Synergistic removal of glyphosate and U(VI) from aqueous solution by goethite: adsorption behaviour and mechanism

Metals and glyphosate (GPS) herbicides adsorbed on minerals affects their mobility and environmental effects. In this study, using goethite as a model soil mineral, GPS and uranium as contaminants to investigate the effects of GPS on adsorption of uranium. The effects of solution pH, initial concentration and contact time on adsorption were investigated. When the initial pH is 4.0, the highest adsorption capacity of goethite for uranium with the absence GPS and the presence of GPS are 69.39 mg g −1 and 78.84 mg g −1 respectively. The adsorption kinetics can be well described by quasi second-order model, and the adsorption process can be described by Langmuir isotherm. Additional evidence for the uptake mechanism was obtained using FTIR and XPS. The carboxylic acid and phosphonic acid groups of the GPS molecule participated in the reaction with goethite and uranium to form goethite-GPS-U(VI) ternary complex.