DissolutionBehavior of Aluminum, Silicon, and Ironof Diaspore Concentrate in NaOH–NaAl(OH)4Solutionsat Elevated Temperature.

Thehigh temperature dissolution behavior of diaspore concentratewas measured in concentrated NaOH–NaAl(OH)4solutions.The dissolution rate of Al was greatly found to be enhanced by increasingNaOH concentration and temperature while decreased with addition ofAl(OH)3. The concentration of Si as the main impurity constantlydecreases with reaction time while the Fe is retained at a limitedlevel. The generalized rate law for mineral dissolution and precipitation,proposed by Lasaga (Lasaga, A. C. Kinetic Theory in the EarthScience; Princeton University Press: Princeton, NJ, USA,1998), was applied to model the kinetic behavior of Al on the basisof KSP(diaspore) and the activity coefficientsof related species in the solution. The resulting kinetic model wascapable of predicting the dissolution rate of Al in the Bayer liquor.The apparent activation energy of the dissolution reaction over thetemperature range from 473.2 to 543.2 K was estimated at 83 kJ·mol–1. [ABSTRACT FROM AUTHOR]