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

Abstract

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 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.

Adsorption of glyphosate on clays and soils from Paraná State: effect of pH and competitive adsorption of phosphate

“…As shown by S-N-K test (p<0.05) the variation of the concentration of CaCl 2 had an effect only on Tibagi and Londrina soils (Table 3). Gimsing and Borggaard (2001) studied the effect of several electrolytes (KCl 10 mmol L -1 or 100 mmol L -1 , CaCl 2 10 mmol L -1 ) on the adsorption of GPS on goethite and they showed that electrolytes had little effect on GPS adsorption. For all clays and Tibagi and Londrina soils, the S-N-K test also showed that the amount of GPS adsorbed by them in different pH and concentrations of CaCl 2 were statistically different (p<0.05) from each other ( Table 3).…”

“…Mcbride and Kung (1989), Gimsing and Boggaard (2001) and Dion et al (2001) studied the competitive adsorption between GPS and phosphate on amorphous iron oxide, goethite and clays (illite, kaolinite), respectively. Gimsing and Borggaard (2001) observed that phosphate was able to desorb GPS, but GPS was unable to desorb phosphate. McBride and Kung (1989) showed that GPS was completely displaced from an amorphous iron oxide by phosphate.…”

Influence of humic substances on phosphate adsorption by aluminium and iron oxides

“…Accordingly, high amounts of glyphosate and phosphate were adsorbed by synthetic oxides, while pure clay silicates adsorbed much less of both adsorbates Borggaard, 2001, 2002). However, while phosphate was strongly preferred by goethite and adsorbed phosphate almost prevented glyphosate adsorption (Gimsing and Borggaard, 2001), affinities by gibbsite and clay silicates for the two adsorbates were more equal (Gimsing and Borggaard, 2002). Furthermore, for these adsorbents, adsorption of glyphosate and phosphate was partly additive as total adsorption of glyphosate plus phosphate from a mixture of the two adsorbates was significantly higher than the amount adsorbed from solutions containing only glyphosate or phosphate (Gimsing and Borggaard, 2002).…”

Glyphosate and phosphorus leaching and residues in boreal sandy soil

“…After spraying glyphosate will be strongly sorbed to soil (Piccolo and Celano 1994;Tiberg 1998;de Jonge and de Jonge 1999;Gimsing and Borggaard 2001;Autio et al 2004;Mamy and Barriuso 2005) and thus its mobility is usually low. As an organophosphorus compound it is able to react with the same soil components as phosphates (Piccolo and Celano 1994;Gerritse et al 1996;Gimsing and Borggaard 2001;Wang et al 2005).…”

“…As an organophosphorus compound it is able to react with the same soil components as phosphates (Piccolo and Celano 1994;Gerritse et al 1996;Gimsing and Borggaard 2001;Wang et al 2005). Competition between glyphosate and phosphorus was first reported by Sprankle et al (1975a and b) and Hance (1976).…”