Effect of KCl and CaCl2 as Background Electrolytes on the Competitive Adsorption of Glyphosate and Phosphate on Goethite

Competitive adsorption between glyphosate and phosphate on goethite was evaluated. The influence of background electrolyte on the adsorption of glyphosate and phosphate was also investigated by using 0.01 M KCl, 0.1 M KCl and 0.01 M CaCl2 as background electrolytes. Experiments showed that phosphate displaced adsorbed glyphosate from goethite, whereas glyphosate did not displace phosphate. Results also showed that the background electrolyte had a strong effect on phosphate adsorption, but little effect on glyphosate adsorption. Thus, there are differences between the adsorption of glyphosate and phosphate. The study also showed that 0.01 M KCl caused dispersion of goethite, resulting in inefficient filtering, and that phosphate precipitated as calcium phosphates in 0.01 M CaCl2 background electrolyte solutions. The results suggest that 0.1 M KCl is a more suitable background electrolyte to determine competitive adsorption processes involving glyphosate and phosphate.