Abstract:The effects of K+ on precipitation rate of arsenic and ferric, phase and chemical composition of As-bearing precipitate, and phase transition behavior were studied during hydrothermal mineralized arsenic precipitation in H3AsO4-FeSO4-K2SO4-H2O system. The results show that the presence of K+ in the system has a significant effect on composition of As-bearing precipitate. In addition to co-precipitation with As (V) to form scorodite (FeAsO4?2H2O) and self-hydrolysis precipitation to basic ferric sulfate Fe(OH)SO4, supersaturated Fe (III) will also competitive precipitation with K+ in the form of K-jarosite(KFe3(SO4)2(OH)6). With conditions of the initial concentration of K+ 5 g/L, arsenic concentration 10 g/L, iron-arsenic molar ratio 1.5, solution pH 1, reaction temperature 160℃, agitation speed 500 r/min, reaction time 3 h, and the oxygen partial pressure 0.6 MPa, the precipitation rates of As and Fe were 96.7 % and 96.5 %, respectively, and the phase compositions of As-bearing precipitate were mainly scorodite, jarosite and basic ferric sulfate, the contents of which were 65.0 %、24.2 % and 10.8 %, respectively, the content of As, Fe, K and S in arsenic slag was 23.39 %、25.72 %、1.84 % and 4.09 % , respectively. The formation of metastable state K-jarosite phase can be effectively inhibited by controlling the initial iron-arsenic molar ratio in a reasonable range, so as to achieve efficient precipitation of arsenic, increase the arsenic content in As-bearing precipitate and reduce its yield.