Dissolution of non-sulfide phases during the chemical and bacterial leaching of a sulfidic black schist

The purpose of this study was to assess the solubilization of silicates during the chemical and bacterial leaching of finely ground black schist in shake flasks. The main sulfide minerals were pyrrhotite (Fe1 − xS) and pyrite (FeS2) with lesser amounts of sphalerite (ZnS), pentlandite (Ni,Fe,Co)9O8), violarite (FeNi2S4), and chalcopyrite (CuFeS2). Quartz, micas, and feldspars were the main Si-containing phases. Dissolution of the non-sulfidic minerals was monitored by analysis of Si, Al, Ca, Mg, and K solubilized from the black schist in 30 day leaching experiments at 22 ± 2 °C. The dissolution of main constituent elements from silicate minerals was a function of the pH of the leach solution and no direct role of bacterial action on the solubilization of silicates was evident. Ferrous or ferric iron addition did not affect the concentrations of elements dissolved from silicates except for mica interlayer K+, which was incorporated into the jarosite fraction.

► Chemical and bacterial leaching tests were performed with a black schist ore sample at 22 °C.
► Bacteria had no direct role in the solubilization of silicate phases.
► The dissolution of feldspars and micas increased with acidity.
► Si and Al dissolution was closely related, suggesting congruent solubilization.
► The concentration of dissolved K decreased with jarosite precipitation.