MGH
Well-known member
Hi all, I’m looking for some help here. Sorry for the long post - just wanting to give as much information as possible.
I have this material in hand on which I can make an offer to toll refine. At the moment, it doesn't look like a very profitable endeavor unless I can get some better insight into what this material is and how best to process it.
Here’s what I know. Obviously there are some important details missing, but this is all I have to go on besides additional testing I could do myself. I’ll put quotes around phrases that I have no direct knowledge of, that are simply what I was told.
A local metals buyer was provided the material. He was told that it was photography waste, “the stuff from the trap under the sink”. Unlike most photography wastes discussed on the forum, this is already a dry solid. Both the owner of the material and the local buyer knew enough to understand that it should contain some amount of silver. It is mostly brown, and includes fine dust and larger chucks. The chunks are very porous and brittle, and can be broken by hand.
Initially there was a 5 gallon bucket full of material like what is shown in the picture below. The local buyer took it to NTR where he says they filled a crucible, melted it, poured it into a mold, and out came “about $900 worth of silver. There was a thick slag on top, but the silver tested at 99% pure”. I estimate that to be about 52 ounces. I asked if he knew the weight of material that was loaded into the crucible but he didn’t know. Still at NTR, they filled another crucible to melt, but this time the material just gassed and sputtered, and didn't really melt. That NTR office sent the material to the Dallas location, but they declined to work with it altogether (I don’t know if they even tried).
With no more success at NTR, the local buyer gave the material to a different local small-time refiner that he regularly deals with. As far as I know this refiner also simply tried to melt the material and observed the same smoking and poor-melting properties, and gave up after obtaining just a small lump of melted metal (again, I have no idea how much material he tried to melt and subsequently ended up with).
It was at this point the local buyer gave me a shot at it. I took an ~800 g sample of what he had left, which is now only about one third of the 5 gallon bucket. I did some small test runs to see how the material would react to different acids. Each test used 3-4 grams of material, and were done in small glass cylinders on a hot plate at about 70C (not graduated cylinders – these are just plain, flat-bottom cylinders about 1 inch wide and 4 inches tall).
With 35% nitric, the reaction was slow. There were small, infrequent bubbles, but no visible NOx fumes evolved. The resulting solution was dark brown, and a brown solid remained. I poured off the solution into another cylinder and intended to cement any silver onto a copper wire, but I had way too much nitric in solution. I allowed the nitric to consume the copper anyway, and at the end ended up with a dusting of solid material which I couldn't discern whether it was silver or just leftover lighter solids from initially pouring off the solution prior to cementation.
With ~10% sulfuric acid, nothing happened at all.
With 32% HCl, the solution immediately turned yellow. There were some bubbles, but the reaction was not especially vigorous. I continued adding HCl until no more reaction occurred. At this point the solution was coffee-brown, and still yellow when diluted. There were some grey and black solids left in the bottom of the cylinder. I rinsed these solids, then melted, obtaining 0.19 grams of dirty silver. I did not record the starting weight, but I estimate it to be about 3.5 g, so this would be a ~5.4% yield.
With the HCl leach seeming the most advantageous, I ran a trial of 200 grams of the material in a 1L beaker. I added a total of 400 mL of 32% HCl and allowed it to react with heat. This time the remaining solids were still brown – perhaps I did not provide enough acid to dissolve base metals. Even so, I rinsed the solids and dried. This produced 53.8 g of light brown solids. I took 16.76 g of this and melted, obtaining 8.53 g of dirty silver. So: (8.53)*(53.8/16.76)/200 = ~13.7% yield.
I’m thinking this photography waste may be contaminated with a lot of iron (perhaps from some iron pipes used in the plumbing of the photo studio?). I’m estimating that this local buyer still has at maximum 25 pounds of the material which, at a 13.7% yield, would produce ~53 ounces of silver. I’m not sure that we could arrive at a mutually agreeable rate for toll refining this material. I think I’d have to ask for at least 20% - more if it’s going to be difficult to process - and that may be more than the local buyer, and subsequently his customer, would be willing to pay.
Has anyone seen this kind of material before, or have any suggestions about how to deal with it?
