The high-purity MgO samples were prepared by carbonation method with the addition of sodium oxalate to remove calcium before the pyrolysis of heavy Mg water. The optimized conditions were obtained by investigating the effects of carbonation concentration (the ratio of solid mass to water mass in the slurry before carbonation), sodium oxalate dosage and aging time on the rate of Ca2+ removal and Mg2+ loss, and the optimized conditions were as follows: the carbonation concentration was 3g/L, the dosage of sodium oxalate was 6 times of the theoretical dosage [in terms of n(Na2C2O4)/n(Ca2+) molar ratio], and the aging time was 6h. The MgO content of the prepared high-purity MgO sample was 99.51%, CaO content was 0.17%, and the recovery of MgO was 91.5%. The results showed that the average size of the magnesium oxide particles was 9 μm, and the particles were uniformly dispersed with regular spherical structure.
Spherical magnesium oxide was prepared by aerosol-assisted method using magnesium chloride as the magnesium source and urea as the precipitant. The precursors and magnesium oxide samples prepared at different reaction temperatures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and nitrogen adsorption-desorption.
The experimental results showed that the specific surface area of the prepared spherical magnesium oxide was 36 m2/g, the average pore size was 34 nm, and the total pore volume was 0.26 cm3/g. The adsorption of Congo red was in accordance with the pseudo-secondary kinetics, and the adsorption equilibrium was reached within 5 min. The adsorption isotherm was in accordance with the Langmuir model, and the saturation adsorption capacity was 764.91 mg/g.