EFFECT OF KC1 AND CaC12 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 KC1, 0.1 M KC1 and 0.01 M CaCI 2 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 KCI caused dispersion of goethite, resulting in inefficient filtering, and that phosphate precipitated as calcium phosphates in 0.01 M CaC12 background electrolyte solutions. The results suggest that 0.1 M KC1 is a more suitable background electrolyte to determine competitive adsorption processes involving glyphosate and phosphate. Key Words---Adsorption, Background Electrolyte, Competition, Glyphosate, Goethite, Phosphate.