Removal of mixed cationic dyes by a biosorbent based on magnetic tragacanth gum hydrogel

Abstract

A magnetic tragacanth gum-grafted poly(acrylic acid) hydrogel (TG-g-PAA/Fe3O4) was applied for removal of malachite green (MG), basic yellow 28 (BY28), and rhodamine 6G (Rh6G) cationic dyes form industrial simulated wastewater via the well-known batch method. The most important parameters such as initial dyes concentrations, adsorbent dosage, pH, and contact time that affected adsorption performance were optimized in all single, binary, and ternary systemes. The adsorption for all dyes in all systemes were well-fitted with Langmuir model than those of the Freundlich model that revealed the linearity of the process. Maximum adsorption capacities (Qm) for MG, BY28, and Rh6G in ternary system were obtained as 626.5, 568.2, and 459.7 mgg-1, resepectively. Kinetic studies exhibited that the removal of all dyes in all systems were best-fitted with the pseudo-second-order model, which proved that the rate-limiting step might be the chemical adsorption. The hydrogel was regenerated by desorption process after loading process and reused for several times. As results, the removal efficiency of adsorbent almost remains the same for the first four cycles, and then decreased gradually.