Hello, new here, glad to find this!
Backstory: I'm in placer gold mining and often times we end up with huge amounts of lead in our concentrates, mostly from ammunition. At times one of the mining sites was a popular shooting spot. We're talking about many pounds of lead per ounce of gold. I am able to separate most everything else from the concentrate with a shaker table, but the lead, being more than 50% density of the gold, is problematic to separate, particularly in larger gold/lead particle size batches (e.g. +10mesh).
My associates have been using 67% industrial grade nitric acid to dissolve lead and clean gold, but it consumes a fair bit of nitric to do it. (Note: I learned that possibly using a 7:1 dilution with water would help. Haven't tried it yet). Moreover, it makes nasty fumes.
So I was looking for an alternative. I looked up lead dissolution and found that one can make lead acetate (which was sugar substitute in prior eras...!) readily by dissolving lead in acetic acid and H202. So I got some from the grocery store (vinegar, 5% acetic, and first aid variety H202, 3%), mixed up a small batch and threw some lead in. Sure enough, it started to react. A day later I had lead acetate and a very small amount of other stuff that didn't dissolve, likely some sand and such. I didn't have any gold in the mixture.
So a mixed up another batch of solution and threw in a few flecks of gold. I didn't see any immediate reaction so I assumed the gold was non-reactive. (Note: WRONG!) Then I took a few ounces of this lead/gold concentrate and threw it in. The next day I believe most of the acid had been consumed, about half the lead, and to my chagrin, most of the gold (perhaps a 3-5 grams). Interesting.
So I began to filter what I had. The solution was gray and I poured it into a glass. I also filtered the solids through a ~100mesh screen and ended up with a nearly black precipitate. The remaining larger solids were mostly still lead chunks, a little gold, and other contaminants, to which I added more acid/H202. It eventually consumed all the lead and left a few scraps of sand and whatnot as in my initial experiment.
However, a day later the gray solution settled out and turned into a nice amber ale beer colored liquid, and even had a little foam on top. At the bottom was the gray precipitate. It would appear that is lead acetate precipitate in a gold-pregnant solution. Okay.
I contacted a hydrometallurgist friend and he explained that H2O2 and just about any acid would dissolve most metals including lead and gold. He suggested filtering the solution to remove the lead acetate, and then adding zinc powder to cement the gold. Then wash, and add sulfuric acid to dissolve the zinc, which would leave the gold as a solid.
I'm getting ready to try that--zinc and various things on order. I like the concept though because it's mostly not grossly toxic.
However, I started researching some more, leading to this forum for instance, and also read up on the AR refining process that jewelers and circuit board recyclers use. So that all leads to questions.
1) Stannous Chloride: will that work in testing an acetic acid-based solution for gold? It would appear so.
2) Would SMB or iron sulfate precipitate the gold out of an acetic acid based solution? My understanding with AR is that urea is then also added to neutralize the nitric acid to prevent the gold precipitate from redissolving. In my case there is some concentrate of acetic acid and H2O2. Is there perhaps a similar reaction I could use to precipitate the gold, vs. the cementation and zinc/sulfuric acid step?
3) AR apparently also dissolves lead. How is lead removed from a pregnant AR solution for refining? Silver for instance is apparently is removed by filtering the precipitate after neutralizing the AR, washing, and then adding ammonia.
4) Any advice on the 7:1 dilute nitric acid method? I imagine that if one simply starts with concentrated nitric, then that eventually gets consumed and is diluted as the reaction proceeds. If one starts with dilute nitric, then I imagine one has to keep adding some to keep the concentration at 7:1 (or whatever pH or concentration that 7:1 dilution of industrial 67% nitric comes out to? ~8%)
Thanks kindly in advance.
Backstory: I'm in placer gold mining and often times we end up with huge amounts of lead in our concentrates, mostly from ammunition. At times one of the mining sites was a popular shooting spot. We're talking about many pounds of lead per ounce of gold. I am able to separate most everything else from the concentrate with a shaker table, but the lead, being more than 50% density of the gold, is problematic to separate, particularly in larger gold/lead particle size batches (e.g. +10mesh).
My associates have been using 67% industrial grade nitric acid to dissolve lead and clean gold, but it consumes a fair bit of nitric to do it. (Note: I learned that possibly using a 7:1 dilution with water would help. Haven't tried it yet). Moreover, it makes nasty fumes.
So I was looking for an alternative. I looked up lead dissolution and found that one can make lead acetate (which was sugar substitute in prior eras...!) readily by dissolving lead in acetic acid and H202. So I got some from the grocery store (vinegar, 5% acetic, and first aid variety H202, 3%), mixed up a small batch and threw some lead in. Sure enough, it started to react. A day later I had lead acetate and a very small amount of other stuff that didn't dissolve, likely some sand and such. I didn't have any gold in the mixture.
So a mixed up another batch of solution and threw in a few flecks of gold. I didn't see any immediate reaction so I assumed the gold was non-reactive. (Note: WRONG!) Then I took a few ounces of this lead/gold concentrate and threw it in. The next day I believe most of the acid had been consumed, about half the lead, and to my chagrin, most of the gold (perhaps a 3-5 grams). Interesting.
So I began to filter what I had. The solution was gray and I poured it into a glass. I also filtered the solids through a ~100mesh screen and ended up with a nearly black precipitate. The remaining larger solids were mostly still lead chunks, a little gold, and other contaminants, to which I added more acid/H202. It eventually consumed all the lead and left a few scraps of sand and whatnot as in my initial experiment.
However, a day later the gray solution settled out and turned into a nice amber ale beer colored liquid, and even had a little foam on top. At the bottom was the gray precipitate. It would appear that is lead acetate precipitate in a gold-pregnant solution. Okay.
I contacted a hydrometallurgist friend and he explained that H2O2 and just about any acid would dissolve most metals including lead and gold. He suggested filtering the solution to remove the lead acetate, and then adding zinc powder to cement the gold. Then wash, and add sulfuric acid to dissolve the zinc, which would leave the gold as a solid.
I'm getting ready to try that--zinc and various things on order. I like the concept though because it's mostly not grossly toxic.
However, I started researching some more, leading to this forum for instance, and also read up on the AR refining process that jewelers and circuit board recyclers use. So that all leads to questions.
1) Stannous Chloride: will that work in testing an acetic acid-based solution for gold? It would appear so.
2) Would SMB or iron sulfate precipitate the gold out of an acetic acid based solution? My understanding with AR is that urea is then also added to neutralize the nitric acid to prevent the gold precipitate from redissolving. In my case there is some concentrate of acetic acid and H2O2. Is there perhaps a similar reaction I could use to precipitate the gold, vs. the cementation and zinc/sulfuric acid step?
3) AR apparently also dissolves lead. How is lead removed from a pregnant AR solution for refining? Silver for instance is apparently is removed by filtering the precipitate after neutralizing the AR, washing, and then adding ammonia.
4) Any advice on the 7:1 dilute nitric acid method? I imagine that if one simply starts with concentrated nitric, then that eventually gets consumed and is diluted as the reaction proceeds. If one starts with dilute nitric, then I imagine one has to keep adding some to keep the concentration at 7:1 (or whatever pH or concentration that 7:1 dilution of industrial 67% nitric comes out to? ~8%)
Thanks kindly in advance.
