# thoughts on gold & other precious metal recovery



## nickvc (Sep 29, 2009)

Concieved wisdom from the time that i refined gold scraps was i always used silver to lower the gold percentage before dissolvng with nitric this i think was the norm.Many members on this forum are rightly worried about the safe disposal of the waste acids etc we create, could there be a better way of recovering some of the high amounts of copper in that waste? It seems to me that most of us can make and use a cell, would it be possible to refine the gold using copper by starting with a high copper alloy as your annode, plating the copper out using sulphuric acid and copper sulphate, but using an annode bag to catch the waste ie gold silver etc. This would get your copper back to be re used and leave just a small amount of other metals to be processed by your preferred method. Im only posting this as an idea and would appreciate members feedback.


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## 4metals (Sep 29, 2009)

From a waste treatment aspect the idea has potential because, as you said, the cell recycles the copper and to an extent recycles the electrolyte.

It all depends on how much copper you will have to add to keep your "inquarted" anodes over 90% copper. For a small hobby refiner it poses a melt capacity issue. Another issue is the co-mingling in the anode slimes of platinum, palladium, silver and gold. The silver and palladuim can be leached in nitric after converting the PdO by roasting. But the gold and platinum will both go up in aqua regia and it's hard to get it all out. By inquarting in silver, dissolving in nitric and cementing with copper you have separated the gold from the other players and purer gold is easily attained. 

Your suggestion will yield less net waste acid and that is a good thing, and if enough material is processed the separate treatments for all precious metals should not be an issue. I think it is an idea, which under the right circumstances, will produce good results.


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## lazersteve (Sep 29, 2009)

I agree with 4Ms about the melting of copper being an issue for small hobbyist. I'm still working towards building a large enough gas fired furnace to cast my recovered waste copper back into bars. 

Torch melting copper in larger batches is not practical in my eyes due to the heat transferring capacity of copper. I tried melting 50 grams of copper electrical wire with my torch once and had only mixed success. I ended up with a terrible looking mass of oxidized copper.

I haven't tried melting any in my mini-firebrick furnace, I may have better results with it, but the scale is still way too small to be useful in the application discussed above.

Steve


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## nickvc (Sep 30, 2009)

Thanks 4metals & Steve I am aware of the problem with melting copper having had to make master alloys to produce mainly 9 carat grain which in reality is a copper alloy as it constitutes the major part of the whole. I built my own furnaces after buying my first one out of lightweight fire bricks and using a bulldog torch running off propane easy to build, cheap and capable of been enlarged.The bricks are easy to cut with a saw so building the furnace was really simple, and if needs be it can be built outside,used and then put back into the garage brick by brick in minutes.The cost of this was no more than £50 approx $80. Part of the alloy was a copper / silicon alloy which allowed the gold to flow more easily when molten if i remember correctly this was 10% silicon but it was used at only 2% of the total ie .2% would this maybe work to alloy the copper to melt easier once melting temperature has been reached? The mix of gold platinum in the slimes is way past my experience im afraid but would an adaptation of the shor system seperate the gold from the platinum? Im no expert on much of this hence the post as im sure that the forum will either prove it can or cant be done economically and without thousands of $ expense.


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## Harold_V (Sep 30, 2009)

Unless you have considerably better luck than I had, the idea of parting gold alloy with a copper cell is insane. The percentage of copper must be high, and the accompanying values low, otherwise a resilient shell forms around the anode, eventually isolating the copper so it can no longer transfer. The same is true of values included in silver, when the silver is parted. Too much is not a good thing. 

The second issue that is troublesome is the rapid escalation of unwanted elements in the electrolyte, which give cause for the copper to deposit very loosely to the cathode, in the form of moss. It sloughs off, contaminating the resulting anode sludge. You may be able to overcome the contamination by using an anode bag, but that won't address the poor deposit, and will make cleaning the anode (if it becomes necessary) very difficult. The negative here is that the copper moss that comes from the cell is not marketable, and requires washing (to remove dragged down contaminants) before melting in order to send to market. At this point, you are investing more in the copper than it is worth. 

