Coagulation/flocculation potential of polyaluminium chloride and bentonite clay tested in the removal of methyl red and crystal violet

Abstract

This study investigated the influence of the physico-chemical properties of methyl red (MR) and crystal violet (CV) on their removal by bentonite clay and polyaluminium chloride (PACl). Different dosages of bentonite clay, PACl and a combination of PACl and bentonite clay were applied. Dye concentration, dosage, pH and slow mixing timing were varied to find optimum removal conditions. Due to the high charge and solubility of dyes, dye solutions were pre-treated by increasing the turbidity and adjusting the pH prior to the treatment with PACl. PACl-lab removed MR better than the commercial PACl (PACl-com), and this could be ascribed to the lower basicity of PACl-lab compared to PACl-com. Bentonite clay showed greater affinity to CV, exhibiting an optimum removal of 99.2 % for CV and 98.8 % for MR. The optimum removal efficiency of PACl-lab for CV was 99.4 and 97.0 % for MR. The combination of PACl-lab and bentonite clay had higher removal efficiency than PACl-lab for MR but not for CV. The dyes’ charge, structure and solubility influence how well the dye will be removed with the flocculation/coagulation technique