Incorporation of arsenate (As(V)) and sulfate species into the ettringite (Ca6Al2(SO4)3(OH)12·26H2O) structure has been considered as a process for arsenic and sulfate fixation in the treatment of an industrial effluent treatment containing 2044 mg/L of sulfate and 24 mg/L of arsenic. Precipitation was carried out with distinct molar ratio of Ca:Al:SO4, lime as a calcium source, and a combination of aluminum polychloride and Al(OH)3 as aluminum supply. Experiments were guided by thermodynamic modeling on PHREEQC which indicated pH 11.5 as the best value to remove sulfate and arsenic simultaneously from this wastewater. This was essential to avoid subsequent sulfate release from ettringite at higher pH due to the formation of Ca4Al2O7:19H2O. Both ettringite and ettringite-As precipitation, at pH 11.5, dropped down the sulfate and arsenic residual concentration to 4 mg/L and < 0.05 mg/L, respectively. The final effluent presented parameters within the acceptable limits of 0.2 mg/L of As and 250 mg/L for sulfate in Minas Gerais State-Brazil.