The issue of the copper deposit being fluffy (the moss I spoke of) may be able to be addressed by controlling voltage. I gave up when my cell, which was made from a ceramic, broke, dumping a couple gallons of copper sulfate on the floor of my garage. It was then that I accepted Hoke's inquartation and started using that process, which I used to the end. 

As 4metals has already alluded, the use of silver is an excellent way to inquart. I chose it because of its ability to retain the platinum group, which was very much a part of the metals I refined (commercially). Many of my customers included dental gold in their submitted materials. 

It will be interesting to see you succeed. Be sure to share your results. 

Harold


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## nickvc (Sep 30, 2009)

Thanks for your response Harold. My background was in commercial refining as you can see and i always used silver to inquart as you did with good results. Virtually all my refining came from and went back to the manufactures based mainly in Birmingham so i had little contact with platinum but did treat palladium on occasion and some electronic scrap but nearly always just exposed gold. Having read a fair few of your responses i know you and a large number of the members of this forum have a far greater knowledge about pgms and in truth also gold refining than i have so any input or comments you have to make will be gratefully recieved. This started as an enquiry from an old customer as to how to recover the gold from rolled gold where obviously the base metal content is very high and the volumes of copper will be worth recovering if possible...... As i said im no expert but i,ll pursue this till im finally convinced that it cant/wont work economically, and if it can surely it reduces unwanted waste and possibly produces a new income stream and has got to be better for the enviroment.


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## Harold_V (Sep 30, 2009)

Under the circumstances you described, assuming the base metal is copper, not a copper alloy, you likely have a shot at success by simply balancing the electrolyte and voltage. You probably understand that it would require melting of the items, to disperse the values in a finely divided state in the copper. 

If the base metal is brass/bronze, I don't feel any amount of juggling will yield success. Fouling of the electrolyte appeared to be my main problem, and it occurred almost instantly. 

It's fairly common knowledge that electrical parting cells are not well suited for working with heavily contaminated materials. They are generally fed with relatively high purity, regardless of the type of cell. By doing so, electrolyte experiences far better useful life, with a more desirable type of deposit, and the end product is assured of the intended purity. 

When parting silver that contained a high percentage of platinum group, along with traces of gold, it wasn't uncommon for me to have to hand scrape the slimes from the anode. Otherwise, I experienced a rapid decline in the silver content of the electrolyte, eventually leading to a virtual total depletion. That was a problem when I processed the silver recovered from my waste materials, which included a considerable amount of material from my stock pot. That was the method I chose for recovering traces of platinum and palladium from barren gold chloride solutions. It was rare to have them totally removed in the digest of the inquarted alloy. 

Returning to the material you discussed, I expect that you'd find traces of lead, but if the material is parted with a copper cell, I'm inclined to think it will manifest itself as lead sulfide, which, hopefully, would be eliminated in filtration. As you know, traces of lead in gold is very destructive of its ductility. 

Be sure to report your results should you make the attempt. While I no longer refine, I still have an interest in areas in which I experienced failures. 

Harold


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## nickvc (Oct 4, 2009)

The samples of the rolled gold are on their way and having taken note of the comments posted ive spoken to a friend/ supplier from my commercial past who has a plating background in many metals and a good knowledge of chemistry to ask his advice,im not to proud to ask or so stupid as not to listen,and he feels that this should be possible . The correct current is an important part of this process and he thinks that the zinc in the alloy will also plate across so it sounds like a brass alloy will be formed,this is not catastrophic as this is still saleable,not perfect but the volume of material been discussed is in tonnage so worth pursuing. Pure copper would be much better as it fetches a higher price but it sounds as if this will be an uneconomic goal and that defeats the whole point of the exercise. When ive tried this i will update the forum with the results re the plating process and any problems encountered and any methods to overcome them (or not) i love a challenge......


