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CO2 mineralization of natural wollastonite into porous silica and CaCO3 powders promoted via membrane electrolysis

Xie, Heping, Wang, Fuhuan, Wang, Yufei, Liu, Tao, Wu, Yifan, Liang, Bin
Environmental earth sciences 2018 v.77 no.4 pp. 149
ammonia, ammonium chloride, anodes, calcium carbonate, calcium silicate, carbon dioxide, cathodes, electrolysis, electrolytes, emissions, energy, energy conservation, greenhouse gases, humans, hydrochloric acid, hydrogen, hydrogen production, mineralization, oxidation, pH, powders, silica, sodium chloride, sodium hydroxide, surface area
CO₂ is a greenhouse gas, whose emissions threaten the existence of human beings. Its inherently safe sequestration can be performed via CO₂ mineralization, which is relatively slow under natural conditions. In this work, an energy-saving membrane electrolysis technique was proposed for accelerating the CO₂ mineralization of wollastonite into SiO₂ and CaCO₃ products. The electrolysis process involved splitting NH₄Cl into HCl and NH₃·H₂O via hydrogen oxidation and water reduction at the anode and cathode of the electrolytic system, respectively. In contrast to the chlor-alkali electrolysis, this method did not involve Cl⁻ oxidation and the standard potential of the anode was reduced. Additionally, NH₄Cl was used as the electrolyte instead of NaCl; as a result, the generation of NH₃·H₂O instead of NaOH occurred in the catholyte and the cathodic pH dramatically decreased, thus reducing the cathodic potential for hydrogen evolution. The observed changes led to a 73.5% decrease in the energy consumption. Moreover, after the process of CO₂ mineralization was optimized, SiO₂ with a specific surface area of 221.8 m² g⁻¹ and CaCO₃ with a purity of 99.9% were obtained.