# help what should i do with cyanide contain gold



## Anonymous (Dec 23, 2009)

i have few drum cyanide electroplating solution that have been abandoned for years what should i do to precipitate the gold from it (the simple and cheapest way) without pure zinc dust or pure zinc metal because it is hard to find them in my country.
there is a white yellowish mud in the bottom but i doubt that is gold mud.
this is the picture


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## goldsilverpro (Dec 23, 2009)

What is the pH of the solution? Before suggesting an answer, I need to know the pH. Stir it before measuring. If you can find some pH papers to measure with, that is fine. I just mainly need to know whether the pH is above or below 7. However, a little more accuracy would be better, if you can manage it.

Do you have any idea what types of parts were plated by this facility? Electronics? Jewelry? Other?

Why do you think this solution contains gold?

The solution appears colorless. It could, therefore, come from a drag-out tank. This is the first water rinse after the parts come out of the plating tank. It is used to collect the bulk of the gold solution clinging to the parts. If so, the gold content would be low, although some drag-out solutions can contain as much as 0.1 oz of gold per gallon. Although there are a few types of colorless gold plating solutions, the alkaline cyanide solutions are light yellow and most acid cyanide solutions are light green or pink.

The yellowish mud could easily contain gold. Gold cyanide (AuCN) is yellowish and this can form on standing, especially when the pH is a little low.

Was the drum tightly sealed? If not, the sludge could be dust.

The more you can tell me about this solution and it's history, the better.


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## Anonymous (Dec 24, 2009)

hello thanks for replying
this is from jewelry oldway electroplating sodium cyanide bath(anode is pure gold and cathode is jewelry) it is not the first rinse solution.
i electroplate jewelry in 1 litre cyanide bath and change the bath with new cyanide solution every 500 gr jewelry, and the old cyanide bath that i have used is stored to that tank. the tank is not sealed.

i measure with ph universal it show 11.
this another picture 





yesterday i try with zincalume(thats the best i can get) and it precipitate gold a little.
can zincalume plate precipitate all the gold in the solution?


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## Harold_V (Dec 25, 2009)

yaphiar said:


> yesterday i try with zincalume(thats the best i can get) and it precipitate gold a little.
> can zincalume plate precipitate all the gold in the solution?


You should be able to effect a full recovery with zinc/aluminum., but the quality of the recovered gold will be suspect. I recommend a full refining before putting it to use. A little free cyanide would be really helpful in the recovery. An ounce in 5 gallons should be sufficient. 

If you must use solid pieces instead of fine particles, allow plenty of time for the conversion. An ounce of zinc should precipitate an ounce of gold. 

When you use zinc dust, and you have free cyanide present, the conversion is instantaneous. 

Harold


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## Anonymous (Dec 25, 2009)

thanks harold for the answer.
if i boil the solution with zincalume in it, would it make precipitation faster?


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## patnor1011 (Dec 25, 2009)

Harold_V said:


> instantaneous


equals



yaphiar said:


> faster


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## Anonymous (Dec 25, 2009)

will gold disappear to the air when i boil the cyanide solution till dry?


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## Harold_V (Dec 25, 2009)

yaphiar said:


> thanks harold for the answer.
> if i boil the solution with zincalume in it, would it make precipitation faster?


I know that heat accelerates chemical reactions, but I don't know if heat would help, or not, in this instance. Might be worth a try, but with a couple small samples. One not heated, the other heated, both with the identical amount of surface area exposed to the solution. 

Harold


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## goldsilverpro (Dec 25, 2009)

To me, this has all been made much simpler than it actually is. Knowing these plating solutions as I do, there is a good chance that the sludge contains solid AuCN - what do you do with that? To get all the gold and prevent killing yourself, things should be done in order. The first thing I would do is check the pH. It can make a difference as to how the material is handled. The man doesn't have zinc and I think aluminum is a poor choice. I'm not sure if aluminum will even form a cyanide complex. It is possible to plate out most of the gold, but the solution first has to be adjusted and the sludge must be dealt with. The starting point is knowing the pH.


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## Harold_V (Dec 25, 2009)

goldsilverpro said:


> To me, this has all been made much simpler than it actually is. Knowing these plating solutions as I do, there is a good chance that the sludge contains solid AuCN - what do you do with that?


I would hope that having free cyanide present would preclude that possibility. Not suggesting that would be the case., however. Please do keep in mind, the solution is question appears to have been used without a gold anode, so it likely is near exhaustion. 



> To get all the gold and prevent killing yourself, things should be done in order. The first thing I would do is check the pH. It can make a difference as to how the material is handled.


No argument on the status of the pH. However, unless something very strange has occurred, I would expect it is within reasonable range. I agree totally that it should be determined, however.



> The man doesn't have zinc and I think aluminum is a poor choice. I'm not sure if aluminum will even form a cyanide complex.


One does with that which is within one's reach. He has made it clear that he has no access to zinc. He has also indicated that he has experienced some degree of success using a zinc/aluminum alloy. To me, that makes sense. Zinc likely prevents the oxidation of aluminum, so it is likely able to reduce gold from cyanide. I know that I used a 7/8" diameter 60601 aluminum rod to stir my cyanide solutions when recovering both silver and gold from cyanide. While my objective was not to rely on the aluminum for the reduction, it appears to react in a minor way. My solution was always at least 10pH, if not slightly higher, and I always introduced a small amount of free cyanide. I also introduced and excess of zinc flour, to insure a complete precipitation. 

