# refining electroplating solutions



## Anonymous (Mar 30, 2008)

i am new to gold and silver refining... I have several gallons of gold electroforming and silver electroforming solutions, that i had purchased while developing a robotic electroforming machine. now that i have no more use for these solutions and am now trying my hat at refining, i was hoping someone could help me with the procedure to actually refine the gold out of these solutions

thanks in advance


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## peter i (Mar 30, 2008)

Be careful, they probably contain enough cyanide to kill the neighbourhood.


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## Harold_V (Mar 30, 2008)

The simplest way to recover the values is to introduce zinc flour to the mix. How much depends on the level of concentration, and the nature of the solution. Zinc will precipitate the values as sponge, which will require further processing after it's retrieved. Right now, concentrate on getting the values out of the solutions. 

It would be quite helpful to know the nature of the solutions. As has been suggested, if they're basic (likely cyanide), they are quite dangerous in ignorant hands (no offense intended) and should be handled properly to avoid killing innocent creatures. Can you discuss the solutions at greater length, including the amount of value expected to be recovered from each of them?

Harold


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## Lou (Mar 30, 2008)

If they do contain cyanide, it is better to leave them to someone who knows what they are doing. You can cement out the values with zinc, but you're still left with the problem of the cyanide. There are many ways to handle it, but I would strongly advise against it without your having some laboratory equipment and a fume hood. It's also convenient if you know whether or not you can actually smell cyanide--some individuals can't, and I would not recommend them working with it.


Lou


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## Anonymous (Mar 30, 2008)

thank you for the help...i do have a hood, and i am experienced when working with cyanide, itself...but for different purposes, usually i use these solutions when testing a new product, IE electroforming solutions, electroplating solutions, and "bombing solution" (which is used to polish jewelry in mass quantity).

However i take no offense, because i am completely ignorant to the chemicals themselves, my understanding goes as far as using them, not producing, or refining them. I actually am not even sure how much gold is in the electroforming solution...at the time of development it was very hard to find information on 14k gold electroforming process, and in fact there was only one source for the solution it self (technic) and i can not seem to find any info with them now. I do know this though the electroforming solution i have is cyanide base, and the electroplating solution i have is not. i have about 7 gallons of electroforming solution and maybe 5 gallons of electroplating

as far as being able to smell the cyanide, i can and it gives me horrible headaches, it is interesting tough you point the smell out, because most people say i am crazy when i say i can smell it.


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## Harold_V (Mar 31, 2008)

Lou is far better able to instruct you on proper disposal of cyanide solutions that are barren, but if memory serves, you would add some calcium hypochlorite to the mix, which will render the cyanide harmless. 

Lou, I'm open to correction. I'm trusting to memory, as I haven't done this for many years. 

Regards extracting the values, it's important that you have some free cyanide in the solution, for the reaction to take place efficiently. If you have any at your disposal, dissolve a few ounces in each batch. Next, use an ounce of zinc flour for each ounce of values that you expect to recover. Stir the solution well, then sprinkle the zinc in. You'll see an instant reaction with gold---the zinc immediately is replaced by gold sponge. An excess of zinc insures virtually complete precipitation. Same goes for the silver, but you may not see the silver precipitate in the same fashion because of the color. If you do not find any free zinc when you have finished, you may wish to add more zinc to insure that you have precipitated all the values. It's cheap insurance. 

Allow the precipitates to settle well, then decant. Wash the precipitates well with water, then you can eliminate the excess zinc with acid. Do all of this in your fume hood----don't take any chances. For gold, you can use nitric, HCl or sulfuric to eliminate the zinc. Avoid the use of nitric with silver. It will dissolve the silver as well as the zinc. Dilute sulfuric may be your best choice. Do it cold, to insure that you don't dissolve silver, or use HCl, which may convert traces of silver to silver chloride. No harm if you recover the chlorides and convert them back to elemental silver. 

How far do you want to go with the recovery of values? My next step (for the gold) would be to dissolve it in AR, evaporate, filter, then precipitate. Silver can be melted and cast in an anode for the silver cell. If you treated it with acid after recovery, it should border on being pure. 

Harold


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## Baja Bob (Mar 31, 2008)

If I remember correctly cyanide is safe at a PH above 9, it starts getting dangerous when the PH goes under 8. Cyanide Gas will be produced as the solution get close to the acid side, ph 7 and below. Harold was correct in recommending calcium hypochlorite, I think sodium hyprochlorite will also work. Keep a ph meter close by, when I worked with cyanide leaches I kept the meter probe in the solution all the time I was working with it. I also had a 5 gallon bucket of saturated hypochlorite solution nearby, in case something went soutn. luck baja bob


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## peter i (Mar 31, 2008)

As a refiner ferrous sulphate is normally at hand, making it easy to test for cyanide:


> Iron(II) sulfate is added to a solution suspected of containing cyanide, such as the filtrate from the sodium fusion test. The resulting mixture is heated for a few minutes, cooled, and acidified with mineral acid.
> 
> The formation of Prussian blue is a positive result for cyanide.



