Iron Pyrites

Recovery of Gold in Pyritic Sulfide Ores The now extinct Us Bureau of Mines conducted numerous studies of gold in pyrite, and sulfide ores over the years, until their untimely demise in the 1990's. Much of the referenced studies and case applications discussed in this brief article came from USMB reports, which even after they ceased to exist, still continue to provide some good scientific information to those working in the mining and mineral processing industries. Sulfide ores, and pyrites in particular, have caused and continue to cause difficulty in recovering the gold values from these ores. In most instances, visible gold can not be seen under microscopic examination of pyrite gold ores. However, if the ore is ground to -200 mesh, most times, a few specs of gold can be visibly seen under microscopic examination. Based upon numerous case studies, it appears that gold particles in pyrite are generally fine, ranging from 75 microns down to 2 or 3 microns. The incidence of fine gold's quantity also appears to be related to the gold concentration, as well. If the assay is 2 ounces per ton, there are generally larger gold particles present along with the typically fine micron sized gold. When the grade diminishes to say, 0.2 ounces per ton, there are generally only micron sized particles associated with the pyrites in the ore. This is not absolute, but it does appear to be the trend. Recovery of gold in sulfide ores has fallen into several categories. First is froth flotation, and second is cyanidation of the ores. Using cyanide to recover gold from sulfide ores generally results in 30 to 35% recovery, and the best I have heard of is around 50% recovery. The fine coating of a iron compound definitely appears to be a key component of the inability of cyanide to efficiently leach low grade pyritic ores. Perhaps there is some room here for a pretreatment, to remove this iron coating and then make the fine particles susceptible to cyanide leaching. To my knowledge, this has never been attempted. Generally speaking, cyanide leaching of low grade pyritic ores is economically unsatisfactory in today's market. Low grade ores that do not respond well to cyanide or flotation are generally referred to a "refractory" ore. Which usually means that it needs to be roasted to release the gold. Roasting has to be one of the most expensive methods of recovering gold with current environmental considerations, and is usually cost prohibitive, except in a few circumstances, where grade and volume justify the economics. Gravity concentration tends to recover the pyrite with the gold, and only removes the lighter minerals, such as quartz, from the ore. The most difficult particles to gravity concentrate are the fines, and 75 microns to 2 microns are definitely very fine. So, even if the ore were ground to 2 microns, it may not be recoverable using current gravity technology. That appears to leave froth flotation as still the best method of recovering the gold from pyritic ores. Sulfide ores, such as chalcopyrite, sphaelerite, galena, and pyrrhotite, and mixtures of these ores have historically been found with micron size gold particles included in them. This generally involves frother, several collectors (promoters) and possibly some modifying or depressing agents as well. Geologists and mineralogists have many theories why and how the gold occurs with the pyrite, and I will not enter into any of these areas, since I am concerned with liberating the gold from the ores. I will say that from my understanding, many seem to agree that in sulfide gold ores, the occurrence of gold appears to occur as a replacement of other minerals, possibly iron. One USBM paper summed up five noticeable characteristics of auriferous pyritic ores. The gold occurs as tiny flakes on the crystallographic planes of the pyrite. The gold flakes are very small in size, 5-10 microns. The pyrite in which small amounts of gold occurs is of crystalline variety (primary pyrite). T

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mtau March 17, 2012 at 5:54pm

Rose: I agree with you about "fracturing". If you have gold locked in black sands, the best method for releasing it is to crush it to -100mesh. Also I agree about leaching sulfide ore- don't do- it as it can create hydrogen cyanide gas, not only deadly, but lethal as in "gas chamber" (for those of us that are old enough to remember).
Spur March 17, 2012 at 3:34pm

One old trick I heard was to roast your Blk sands ( out side , it can contain bad vapors) Get your sands red hot then dump them in a bucket of Cold water, this is called Fracturing.
Spur March 17, 2012 at 3:23pm

