Investigation of Continuous Autoclave Technology for Alumina Production From Kaolin Clay

This study investigates the development of an autoclave nitric acid leaching technology for the extraction of alumina from kaolin clays as an alternative non-bauxite aluminum resource. The research was motivated by the limitations of conventional atmospheric leaching, including high nitric acid consumption, low alumina recovery, and significant dissolution of iron impurities. Laboratory-scale experiments were conducted using raw, calcined, and enriched kaolin samples in titanium autoclaves under various temperatures, acid dosages, and processing times. The results showed that calcined non-enriched kaolin exhibited the highest leaching performance. The optimal process parameters were determined to be a temperature of 200°C, nitric acid dosage of 85–90%, and a leaching duration of 3 hours, achieving alumina extraction of up to 87% with minimal iron contamination. A multi-stage autoclave battery operating under quasi-continuous conditions was also evaluated. The developed technology reduced nitric acid consumption by more than 35%, improved reagent utilization, and demonstrated strong potential for industrial-scale alumina production from kaolin clay.