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A series of ex-situ precipitation experiments were firstly performed to investigate the effects of Eh/pH and impurity molar ratio on the transition of arsenic bearing precipitates from amorphous phase to crystalline phase. Based on the analyses of the ex-situ experiments, another series of in-situ precipitation experiments were designed and conducted to explore the effects of current density, circulation pattern, inlet position, seed crystals' concentration, and impurity molar ratio on the formation and growth of crystalline precipitates containing arsenic. It was found that higher Eh and pH values, as well as the impurity ratio of Sb/Bi<1 are beneficial to the transition of arsenic bearing precipitates from amorphous state to crystalline state. Nevertheless, the effects of current density, circulation pattern, inlet position, seed crystals' concentration, and impurity molar ratio on the in-situ formation of crystalline particles containing arsenic are more complex, with the optimal conditions identified as the current density of 500 A/m2, the circulation pattern with one lower-inlet/one upper-outlet, the inlet position close to the cathode, the seed crystals' concentration of 1 g/L, and the As:Sb:Bi molar ratio of 20:1:2. • Ex-situ and in-situ precipitation experiments were designed and performed. • Higher pH and Eh promote the formation of arsenic bearing crystalline particles. • Sb/Bi<1 is necessary for the generation of crystalline arsenic bearing particles. • The effects of current density, seed crystals' concentration are more complex. • The optimal conditions for in-situ precipitation were identified. [ABSTRACT FROM AUTHOR]