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

Anne Louise Gimsing and Ole K. Borggaard
The Royal Veterinary and Agricultural University, Chemistry Department, Thorvaldsensvej 40, DK-1871 Frederiksberg C Denmark
E-mail of corresponding author: angi@kvl.dk

Abstract: 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.

Key Words: Adsorption • Background Electrolyte • Competition • Glyphosate • Goethite • Phosphate

Clays and Clay Minerals; June 2001 v. 49; no. 3; p. 270-275; DOI: 10.1346/CCMN.2001.0490310
© 2001, The Clay Minerals Society
Clay Minerals Society (www.clays.org)