Kinetics of azo dyes sorption onto low-cost sorbents

Abstract

Removal of dyes from wastewater is of paramount importance for water quality. Biological methods alone are not capable of dealing with such pollution. Even small amounts of dye in water are highly visible and difficult to remove using conventional methods. Dyes are chemically complex, and advanced techniques such as chemical and photo-oxidation, adsorption or membrane separation must be used for their removal. Adsorption is commonly used at a final stage of dye removal process when high-purity water is required. Sorption kinetics is a key parameter for assessing sorbent efficiency in removing dyes. Results of tests on sorption kinetics of selected azo dyes (Reactive Blue 81, Reactive Red 120, Direct Orange 26 and Direct Black 22) are presented in the paper. Sorption tests were carried out using rye straw with and without thermal and chemical pre-treatment processes. Experimental data were analysed using the relevant kinetic equations. In most cases, the equation used was the Elovich model.