If the test is performed on a few drops of the solution in a test tube or a spot plate, the risk should be minimal.

There is quite a thesis on the destruction of cyanide with hypochlorite here:
http://shorinternational.com/cyanodestruct.htm

Notice that pH is important.

Any hypochlorite should do the trick.



After precipitating and isolating the noble metals, remember that the wash water will also contain cyanide. It should be added to the rest of the solution an destroyed along with it.

I've only done it once to render safe a container marked "cyanide waste" . (it was found cleaning out a lab)


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## Lou (Mar 31, 2008)

magicmykee said:


> thank you for the help...i do have a hood, and i am experienced when working with cyanide, itself...but for different purposes, usually i use these solutions when testing a new product, IE electroforming solutions, electroplating solutions, and "bombing solution" (which is used to polish jewelry in mass quantity).
> 
> However i take no offense, because i am completely ignorant to the chemicals themselves, my understanding goes as far as using them, not producing, or refining them. I actually am not even sure how much gold is in the electroforming solution...at the time of development it was very hard to find information on 14k gold electroforming process, and in fact there was only one source for the solution it self (technic) and i can not seem to find any info with them now. I do know this though the electroforming solution i have is cyanide base, and the electroplating solution i have is not. i have about 7 gallons of electroforming solution and maybe 5 gallons of electroplating
> 
> as far as being able to smell the cyanide, i can and it gives me horrible headaches, it is interesting tough you point the smell out, because most people say i am crazy when i say i can smell it.




Sorry if I came across as being brusque, I just generally discourage people from working with CN- as it is a potent poison and one lungful of HCN will at least knock you to the floor. 

I mentioned that some people can smell it and others can't because it is important to using it safely. I can smell it, and indeed I have worked with it (I even know what it tastes like  ). It's a genetic variation, akin to how some individuals can smell blood, and others not, or how some individuals can taste phenylthiocarbamide (exceedingly bitter, also quite toxic!)

Harold and Peter both gave you good instruction on precipitating the values and on oxidizing the cyanide to cyanate with hypochlorite (which must be done at about 50F/15C or below).



Lou


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## Anonymous (Apr 2, 2008)

I just wanted to thank you guys for helping on this... i will let you know how it goes !


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## goldsilverpro (Apr 3, 2008)

Before using zinc dust, adjust the pH to 12 min. with sodium hydroxide. 12 is the safe pH - not 9. Also, in order for the gold to drop, some zinc must dissolve. This will occur more efficiently if the pH is 12, or a little higher. After adding enough zinc dust to drop all the gold, allow the gold plus excess zinc to settle, preferably overnight. During settling, hang a zinc bar in the solution. This will prevent the gold from redissolving in the cyanide. 

The above assumes a cyanide matrix, of course. A true cyanide gold electroforming solution can contain about 4 tr.oz. of gold per gallon.

Fume Hood! Fume Hood! Fume Hood!


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## Irons (Apr 3, 2008)

I've used Aluminum to reduce Gold from Cyanide but I found that the Gold partially alloyed with the Aluminum resulting in "Purple Plague" contamination.

Just for info.


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## goldsilverpro (Apr 3, 2008)

The best thing to use in CN gold solutions is sold by the name, "zinc dust." It is normally 325 mesh. There are many manufacturers. It is usually packaged in 50# metal pails. It is also sold in smaller quantities by companies that repackage chemicals. Sorry, but I have no present sources.

It is often lumpy, especially if it's not kept dry. I usually put it into a small squeeze type flour sifter, to break up the lumps, and sprinkle it into the solution, with stirring. When the precipitate turns slightly gray (from excess zinc), all of the gold should be out of solution. Go slow with the zinc. If the conditions are right, the Au/Zn weight ratio is about 1 to 1. After adjusting the pH to 12 (and, before adding the zinc), it often helps to add about 1 oz of sodium cyanide per gallon of solution.

FUME HOOD!


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## Lou (Apr 3, 2008)

I didn't catch that pH of 9! Yes, you definitely want it rather basic, 11 or 12 like GSP said. While you could have it at pH 9, there will be free HCN. This is not problematic if you have a large bulk of solution ('tis quite happy to remain dissolved in cool water), but why take chances?

I seem to recall the name of merrilite zinc. Ever heard of that GSP.

I know http://www.lmine.com sells it for relatively cheap.


Lou


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## goldsilverpro (Apr 3, 2008)

What Legend calls Merrilite sounds like zinc dust to me. Probably got its name from the Merrill-Crowe process. Sounds OK. The zinc doesn't have to be very pure.


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