Abstract:The feasibility to recover Mg2+, Ca2+ and NH4+-N in electrolytic manganese wastewater by CO2 from exhaust gas generated from manganese ore acid leaching section was investigated. The optimum process conditions and mechanism to recover Mg2+, Ca2+ and NH4+-N in wastewater by CO2 were determined. The results show that recovery of Mg2+ is 97.58% with initial concentration of Mg2+ in wastewater of 1 200 mg/L, recovery of Ca2+ is 99.68% with initial concentration of Ca2+ in wastewater of 560 mg/L, and recovery of NH4+-N is 80.71% with initial concentration of NH4+-N in wastewater of 875 mg/L under the conditions including reaction time of 240 min, reaction temperature of 45 ℃, pH value of 9.2, carbon dioxide volume concentration of 15%, and stirring rate of 600 r/min. Recovery of Mg2+ is mainly controlled by diffusion process and is in accordance with first-order kinetic equation with apparent activation energy of 61.40 kJ/mol. Mg2+ and Ca2+ in wastewater is mainly recovered by formation of Mg(OH)2?MgCO3 precipitate, and NH4+-N is mainly removed by adsorption on surface of newly formed precipitated crystal.