# Dropping silver from unknown silver cyanide solution?



## peter i (Feb 1, 2010)

I have "inherited" a large bottle of silver cyanide solution used as "silver strike". It is 20 years old, and I do not know the concentration.

My plan is to add zinc dust to drop the silver, then destroy the cyanide with chlorox or hydrogen peroxide.

But the question? How do I know how much zinc to use?


The primitive method would be to use plenty of zinc on a smaller volume, wash with water and hydrochloric and weigh. Then use the stoichiometric amount of zinc for the rest of it.....

Is there an easier way to do it?


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## goldsilverpro (Feb 1, 2010)

Peter, my friend,

I hope it's a huge bottle. Unlike silver plating baths, strike baths *must* be low in silver and high in cyanide to prevent immersion deposits (and, therefore, poor adhesion) from occurring. They use the strike bath, to first lay a thin layer of adherent silver, before using the plating bath. New strike baths only range from about .2 to .5 tr.oz. of silver per gallon (1.6 - 4.1 g/l). Silver cyanide plating baths usually range from 4 - 10 oz/gal.

I would guess that it will take maybe 2-3 times as much weight of zinc as you have silver, but it's always better to use a little excess of zinc. When you drop gold from cyanide solutions with zinc, the gold ppt. is brown and you know when you have an excess of zinc when the powder in the solution turns gray. However, silver and zinc powder are both gray, so you have no visual indications.

There is no simple way to analyze the silver. You can weigh a piece of Pt screen, if you have it, before and after, and try to plate out all the silver onto it from a 5-10 ml sample diluted to about 50-75 ml in a 100ml beaker. Use an amp, or two, for maybe 30 minutes, with slow agitation (magnetic stirrer). Try to regulate things so all the silver stays on the Pt and doesn't fall off. Rinse very carefully and dry it slowly, but completely, before the final weighing. I haven't tried this for silver, so I can't be exact about things, but I've done this for gold cyanide solutions many times. It should work the same. You might try stainless sheet or lead for this, instead of the Pt, although I don't think it will stick well to the stainless, unless it is etched first with about 10-20% HCl, by volume. You can fume a 5ml sample with some conc. H2SO4 and then titrate the silver, but that's another story. Do you have access to an AA??? That, of course, would be the easiest.

I think I would leach out the excess Zn with dilute H2SO4 (10-15%, by volume - maybe a little heat at the end), instead of HCl. With very finely divided silver, there's always the possibility of making some AgCl with the HCl.

Chris


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## peter i (Feb 2, 2010)

Thanks

I feared something like that  

In other words, the silver is probably not worth the trouble (a little experimentation just for the academic interest could of course be an excuse)


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