Experimental and molecular dynamics simulation study on the effect of polyacrylamide on bauxite flotation

In this work, the effect of polyacrylamide (PAM) on bauxite flotation was comprehensively studied using both experimental and molecular dynamics simulation (MDS) methods. It was found that the recovery and selectivity of bauxite flotation decreased rapidly when the concentration of PAM exceeded a critical value. MDS study revealed that PAM could adsorb on diaspore and kaolinite through hydrogen bonding between the amide groups of PAM molecules and Al-OH on mineral surfaces. The hydrocarbon chains of PAM were oriented outwards at low concentration and increased the hydrophobicity of mineral surfaces, while PAM molecules entangled each other through intermolecular interaction at high concentration and reduced the hydrophobicity of mineral surfaces, which was in good agreement with the contact angle measurement results. High PAM concentration could possibly hamper the adsorption of collectors by steric hindrance. In addition, PAM could cause the unselective flocculation of diaspore and kaolinite, reducing the separation efficiency of bauxite flotation. Hexametaphosphate was able to improve the performance of bauxite flotation in presence of PAM at a proper dosage by reducing the unselective flocculation of diaspore and kaolinite.