snoman701 said:
goldsilverpro said:
If I remember right, a bone ash cupel will hold a weight of lead oxide equal to the weight of the cupel.
I don't agree with hydrometallurgical being as good as fire assay. Of the some 10,000 fire assays I have done, I would say that about 80% were electronic components. These were mostly (probably 98-99%) done with no chemical preparation at all. Hydrometallurgical methods on much of these could be complex and quite subject to losses, I would suspect. Also, the time and labor of using hydrometallurgical methods would usually be much greater than with fire assay.
Given your experience with e-scrap, any issues using bismuth as a collector?
I'm still leaning more towards lead. I'll be able to pick up an air cleaner/scrubber at auction for a reasonable price.
My goal is something that's cheap and low maintenance to run.
I don't get any of my inventory free, and it would be a LOT easier to determine if I should buy if I could just mill a few chips down to determine yield. The lead will just cost more on the front end for the appropriate air handling.
Haven't used bismuth. Always thought it was to expensive. Litharge (PbO=92.8% Pb)) is yellow and minium (Pb3O4=90.7%) is bright red-orange. I have heard the minium called red litharge, but the yellow PbO is the only true litharge. A couple of times I was out of PbO, so I used Pb3O4. As far as the results were concerned, they worked the same. I could tell no difference. Litharge itself forms a basic flux, the opposite of an acid flux. It also deoxidizes, desulphurizes, and, when reduced to lead metal by the carbon formed by a small amount of flour or sugar, it collects the Au and Ag and some of the PGMs. In the old days, they used lees, the solids that form in a wine cask, to reduce the PbO. Litharge vaporizes at 1472F and lead at 2012F. Therefore, the source of the 10% lead loss must be the litharge that forms on the inside surface of the cupel, where most is absorbed into the cupel. Like I said, though, black evil smoky fumes form over the cupels during the cupellation. At the very least, you must evacuate the fumes from the building.
I used a lot of litharge. Too much is better than not enough. I never pre-mixed fluxes and probably 90% of my assays required a fusion step before cupellation. Fire assay, as far as fluxing is concerned is quite forgiving. For a 30 gram crucible, my most common mix was 2 heaping tsp of litharge, 2 of anhydrous borax, 1 of anhydrous soda ash, 1 of silica sand, and maybe 1/2g of sugar. This worked for about 90-95% of the electronic components. I kept these fluxing chemicals near the furnace in wooden bins I made. If the slag was too thick, I would run the sample again with a little fluorspar. If there was a lot of copper, I put it into the slag by first heating the sample with some yellow sulfur for awhile to form copper sulfide.
Fire assaying is extremely simple, once you know what you're doing and have everything you need. I could easily train a person in an 8 hr day. In my book, I list 25 pieces of equipment (like the assay furnace or small 6 or 2 place cone molds or a Stainless kitchen knife or a small ball peen hammer, etc., etc.) and 8 different chemicals that you need. I just read over the list and I don't see how you could do without any of them. The scale and the furnace are the biggest ticket items. Most of the others are cheap.