Thanks,
Matt H.
I have this material in hand on which I can make an offer to toll refine. At the moment, it doesn't look like a very profitable endeavor unless I can get some better insight into what this material is and how best to process it.
Here’s what I know. Obviously there are some important details missing, but this is all I have to go on besides additional testing I could do myself. I’ll put quotes around phrases that I have no direct knowledge of, that are simply what I was told.
A local metals buyer was provided the material. He was told that it was photography waste, “the stuff from the trap under the sink”. Unlike most photography wastes discussed on the forum, this is already a dry solid. Both the owner of the material and the local buyer knew enough to understand that it should contain some amount of silver. It is mostly brown, and includes fine dust and larger chucks. The chunks are very porous and brittle, and can be broken by hand.
Initially there was a 5 gallon bucket full of material like what is shown in the picture below. The local buyer took it to NTR where he says they filled a crucible, melted it, poured it into a mold, and out came “about $900 worth of silver. There was a thick slag on top, but the silver tested at 99% pure”. I estimate that to be about 52 ounces. I asked if he knew the weight of material that was loaded into the crucible but he didn’t know. Still at NTR, they filled another crucible to melt, but this time the material just gassed and sputtered, and didn't really melt. That NTR office sent the material to the Dallas location, but they declined to work with it altogether (I don’t know if they even tried).
With no more success at NTR, the local buyer gave the material to a different local small-time refiner that he regularly deals with. As far as I know this refiner also simply tried to melt the material and observed the same smoking and poor-melting properties, and gave up after obtaining just a small lump of melted metal (again, I have no idea how much material he tried to melt and subsequently ended up with).
It was at this point the local buyer gave me a shot at it. I took an ~800 g sample of what he had left, which is now only about one third of the 5 gallon bucket. I did some small test runs to see how the material would react to different acids. Each test used 3-4 grams of material, and were done in small glass cylinders on a hot plate at about 70C (not graduated cylinders – these are just plain, flat-bottom cylinders about 1 inch wide and 4 inches tall).
With 35% nitric, the reaction was slow. There were small, infrequent bubbles, but no visible NOx fumes evolved. The resulting solution was dark brown, and a brown solid remained. I poured off the solution into another cylinder and intended to cement any silver onto a copper wire, but I had way too much nitric in solution. I allowed the nitric to consume the copper anyway, and at the end ended up with a dusting of solid material which I couldn't discern whether it was silver or just leftover lighter solids from initially pouring off the solution prior to cementation.
With ~10% sulfuric acid, nothing happened at all.
With 32% HCl, the solution immediately turned yellow. There were some bubbles, but the reaction was not especially vigorous. I continued adding HCl until no more reaction occurred. At this point the solution was coffee-brown, and still yellow when diluted. There were some grey and black solids left in the bottom of the cylinder. I rinsed these solids, then melted, obtaining 0.19 grams of dirty silver. I did not record the starting weight, but I estimate it to be about 3.5 g, so this would be a ~5.4% yield.
With the HCl leach seeming the most advantageous, I ran a trial of 200 grams of the material in a 1L beaker. I added a total of 400 mL of 32% HCl and allowed it to react with heat. This time the remaining solids were still brown – perhaps I did not provide enough acid to dissolve base metals. Even so, I rinsed the solids and dried. This produced 53.8 g of light brown solids. I took 16.76 g of this and melted, obtaining 8.53 g of dirty silver. So: (8.53)*(53.8/16.76)/200 = ~13.7% yield.
I’m thinking this photography waste may be contaminated with a lot of iron (perhaps from some iron pipes used in the plumbing of the photo studio?). I’m estimating that this local buyer still has at maximum 25 pounds of the material which, at a 13.7% yield, would produce ~53 ounces of silver. I’m not sure that we could arrive at a mutually agreeable rate for toll refining this material. I think I’d have to ask for at least 20% - more if it’s going to be difficult to process - and that may be more than the local buyer, and subsequently his customer, would be willing to pay.
Has anyone seen this kind of material before, or have any suggestions about how to deal with it?
Thanks,
Matt H.
