Simultaneous synthesis of ettringite and absorbate incorporation by aqueous agitation of a mechanochemically prepared precursor

Abstract

Co-grinding of calcium hydroxide, aluminum hydroxide and gypsum was performed to prepare an activated precursor for synthesizing ettringite (simple formula 3CaO·Al₂O₃·3CaSO₄·32H₂O). Agitation of the precursor in an aqueous solution with a target absorbate, even at room temperature, allowed not only the synthesis of ettringite, but also absorbate incorporation at stoichiometric amounts accompanying the synthesis reaction. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric differential thermal analyses (TG-DSC) were conducted to characterize the precursors and synthesized products. Potassium phosphate was used as the target absorbate to evaluate possible incorporation of both sulphate and phosphate coexisting in the ettringite structure. This confirmed that the novel idea of incorporating pollution components in a reaction may allow for removing efficiencies that are much higher than obtainable from traditional sorption operation.