Soybean hulls as a low-cost biosorbent for removal of methylene blue contaminant

Methylene blue is a cationic dye used for dyeing cotton, wool, and silk. This dye can cause impacts when reaching water resources due to the reduction of sunlight infiltration, besides the health problems if ingested. Therefore, the complete removal of this contaminant in industrial effluents is indispensable. Currently, soybean hulls residues are used in animal feed supplementation; however, since soybean oil production is large, expressive quantities is discarded in landfills. Thus, the present study aim is to evaluate the adsorption capacity of methylene blue onto soybean hulls as an alternative use of this agroindustrial residue. The material was characterized through morphological and chemical analysis which showed porosity, heterogeneity, and functional groups that favor the adsorption. Due to the mainly negative charge of the surface, the pH did not affect the cationic dye uptake, enabling a wide pH range. After the adsorption studies, the best experimental conditions were at temperatures of 298 K, mass of 0.025 g, and contact time of 180 min, resulting in the maximum adsorption capacity of 169.90 mg g(-1). When compared with other low-cost biosorbent and activated carbons, it can be perceived a potential applicability of soybean hulls in wastewater treatment as an alternative use.