Sulfuric I purchased last month Ace Hardware $32.99 1 gallon. Liquid Fire 92-94%
Wash off the silver coating in concentrated sulfuric acid.
- Thread starter anarxi
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I have to test my experimental process using sulfuric acid.
I used a small volume, about 50 mls of sulfuric with somewhere around 100 grams of small silver-plated parts (I used the smallest parts to maximize the ratio of silver-to-base metal, so measuring the results would be simpler).
I heated it and cooled the sulfuric acid twice with the double the mass of plated parts the acid could dissolve (using copper's molar mass for the calculation, since most of the metal will be copper), saturating the acid with metal. Then I diluted the solution gradually with water to about double the volume total and heated again.
The silver only transiently dissolved each time and reduced on the remaining metal as small crystals, which could then be stirred loose after the final heating and cooling in the dilute acid. This made it very simple to remove the larger base metal lumps from the fine silt of silver. Any thin base metal dissolved completely and remained as primarily copper and tin sulfate solution. This took advantage off the fact that silver and silver sulfate dissolve less and less the more dilute sulfuric acid becomes, while copper and tin sulfate dissolve very well in dilute sulfuric.
I tested the recovery by removing and then dissolving all remaining base metal parts in nitric and then dripping HCl into it to see if any silver chloride dropped out. There was barely a visible trace of sediment when HCl was added, compared to roughly half a gram of silver when all was said and done, so the experiment had easily over a 99% recovery.
The tiny crystals and other precipitate in the original beaker were a mix of silver, and a small amount of silver sulfate and lead sulfate.
It's a time-consuming process with the 3 rounds of heating and cooling and slow dilution step, but otherwise proceeds fairly straightforward and only requires sulfuric acid and water as reagents. Treating the waste solution was very simple, since copper reduces out on iron quite completely in sulfate solution. Tin also eventually reduced out too, leaving a solution of almost entirely iron sulfate, which is virtually non-toxic.
When I get time again, I'll perform a second experiment to see if I can duplicate the results with a somewhat larger volume, roughly 250mls, and about 500 grams of metal.
I used a small volume, about 50 mls of sulfuric with somewhere around 100 grams of small silver-plated parts (I used the smallest parts to maximize the ratio of silver-to-base metal, so measuring the results would be simpler).
I heated it and cooled the sulfuric acid twice with the double the mass of plated parts the acid could dissolve (using copper's molar mass for the calculation, since most of the metal will be copper), saturating the acid with metal. Then I diluted the solution gradually with water to about double the volume total and heated again.
The silver only transiently dissolved each time and reduced on the remaining metal as small crystals, which could then be stirred loose after the final heating and cooling in the dilute acid. This made it very simple to remove the larger base metal lumps from the fine silt of silver. Any thin base metal dissolved completely and remained as primarily copper and tin sulfate solution. This took advantage off the fact that silver and silver sulfate dissolve less and less the more dilute sulfuric acid becomes, while copper and tin sulfate dissolve very well in dilute sulfuric.
I tested the recovery by removing and then dissolving all remaining base metal parts in nitric and then dripping HCl into it to see if any silver chloride dropped out. There was barely a visible trace of sediment when HCl was added, compared to roughly half a gram of silver when all was said and done, so the experiment had easily over a 99% recovery.
The tiny crystals and other precipitate in the original beaker were a mix of silver, and a small amount of silver sulfate and lead sulfate.
It's a time-consuming process with the 3 rounds of heating and cooling and slow dilution step, but otherwise proceeds fairly straightforward and only requires sulfuric acid and water as reagents. Treating the waste solution was very simple, since copper reduces out on iron quite completely in sulfate solution. Tin also eventually reduced out too, leaving a solution of almost entirely iron sulfate, which is virtually non-toxic.
When I get time again, I'll perform a second experiment to see if I can duplicate the results with a somewhat larger volume, roughly 250mls, and about 500 grams of metal.
