Optimization of hydrocalumite preparation under microwave irradiation for recovering aluminium from a saline slag

Aluminium was successfully extracted by treating an aluminium slag with aqueous NaOH under reflux conditions. This solution was purified by precipitation of silicon species by addition of HCl up to pH = 1, and used for preparing hydrocalumite (Ca2Al(OH)6Cl·2H2O) by the coprecipitation method. The effect of temperature on the properties of hydrocalumite prepared under microwave (MW) irradiation was studied. Characterization of the obtained solid was carried out by powder X-ray diffraction (PXRD), thermal analysis, FT–IR spectroscopy, chemical analysis, electron microscopy and N2 adsorption–desorption at −196 °C. The results showed that the use of the extracted aluminium solution allowed to obtain hydrocalumite by the coprecipitation method and that the temperature of the MW ageing treatment had a large effect on the formation of side phases, in addition to hydrocalumite. The results here reported demonstrate that formation of hydrocalumite is an effective method for the recovering of aluminium from its waste. [Display omitted] •Aluminium was successfully extracted form a saline slag.•Crystalline hydrocalumite was prepared by microwave treatment of the extracted liquor.•Treatment temperature MW had an important effect on formed phases.•Hydrocalumite and katoite coexisted between 100 and 120 °C.•Pure hydrocalumite was obtained at 125 °C under MW treatment.