Removal of Mixed Cationic Dyes by a Biosorbent Based on Magnetic Tragacanth Gum Hydrogel

A magnetic tragacanth gum-grafted poly(acrylic acid) hydrogel (TG-g-PAA/Fe3O4) was applied for the removal of Malachite Green (MG), basic yellow 28 (BY28) and rhodamine 6G (Rh6G) dyes form industrial simulated wastewater. The most important parameters (e.g., initial dye concentrations, adsorbent dosage, pH, and contact time) were optimized in all single, binary, and ternary systems. The adsorption processes were better fitted with the Langmuir model than the Freundlich model which revealed the linearity of the processes. Maximum adsorption capacities (Qm) for MG, BY28, and Rh6G in the ternary system were obtained as 626.5, 568.2, and 459.7 mg/g, respectively. Kinetic studies exhibited that the removal of all dyes in all systems was best fitted with the pseudo-second-order model, which proved the rate-limiting step might be the chemical adsorption. The hydrogel was regenerated by the desorption process after the loading process and reused several times. As a result, the removal efficiency of the adsorbent almost remains the same for the first four cycles.