Leaching kinetics and mechanism of alunite from alunite tailings in highly concentrated KOH solution

Alunite tailings, a secondary resource from copper metallurgy industry in China, are considered a potential resource for both the production of alumina and potash fertilizer, since alunite tailings contain abundant alunite with associated impurities of kaolinite, dickite and quartz. In this work, the direct leaching of alunite from alunite tailings in the highly concentrated KOH solution is proposed. Under appropriate leaching conditions, such as temperature below 90 degrees C and KOH concentration above 13.5 mol.L-1, most of alunite is dissolved while kaolinite, dickite and quartz are still remained in the residue. Mastersizer, X-ray diffraction, infrared radiation spectrometer, Raman spectrometer and scanning electron microscopy/energy-dispersive spectroscopy are used to characterize alunite tailings samples before and after leaching. The leaching kinetics of alunite from alunite tailings in the concentrated KOH solution is described using a shrinking core model controlled by the surface chemical reaction. The key kinetics parameters, such as the activated energy and the reaction order, are determined based on the leaching experimental data. The dissolution mechanism of alunite from alunite tailings in the concentrated KOH solution is considered, and is used to account for the reaction order.