Arsenic

Jarosite

Mineralogy

Ferric

Inorganic chemistry

Sulfate

Arsenopyrite

Geology

Physical chemistry

Arsenate

Organic chemistry

Pyrite

Chalcopyrite

Environmental chemistry

Acid mine drainage

Chemistry

Tailings

Hematite

Copper

Journal of Hazardous Materials

Acid mine drainage (AMD) formation and toxic arsenic (As) pollution are serious environmental problems encountered worldwide. In this study, we investigated the crucial roles played by common secondary mineral phases formed during the natural weathering of pyrite-bearing wastes—soluble salts (melanterite, FeSO4·7H2O) and metal oxides (hematite, Fe2O3)—on AMD formation and As mobility under acidic conditions (pH 1.5–4) prevalent in historic tailings storage facilities, pyrite-bearing rock dumps and AMD-contaminated soils and sediments. Our results using a pyrite-rich natural geological material containing arsenopyrite (FeAsS) showed that melanterite and hematite both directly—by supplying H+ and/or oxidants (Fe3+)—and indirectly—via changes in the nature of oxidation layer formed on pyrite—influenced pyrite oxidation dynamics. Based on SEM-EDS, DRIFT spectroscopy and XPS results, the oxidation layer on pyrite was mainly composed of ferric arsenate and K-Jarosite when melanterite was abundant with/without hematite but changed to Fe-oxyhydroxide/oxide and scorodite when melanterite was low and hematite was present. This study also observed the formation of a mechanically ‘strong’ coating on pyrite that suppressed the mineral’s oxidation. Finally, As mobility under acidic conditions was limited by its precipitation as ferric arsenate, scorodite, or a Fe/Al arsenate phase, including its strong adsorption to Fe-oxyhydroxides/oxides.

Acid mine drainage formation and arsenic mobility under strongly acidic conditions: Importance of soluble phases, iron oxyhydroxides/oxides and nature of oxidation layer on pyrite