A thermodynamic and kinetic study of catalyzed hydrolysis of aluminum nitride in secondary aluminum dross

Abstract

Aluminum dross, a harmful and abundant solid waste generated in aluminum industry, releases toxic ammonia and causes severe environmental pollution and public health disaster. Secondary aluminum dross (SAD) can be effectively treated by the efficient and complete decomposition of aluminum nitride (AlN). The hydrolysis behavior of AlN in SAD was evaluated by thermodynamic analysis and kinetic leaching experiments. Various factors such as temperature, time, liquid-to-solid ratio, additive type, and additive dosage were evaluated to optimize the hydrolysis of AlN. The chemical composition, mineralogical phases, particle size distribution, and morphology of SAD and leaching residue were determined by X-ray diffraction, X-ray fluorescence spectroscopy, laser particle size analysis, and scanning electron microscopy, respectively. The decomposition of AlN reached 96.24% under the following optimum conditions: leaching time of 180min, leaching temperature of 95°C, additive of 4wt% sodium hydroxide, and liquid-to-solid ratio of 6mLg−1. Meanwhile, the removal efficiency of chlorine and fluorine during leaching reached 95.63% and 69.17%, respectively. The hydrolysis data indicate that the effects of relevant factors on AlN removal are consistent with the shrinking unreacted-core model, where internal layer diffusion is the rate-controlling step. The rate-controlling step was changed to chemical reaction control with the addition of sodium hydroxide, which corrodes bayerite on the surface of AlN. The activation energy of AlN hydrolysis in SAD is 38.64kJmol−1.