Reno Chris
Well-known member
- Joined
- May 5, 2011
- Messages
- 274
There is no one universal way of treating sulfide rich precious metal ores - in the mineral kingdom there are all sorts of complex minerals which contain, in addition to gold or silver, complex combinations of lead, zinc, copper, iron, nickel, manganese, palladium, mercury, antimony, arsenic and others. In addition to sulfur, one may also have ores with selenium, tellurium, and others. Gangue minerals are not just quartz and calcite, but may include a whole host of fluorides, oxides, sulfates, chlorides, silicates, etc. The point is that sulfide ores can be highly variable.
You can see that with sulfide ores, there are a million and one possibilities and while some types can be treated similarly, there are many different categories or types. There can never be a one size fits all approach. We can all wish for rich free gold ore! With that stuff, you just crush it up, pan it out and melt to make a button (or refine it if you like). But sulfides are another story. You need to convert whatever metals you have from mineral to metal, and do it without making a big mess, and without a big stink of sulfur dioxide and smoke to offend your neighbors, either. This is not necessarily easy. Then once converted to a metallic state, you must still separate the precious metals from the base metals. This is why the old timers had such difficulty with these ores and in many places simply gave up when the mines worked their way down to the sulfides. Rebellious or refractory ores they were called.
I have about 200+ pounds (roughly 100kg) of rich silver gold ore that runs roughly 3 ounces per ton of gold and 70 ounces of silver. On that basis, my 200 pounds should contain about 0.3 ounces of gold and 7 ounces of silver - but I know that I won't get 100% recovery. There is also considerable iron, zinc and lead present, with some minor copper and very small amounts Antimony and Arsenic. All these elements are in the form of sulfides and complex sulfides (except the gold which is mostly free in tiny particles). I am not kidding myself that this is some money making scheme. It's a demonstration project to prove I can do this - though I will make a few bucks, just not much when you consider the time invested. The output of PMs will far exceed the cost of reagents and fuel, but I figure I will be getting less than 50 cents an hour for my time and one can hardly consider that as a way to make good money. I will have expensive equipment in use from crushers to furnaces to lab ware and acids. If I could buy a shaker table I could run the cost up by a few thousand, but I just can't justify that expenditure at this point.
This is going to take some months to accomplish, as I will only be working on it off and on. I will take photos as things as they progress and share them here. My goal is to recover 10 to 15 grams of gold, 7 to 10 ounces of silver, minor copper (perhaps a few ounces) and a number of pounds of lead (the lead will be used to cast bullets). I may also attempt to recycle the zinc and copper I consume in the Parkes and silver cementation steps. Disclaimer - this is not intended as a full "how to" type of lesson with all the process details and necessary safety precautions clearly spelled out. I am sharing my efforts with the forum so you can see what is involved. If you attempt something like this yourself, you will need to possess the necessary mineral processing expertise on your own and understand all the dangers involved and know enough on your own to take all the necessary safety precautions. I am not offering to serve as anyone's consultant. A good description of the steps I will use are as follows:
1. Crush the Rock.
The rock cannot be processed as large chunks and cobbles - the form it is in now. It must be crushed to a powder to process. I have 2 crushers and will take the ore down to minus 20 mesh. Yet even before it can even be run through my crushers, I will need to break down the larger pieces by hand with a 2 pound hammer. I will have a dust collection system for the crusher operation which I will show (it will use a shop vac unit I have).
2. Reduce the bulk of the ore.
My 200 pounds of ore is a lot of rock to deal with. I will concentrate it down to the heavy components. Sulfides are generally dense minerals and gold is as well, so I will concentrate using a specially made sluice system. I wish I could use a shaker table, but these are several thousand dollars to purchase, an amount much more than I want to spend on this project. Yep, I will lose some, but I do not have infinite monetary resources. The ore has a 5 to 10 percent sulfide content, so I expect about 10 to 20 pounds of sulfide concentrate. Dealing with 10 to 20 pounds is a lot easier than 200 pounds. There will be some loss of values in this operation - but I accept this because although the method is less than optimal, it's the best I can put together.
