smelterville
New member
- Joined
- Jun 28, 2015
- Messages
- 2
Hi All-
I have been a long time reader on the forum and I appreciate all your posts and knowledge. I thought I would test the waters with some questions and see if you guys can give me a hand with my current smelting project.
I have a shaker table and I am concentrating out a lot of free gold from my hard rock ore. I have gathered the necessary things to smelt (furnace, flux, crucibles, etc.) and I have tried my first few pours with disappointing results.
Here are the some of the details.
I have took about 1 lb of my high grade shaker table con and dried it out. There was about 1/2 oz of free gold in the one pound of dry cons. My cons carry some nasty things for smelting such as: some copper, tellurium, and bismuth. From what I have read these things are really difficult in the assay process and special care needs to be taken.
One problem is I can't find anything detailing how to deal with them in the smelting process so here is what I did. I purchased some refining flux from Legend inc in NV. Here is what they say about it on their website "Legend's premixed REFINING Flux is suitable for a wide variety of melting jobs. End users can adjust the components to adapt this flux to their specific needs. Typically used for smelting, refining, and melting concentrates."
It contains the following: 20% potassium nitrate, 8.75% soda ash, 62.5% borax, 8.75% silica.
My thought was that I would need an oxidizer for the tellurium and bismuth. I was trying to get away from roasting, too and I have read in "The Chemistry of Gold Extraction" By John Marsden, Iain House, that by using an oxidizing agent in the flux the roasting step can be avoided, however there may not be quite as high a recovery as if the roasting step is undertaken.
For my first smelt and pour I did the following ratios: 1 part concentrates, 1/2 part silica sand (I added this as the refining flux seemed to be quite low on silica compared to most other fluxes), 2.5 parts Legend flux. I brought it up to 2200 degrees and I stirred it 3 separate times (once every 1/2 hour) and then after 2 hours I poured the material into my conical mold. The result was a black slag (good? or should it be more clear/greensih like from an optimum assay slag?) but the top and sides of the slag had a sliver metallic like residue with some interlaced stripes of slag and sliver metallic material. I did get a button of metal at the bottom of the cone, it was about 1/2 oz +/-, but it was coated in what looked like the silver metallic substance on the outside of the slag. The silver coating (matte?) on the button was very brittle and once chipped off the button it revealed a copper colored button. See pics below.
Being disappointed I didn't get a shiny gold button I crushed the slag, flattened out the copper colored button (very malleable, not brittle at all) for lots of surface area, and mixed in 2 more parts flux (2 parts to the original cons charge) and re-ran the smelt again. This time after doing some more reading on the subject it was suggested to add some pieces of iron to the mix when using an oxidizing flux so I put in a few strips of mild steel strips to the crucible.
This time the shiny metallic residue from the earlier smelt was very minimal (almost none on the slag block) and the slag was a jet black color again. The problem now is I have no button at all. There was nothing at the bottom of my cone mold, except black slag. I am not sure where my metals went?
I am sure I am forgetting some important information, but I think I will sign off now and let this steep with you guys for a while. Any questions/suggestions are most welcome. My last question is: Is there any way for me to get my gold back???
Thanks,
I have been a long time reader on the forum and I appreciate all your posts and knowledge. I thought I would test the waters with some questions and see if you guys can give me a hand with my current smelting project.
I have a shaker table and I am concentrating out a lot of free gold from my hard rock ore. I have gathered the necessary things to smelt (furnace, flux, crucibles, etc.) and I have tried my first few pours with disappointing results.
Here are the some of the details.
I have took about 1 lb of my high grade shaker table con and dried it out. There was about 1/2 oz of free gold in the one pound of dry cons. My cons carry some nasty things for smelting such as: some copper, tellurium, and bismuth. From what I have read these things are really difficult in the assay process and special care needs to be taken.
One problem is I can't find anything detailing how to deal with them in the smelting process so here is what I did. I purchased some refining flux from Legend inc in NV. Here is what they say about it on their website "Legend's premixed REFINING Flux is suitable for a wide variety of melting jobs. End users can adjust the components to adapt this flux to their specific needs. Typically used for smelting, refining, and melting concentrates."
It contains the following: 20% potassium nitrate, 8.75% soda ash, 62.5% borax, 8.75% silica.
My thought was that I would need an oxidizer for the tellurium and bismuth. I was trying to get away from roasting, too and I have read in "The Chemistry of Gold Extraction" By John Marsden, Iain House, that by using an oxidizing agent in the flux the roasting step can be avoided, however there may not be quite as high a recovery as if the roasting step is undertaken.
For my first smelt and pour I did the following ratios: 1 part concentrates, 1/2 part silica sand (I added this as the refining flux seemed to be quite low on silica compared to most other fluxes), 2.5 parts Legend flux. I brought it up to 2200 degrees and I stirred it 3 separate times (once every 1/2 hour) and then after 2 hours I poured the material into my conical mold. The result was a black slag (good? or should it be more clear/greensih like from an optimum assay slag?) but the top and sides of the slag had a sliver metallic like residue with some interlaced stripes of slag and sliver metallic material. I did get a button of metal at the bottom of the cone, it was about 1/2 oz +/-, but it was coated in what looked like the silver metallic substance on the outside of the slag. The silver coating (matte?) on the button was very brittle and once chipped off the button it revealed a copper colored button. See pics below.
Being disappointed I didn't get a shiny gold button I crushed the slag, flattened out the copper colored button (very malleable, not brittle at all) for lots of surface area, and mixed in 2 more parts flux (2 parts to the original cons charge) and re-ran the smelt again. This time after doing some more reading on the subject it was suggested to add some pieces of iron to the mix when using an oxidizing flux so I put in a few strips of mild steel strips to the crucible.
This time the shiny metallic residue from the earlier smelt was very minimal (almost none on the slag block) and the slag was a jet black color again. The problem now is I have no button at all. There was nothing at the bottom of my cone mold, except black slag. I am not sure where my metals went?
I am sure I am forgetting some important information, but I think I will sign off now and let this steep with you guys for a while. Any questions/suggestions are most welcome. My last question is: Is there any way for me to get my gold back???
Thanks,