Dissolution of La2O3 in HCl¯H2O, HCl¯CH3OH¯H2O and HCl¯CH3OH solutions

The effects of HCl concentration and temperature on the dissolution of La2O3 in aqueous (HCl¯H2O), mixed-aqueous (HCl¯CH3OH¯H2O) and non-aqueous (HCl¯CH3OH) solvents have been studied. Increase of methanol in solvents was determined to cause corresponding decreases in conductivity, ESCE, pH values with corresponding increase in ER values and better results were obtained for dissolution in the order non-aqueous>mixed-aqueous>aqueous solvent systems. Increase in dissolution was attributed to the prevention of lanthanum hydroxide precipitation in non-aqueous medium. Lanthanum compounds formed in non-aqueous medium at 25°C were isolated and identified using X-ray diffraction, thermal and chemical analysis methods and the thermal changes observed in these compounds between 25°C and 1100°C were investigated. LaCl3·x1CH3OH and LaCl3·x2CH3OH·3H2O (x1+x2=2.35) were formed in non-aqueous medium and these compounds were converted into LaCl3·1.14CH3OH with complete and partial loss of water and methanol around 165°C, respectively. Methanol was completely removed around 200°C with formation of LaCl3 and some LaOCl and due to the decomposition of LaCl3 above 200°C, LaOCl was detected as the only stable phase above 700°C.