Removal of direct red 12B and methylene blue from water by adsorption onto Fe (III)/Cr (III) hydroxide, an industrial solid waste.

Removal of direct red 12B and methylene blue by adsorption onto Fe (III)/Cr (III) hydroxide was studied using various parameters such as agitation time, dye concentration, adsorbent dose and pH. Equilibrium adsorption data followed both Langmuir and Freundlich isotherms. Adsorption followed second-order rate kinetics. The Langmuir adsorption capacity (Qo) was found to be 5.0 and 22.8 mg dye per g of the adsorbent for direct red 12B and methylene blue, respectively. Acidic pH was favorable for the adsorption of direct red 12B and basic pH for methylene blue. Desorption studies showed that chemisorption seems to be the major mode of adsorption.