Removal of Colour from Synthetic Textile Dyestuffs by Adsorption onto Preformed Flocs

摘要

This communication presents the results of an investigation conducted on colour removal from aqueous solutions of three model textile dyes namely, C.I. Acid blue 45, C.I. Acid blue113 and C.I. Direct Yellow 6 by adsorption onto preformed flocs of Alum, Ferric chloride and Ferrous Sulphate. Agitated non-flow batch kinetic and isothermal equilibrium experiments were conducted and the experimental results revealed the potential of preformed flocs in the removal of colour of dyes. Dyes responded favourably and exhibited good to excellent colour removal ranging from78% to 98%. Sorption process proceeded quite rapid initially and attained equilibrium in 30 minutes. Sorptive removal increased with increased floc dosages of 100 to 1500 mg/L. Preformed floc-dye sorption reaction is of the type first order though initial uptake was high.Isothermal equilibrium adsorption data fitted well to Langmuir model suggesting formation of a unimolecular monolayer of dyes over a homogeneous surface of uniform energy. The potential of sorption is of the order: Ferric chloride > Ferrous Sulphate > Alum. A comparison of colour removal by preformed flocs with that of conventional coagulation with the same coagulants revealed the superiority of Ferrous sulphate in which case removal increased from no removal to as high as 70%. In other cases, the improvement in colour removal is marginal.