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## goldsilverpro (Oct 4, 2009)

All the commercial brass plating formulas I've seen are cyanide or fluoborate based. That means that, if you try to plate a sound deposit of zinc and copper together from most any other matrix (sulfate, nitrate, chloride, etc.), you will likely be unsuccessful. Multiple metals (more than one) are very difficult to plate. The problem isn't that both copper and zinc will deposit. The problem is that the deposit will be almost impossible to collect. It will be loosely adherent, spongy, and very difficult to rinse. It is common to see the metals deposited fall off and form large, floating, t*rd-like masses that short out the electrodes.

In general, you can have not more than one metal in solution, even in trace amounts. The solution must be made up with certain chemicals, in exacting amounts. Otherwise, the metal deposited will most surely not be marketable.


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## nickvc (Oct 4, 2009)

goldsilverpro said:


> All the commercial brass plating formulas I've seen are cyanide or fluoborate based. That means that, if you try to plate a sound deposit of zinc and copper together from most any other matrix (sulfate, nitrate, chloride, etc.), you will likely be unsuccessful. Multiple metals (more than one) are very difficult to plate. The problem isn't that both copper and zinc will deposit. The problem is that the deposit will be almost impossible to collect. It will be loosely adherent, spongy, and very difficult to rinse. It is common to see the metals deposited fall off and form large, floating, t*rd-like masses that short out the electrodes.
> 
> In general, you can have not more than one metal in solution, even in trace amounts. The solution must be made up with certain chemicals, in exacting amounts. Otherwise, the metal deposited will most surely not be marketable.


Thanks for the reply. i assumed that using sulphuric acid and copper sulphate as the electrolite only the copper would plate out ? As i said before i was going to use a copper cathode and place the annode in a bag to catch the slimes but my plating pal thinks the zinc might plate as well which if as solid on the cathode isnt awful but if your senario is right its going to be a real pain in the place designated........The base alloy in the rolled gold im hoping is copper and the quantity of zinc in a typical british 9 carat alloy is not above 20% so if its 1/20 9 ct rolled gold thats 1% zinc with 1.875% au and 0.6%ag and the balance copper which is why im looking at it from a copper refining angle i dont think its possible to reclaim it through dissolution in nitric profitably and the volumes are supposed to be large. Any further thoughts from yourself or any other member of the forum i,d welcome them. Good luck on your new venture but from what i can see you wont need it, a good honest independant assayer is just whats needed, especially one with your knowledge and experience in the precious metal world.


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## goldsilverpro (Oct 4, 2009)

I heard about a guy in the desert in NM that was recovering the gold from "refiner's bars". Most refiners incinerate all electronic materials. Then they ball mill the ash/metals and run it through about a 10 mesh screen. Most of the metals stay on top of the screen. These metals are all melted together and cast into bars. These are called "refiner's bars" and they are usually shipped to a primary copper smelter for PM and copper recovery. The bars typically run 65% copper and can contain as many as 10 to 20, or so, other metals.

It would be impossible to breakdown the bars, electrolytically, and plate out the copper and other base metals in a sound form on a cathode. That's why the refiners ship the material.

The guy in New Mexico used a membrane to separate the anode and cathode compartments. I think he used a 10%-15% sulfuric electrolyte. The "refiner's bars" were bagged and placed in the anode compartment and current was applied. The PMs and other insolubles were collected in the bags and the copper and other soluble metals dissolved into the sulfuric. The dissolved metals were prevented from reaching the cathode by the membrane. The copper and other dissolved metals were eventually cemented from the waste solutions, most probably with scrap iron.

This technique could be used for many different types of materials. The beauty of this is that it makes no difference what the other metals are, as long as they are soluble in the particular electrolyte you have chosen. Copper base gold filled or rolled could be cast into bars and easily run in this manner, using a dilute sulfuric. Karat gold could possibly be inquarted with copper and run in this way. On a small scale, a Coors porous cup could be used in place of a membrane. The Shor Simplicity refining machine works somewhat like this, although I wouldn't recommend buying one due to the high price. There are threads on this forum that discuss using an unglazed clay flower pot (with the bottom hole sealed) as the porous cup.


