title: Sulfate removal from wastewater using ettringite precipitation: Magnesium ion inhibition and process optimization.
abstract: One of the main challenges in industrial wastewater treatment and recovery is the removal of sulfate, which usually coexists with Ca2+and Mg2+. The effect of Mg2+on sulfate removal by ettringite precipitation was investigated, and the process was optimized in the absence and presence of Mg2+. In the absence of Mg2+, the optimum conditions with sulfate removal of 99.7% were obtained at calcium-to-sulfate ratio of 3.20, aluminum-to-sulfate ratio of 1.25 and pH of 11.3 using response surface methodology. In the presence of Mg2+, sulfate removal efficiency decreased with increasing Mg2+concentration, and the inhibitory effect of Mg2+matched the competitive inhibition Monod model with half maximum inhibition concentration of 57.4 mmol/L. X-ray diffraction and Fourier transform infrared spectroscopy analyses of precipitates revealed that ettringite was converted to hydrotalcite-type (HT) compound in the presence of Mg2+. The morphology of precipitates was transformed from prismatic crystals to stacked layered crystals, which confirmed that Mg2+competes with Ca2+for Al3+to form HT compound. A two-stage process was designed with Mg2+removal before ettringite precipitation to eliminate the inhibitory effect, and is potential to realize sludge recovery at the same time of effective removal of sulfate and hardness.
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China.
authors.forename: Weixiao
authors.initials: W
authors.lastname: Dou
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China. Electronic address: zhouzhen@shiep.edu.cn.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China. Electronic address: jiangluman@shiep.edu.cn.
authors.forename: Lu-Man
authors.initials: LM
authors.lastname: Jiang
authors.affiliation: Jiangsu Hairong Thermal & Environmental Engineering Co., Ltd, 10 Sanmiao Village, Xingren Town, Tongzhou District, Nantong, Jiangsu 226371, China.
authors.forename: Aijian
authors.initials: A
authors.lastname: Jiang
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China.
authors.forename: Rongwei
authors.initials: R
authors.lastname: Huang
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China.
authors.forename: Xiaoce
authors.initials: X
authors.lastname: Tian
authors.affiliation: College of Environmental and Chemical Engineering, Shanghai University of Electric Power, 2588 Changyang Road, Shanghai 200090, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Jiangsu Hairong Thermal & Environmental Engineering Co., Ltd, 10 Sanmiao Village, Xingren Town, Tongzhou District, Nantong, Jiangsu 226371, China.
authors.forename: Dongqing
authors.initials: D
authors.lastname: Chen
mesh_terms: D011232:Chemical Precipitation; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D008903:Minerals; D013431:Sulfates; D062065:Wastewater; D014961:X-Ray Diffraction
chemical_list: D008274:Magnesium; D008903:Minerals; D013431:Sulfates; D062065:Wastewater; C501337:ettringite
keywords: Ettringite; Flue gas desulfurization wastewater; Inhibitory effect; Magnesium; Sulfate removal