The influence of sodium alginate on kaolinite flocculation in presence of metal ions: Guidance for green processing

Abstract

In this study, the responsiveness of Na⁺, Mg²⁺, Ca²⁺ and Al³⁺ to sodium alginate (SA) and their influence on kaolinite dispersion/flocculation behavior were investigated through rheology and turbidity tests. The effects of metal ions on the interaction between SA and kaolinite were analyzed by zeta potential, fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). The results showed that Na⁺ and Mg²⁺ resulted in a decreasing of the viscosity and modulus of SA solution for they have the electrostatic shielding effect on SA. Ca²⁺ and Al³⁺ significantly increased the viscosity and modulus of SA solution because Ca²⁺ and Al³⁺ not only have the electrostatic shielding effect on SA but also could form the different network structure complexes. The order of the responsiveness of metal ions and SA sorted by intensity level was: Al³⁺> Ca²⁺>Mg²⁺> Na⁺. SA has a dispersion effect on kaolinite particles under the background of Na⁺ and Mg²⁺, and SA has a flocculation effect on kaolinite particles in the presence of Ca²⁺ and Al³⁺. The flocculation efficiency of SA on kaolinite suspension containing Al³⁺ was much higher than that of SA on kaolinite suspension in the presence of Ca²⁺. Zeta potential and FTIR results showed that SA could be adsorbed on the kaolinite surface through electrostatic force and hydrogen bond in the presence of Na⁺ and Mg²⁺. Microscope observation^, XPS and DFT results showed SA could not only form chemical adsorption with Ca²⁺/Al³⁺ on the kaolinite surface but also be cross-linked with Ca²⁺/Al³⁺ to form a network structure, which could sweep and trap kaolinite particles in suspension. This work has strategic significance for the responsiveness of natural polysaccharide to metal ions and their application in environmental protection of mine wastewater, as well as the clean and circular utilization of water.