Enhanced alumina recovery from kaolin using CaCl ₂ calcination‐ H

Abstract

This work aims to recover maximum aluminium values from a low‐grade kaolin sample via a calcination‐coupled acid leaching process. The chemical analysis of the as‐received sample suggests the presence of 54% SiO ₂ and 32% Al ₂ O ₃ , along with 11% loss on ignition. Major minerals present in the sample are quartz and kaolinite. The calcined kaolin (850°C, 60 min) on leaching with sulphuric acid (4 M, 95°C, 1.5 h) indicates recovery of only 62% Al ₂ O ₃ . Possibly, this low recovery is due to the overcrowding of silica particles over the metakaolin particles. However, under similar conditions, when the raw kaolin is calcined with CaCl ₂ , followed by the acid leaching process, the alumina recovery reaches 94%. The dosage of CaCl ₂ , temperature, time, and solid % were all optimized during the experimentation to achieve higher recoverable alumina values. The calcium ion (from CaCl ₂ ) in the presence of metakaolin and quartz forms acid‐soluble phases like anorthite and di‐calcium‐silicate (larnite). Various characterization of the feed and processed samples were carried out using X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR), scanning electron microscope (SEM)–energy dispersive X‐ray spectra (EDX), and transmission electron microscopy (TEM), which support the obtained results and the possible reasons for the higher recovery discussekd in this work.