Hello i am new to the forum my name is jeff anyways i have a batch of sterling silver (around 4lbs) that im trying to refine i melted it down to shot and did a 50/50 70% nitric acid water and the first batch turned green not blue like it always does what could be causeing this? Im currently cementing the first batch and it is cementing but this has never happened any thoughts? Any imput would be greatly appreciated thank you
Refining sterling silver with nitric acid
- Thread starter Jeff0172
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Red colorered and in=visible NOx gases can color the bluish copper nitrate solution to look more toward a green color, the color will normally shift more to blue as the NOx gases are deplete from solution.
Brownish you may wish to check for Palladium.
Brownish you may wish to check for Palladium.
To clarify its like clear green like lime jello i cemented last night and didnt yeld that much but it was a small batch only about 5 oz of silver rings and pendants which some where plated in plat and rhodium i cemented it and put the solution in a jug to examine at a later date
Geo
Well-known member
Do you have stannous chloride? In my experience, some older silver may contain another precious metal called palladium. It can make dissolved silver look green. Just because it's green doesn't necessarily mean it contains Pd but it is very suspect. Another indication is if black powder cements with your silver and makes the cemented silver look dingy or dark. Add a drop of your solution to a white plastic spoon and add a couple of drops of stannous chloride. If it is positive, the initial reaction color can be red, orange or yellow that slowly turns very green over the course of five minutes or so.
Also, depending on your chemistry background, a much more simple process to pure silver that bypasses the cementation and silver cell purification is the formic acid conversion. It is the process I have been using for awhile and it is really effective. The silver nitrate is converted to silver chloride and rinsed clean of color. Convert the silver chloride to silver oxide with sodium hydroxide. All the oxide to settle completely or filter well. Rinse until clear. Add the silver oxide to a beaker and cover with water. Heat until near boiling but not boiling. Add formic acid in small increments of a few ml's at a time while stirring. The reaction is vigorous and will boil over if too much is added at one time. The beaker will become mirrored on the inside. This is an indication that the reaction is almost complete. Continue adding formic acid until there is no more reaction. Continue heating for 30 minutes to allow any unreacted oxides to react. The silver will appear to be silver metal sponge. It should be heavy and will settle instantly after stirring. Rinse well and dry. If you have done everything correctly, purity should be .999 or better.
This should be done in a fume hood or while wearing a respirator. Formic acid has a health rating of 3 on the NFPA 704 (fire diamond). Wear gloves and eye protection and any other appropriate personal protection equipment when working with formic acid.
Also, depending on your chemistry background, a much more simple process to pure silver that bypasses the cementation and silver cell purification is the formic acid conversion. It is the process I have been using for awhile and it is really effective. The silver nitrate is converted to silver chloride and rinsed clean of color. Convert the silver chloride to silver oxide with sodium hydroxide. All the oxide to settle completely or filter well. Rinse until clear. Add the silver oxide to a beaker and cover with water. Heat until near boiling but not boiling. Add formic acid in small increments of a few ml's at a time while stirring. The reaction is vigorous and will boil over if too much is added at one time. The beaker will become mirrored on the inside. This is an indication that the reaction is almost complete. Continue adding formic acid until there is no more reaction. Continue heating for 30 minutes to allow any unreacted oxides to react. The silver will appear to be silver metal sponge. It should be heavy and will settle instantly after stirring. Rinse well and dry. If you have done everything correctly, purity should be .999 or better.
This should be done in a fume hood or while wearing a respirator. Formic acid has a health rating of 3 on the NFPA 704 (fire diamond). Wear gloves and eye protection and any other appropriate personal protection equipment when working with formic acid.
Im out of stannous chloride but ill get some more and do the test and post the results it does make sense yes i have a fume hood so that wouldnt be a issue i have never done the extraction your talking about so ill test it and post back the results the second batch was pretty desent but again the solution was a little but greenish not pure green like the first batch but the second batch is yielding much more silver compared to volume i would love to try what you are talking about i would just have to get all the saftey gear i have the fume hood but when it comes to safety no amount of money is worth the risk i would rather be over prepared