3. Perform a series of giant fire assay fusions.
The sulfides contain some galena (lead sulfide) but not enough lead to serve as collector for a full fire assay on that material alone, so I will add some other galena from another source (which also contains some good silver, but very little gold) and some Litharge (plus a bit of charcoal to help reduce the litharge). I will add a good amount of sodium carbonate and borax to form a flux. I will perhaps, also add some crushed glass as well to make sure there is enough silica to form a decent slag cover on the molten sulfide matte and maybe even a little crushed fluorite as well. The old assay trick of using scrap iron (normally nails) to reduce the molten galena will be used. THe formula is: PbS + Fe = FeS + Pb The reaction is driven because Fe is a more chemically active metal than lead (silver and copper are also displaced as they are less active than iron). I will carefully stir the whole molten mass with an iron rod (while the crucible is still secure within the furnace to be safe). The lead should capture the PMs, and when I pour the whole mass into a cone mold, I should get three products - a slag glass, a sulfide matte of mostly iron sulfides, and a lead button. I will use a large crucible and hope to process around 3+ kg of total material (flux + scrap iron + extra galena + sulfide ore concentrates) in each charge, with resulting a lead button of roughly around 1 to 1.25 Kg in size each time.
The assay fusion will be done with a propane furnace out in the desert, in a fire safe location where odors and smoke not will harm or offend anyone. I also will use a mask with a HEPA filter to make sure I do not breathe any hazardous smoke. It may take 4 to 6 or so charges and pours to process all the concentrates from step 2. The lead will be retained and saved for step 4.
4. Perform a Parkes Process capture of the copper, gold and silver.
On completion of the assay like fusion reduction process, I should have 5 to 8 Kg of gold, silver and copper bearing lead, which I will melt and mix with a couple pounds of zinc and stir. I will not take the mix up to a high temperature to try to dross out the copper, I will just collect the copper with the zinc and separate it later (there should not be much copper anyway). I read a thread on this forum where a member used a motor to create stirring for the necessary surface contact for the migration of the PMs and copper into the zinc. I will just stir for a time by hand with an iron rod. At the conclusion, I will pour off the material into a cone mold and after separation, I should have a low PM lead metal suitable for bullets and a few pounds of PM bearing zinc alloy.
5. Part the zinc from the gold, silver and copper with Hydrochloric Acid
It may be that for use of Hydrochloric, inquarting may be necessary, but I will try without doing so first. When complete, I should have zinc in solution and the copper, gold and silver as an insoluble black powder. I will wash the powder well with warm water. I may attempt recovering the zinc by electrolytic methods - I should be able to get most of the zinc out.
6. Part the gold and silver with nitric acid
The silver and any small amounts of copper present will be soluble in plain nitric, and I will cement out the silver with metallic copper, then recover all the copper electrolyticly. I will then pour the silver into a fairly pure button and the gold and final nitric insoluble materials into their own button and at that point the final extraction process will be complete. The gold will not be .999, but it should be maybe 90+ which will be good enough for my purposes.
You can see that with sulfide ores, there are a million and one possibilities and while some types can be treated similarly, there are many different categories or types. There can never be a one size fits all approach. We can all wish for rich free gold ore! With that stuff, you just crush it up, pan it out and melt to make a button (or refine it if you like). But sulfides are another story. You need to convert whatever metals you have from mineral to metal, and do it without making a big mess, and without a big stink of sulfur dioxide and smoke to offend your neighbors, either. This is not necessarily easy. Then once converted to a metallic state, you must still separate the precious metals from the base metals. This is why the old timers had such difficulty with these ores and in many places simply gave up when the mines worked their way down to the sulfides. Rebellious or refractory ores they were called.
I have about 200+ pounds (roughly 100kg) of rich silver gold ore that runs roughly 3 ounces per ton of gold and 70 ounces of silver. On that basis, my 200 pounds should contain about 0.3 ounces of gold and 7 ounces of silver - but I know that I won't get 100% recovery. There is also considerable iron, zinc and lead present, with some minor copper and very small amounts Antimony and Arsenic. All these elements are in the form of sulfides and complex sulfides (except the gold which is mostly free in tiny particles). I am not kidding myself that this is some money making scheme. It's a demonstration project to prove I can do this - though I will make a few bucks, just not much when you consider the time invested. The output of PMs will far exceed the cost of reagents and fuel, but I figure I will be getting less than 50 cents an hour for my time and one can hardly consider that as a way to make good money. I will have expensive equipment in use from crushers to furnaces to lab ware and acids. If I could buy a shaker table I could run the cost up by a few thousand, but I just can't justify that expenditure at this point.
