Study of decolorisation of binary dye mixture by response surface methodology

Decolorisation of a complex mixture of two different classes of textile dyes Direct Red 81 (DR81) and Rhodamine B (RHB), simulating one of the most important condition in real textile effluent was investigated onto deoiled Argemone Mexicana seeds (A. Mexicana). The adsorption behaviour of DR81 and RHB dyes was simultaneously analyzed in the mixture using derivative spectrophotometric method. Central composite design (CCD) was employed for designing the experiments for this complex binary mixture where significance of important parameters and possible interactions were analyzed by response surface methodology (RSM). Maximum adsorption of DR81 and RHB by A. Mexicana was obtained at 53 degrees C after 63.33 min with 0.1 g of adsorbent and 8 x 1(0-)6 M DR81, 12 x 10(-6) M RHB with composite desirability of 0.99. The predicted values for percentage removal of dyes from the mixture were in good agreement with the experimental values with R-2 > 96% for both the dyes. CCD superimposed RSM confirmed that presence of different dyes in a solution created a competition for the adsorbent sites and hence interaction of dyes was one of the most important factor to be studied to simulate the real effluent. The adsorbent showed remarkable adsorption capacities for both the dyes in the mixture. (C) 2017 Elsevier Ltd. All rights reserved.