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Membrane Water Treatment
  Volume 13, Number 4, July 2022 , pages 183-189

Removal of sulfate ion from semiconductor wastewater by ettringite precipitation
Chong-Min Chung

    This study seeks towards an optimal way to control sulfate ions in semiconductor wastewater effluent with potential eco-toxicity. We developed a system based on ettringite (Ca6Al2(SO4)3(OH)12∙26H2O). The basic idea is that the pH of the water is raised to approximately 12 with Ca(OH)2. After, aluminium salt is added, leading to the precipitation of ettringite. Lab-scale batch and continuous experiment results with real semiconductor wastewater demonstrated that 1.5 and 1 of stoichiometric quantities for Ca2+ and Al3+ with pH above 12.7 could be considered as the optimal operation condition with 15% of sludge recycle to the influent. A mixed AlCl3 + Fe reagent was selected as the beneficial Al3+ source in ettringite process, which resulted in 80% of sludge volume reduction and improved sludge dewaterability. The results of continuous experiment showed that with precipitation as ettringite, sulfate concentration can be stably reduced to less than 50 mg/L in effluent from the influent 2,050 ± 175 mg/L on average (1,705 ~ 2,633 mg/L).
Key Words
    eco-toxicity; ettringite; semiconductor wastewater; sludge volume reduction; sulfate ion;
Chong-Min Chung: Department of Environment Science & Biotechnology, Jeonju University, Jeonju 55069, Republic of Korea

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