Manipulating Iron Precipitation and Gold Deportment During Pressure Oxidation

Pressure oxidation (POX) is the most utilized method for chemically liberating gold from sulfides. However, in the context of decreasing gold grades and increasingly complex mineralogy as well as variable qualities of process solutions, operations using POX can be challenged by high reagent consumption and in ensuring high gold recoveries. While POX technology is considered mature, a complete understanding of the phase transformations and gold deportment has yet to be described. In this work, by manipulating autoclave conditions, we report on batch pressure oxidation experiments where jarosite-only and hematite-only precipitates are obtained. The pressure oxidation reaction kinetics are monitored in-situ, via oxidation–reduction potential and pH measurements and interpreted with respect to recently calibrated equilibrium chemical thermodynamic data for the Fe(II)-Fe(III)-SO₄-H₂O system. Using a combination of assays, X-ray diffraction, and high-resolution SEM–EDS spectroscopy of feed and residue samples, insight into the chemical reactions taking place and gold redistribution is obtained. This research approach of combining in-situ measurements, chemical equilibrium and advanced sample characterisation will help in establishing new ways to improve process operations with existing process infrastructure.