Preparation of organic-inorganic composite flocculant from red mud and treatment of coal slurry water research

This study synthesized an organic-inorganic composite flocculant from raw materials obtained through the hydrometallurgical extraction of red mud and cassava starch. The tapioca starch was treated by the semi-dry method with 3-chloro-2-hydroxypropyltrimethylammonium chloride employed as the modifier. The synthesized flocculant effectively removes fine, slow-settling particles from coal slurry wastewater in Ordos, Inner Mongolia. The organic-inorganic composite flocculant was characterized by laser particle size analysis, x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). Spectroscopic analyses confirmed the chemical grafting of aluminum and iron species onto starch macromolecules via covalent coordination bonds, facilitating effective polymerization. A systematic investigation of critical synthesis parameters revealed their governing effects on the flocculation efficiency of the composite material in coal slurry wastewater treatment. Elevated polymerization temperatures significantly improved flocculation efficiency by enhancing coordination bonding between starch hydroxyl groups and Al/Fe species, as evidenced by FTIR peak shifts and XPS binding energy changes. Optical microscopy analysis revealed that the organic-inorganic composite flocculant effectively encapsulates coal slurry particles through a dual adsorption-bridging mechanism electrostatic adsorption of charged Al/Fe-starch complexes onto particle surfaces, followed by polymer bridging between adjacent particles. The starch component of the flocculant is readily biodegradable, preventing the long-term environmental risks associated with residual synthetic flocculant monomers (e.g., polyacrylamide). Meanwhile, the aluminum–iron ions remain in stable forms with minimal residual concentrations, significantly reducing secondary water pollution risks.