DISSOLUTION BEHAVIOR OF ALPHA-ALUMINA IN SOLUTIONS CONTAINING MG2+ IONS

Dissolution behavior of high-purity a-alumina particles was studied in acidic solutions (pH 2.6-5.5) and basic solutions (pH 7.2-9.3) contai ning Mg2+ ions at room temperature. The amount of dissolved alpha-alum ina was dominated by the solubility limit of aluminium hydroxide forme d on the surface of alpha-alumina. The alpha-alumina in an acidic susp ension of 5 vol% solids dissolved to increase pH of the suspension and to produce a supersaturated solution of Al3+ ions in which nucleation and growth of aluminium hydroxide proceeded until the Al3+ concentrat ion reached the solubility limit of aluminium hydroxide. Little adsorp tion of Mg2+ ions onto the positively charged alumina surface (< 0.5 m u mol/m(2)) was examined in the acidic suspensions at pH 4.1-4.3. The amount of alumina dissolved in the basic suspensions was less than tha t in the acidic solutions. Weakly charged negative alumina surface of 1 m(2) in the basic suspension at pH 7.9 adsorbed Mg2+ ions of 1.9 mu mol.