Mineral transformation and dissolution of jarosite coprecipitated with hazardous oxyanions and their mobility changes

Abstract

Jarosite coprecipitation with hazardous oxyanions can attenuate the concentrations of these elements in acid mine drainage. However, jarosite can be easily transformed to goethite with changes in geochemical conditions. Consequently, the released oxyanions can greatly affect environments. The changes in the mineralogy and mobility of five oxyanions, namely AsO4, SeO3, SeO4, MoO4, and CrO4, which were coprecipitated with jarosite, are investigated herein during the mineral transformation. Our results show that the oxyanion species and the pH values greatly affect the mineral transformation and dissolution rates of jarosite-containing oxyanions. The transformation and dissolution rates of the jarosite samples at pH 8 are noticeably higher than those at pH 4. The X-ray diffraction results show that the CrO4 and SeO4 jarosites are as effectively transformed to goethite as the jarosite without oxyanions, while the SeO3 and AsO4 jarosites are least transformed, resulting in different sulfate and oxyanion concentrations in the solution. The oxyanions in jarosite are the main controlling factor in the mineral transformation and dissolution rates. In acid mine drainage, although CrO4 is easily attenuated by the jarosite precipitation, it has the highest mobility during the goethite transformation. On the contrary, AsO4 shows the opposite case.