Strengthening Solid–liquid Separation of Bauxite Residue through the Synergy of Charge Neutralization and Flocculation

Abstract

The strong surface charge of bauxite residue (BR) and its high fineness have made its rapid and high-efficiency solid–liquid separation an urgent problem to be solved. The proposed two-step procedure involving charge neutralization and flocculation through the synergy of lime and polyacrylamide (PAM) was carried out. The results showed that the synergy of lime (1%) and PAM (40 g/t) significantly accelerated solid–liquid separation from 0.64 m/h to 2.24 m/h compared with the addition of PAM alone. The turbidity of the supernatant decreased from 61,920 NTU to 232 NTU. The addition of lime (alone) can reach similar results but at high dosages, that is 4 times compared with that of the synergy. Surface electrical behavior and X-ray photoelectron spectroscopy analysis showed that lime significantly neutralized the surface charge and decreased the electrostatic repulsion between BR particles with the absorption of Ca on its surface in the form of Ca-OH. Charge neutralization cause the increase in BR particle sizes from below 20 µm to about 30 µm, which further increased to 50 µm through charge neutralization and flocculation. The study provided a feasible method for the rapid and high-efficiency solid–liquid separation of BR and the relevant theoretical foundation.