Abstract
The dissolution behavior of sintered MgO–pyrochlore (Nd 2Zr 2O 7 was chosen for this study) composites in HNO 3 and H 2SO 4 solutions has been studied. The dissolution in 11 M HNO 3 and 7.9 M H 2SO 4 at 60 °C resulted in a selective dissolution of MgO. It was found that initially the fraction of dissolved MgO increases linearly with dissolution time. Magnetic bar stirring enhanced the mass transfer rate and resulted in a higher dissolution rate of MgO compared with the static and ultrasonic dissolution. It also provided mechanical forces to completely disintegrate the undissolved Nd 2Zr 2O 7 porous matrix into residual powder. Both MgO and Nd 2Zr 2O 7 can be dissolved in boiling concentrated (18 M) H 2SO 4, and Nd 2Zr 2O 7 dissolves incongruently. The dissolution of Mg 2+ and Nd 3+ followed first order kinetics, but Zr 4+ precipitated out due to low solubility in concentrated H 2SO 4.
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