Approaches to improve alumina extraction based on the phase transformation mechanism of recovering alkali and extracting alumina by the calcification-carbonization method

Abstract

Formation of the desilication product (DSP) in the Bayer process causes alkali and alumina loss in the red mud and serious environmental pollution. This paper elucidated the mechanism of the calcification-carbonization method for recovering alkali and extracting alumina in red mud through analyzing phase transformation and particle morphology evolution. Furthermore, approaches to improve alumina extraction throughout the process were proposed. The results showed that more than 93% alkali was recovered and alumina entering the calcified liquor increased as calcification temperature increased. Spherical-like aggregates of dense hydrogarnet were formed in the calcification process. The compact structure of hydrogarnet was destroyed by mechanical activation to enhance the carbonization decomposition ratio. The alumina extraction ratio increased from 32.9% to 43.1%, and fewer carbonization cycles were needed to reach the alumina extraction limit due to the mechanical activation of calcified slag. The increased temperature in the alumina leaching process impeded the alumina extraction and caused alkali loss.