The aqueous solutions of three different highly coloured anionic dyes (reactive, acidic and direct dyes), commonly used in the dyeing process, were studied for decolourization by coagulation. For optimum results the variables studied with polyaluminium chloride (PAC) were pH, dosage and temperature. Coagulation efficiencies of natural polyelectrolytes such as psyllium and chitosan alone or as coagulant aids in conjunction with PAC were studied and compared. In conjunction with a minimal dose of PAC, chitosan and psyllium were found to be very effective for the decolourization of acidic and direct dyes. Reactive dyes with anthraquinone chromophore were the most difficult to decolourize.

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