Effects of different oxyanions in solution on the precipitation of jarosite at room temperature

The effects of five different oxyanions, AsO4, SeO3, SeO4, MoO4, and CrO4, on the precipitation of jarosite at room temperature were investigated by X-ray diffraction, scanning electron microscopy, and chemical analysis. Different amounts (2, 5, and 10 mol%) of oxyanions in the starting solution and different aging times (1 h-40 days) were used for the experiment. In the initial stage, only the amorphous phase appears for all samples. With increasing aging time, jarosite and jarosite with oxyanions start precipitating at room temperature with different precipitation rates and crystallinities. Jarosite with AsO4 shows the lowest precipitation rate and lowest crystallinity. With increasing amounts of oxyanions, the crystallization rate decreases, especially for jarosite with AsO4. The jarosite samples with CrO4 and SeO4 show the fastest precipitation and highest crystallinities. For the jarosite samples with a low precipitation rate and low crystallinity, the amorphous phase contains high concentrations of oxyanions, probably because of the fast precipitation of the amorphous iron oxyanion phase; however, the phase with fast jarosite precipitation contains fewer oxyanions. The results show that coprecipitation of jarosite can play a more important role in controlling the behavior of CrO4 than AsO4 in acid mine drainage.