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urbanminer

Sulfides

47 posts in this topic

Most sulfide ores are processed by flotation.

Depending on the ore, gravity methods can produce a fair concentrate - not as good as flotation.

The problem with sulfides is extraction of values - Most extraction of sulfides is by smelting. There are no smelters in the US accepting custom ores that I know of (Thanks EPA, now we are dependent on others). That means shipping to Mexico, Canada or maybe even China!

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It all depends on your sulfide product - what you have to leach.

Leaching works poorly on coarser gold - it just takes forever to dissolve.

Some types of sulfides react badly with leach systems, destroying the leach chemicals.

If you have significant silver in your ore, many non-cyanide leach systems dont recover silver. It will be left behind in the ore.
Cyanide is a strong poison, but works well if properly controlled. Many alternative leach systems are poisonous too, though not quite as poisonous as cyanide. (none of these are really things you want in a household environment with kids, dogs, neighbors, etc. - using them in many cities would be a violation of local zoning laws)

Stay away from acidic leaches, they react with the sulfur in the sulfides and you will end up with a hazardous waste mess. Heavy metals like lead in the ores can be a problem.

Is it worth it? Depends on the amount of sulfides you have, their richness, the nature of the sulfides, facilities you have for working the ores, etc.

There are some cases where it does work, but its a case by case determination. Sulfides are normally a tough situation to deal with.

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We have been testing ores from our mine with a SSN leach.  We have sulfides present in our ore and the SSN seems to do okay.  There is even an inexpensive test kit available that uses SSN to leach and stannous chloride as a color indicator.  You can get the kit for $40. If you get positive results it is easy to make the leach yourself under the proper safety precautions.  Then you can use zinc to recover the values.   

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Interesting!  Ok, call me stupid, or just uninformed, but what does SSN stand for?  Where can a person find this test kit?  I'd be interested in learning more about this process!

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SSN is Saturated Saline (salt water), Nitric Acid.  I won't mention the product name on here because it seems the administrators get a little worked up over things like that; but if you do a google search for "field gold test kit," the very first couple of results feature the kit. 

 

Be very careful to use the kit in a very well ventilated area, and make sure you get arm length chemical grade gloves.  The acids involved will burn your skin and your lungs if proper precautions are not taken.  For your testing containers never use anything other than plastic (not the brittle type), glass or ceramic.  Do a lot of research, as much as you can.  If you have any other questions let me know. 

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As I mentioned previously, acidic leaches pull heavy metals out of your sulfides like lead, arsenic, antimony, etc. You end up with a hazardous waste mess that you cant get rid of cheaply, and depending on your sulfide mix, you may have difficulty recovering the precious metal values from the solution. Pouring the waste down your drain is illegal and the acids can do serious damage to your pipes as they were not made for that sort of thing. Pour a little down your drain once and your chances of getting caught are very slim, do it a bunch of times and you will likely get a major fine and quite possibly time in Jail (I knew a guy who dumped metal solutions in his toilet, and did so regularly. He was caught and I think he did six months in jail, plus a large fine).

 

Nitric acid can burn your skin in only a couple of seconds. Even if only a tiny part of a drop lands on your skin, you will know it immediately. If it lands on your clothes, it burns holes in them. I used to use it at a chemical lab that I worked at.

 

The test kit will only tell you if you have gold or no gold. It will not tell you if you have a significant amount of gold or just a very small amount. Its a present or not present type of test, not a tell you how much you have type of test.

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Certainly no expertise in this area... just a couple ?'s.

I read about the SSN leach a few years ago.  A certain study determined that a ratio of 7:1 worked best on a variety of ores.  It sounded promising and simple to try.

I recall reading that you can re-use the old leach solution over and over after you have recovered your pm's.  

Wouldn't that mitigate the concern for the disposal of the toxic, heavy metals?  

Some landfills will take toxic stuff like old batteries, paint, pharmaceuticals, oil and antifreeze.   Would they not also take a few gallons of your toxic heavy metal solution?  

Just curious.

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I read about the SSN leach a few years ago.  A certain study determined that a ratio of 7:1 worked best on a variety of ores.  It sounded promising and simple to try.

It is not simple by any means, generates nasty acidic gasses, sulfur smells, etc. No commercial assay or testing labs use it because of the mess. I've had loads of guys ask me (after they have done it) how to get the values out of the solution once contaminants make it tough to capture the precious metals in solution. Some minerals can capture the gold and silver out of solution, so the values are still in the solids when you expect them to be in the solution. Those who have done it don't think its simple any more.


I recall reading that you can re-use the old leach solution over and over after you have recovered your pm's.  

Nope, that's wrong. The acid reacts with the sulfides, consuming the acid. If your ore only has traces or tiny amounts of sulfides (like less than 1%), you might be able to reuse it. If there are even a 5 percent sulfides, your ore will eat up the acid and it wont be reusable.

 

Wouldn't that mitigate the concern for the disposal of the toxic, heavy metals?  

Nope, eventually you will need to get rid of the stuff.


Some landfills will take toxic stuff like old batteries, paint, pharmaceuticals, oil and antifreeze.   Would they not also take a few gallons of your toxic heavy metal solution?  

There are a variety of classes of toxic waste, some more dangerous than others. that household stuff they accumulate and ship to other waste handlers who specialize in that sort of thing. They cant legally take things like acid waste solutions full of heavy metals, or they will be in violation of federal law. Give them a call and tell them you have a few gallons of toxic acid waste rich in various heavy metals like lead, copper and arsenic, which you want to get rid of. Then ask if they will take the waste off your hands and if so, for how much.

Let us know what they tell you.

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I understand the "pandora's box" type of situation being created here.  As a test kit, it has it's place, but on a larger scale can become a nightmare.  Another question, and another "pandora's box", what about roasting?  Is it viable, legal, on the small scale?

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We have had great sucess recovering gold from sulfides with out thiourea based solution. Our recovery rate is usually 94 to 96%. The key to recovery with sulfides is the grind size of the ore while leaching to make sure that your leach solution can make Co tact with the precious metal. You can read more about leaching sulfides on our website at www.tcbinter.com on our sulfides page.

Ken Jewell

TCB International

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Roasting or smelting might be done on a very, very small scale in a backyard, but if you are wanting to do it on a scale large enough to operate a business and show a profit, you will be creating some serious air pollution. Sulfur dioxide is a choking toxic pollutant.  To build a facility, you will need permits from any government agencies. Copper smelters take many millions of dollars to construct and operate. Its not recommended for the small operator.

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A good example of why some recovery methods are not pratical for a small scale operation, is around the 1920s, small scale smelters were being sold to miners, who at first liked the idea of not having to ship ore, which can be a huge cost depending on the location.

 

But they quickly learned that having a smelter meant for one thing that they would have keep a constant supply of ore feeding it.

And they would have more to haul in to support the smelter.

 

It just was not practical to do on a small scale and that is the reason many small mines today will grind and concentrate, like on a table and then ship the ore to a refinery that can handle your type of ore.

 

Something to think about when shipping ore.  This happened to a friend of mine, who ground concentrated and shipped silver ore to Montanna, things were good. He then found another silver mine that assayed better, so he ground and shipped, but when the mill tested the ore, he was told he would charged more because the ore had to be proccessed differently than the first ore he brought to them.

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