# precipitating silver?



## 24kgold (Mar 2, 2012)

Can i use sodium metabisulfite to precipitate silver from nitric acid instead of using copper?.


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## Geo (Mar 2, 2012)

SO2 (sulfur dioxide) is the gas that evolves from SMB and its very selective as to what metal it reduces in solution. silver is not one of them. the reason you have trace amounts of silver in your gold when using SMB is due to "drag down" as SMB does not precipitate silver. the two recomended methods for precipitating silver is converting to silver chloride (this is not normally recomended because it adds another process) and cementation with copper. if the solution is relatively clean (not alot of mixed metals) and your copper is clean (like a new piece of copper pipe) you can get cemented silver as pure as 99.5%.


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## CASACEO (May 20, 2012)

Okay, I have a question and haven't found my answer yet and this seems like the place I should ask. I dissolved silver plated copper pins in nitric acid. Left sit for a couple days. Mostly all of the metals dissolved, short of a couple partially digested pins. I have a light blue solution and a white/gray powder on the bottom. (I have just learned to set it out in the sun for a couple hours to see if it's silver, it will change colors. Will do later when the sun rises). My question is this, when cementing with copper does the silver actually get harder then a fluffy powder? (or) has my silver reached it's maximum hardness through the presence of dissolved copper in the solution?


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## Harold_V (May 20, 2012)

If you didn't fully dissolve the pins, you can expect that the small amount that remained will have cemented silver. Whether you recovered all of it, or not, would depend on the amount of silver that was put in solution, and the amount of base metal that remained. In order to determine if the silver is all down, take a drop sample and place it in a spot plate cavity, then add a drop of HCl, or a grain of salt. If a white cloud forms, you still have silver in solution. In keeping with this concept, the silver that has been cemented should not be expected to change color, although if it has a coating of silver nitrate, it may. 

Silver that cements tends to be finely divided, and resembles Portland cement to some degree, thus its name, cement silver. It isn't hard, but quite soft and fluffy. That's not always the case, as under peculiar circumstances, silver will plate as a solid film on copper, firmly adhering and eventually fully encapsulating the base metal with a hard film of silver. That's not likely to happen when you are cementing with brass, however. 

Don't know if I answered your question to your satisfaction--it's not clear to me exactly what you seek to learn. 

Harold


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## CASACEO (May 20, 2012)

Thanks Harold! You did answer my question.


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