Measuring 0.9999 pure silver

[James Ball]

I am making pure silver using starting materials of 0.999 silver shot and ACS grade silver nitrate. I would like to see measurements of silver out to 0.9999 or better. This would be a diffucult measruements. Anyone know of a lab out there that can measure to this precision?

 

[Lou]

We do this by ICP-OES routinely. At about 99.999 and higher we go to ICP-MS or GD-MS.

American Analytical in Akron, OH has experience doing impurities by difference silver assays.

 

[4metals]

Lou had posted a method a while back involving dissolving some silver and drying the solution and looking for discoloration as an indicator, but I cannot find it. Maybe if we are really nice, and don’t ask Lou to identify any more rocks, he can post it again!

 

[4metals]

I found it!

This is a test that can give you an indication of purity but it is not quantitative.

In the fume hood, dissolve a 1 gram sample of the silver shot in distilled water and reagent Nitric acid. (2:1) on a hot plate. There should be no color to this solution, if there is, it is because of the impurities. I.2 ml of nitric will dissolve a gram of pure Silver, so add 4 ml of the 2:1 mixture to allow a little extra Nitric Acid to dissolve the sample completely. As this is not a quantitative test, it does not have to be exactly 1 gram. Select a single Silver shot as close to 1 gram as possible, preferably slightly less than 1 gram, and add sufficient acid.

On a hot plate, evaporate this silver nitrate in a porcelain dish still looking for color. When it gets dry enough not to spit and close to crystallizing, raise the temperature to 825ºF by putting it in a pre-heated assay kiln and hold it there for 5 minutes at temperature. At this temperature the dish will have a faint barely visible glow.

Let the crystallized silver nitrate cool and re-dissolve it in hot distilled water rinsing it into a clear beaker. Now you are looking for sediment on the bottom. Sediment indicates metal oxides that form when the silver nitrate fuses at 825ºF. Looking through the bottom of the glass beaker sitting on a black background makes most sediments more visible. Follow this by holding the beaker up in a brightly lit room and look for any coloration against a white background.

All of the impurities in your silver will form the sediment with this test. So if you have no coloration and no sediment, you are over .9999 pure silver.

Obviously clean glassware and porcelain are critical to this process.

 

[Lou]

I should add the caveat that the color of the solution only stays clear (water white) if excess nitric is present and it is hot and the silver is pure.

This was adapted from a method given to me by an old timer at Kodak (now Rochester Silverworks) who explained to me that it is a basic litmus test of photo grade silver nitrate (which is usually 5N) for the heavier base metals, like Pb, Cu, Pd, etc.

 

[Anil]

Very simple method if you have a fume hood with exhaust connected to a water bath for absorbing nitrous fumes.
1 gm silver with 20 ml ( it can't be 1.2ml for sure) of 1.3 specific gravity nitric acid in a clear borosilicate glass bottle and heat just at around 80-90 dig C on a hot plate. Pure silver will dissolve forming a crystal clear AgNo3 solution with not a spec of impurity behind (A very first indication that the silver is pure). Dilute it to 300 ml DM water and put 10 ml of HCL (33%) to precipitate AgCl2 and shake it well. Allow AgCl3 to settle down for 4-5 in a dark area to prevent exposure to sunlight. Decant water by siphoning tube not disturb the settled AGCl2 in the bottom. Slowly transfer chloride in a polished graphite crucible and slowly dry the chloride raising the temperature to 180 degrees C to completely remove moisture. The AgCl2 cake once brought to room temperature in a glass desiccator, weigh again on the same scale (0.01gm readability). The weight of the cake is multiplied by 0.75 to give you a reading close to 999,9 mg ensuring the silver is 100% pure. This is an old and proven method called as "Bottle Assay Method" a gravimetric method used in many mints across the world till improved and faster technology now developed for assays such as the potentiometric titration method.

NOTE: If you have XRF equipment around, calibrated for silver, it will just take 30 seconds to prove that silver is nearly pure. (Qualitative analysis)

 

[James Ball]

I used the refining the lab from United Precious Metal Refining from NY. I had them do ICP-OES on 3 samples. Each sample was from a different batch of silver from my silver electrolysis cell. I am pleased to see that all three were >99.99% pure. See attachment.

 

[4metals]

Congrats on a job well done. It would be interesting if you have the equipment to do it, if you now perform one or both of the tests described above to see the visual correlation. It may save you the cost of the ICP testing in the future.

 

[James Ball]

Congrats on a job well done. It would be interesting if you have the equipment to do it, if you now perform one or both of the tests described above to see the visual correlation. It may save you the cost of the ICP testing in the future.

I used to have the equipment at the company I worked for. I was doing ICP-OES for aluminum concentrations. I am retired now and pay for the service. It is not something I will routinely be paying for.

 

[James Ball]

Very simple method if you have a fume hood with exhaust connected to a water bath for absorbing nitrous fumes.
1 gm silver with 20 ml ( it can't be 1.2ml for sure) of 1.3 specific gravity nitric acid in a clear borosilicate glass bottle and heat just at around 80-90 dig C on a hot plate. Pure silver will dissolve forming a crystal clear AgNo3 solution with not a spec of impurity behind (A very first indication that the silver is pure). Dilute it to 300 ml DM water and put 10 ml of HCL (33%) to precipitate AgCl2 and shake it well. Allow AgCl3 to settle down for 4-5 in a dark area to prevent exposure to sunlight. Decant water by siphoning tube not disturb the settled AGCl2 in the bottom. Slowly transfer chloride in a polished graphite crucible and slowly dry the chloride raising the temperature to 180 degrees C to completely remove moisture. The AgCl2 cake once brought to room temperature in a glass desiccator, weigh again on the same scale (0.01gm readability). The weight of the cake is multiplied by 0.75 to give you a reading close to 999,9 mg ensuring the silver is 100% pure. This is an old and proven method called as "Bottle Assay Method" a gravimetric method used in many mints across the world till improved and faster technology now developed for assays such as the potentiometric titration method.

NOTE: If you have XRF equipment around, calibrated for silver, it will just take 30 seconds to prove that silver is nearly pure. (Qualitative analysis)

Bringing silver chloride (AgCl not AgCl3 or AgCl2, bty) to constant weight by drying in a dessicator oven for analysis of chloride was the first experiment I did in my sophmore class of Analytical Chemistry that was required of BS chemistry majors. The XRF does not measure below the surface for any significant depth, I used a drill to get samples from two bars and used a crystal from my silver cell for my ICP samples. The nice thing about ICP is that one can see what metals are contaminating this silver. Copper was the big one as expected.

 

[4metals]

I used to have the equipment at the company I worked for. I was doing ICP-OES for aluminum concentrations. I am retired now and pay for the service. It is not something I will routinely be paying for.

I always try to suggest methods for those members without either an analytical lab or the chemical background you have.

When I first came to the forum many of the members had little to no chemical background and were gaining all of their refining knowledge from reading on the forum. Over the years we have seen a growth in both experienced refiner participation and participation by members with chemical backgrounds. And it is bringing the forum up to new levels.

Ironically those without prior experience or chemical training seem to ask the strangest questions and try to push the plausibility of what is possible. Combining with members that understand the chemistry, responses to their questions now get an even wider variety of experience to answer the questions resulting in better understanding for all of us.

So who says you can’t teach an old dog new tricks!