Adsorption study with NaOH chemically treated soybean hull for textile dye removal

Abstract

The activities of the textile industry generate effluents containing high chemical load, due to the presence of toxic dyes, causing water contamination. Adsorption is a promising technique for the removal of effluent dyes, however, studies are needed to look for alternative adsorbent materials, aiming at low cost and removal efficiency. The soybean hull (Glycine max) is an agroindustrial residue widely generated in Brazil, but its application is only for animal feed. The objective of this work was to evaluate the adsorption potential of chemically treated soybean hull with sodium hydroxide (NaOH) in the removal of 5G reactive blue dye. The biosorbent was subjected to NaOH treatment at different concentrations (0.01, 0.1 and 0.5 mol L-1), influence of temperature (30, 40 and 50 ºC), rotation speed (30, 60 and 90 rpm) and pH (1 to 11) was verified. The kinetics and equilibrium isotherms were performed using the best conditions obtained in the preliminary tests, and the experimental data adjusted to the theoretical models previously described in the literature. The studied variables indicated that the highest removal (about 88%) occurred under the conditions of 0.01 mol L-1 NaOH concentration, 50 ºC, 90 rpm and pH 2. In the kinetics, it was observed that the equilibrium was achieved in about 240 min, with the best fit of the pseudo-second order model. In isotherms, the Langmuir model better predicts experimental data, predicting a maximum adsorption capacity of 16.46 mg g-1. The soybean hull was effective in removing dyes in aqueous solution, however, NaOH treatment showed no relevant improvement in adsorptive capacity.