PREPARATION OF CALCIUM SULFATE HEMIHYDRATE WHISKERS FROM COMPLEX JAROSITE WASTE

Complex jarosite waste was obtained from zinc metal hydrometallurgical process, which contained gypsum and ammonium jarosite (NH4Fe3(SO4)(2)(OH)(6)). The influence of impurity ions (Fe3+ and NH4+) on the calcium sulfate hemihydrate (HH) morphology was studied using pure gypsum as the raw material, respectively. HH crystals with a high aspect ratio were obtained without the impurity ions. The diameter increased and the aspect ratio of the HH decreased, while the addition of iron sulfate and ammonia sulfate increased. Ammonium iron (NH4+) can be removed by using calcium oxide to decompose the ammonium jarosite in the waste and then to wash the sediment with tap water. The sediment (calcified jarosite sediment) mainly contained CaSO4 center dot 2H(2)O and Fe(OH)(3). The influence of cultivating time on HH crystals growth was researched by using the sediment as raw materials. The diameter of the whiskers increased, while the hydrothermal time increased. The whiskers were obtained, with high a aspect ratio (10-60), large diameter (1-4 mu m) and smooth surface, after the sediment was treated at 140 degrees C for 6 h in pH = 5 solution.