Effect of relative humidity on oxidation products of arsenopyrite and löllingite

0558660 - GLÚ 2023 RIV NL eng J - Journal Article
Drahota, P. - Ettler, V. - Culka, A. - Rohovec, Jan - Jedlička, R.
Effect of relative humidity on oxidation products of arsenopyrite and löllingite.
Chemical Geology. Roč. 605, September (2022), č. článku 120945. ISSN 0009-2541. E-ISSN 1872-6836
Institutional support: RVO:67985831
Keywords : Arsenopyrite * Löllingite * Oxidation products * Relative humidity
OECD category: Geology
Impact factor: 3.9, year: 2022
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S000925412200239X

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 ≤ 81%. In comparison, well crystallized scorodite and arsenolite were the dominant oxidation products in Lö concentrates at every RH. Increasing RH significantly increased the oxidation rate of sulfide and arsenide minerals in the concentrates. The highest sulfide and arsenide oxidation rates in the Lö concentrate occurred at RH 100%, and was approximately 40 times faster than at RH 81%. In comparison, the highest oxidation rate of sulfides in the Apy concentrate occurred at RH 94%, and was 6 to 7 times faster that than at RH 81%. Differences in the mineralogical compositions of oxidation products in the Apy and Lö concentrate reflect the high levels of sulfate in the Apy concentrate. This triggered formation of PCFA and retarded its transformation to scorodite. The substantial role of sulfate in the oxidation process is reinforced by the finding that stagnation of the sulfide oxidation rate in the Apy concentrate at high RH (> 94%) was probably due to the formation of ferric ion complexes in the presence of high levels of sulfate ions.
Permanent Link: https://hdl.handle.net/11104/0334144