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Ask The Experts - How do I recover gold in pyrite?

October 2018 by Chris Ralph

Q: I am interested separating gold from pyrite. I would like to know how do I best recover the gold contained in the pyrite. I will remain highly obliged and grateful if you could kindly help me sir. Regards,
H.A. Ngamreiwung

A: It’s true that pyrite from gold mines will contain a small amount of gold. It is microscopic and is found inside the pyrite crystal. Miners who process gold ores will get free gold particles that can be melted into bars, but they also recover pyrite that has small amounts of gold within it. Often the majority of the gold is in the free particles, but sometimes the pyrite can also contain important amounts of gold. It is not easy to get the gold out of that pyrite—there is no simple and easy method.

The best answer as to how to recover that gold depends on the amount of pyrite you intend to process. If you have only a few pounds, it can be roasted by heat in the open air and then mixed with a flux like sodium borate and melted with a collector metal like copper. The melt can be poured into a mold and the gold will now be alloyed in the copper. An ounce of copper per pound of roasted pyrite will be plenty. Most refiners have no problem accepting copper mixed in with your gold. Extreme caution and appropriate safety equipment is required with open air roasting as many gold ores also contain arsenopyrite, and if present it will be mixed in with your pyrite. Roasting this mineral can produce deadly arsenic fumes.

The other possibility is shipping to a custom milling operation that can process the pyrite, but shipping and processing can be expensive. If you are a small miner, it may not be economically worthwhile to recover that gold inside the pyrite.

For large tonnages, big commercial mines oxidize their pyrite in roasters or autoclaves. This is very expensive equipment, costing many millions of dollars. It is only justified for the biggest operations. Once the pyrite has been oxidized and the sulfur driven off, the remaining iron oxide material is treated by cyanide to recover the gold.