Synthesis and characterization of humic acid immobilized-polymer/bentonite composites and their ability to adsorb basic dyes from aqueous solutions

A new polyacrylamide-bentonite composite with amine functionality (Am-PAA-B) was prepared by direct polymerization in the presence of N,N'-methylenebisacrylamide as a crosslinking agent and potassium peroxydisulphate as an initiator followed by reaction with ethylenediammine. The Am-PAA-B was modified by immobilizing humic acid and tested as an adsorbent to remove basic dyes (Malachite Green, Methylene Blue and Crystal Violet) from aqueous solutions. XRD, conductometric and potentiometric titrations were used to characterize the adsorbent. The adsorbent behaved like a cation exchanger and more than 99.0% removal of dyes was observed at the pH range 5.0 to 8.0. The adsorption kinetic data were interpreted by pseudo-second-order rate equation and the film diffusion was the rate-limiting step. The equilibrium data were fitted well with the Freundlich isotherm model. Desorption of dyes was achieved by treatment with 0.1 M HNO₃ and four adsorption desorption cycles were performed without significant decrease in adsorption capacity.