2010)

Here's another, just to give an example of what I'm trying to do (the emerald green really describes the solution I have each and every time!):

1) Neutralize the Nitric acid to permit filtering, testing and separation

Now that you have the A.R. mixture, you must neutralize the HNO3 using Urea (http://en.wikipedia.org/wiki/Urea), which will leave only HCL and metallic chloride, plus any other impurities. Urea can be found on eBay if you can't locate it yourself. I think you can use other chemicals but care must be taken not to disturb the HCL and 'drop' the metals from the chloride compounds (yet).

To add the Urea, you should first dissolve it in a separate container of hot/warm water. Then add the solution slowly to the A.R. until any 'fizzing' stops. This means the HNO3 is neutralized. You can also test pH (it should change from 0.1 to 1.0) but to continue until fizzing stops is the easy way. BTW it doesnt matter if you add too much Urea.

3) To recover gold from the A.R.:

Filter the neutralised AR - which will typically be emerald green if there is much gold present (like grams+), or yellow or blue if other metals are more dominant - into a separate container using filter paper. The filtered AR should be clear of particles. Just coloured liquid.

Mix some Sodium Metabisulphite (Na2S2O5 or 'SMB') with water and start adding it very slowly, like a drip at a time. Especially so if you don't think there is much gold present.

The SMB will cause the gold to split from the chloride compound and settle on the bottom as a nasty brown mud. It usually takes about 30 minutes (but can take an hour or two) and the solution should be allowed to stand between adding the SMB.

The stannous chloride you mixed earlier should be used to test the solution before each addition of SMB, as it will indicate when no gold remains in solution.

4) Cleaning up

Pour off the AR solution into another container, keeping the brown gold 'mud' for washing next in deionised water. After rinsing and settling a few times (don't lose any) - wash it in aqueous ammonia. Then heat it with flame to melt. It will change colour and form a 24k pure gold bead. (It is better to melt it with some borax flux to produce a nice shiny bead with no impurities).


Other metals - you can precipitate or 'drop' gold with Sodium Metabisulphate, or Palladium with Sodium Chlorate, or Platinum(&Palladium) with Ammonium Chloride, or Silver (from Nitric acid - it doesn't dissolve in AR) with table salt. Urea should only be used when precipitating gold - don't use it when precipitating Platinum group metals. Palladium should also be recovered before Platinum if doing so selectively. Platinum only dissolves appreciably in hot AR.

Thats pretty much everything you need to know to detect, extract and purify precious metals from any source. Let me know if you detect anything interesting


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## Richard TJ (Jun 4, 2010)

I owe you all a sincerest appology. I screwed up royally- I've added Sodium metabisulphate to neutralised AR which gives zero precipitation at all (don't ever use campden tablets). Instead, I should have used Sodium Metabisulphite, which fortunately arrived from a brewery today. Time to filter and test on a small sample me thinks!

Again, my sincerest appologies for all the above ramblings.


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## goldsilverpro (Jun 4, 2010)

Richard TJ said:


> Okay, I've read just about everything I can on Gold refining through chem pocesses. Got a pretty good idea of the various processes and run an e-waste recycling company that processes tons of computers every week. Chopped off and collected a couple of boxes full of plated connectors (some really old stuff as well, with heavier plating), IC's, CPU's, memory sticks (fingers only) etc etc.



No offense but, so far, IMHO, *nothing* you have come up with makes any sense at all. I think you're putting the cart way before the horse. The "horse", in this case, is profit. There are several way of dealing with this material. To properly make a decision, you need to know and to evaluate all of your possible options and do a cost analysis on each one. To do this, you also must know the PM values of the various types of material. And, you must know your labor costs of collecting and sorting the various types of PM-bearing material.

I assume you want to make a profit on this. If so, and, if you're processing a lot of material, you'll never profit (unless, I would guess, the gold value of the material you're processing is at least $100-$150 per pound - probably the higher figure) by dissolving the base metals, whether by nitric alone or by aqua regia or by using AP. Dissolving everything with aqua regia is really a bad idea. If you want to dissolve a lot of base metals, you'll need a lot of equipment plus a fume scrubber and permits. Also, you'll generate at least a gallon of heavy metal acid waste for every pound of material you process. This can either be hauled away or treated. Neither way is cheap.

There are better ways of doing this. For example, if the volume is large enough, you may find it's cheaper, overall, to accumulate the material and have a rep (professional representative, such as Ledoux) handle it at the refiner and do all the assays. At first glance, this seems expensive. However, when you compare it with the costs of doing it yourself, it might be less expensive.

To continue this properly, what weight of PM scrap will you generate per week? It would also help if you could break this down into the various types of material - be specific. Different types of material could take different approaches. At the present, what are you doing with it? If you are selling it, how much are you getting for it?


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## lazersteve (Jun 4, 2010)

I might as well weigh in on this one also guys if you don't mind.

Richard, 

Correct me if I'm wrong, but when you say 'washed with nitric' do you mean you gave the scrap a nice short lived rinse with nitric acid? If so you should realize that chemical reactions take time to be driven to completion. Following the the steps of any process in rapid succession is not even close to preforming the reactions properly. When nitric is used on scrap the end result should be free of copper if done properly.

Secondly, refining is not like making soup, you don't just gather the ingredients and drop them all in and boil until it's done. Perhaps I'm reading your posts wrong, but it reads as though your are just rushing through the steps listed to get to the finishing step as quickly as you can. Again, refining does not work like that. Every step must be taken to completion even if it means waiting hours or days for each step to be complete. 



RichardTJ said:


> ...the emerald green really describes the solution I have each and every time!



Emerald green solutions pregnant with gold indicate the presence of lots of copper impurities and is proof positive you are not removing the base metals first.

In addition to Harold and GSP's suggestions above, I would like to suggest that you forget everything else you have read away from this forum and start fresh with a cover to cover study of Hokes book. Follow this up with some detailed research into the yields and best practices for the type of scrap you have. Once you have done your homework, then process a very small (100g or less) sample of some really easy scrap (like clean cut fingers) using the acid peroxide process as detailed in video format on my website. Once you can get a good shiny gold button without fluxing (aside form glazing the dish) from AP then venture into the realm of AR. 

You are very lucky you were not seriously injured by the explosive reaction you produced. Due diligence and a lot of reading here may have prevented that incident.

In closing, it's highly unlikely that you will find more accurate details on processing any kind of scrap you want, somewhere besides this forum. There are truly no 'new refining techniques' for the most part. Everyone has just copied someone's work through out the years and posted it elsewhere and here. After all refining has been around for thousands of years, and long before the science of chemistry the ancients where refining gold. Every time some one takes a well rounded process and tweaks it just a little to 'personalize it for originality' they are inducing a little more confusion into the mix. The ancient processes are very simple once you understand what the reagents are and the underlying fundamental processes. Hoke will give you these.

Please take a step back and above all, be safe. In my humble opinion, the older a process, the more valuable it is to me. When reading in the future, be sure to check the dates of the information you are reading. If it's very new, it may likely be a rework of a simpler process elsewhere.

Steve


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## glorycloud (Jun 4, 2010)

Well said Steve!!


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## Richard TJ (Jun 9, 2010)

Folks,

Many thanks for the replies. Made me rethink processes and ultimately resulted in achieving the desired results from a batch of 6 x ceramic CPUs (P1 and 486), now have a small quantity of gold sediment sitting in a beaker of water (brown sediment). Even managed to refine the silver seperately and have that in a second beaker (brilliant white powder). Will stick to small batches for a few weeks, before trying an up-scaled version.


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