Acid leaching of CaOSiO2 resources

Waste resources containing CaO and SiO2 were leached by an acetic acid solution. Most CaO exist as calcium aluminosilicate and calcium silicate in steel slag and wollastonite, respectively. Silicate leaching was enhanced steeply by heating to 50 °C or increasing acid concentrations to 4 wt%. The Si and/or Al in the leachate then precipitated independently, depending on the solubility. This enabled to improve the selectivities of Ca and Si in the leachate and precipitate, respectively. However, CaO and SiO2 are separate constituents of waste cement. The dissolution of Ca thus took place relatively fast while the ‘free’ silica leached little.