Iron and sulphur management options during Ni recovery from (bio)leaching of pyrrhotite tailings Part 2: Strategies for sulphur fixation during biomass-induced magnetization of goethite and jarosite

•KOH fixes 91% of sulfur as H2O-soluble K2SO4 during jarosite-goethite magnetization.•Oxidation treatment lowers the sulfur content in the magnetite product down to 0.08%.•Through CaCl2 exchange, high-purity gypsum precipitates from the K2SO4 solution.