I can not take credit for my prier post, I copied and pasted it. I tried to post the link but it did not post. So I am here now to post the link from where I got the Info. This reminds me of when I was a kid, my Dad got me some little yellow chicks when I whanted a dog. after feding and caring for them for over a year the Coyties can and Ate them all. If I had a dog them coyties would have never showed up. http://mine-engineer.com/mining/minproc/gold-in-pyrite.htm
Steve Wilson March 17, 2012 at 9:09am

Thank you all for the good info. Steve
Spur March 16, 2012 at 10:13pm

Recovery of Gold in Pyritic Sulfide Ores The now extinct Us Bureau of Mines conducted numerous studies of gold in pyrite, and sulfide ores over the years, until their untimely demise in the 1990's. Much of the referenced studies and case applications discussed in this brief article came from USMB reports, which even after they ceased to exist, still continue to provide some good scientific information to those working in the mining and mineral processing industries. Sulfide ores, and pyrites in particular, have caused and continue to cause difficulty in recovering the gold values from these ores. In most instances, visible gold can not be seen under microscopic examination of pyrite gold ores. However, if the ore is ground to -200 mesh, most times, a few specs of gold can be visibly seen under microscopic examination. Based upon numerous case studies, it appears that gold particles in pyrite are generally fine, ranging from 75 microns down to 2 or 3 microns. The incidence of fine gold's quantity also appears to be related to the gold concentration, as well. If the assay is 2 ounces per ton, there are generally larger gold particles present along with the typically fine micron sized gold. When the grade diminishes to say, 0.2 ounces per ton, there are generally only micron sized particles associated with the pyrites in the ore. This is not absolute, but it does appear to be the trend. Recovery of gold in sulfide ores has fallen into several categories. First is froth flotation, and second is cyanidation of the ores. Using cyanide to recover gold from sulfide ores generally results in 30 to 35% recovery, and the best I have heard of is around 50% recovery. The fine coating of a iron compound definitely appears to be a key component of the inability of cyanide to efficiently leach low grade pyritic ores. Perhaps there is some room here for a pretreatment, to remove this iron coating and then make the fine particles susceptible to cyanide leaching. To my knowledge, this has never been attempted. Generally speaking, cyanide leaching of low grade pyritic ores is economically unsatisfactory in today's market. Low grade ores that do not respond well to cyanide or flotation are generally referred to a "refractory" ore. Which usually means that it needs to be roasted to release the gold. Roasting has to be one of the most expensive methods of recovering gold with current environmental considerations, and is usually cost prohibitive, except in a few circumstances, where grade and volume justify the economics. Gravity concentration tends to recover the pyrite with the gold, and only removes the lighter minerals, such as quartz, from the ore. The most difficult particles to gravity concentrate are the fines, and 75 microns to 2 microns are definitely very fine. So, even if the ore were ground to 2 microns, it may not be recoverable using current gravity technology. That appears to leave froth flotation as still the best method of recovering the gold from pyritic ores. Sulfide ores, such as chalcopyrite, sphaelerite, galena, and pyrrhotite, and mixtures of these ores have historically been found with micron size gold particles included in them. This generally involves frother, several collectors (promoters) and possibly some modifying or depressing agents as well. Geologists and mineralogists have many theories why and how the gold occurs with the pyrite, and I will not enter into any of these areas, since I am concerned with liberating the gold from the ores. I will say that from my understanding, many seem to agree that in sulfide gold ores, the occurrence of gold appears to occur as a replacement of other minerals, possibly iron. One USBM paper summed up five noticeable characteristics of auriferous pyritic ores. The gold occurs as tiny flakes on the crystallographic planes of the pyrite. The gold flakes are very small in size, 5-10 microns. The pyrite in which small amounts of gold occurs is of crystalline variety (primary pyrite). T
Spur March 16, 2012 at 8:32pm

once agin I fill I should be taking Notes, thank you mtau.
mtau March 16, 2012 at 7:27pm

Iron pyrite is a sulfide of iron. There are several acids that will disolve it, but all of them will give off toxic fumes. Your best bet is to crush it, then roast it, then concentrate it to get out the gold. Make sure that you heat it out doors, as it will give off SO2 (sulfer dioxide), and you don't want to breath that either.

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