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## nickvc (Oct 4, 2009)

Thanks again goldsilverpro. Im goimg to try the easy way first, as in just trying the method i suggested(LOL) ,if that fails which by the look of things it will, a ceramic filter was going to be my next option. I was talking to a chemist who tells me im next to the biggest producers of ceramic filters in the world in Stourbridge UK so if it comes to that i can get one fairly easily . I knew very little about refining gold or silver when i set up my first business i just traded metals, but as i got busier i thought what the hell, so i tried a few experiments just to prove i could do it,ended up refining anything between 10 to 20 kilos of fine a week,nearly all carated scraps and bars with some sweeps and the odd solution and batches of high grade plated scrap.I can honestly say that im a chemistry moron but i listen to anyone who has a good proven background in metals, refining or chemistry and try to apply their knowledge to a commercial application. I hope this strikes a chord with many of the members of this forum between us all we have been a pain to the major players and long may it be so...


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## nickvc (Oct 13, 2009)

Well i started the experiment this week and so far so good. Im only messing at the moment using a small plastic dish to hold the electrolite a hobby mini rectifier a piece of copper for the cathode and a bar of 134 grams of 4.8% Au roled gold, i had it assayed just to be sure i get ball the gold out. The cathode is building nicely and the bar depleting likewise im getting some floating cack but only if i try to run the cell at to high an ampage,more advice needed here i think. I,ll post photos of it all when i finish it off, and have the cu assayed to see how well it works......or not!!! Im also going to put photos on of my furnace which really is so simple and cheap that all of the members on here could build one in minites.


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## goldsilverpro (Oct 13, 2009)

At 100% efficiency, it will take about 110 amp hours to dissolve your bar - that's 110 [email protected] amp or 55 [email protected] amps or 22 [email protected] amps or, whatever. Actually, these times are low, since nothing runs at 100% efficiency.

How many amps are you running? How much copper sulfate and sulfuric are you using per liter (or, gallon)? How much solution. 

I would guess that you haven't run long it enough to foul the electrolyte to the point that the plating causes problems. It will, unless the base of the GF was almost pure copper. 

You might try bagging the anode to keep the junk in. Bagging the cathode might keep in all the sponge that you inevitably will create. Have someone sew bags out of fairly heavy polyester cloth (Walmart) using polyester thread. Tie the bags at the top and keep the tied end out of the solution. The anode bag can be burned before going into aqua regia. 

The silver is not very soluble in that system. I would imagine that most of it will be with the gold.


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## nickvc (Oct 13, 2009)

Thanks yet again GSP for your response. Im playing with this just to see what is and isnt possible. The cack comes off if i try to run at 3 or 4 amps but if i reduce it down to under 1 amp it seems to dissapear back into the electrolite ,the electolite seem to be holding up pretty well so far, but at the moment couldnt tell you the breakdown of this as my plater friend did the mix for me. The slimes dont bother me too much as the plan is just to melt it after washing and trading the resultant bar,its pointless to refine them as i wont get a better price 4 the fine Au so cant see the point, theres little call in the uk 4 fine Au. a good assay will yield 98% of fix. No extra profit in taking it any further down the refining route so im not going to bother..


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## Anonymous (Oct 13, 2009)

I am not a plater, but have done some reading on it and have some thaughts they my not work or may be they will.
I was reading about a unit that is used to recover copper from dilute solutions. I was thinking of diluting my solutions down
and using lead for a anode and copper for a cathode. I was planning on treating the excess copper chloride with sulfuric and distilling the HCL back off, but I am going to try using it for precipatent first. this should regenerate a weak sulfuric which I would evaporate/boil back down to start over. Since to me you are 100 percent right about refining exspecially if you are like me and just do not have the volume to get anyones attention, at least for now.
I think a dilute solution will also lesson any interference by nickel and other base metals. 

