A STUDY OF COAGULANT PRODUCTION FROM RED MUD AND ITS USE FOR HEAVY METALS REMOVAL

ABSTRACT Coagulant production using red mud and waste base as raw material is described together with phase and chemical composition changes in red mud during coagulant production and usage. Investigation of phase and chemical composition was carried out using X-ray diffraction analysis (XRD) and sequential extraction. Acid treatment of the red mud resulted in the removal of the exchangeable fraction, carbonates and alkalis. Base addition into acid treated and centrifuged red mud caused its flocculation and sorption by surface enlargement. Mineral phase transition in coagulant (activated red mud) with time was not found. An amount of 1g of this coagulant was able to sorb 99.347 mg of Cu, 95.002 mg of Zn and 98.695 mg of Pb from aqueous solution containing 100 mg/l of those metals. Among three metals investigated, Zn sorption was the most affected with changes in pH value of treated solution. The sorption of metal cations (Cu(II), Zn(II) and Pb(II)) from the metal–EDTA solution onto the activated red mud (ARM) for different metal–EDTA concentrations (1–100 mg/l) was also investigated. It was found that, among the three tested metals, the sorption of Cu onto the ARM was most affected by EDTA. The removal of these three metals from the metal–EDTA mixture solution was also studied by using two other types of coagulants: ferric chloride and polyaluminium chloride (PAC). In the case of the FeCl3, the addition of EDTA had a slight influence on the Cu removal and none on the Pb and Zn removal, while in the case of the PAC, the greatest influence was found for all these metals.