Once values were recovered, my solution was placed back in service. That way if traces were left behind, they were eventually recovered. Indications were, however, that that was never the case. I always had residual zinc in my recovered values, due to introducing more that was required to insure a complete recovery. 

I processed only one large batch of plating solution, that from a commercial plating business. I had respectable results using the process I discussed. I realize that there are various types of plating solutions, however, and do understand that recovery can be difficult. 

Knowing the source of his solution, and the fact that it was used for a given period of time, I expect that there is little gold present, but well worth the effort to recover. I'll be interested in seeing the outcome. 

Harold


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## Anonymous (Dec 26, 2009)

i finally get the zinc dust 800 mesh but its expensive bout 40 us/kg. i gonna try this nite.
thanks harold and goldsilverpro for the suggestion.
i ll post the result soon


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## goldsilverpro (Dec 26, 2009)

Here's why I wanted to know the pH.

If the solution was used to plate electronics, the odds are that the solution was of the acid cyanide type, with a pH of about 4 - 6. In this case, there is no free cyanide in the solution. If the bath is of this type, there is likely to be some AuCN in the sludge, especially if the pH is below 4.

If used to plate jewelry, it is probably a cyanide bath with a pH of about 10.3. In this case, there is probably free cyanide and, if so, there is no AuCN in the sludge. 

Cyanide is the only thing that will dissolve AuCN and make it available for precipitation with the zinc. Since you now have zinc, the following *IDEAL* cycle will work for both types, assuming there is gold in the solution to start with. If you do it right, a kg of zinc will drop out from 15 to 30 oz of gold, so it's not expensive in the long run.

*IN THE ORDER GIVEN!*

1) Using sodium or potassium hydroxide, adjust the pH to 12. Go slow and try not to exceed this because an excess will end up using more zinc.

2) With stirring, dissolve about 1/2 oz of sodium or potassium cyanide per gallon of solution. Note that this is only necessary if the bath originally was of the acid type. However, although not necessary for an alkaline cyanide bath, it won't hurt to add the cyanide.

3) If AuCN is present, it helps to heat the solution, with stirring, to make sure it all dissolves.

4) With stirring, sprinkle just a little zinc dust in the solution. If the zinc dust is in clumps, you should break it up before adding. The easiest way is to use a fine flour sifter. When stirring, observe the color of the precipitate. To see this, it helps to use a plunger type stirrer (a 6 inch square, or circle, of thick plastic securely mounted on the end of a plastic pipe works well) that will lift the precipitate to the top. If gold is present, it will be brown at first. With further small additions of zinc, it will, at some point, turn gray. At this point, stop adding - you have an excess of zinc. If there is no gold (or, copper) in the solution, it will turn gray with the first small addition. If, for some reason, there is copper present, you will get a red-brown precipitate at first. This can be misleading.

5) Allow to settle (sometimes, it takes 4 or 5 hours) and then siphon or dip off the solution without disturbing the sludge. Note: it is possible that, during the settling period, some of the gold will re-dissolve. To prevent this, hang a zinc bar, or two, in the solution while it is settling.

6) Filter the sludge and rinse several times with hot water to remove any cyanide solution.

7) Put the sludge and the filter paper into a plastic bucket. Cover slightly with hot water and stir to break up the sludge. *UNDER A FUME HOOD* (just in case cyanide is still present), add a little concentrated nitric acid. It should react immediately with the zinc. When the reaction dies down, add a little more. At some point, an addition of nitric won't produce a further reaction. Stop adding nitric - all the excess zinc, and most other metals present, are dissolved.

8 ) Settle and decant or siphon off the solution without disturbing the sludge. Filter and rinse the sludge.

9) Dissolve the sludge in aqua regia (hot is best). Since there is probably a lot of dirt still in the sludge, it probably won't all dissolve. Filter, rinse well, and treat the aqua regia solution as normal.

*NOTE:* 
After step (3), you could allow the solution to settle and then siphon, filter and rinse to get rid of the dirt before dropping the gold. This could make things easier in the long run. 

After adding the cyanide and getting rid of the dirt, a simpler option would be to try and plate most of the gold out, using 2 stainless sheet electrodes (1 cathode and 1 anode) of the same size, hanging opposite each other on each side of the drum. Measure the surface area of one side of the cathode (-) sheet and use about 3 amps per square foot of surface area. At 100% efficiency, about 7.3 grams will plate out per amp per hour. However, as the gold concentration goes down, the efficiency will decrease considerably. If you try this, you could put the cathode inside of a sewn cloth bag with no holes in it - polyester cloth is about the best - to catch any gold particles that might fall off. Of course, you could eliminate the bag and siphon and collect the particles off the bottom of the drum - assuming you got rid of the dirt. If you go the plating route, I would suggest you first try a 3 or 4 gallon sample, in a 5 gallon plastic bucket, to start with. By plating, you probably won't get all of the gold. However, you may be able to get all but about 0.1 grams, or less, per gallon of solution.

Chris


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## Anonymous (Dec 27, 2009)

in order number 9, why dissolve the sludge in AR? can i just melting it? is the sludge gold metal dust?


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## goldsilverpro (Dec 27, 2009)

> in order number 9, why dissolve the sludge in AR? can i just melting it? is the sludge gold metal dust?


The gold will rarely (if ever) be pure (at least 999.5 Fine) in this or most any other system in which you've leached out base metals unless you purify it with aqua regia.


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