Jim


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## nickvc (Oct 31, 2009)

An update on my lack of progress.It all started fine but eventually the floating junk started to appear...GSP was right should have thought more about what he advised . Having access to xrf machines i should have checked the cu content  Never mind got some more RG and im just going to rinse of all the metals etc and remelt with the new metal PLUS an equal amount of scrap cu and then get a cu readout.This will also allow a larger thinner bar with a high enough cu content to allow the process to work much more efficiently..LOL. Im going to try and post the photos of my easy build furnace this week so any members who are interested can see if it has any applications for them ,this will make larger melts available to everyone very cheaply. Apologies in advaance if i post them to large i really am a computer dweeb.


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## Oz (Oct 31, 2009)

Nick,

If anyone here can provide an inexpensive reducing atmosphere furnace for copper, it would be a service to many.

I look forward to your pictures.


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## nickvc (Jan 13, 2010)

Right christmas panics over time to try the copper parting cell experiment again. Melted a larger quantity of rolled gold and scrap copper 869gms and had an xrf scan done,Au3.53% Ag1.50% Zn7.85% Cu87.0% wondering if this higher % of Cu will allow the cell to work better and avoid the fouling problems??? Will take the pictures of my furnace now and will try to post those too,my apologies in advance if they dont load as stated before not clever with computers


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## goldsilverpro (Jan 13, 2010)

Nick,

It might start out better, but I think that the zinc will eventually raise it's ugly head. Maybe there's an additive you could use to tie up the zinc and prevent it from plating out or maybe something that would selectively drop out the zinc before you start plating. I will look through my books. Also, in these non-cyanide days, someone may have come up with an acid brass bath that will plate out both the Cu and Zn. Here's the only thing I could find. The formula is strange. It has both copper sulfate and NaOH in it. I would think that copper hydroxide would precipitate. Maybe the glycolic acid keeps it in solution.
http://www.pfonline.com/articles/clinics/1208cl_plate4.html

As it says in the article, cyanide baths are used to plate brass (Cu/Zn). However, cyanide wouldn't work for you since the Au and Ag will also plate out and you would end up where you started.


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## nickvc (Jan 13, 2010)

Thanks GSP . I did think the Zn would be the pain if i could find an alternative to cyanide i think it would be of much more interest to the rest of the members of the forum,i have used it for years and as yet it hasnt been banned here :shock: controlled but not banned.As this is just an experiment time isnt critical and the Au is just an accumulation over time so another month or two makes no odds so im happy to wait till your research is done and then try again. Im wondering if a porous membrane might be the way forward  if the copper can be separated from the rest the jobs nearly there :roll:


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## goldsilverpro (Jan 13, 2010)

Sure, a membrane will work. In a 10-15% sulfuric, it will dissolve the Cu and Zn, but not the Au and Ag. The cathode will be isolated from the solution, so nothing will plate out and you wouldn't have to worry about that.


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## nickvc (Feb 25, 2010)

Right starting again same bar as an annode but this time trying the porous membrane in the hope it controls the zinc better,the membrane is the outer part of an induction furnace pot ie graphite liner removed,its about 5 inches by 9 and its in a plastic bucket with sulphuric and copper,i managed to scrounge some titanium wire which i,ve coiled roughly to hold the bar and placed a piece of copper in the bucket as the cathode,going to run this for several days and see what happens :roll: Sorry for not putting my furnace pictures up but i cant seem to manage it  as i said not good with technology,need to borrow a kid of someone they would do it in minites :lol:


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## g_axelsson (Jul 19, 2010)

Any progress?

I think this is an interesting idea with a lot of potential if we can get the bugs out of the system.
One thing I think could form a problem is to use an electrical conductive membrane as graphite. It would short out the passage of hydrogen ions through the barrier and start plate out copper on the surface. I also would expect that the graphite would break down on the surface and wear off.

I would try this with a nonconductive porous barrier. As soon as I get some free time... any decade now.

:mrgreen: 

/Göran


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