This is going to take some months to accomplish, as I will only be working on it off and on. I will take photos as things as they progress and share them here. My goal is to recover 10 to 15 grams of gold, 7 to 10 ounces of silver, minor copper (perhaps a few ounces) and a number of pounds of lead (the lead will be used to cast bullets). I may also attempt to recycle the zinc and copper I consume in the Parkes and silver cementation steps. Disclaimer - this is not intended as a full "how to" type of lesson with all the process details and necessary safety precautions clearly spelled out. I am sharing my efforts with the forum so you can see what is involved. If you attempt something like this yourself, you will need to possess the necessary mineral processing expertise on your own and understand all the dangers involved and know enough on your own to take all the necessary safety precautions. I am not offering to serve as anyone's consultant. A good description of the steps I will use are as follows:
1. Crush the Rock.
The rock cannot be processed as large chunks and cobbles - the form it is in now. It must be crushed to a powder to process. I have 2 crushers and will take the ore down to minus 20 mesh. Yet even before it can even be run through my crushers, I will need to break down the larger pieces by hand with a 2 pound hammer. I will have a dust collection system for the crusher operation which I will show (it will use a shop vac unit I have).
2. Reduce the bulk of the ore.
My 200 pounds of ore is a lot of rock to deal with. I will concentrate it down to the heavy components. Sulfides are generally dense minerals and gold is as well, so I will concentrate using a specially made sluice system. I wish I could use a shaker table, but these are several thousand dollars to purchase, an amount much more than I want to spend on this project. Yep, I will lose some, but I do not have infinite monetary resources. The ore has a 5 to 10 percent sulfide content, so I expect about 10 to 20 pounds of sulfide concentrate. Dealing with 10 to 20 pounds is a lot easier than 200 pounds. There will be some loss of values in this operation - but I accept this because although the method is less than optimal, it's the best I can put together.
3. Perform a series of giant fire assay fusions.
The sulfides contain some galena (lead sulfide) but not enough lead to serve as collector for a full fire assay on that material alone, so I will add some other galena from another source (which also contains some good silver, but very little gold) and some Litharge (plus a bit of charcoal to help reduce the litharge). I will add a good amount of sodium carbonate and borax to form a flux. I will perhaps, also add some crushed glass as well to make sure there is enough silica to form a decent slag cover on the molten sulfide matte and maybe even a little crushed fluorite as well. The old assay trick of using scrap iron (normally nails) to reduce the molten galena will be used. THe formula is: PbS + Fe = FeS + Pb The reaction is driven because Fe is a more chemically active metal than lead (silver and copper are also displaced as they are less active than iron). I will carefully stir the whole molten mass with an iron rod (while the crucible is still secure within the furnace to be safe). The lead should capture the PMs, and when I pour the whole mass into a cone mold, I should get three products - a slag glass, a sulfide matte of mostly iron sulfides, and a lead button. I will use a large crucible and hope to process around 3+ kg of total material (flux + scrap iron + extra galena + sulfide ore concentrates) in each charge, with resulting a lead button of roughly around 1 to 1.25 Kg in size each time.
The assay fusion will be done with a propane furnace out in the desert, in a fire safe location where odors and smoke not will harm or offend anyone. I also will use a mask with a HEPA filter to make sure I do not breathe any hazardous smoke. It may take 4 to 6 or so charges and pours to process all the concentrates from step 2. The lead will be retained and saved for step 4.
4. Perform a Parkes Process capture of the copper, gold and silver.
On completion of the assay like fusion reduction process, I should have 5 to 8 Kg of gold, silver and copper bearing lead, which I will melt and mix with a couple pounds of zinc and stir. I will not take the mix up to a high temperature to try to dross out the copper, I will just collect the copper with the zinc and separate it later (there should not be much copper anyway). I read a thread on this forum where a member used a motor to create stirring for the necessary surface contact for the migration of the PMs and copper into the zinc. I will just stir for a time by hand with an iron rod. At the conclusion, I will pour off the material into a cone mold and after separation, I should have a low PM lead metal suitable for bullets and a few pounds of PM bearing zinc alloy.
5. Part the zinc from the gold, silver and copper with Hydrochloric Acid
It may be that for use of Hydrochloric, inquarting may be necessary, but I will try without doing so first. When complete, I should have zinc in solution and the copper, gold and silver as an insoluble black powder. I will wash the powder well with warm water. I may attempt recovering the zinc by electrolytic methods - I should be able to get most of the zinc out.
6. Part the gold and silver with nitric acid
The silver and any small amounts of copper present will be soluble in plain nitric, and I will cement out the silver with metallic copper, then recover all the copper electrolyticly. I will then pour the silver into a fairly pure button and the gold and final nitric insoluble materials into their own button and at that point the final extraction process will be complete. The gold will not be .999, but it should be maybe 90+ which will be good enough for my purposes.