Enhanced metal adsorption by soybean hulls modified with citric acid

A method was developed to enhance metal ion adsorption of soybean hulls for wastewater treatment using copper ion (Cu2+) as a typical metal ion. Hulls , extracted with 0.1 N NaOH, were modified with different citric acid (CA) concentrations (0.1-1.2 M) at 120 degrees C for 90 min. CA-modified hulls h ad adsorption capacities for Cu2+ from 0.68 to 2.44 mmoles/g, which was muc h higher than for unmodified hulls (0.39 mmoles/g). The total negative char ge for these hulls also increased with increasing CA concentration and was about twice the copper ion adsorption capacity at all CA concentrations. Th e need for NaOH (base) extraction (BE) before CA modification was examined. CA-modified, non-extracted (NE) and CA-modified, BE hulls were compared fo r adsorption kinetics and adsorption capacity. Base extraction resulted in modified hulls with faster adsorption kinetics and slightly lower adsorptio n capacity for copper ion than NE hulls. For BE, CA-modified hulls, increas ing the temperature from 25 degrees C to 60 degrees C appeared to have no e ffect on the rate of copper ion removal from solution. CA modification of s oybean hulls greatly enhanced metal ion removal and resulted in a product w ith possible commercial potential for metal ion remediation. (C) 1999 Publi shed by Elsevier Science Ltd. All rights reserved.