Friday, June 1, 2012

Acid and Pyrite

Many people are interested in minerals – but some are also interested in how minerals interact with other things. This is for very practical reasons. A mining engineer will want to know something about all the minerals related to – found in – an ore deposit, and there could be dozens. A clear understanding is required of both the minerals and their interactions with heat and acids. Without this, it is impossible to sort out each mineral from the raw ore. Each will react differently to different processes and solutions. The mine infrastructure designers – the people who build 50 million-dollar mills - then can set up a mill and plant  to extract what they want from the ore… Lacking this understanding the ore will just remain strange-looking dirt.

Keep in mind that the minerals were concentrated by a complex chemical-physical process in the first place. Many people think of fluids in the Earth as being the same thing as potable groundwater – but the fluids forming and interacting with ore deposits can often be hot and very acidic (that’s why the concentration happens). Experiments with different solutions on different mineral species help mining engineers and geochemists to work out the extraction process. Pyrite is commonly found in almost all sulfide deposits, and must be removed first to extract the gold, copper, molybdenum, silver, lead, tin, etc., being sought after. Our early ancestors – creators of the Bronze Age of ancient Greece – had already worked out much of this process millennia ago.

Will nitric and/or muriatic acid affect pyrite?
Thanks for your time. – Aaron C.

Muriatic acid is just a tech grade of hydrochloric acid.

Pyrite fuses easily under heat, becoming magnetic and giving off sulfur dioxide fumes (SO2 – that burnt-match smell). Pyrite is insoluble in hydrochloric acid (not an oxidizer). However, a fine powder (which exposes much more of the pyrite surface area) will dissolve in concentrated nitric acid (HNO3), which IS an oxidizer.

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