The mineral pyrite, also known as fool's gold, is the most abundant sulfide mineral. The mineral's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold but it may hold more than just a resemblance to the precious metal.
A new study, published in the journal Geology in collaboration with the University of Western Australia and the China University of Geoscience, offers an understanding of the mineralogical nature of the gold trapped in pyrite. This in turn may lead to more abundant and environmentally friendly methods for extracting gold from pyrite.
“The discovery rate of new gold deposits is in decline worldwide with the quality of ore degrading, parallel to the value of precious metal increasing,” lead researcher Dr Denis Fougerouse from Curtin’s School of Earth and Planetary Sciences said in a statement.
“Previously gold extractors have been able to find gold in pyrite either as nanoparticles or as a pyrite-gold alloy, but what we have discovered is that gold can also be hosted in nanoscale crystal defects, representing a new kind of “invisible” gold.
“The more deformed the crystal is, the more gold there is locked up in defects. The gold is hosted in nanoscale defects called dislocations — one hundred thousand times smaller than the width of a human hair — so a special technique called atom probe tomography is needed to observe it.”
Fougerouse added that the gold in pyrite has not previously been recognized and is only observable using a scientific instrument called an atom probe. Now, Fougerouse and his teams are researching gold extraction methods with less adverse impacts on the environment using pyrite as a source.
What aspects of it can this improve?
“Generally, gold is extracted using pressure oxidizing techniques (similar to cooking), but this process is energy hungry. We wanted to look into an eco-friendlier way of extraction,” Fougerouse said.
“We looked into an extraction process called selective leaching, using a fluid to selectively dissolve the gold from the pyrite. Not only do the dislocations trap the gold, but they also behave as fluid pathways that enable the gold to be “leached” without affecting the entire pyrite.”