A new alternative and efficient low-cost process for the removal of reactive dyes in textile wastewater by using soybean hull as adsorbent

The main objective of this work is to use soybean hull (SBH) waste as an adsorbent for the removal of two industrial textile dyes: Reactive Blue 21 (RB21) and Reactive Yellow 145 (RY145). Physical characterization of SBH and kinetic and equilibrium experiments were performed to determine the adsorption conditions. The best adsorption condition was pH 2.0 because the zero electrical charge of soybean hulls (pHZ = 0) is 5.27; thus, in an acidic pH, the adsorbent is positively charged, and the dyes keep their anionic charges due to the –SO3− and –OSO3− groups. Kinetic data were better represented by the Elovich kinetic model, evidencing two well-differentiated mass transfer regions, which agrees with a pseudo-second-order kinetic mechanism. The experimental data showed that RB21 and RY145 were fitted with Hill and Redlich–Peterson isotherm models, respectively. Consequently, the maximum adsorption capacities of SBH for RB21 and RY145 dyes were 149 mg/g and 87 mg/g, respectively. Dye adsorption in packed bed column was also assayed at different bed heights, flow rates, and inlet concentration of dyes. The Thomas, Yoon–Nelson, and modified dose-response (MDR) models fitted well to the breakthrough curves, the MDR model being the one with the highest correlation coefficients, with 96.5% and 94.4% removal of RY145 and RB21 dyes, respectively.