# Recover silver from Silver Potassium Cyanide



## hrushi (Feb 8, 2009)

Can anyone help me to recover silver from Silver Potassium Cyanide which used in plating industries. 

Thanks
Hrushikesh


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## Juan Manuel Arcos Frank (Feb 8, 2009)

Hrushi:

Working with cyanide solution represents a very high risk.Here is my advice for you:

First of all and before starting to work with cyanide solution,please,read the Cyanide Code I have posted on "Books section",then read the process to destroy cyanide waste solutions in the same "Books section".

Basically you have to use a pH of 12,lower pH yields to hydrogen Cynide,a very toxic gas wich smells like almonds,then add zinc dust,the silver goes down BUT the best and safe way to do this will be provided by GSP or Harold_V,both have experience with cyanide solutions better than mine.

Best Regards

Manuel


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## Platdigger (Feb 8, 2009)

Juan, I found a download and a link you gave about cyanide.
But they were not in the" books" section.
Is there something else?
Randy


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## Harold_V (Feb 9, 2009)

Juan Manuel Arcos Frank said:


> Basically you have to use a pH of 12,lower pH yields to hydrogen Cynide,a very toxic gas wich smells like almonds,then add zinc dust,the silver goes down BUT the best and safe way to do this will be provided by GSP or Harold_V,both have experience with cyanide solutions better than mine.



Actually, pretty good advice. The pH is somewhat more forgiving than you implied, but it's better to be safe than sorry. PH can slip as low as 9½ and still be safe. 

The solution should contain a little free cyanide----and best results are achieved using zinc flour (fine dust). You can expect an ounce of silver for every ounce of zinc used, to the point of total extraction. 

I suggest a large vessel, stirred well, with the zinc sprinkled in while the solution is in motion. Stir again, using an aluminum rod if available. Allow to settle well, then decant. A second precipitation with a small amount of zinc will insure that all of the values have been recovered. Rinse the solids well with water, then process with cold dilute HCl to eliminate free zinc. If the solution contained traces of gold, the wash could be with dilute nitric, separating silver from the gold.

Harold


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## Juan Manuel Arcos Frank (Feb 9, 2009)

Platdigger:

You are right...I posted the Cyanide Code and a method for destroy cianide waste solutions with clorox...the Code is available at www.cyanidecode.org and the method is at www.shorinternational.com

Thanks.

Manuel


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## Juan Manuel Arcos Frank (Feb 9, 2009)

Harold_V:

Thanks for the instructions...now we know the safe way to do it.

Have a nice day.

Manuel


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## hrushi (Feb 9, 2009)

Thanks 
but how to destruct cyanide

Hrushi


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## peter i (Feb 10, 2009)

hrushi said:


> Thanks
> but how to destruct cyanide
> 
> Hrushi



See the link posted by Juan above.

Remember that cyanide is very likely to destroy you, rather than you destroying the cyanide, if you goof!

Keep it alkaline and test for excess chlorine to ensure complete reaction.


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## goldsilverpro (Feb 15, 2009)

Is the silver potassium cyanide in salt form or is it already dissolved? If in salt form, dissolve it in water. It's quite soluble. I would dissolve it at a rate of about 3 to 5 oz/gallon of water. I put it in an open top 55 gal plastic drum, but I was always working with large quantities.

For safety reasons, I preferred adjusting it up to a pH of 12 with NaOH. Also, every reference I've seen says to use a pH of 12. Don't overadd or the extra NaOH will dissolve zinc and will waste it.

Like Harold said, you may need a little free cyanide to get the precipitation started, especially if you started with salts. I would suggest adding about 1/4 to 1/2 ounce/gallon of KCN or NaCN to the solution, if you have problems.

For stirring, I used a plunger type stirrer made from a plastic disk about 5" in diameter, with several 1/2" holes drilled in it, attached to the end of a length of plastic pipe. I cut the disk from the material I cut off the top of the plastic drum. The stirrer is slowly moved up and down in the solution. This type stirrer is by far the best, since you get total mixing with the least effort. Stirring rods tend to only move the solution in circles. I always had several sizes handy for different applications and for different sized containers. For hot solutions, the pipe will tend to warp. To avoid this, I put a length of rebar inside the pipe and capped the pipe on both ends. This also prevents the stirrer from floating. To assemble, starting at the handle end, I went cap - pipe with rebar in it - coupling - very short piece of pipe - disk - cap. The very short piece of pipe was cemented into the coupling and bottom cap and was of a proper length to hold the disk snugly between the coupling and cap.

The zinc dust tends to clump, so I weighed it out and added it from a small squeeze type flour sifter to break up the clumps.

It is hard to tell when all the silver has been dropped out. There are analytical methods, but they usually require equipment and some methods are fairly complex. Like Harold said, it takes about a ounce of zinc per ounce of silver. This will vary based on the pH. For this reason, people tend to add extra zinc. You will pay the piper, however, since all extra zinc must be gotten rid of.

Once all the silver is precipitated, I hung 2 or 3 zinc bars in the solution and let the silver and excess zinc settle overnight. The bars prevent the silver from re-dissolving.

The same procedure was used for gold cyanide solutions.

The collected silver/zinc mud must be rinsed very well with hot water, in a filter, in order to remove all traces of cyanide solution. The next step uses acid to remove the excess zinc and any cyanide left in the mud will produce hydrogen cyanide, which is the gas used in prison gas chambers. No matter how well you've rinsed, don't attempt this unless you have a good FUME HOOD.

With gold, you can simply dissolve the zinc with nitric and leave the gold as a solid. With silver, however, the choice of acid is more important. Nitric will dissolve both silver and zinc. You could possibly use nitric and then use copper to cement out the silver - that was usually the way I did it. Don't use HCl, because the silver is finely divided and you will produce some silver chloride. You could probably use a weak sulfuric - about 10%. To avoid acids, you might try a weak NaOH solution, although I would be skeptical about the total removal of zinc.

Zinc is very reactive with acids and strong bases. With just a small amount, the solution gets very hot and can easily foam over. To prevent this, I cover the mud well with distilled water and, UNDER THE FUME HOOD, add the acid a few ml at a time. When the reaction dies down, I give it a stir and add a few ml more acid. Be patient. Use a deep container sitting in a plastic tray.


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## eemtek (Aug 17, 2009)

try this but with a good fume hood and lots of caution.. take a thin zink plat large enough to fit into your tank. as you put it in, add a little hcl.. lets say a cup per gallon.. slowly add it because of the bubblings.. add only half of it now, and add a little more after a while. you will lower the ph, but the mud will actually fall instead of stick to zink.. collect your mud and wash with vinegar.. then smelt to see where you are with it..


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