Dissolution behavior of high-purity a-alumina parti cles was studied in acidic solutions (pH 2.6-5.5) and basic solutions (pH 7.2-9.3) containing Mg2+ ions at room temperature. The amount of dissolved a-alumina was dominated by the solubility limit of aluminium hydroxide formed on the surface of a-alumina. The a alumina in an acidic suspension of 5 vol% solids dis solved to increase pH of the suspension and to produce a supersaturated solution of A13+ ions in which nuclea tion and growth of aluminium hydroxide proceeded un til the A13+ concentration reached the solubility limit of aluminium hydroxide. Little adsorption of Mg2+ ions onto the positively charged alumina surface (<0.5ƒÊmol/m2) was examined in the acidic suspen sions at pH 4.1-4.3. The amount of alumina dissolved in the basic suspensions was less than that in the acidic solutions. Weakly charged negative alumina surface of 1m2 in the basic suspension at pH 7.9 adsorbed Mg2+ ions of 1.9 pmol.

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