Glyphosate Adsorption by Commercial Materials and Industrial Waste: Equilibrium and Kinetics

Since glyphosate has been widely used in agriculture, it has frequently been detected in water bodies and has posed risks to environmental quality and human health. This study investigated glyphosate adsorption by commercial adsorbents (zeolite and activated carbon) and industrial residues (furnace slag, burning ashes, and foundry sand). Initial studies assessed the influence of pH (4, 7, and 10) and surface treatments with aqueous solutions of CuSO4, SDS, AgNO3, Fe(NO3)3, CTAB, and ZnO on glyphosate removal. Among all materials and treatments, untreated burning ashes showed the highest removal efficiency and were selected for dosage, kinetic, and isotherm investigations. Glyphosate adsorption onto burning ashes was pH-insensitive and achieved 100% removal with the detection limit of 0.025 mg·L–1. In the dosage study (at an initial glyphosate concentration of 5 mg·L–1), 100% removal was reached when the ash dose was 25 g·L–1 and 87.91% when the dose was 1.25 g·L–1. The dose of 1.25 g·L–1 was defined as optimal not only because it met drinking water regulatory limits but also because it minimized material consumption. Regarding kinetics and equilibrium, some studies indicated that glyphosate adsorption equilibrium in ash was reached after 8 h with a maximum adsorption capacity of 5.39 mg·g–1. The Avrami kinetic model and the Temkin isotherm model exhibited the best fit to the experimental data. Glyphosate and AMPA were quantified by liquid chromatography-mass spectrometry (LC-MS) after derivatization. Results showed that burning ashes are capable of removing >95% of the initial concentration of up to 5 mg·L–1 glyphosate. Conclusions of this study indicate that the use of waste material is a promising and sustainable alternative for the removal of glyphosate from aqueous solutions.