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

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 center dot 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 center dot 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 m(2) g(-1) and CaCO3 with a purity of 99.9% were obtained.