Abstract
Arsenopyrite (FeAsS) and löllingite (FeAs2) are among the most common primary As minerals in the wastes produced by mining and associated ore processing activities. This study explores the oxidation of these minerals at high relative humidity that frequently occur in underground mines and unsaturated waste piles and tailings.
Our objectives were to examine the effect of relative humidity on the mineralogy of secondary phases that formed after 40 months of exposure of arsenopyrite-rich (Apy) and löllingite-rich (Lö) concentrates to six constant relative humidity (RH) levels between 75% and 100%. X-ray diffraction, electron microprobe, Raman microspectrometry, and sequential extraction results showed that the dominant oxidation product in Apy concentrates at any controlled RH level was poorly crystalline ferric arsenate (PCFA).
This phase revealed increasing dehydration, and release of sulfate with increasing RH >= 94%; indicating that high humidity accelerates the transformation process of PCFA to scorodite. Newly formed elemental sulfur, parascorodite, hydroniumjarosite, and ferric (hydr)oxides were minor (to trace) phases in Apy concentrates; and the latter two phases only formed on the surface of pyrite as a result of the limited transport of solutes between individual grains of sulfides at RH 94%) was probably due to the formation of ferric ion complexes in the presence of high levels of sulfate ions.