Study on the behavior of potassium in bauxite during the digestion phase of Bayer process

Abstract

Potassium in bauxite can migrate to alumina in Bayer process, thus affecting the aluminum electrolysis. This results in decreased current efficiency and a reduced lifespan of the electrolytic cell. However, studies on the behavior of potassium during bauxite dissolution have not been reported. This study aimed to examine the effects of CaO addition, temperature, time, and caustic soda concentration on potassium dissolution behavior in bauxite. The results demonstrated that adding CaO, increasing the dissolution time, and increasing the dissolution temperature could significantly improve the dissolution efficiency of potassium, but increasing the concentration of caustic soda could decrease the dissolution efficiency of potassium. The dissolution efficiency of potassium was 45.76 % under the conditions of industrial production of alumina (CaO content 10 %, dissolution time 60 min, dissolution temperature 260 ℃, caustic soda concentration 235 g/L). The potassium ions in the solution combined with silicates and sulfur in the form of vishnevite (Na_6.5K_1.02Ca_0.12(Si₆Al₆O₂₄)(SO₄)_0.96(H₂O)₂) and hauyne (K_1.6Ca_2.4Na_4.32(Al₆Si₆O₂₄)(SO₄)_1.52) into the red mud. The investigation of surface morphological features and roughness evolution of bauxite and red mud by atomic force microscopy offers direct nanoscopic evidence for the dissolution of bauxite. The potassium dissolution was controlled by an interfacial chemical reaction, and the calculated activation energy of the reaction was 41.85 kJ/mol under experimental conditions. This study aims to provide a reference for the efficient use of bauxite.