La3+ and Al3+ loaded D151 as salt‐resistant resins for efficient adsorption of glyphosate: Effects of ionic radius

Abstract La 3+ and Al 3+ loaded D151 resin [R‐La and R‐Al, respectively] were used as salt‐resistant resins for the efficient adsorption of glyphosate. The results showed that La 3+ with a larger ionic radius could accommodate more glyphosate as ligands, resulting in higher glyphosate adsorption capacity of R‐La than that of R‐Al. Both R‐La and R‐Al exhibited maximum adsorption capacities at pH 2.52, where glyphosate existed in its ionization equilibrium of pKa 2 . Consistent with the larger ionic radius of La 3+ , R‐La featured larger q m and K L than R‐Al at the same temperature. Owing to the smaller radius of Al 3+ , the enthalpy values for the coordination adsorption of glyphosate by R‐Al were larger than those of R‐La at the same adsorption capacity. Owing to the smaller radius of Al 3+ , R‐Al exhibited stronger coordination adsorption for glyphosate and significantly higher salt tolerance than R‐La. The adsorption mechanisms indicated that both R‐La and R‐Al could adsorb glyphosate through the coordination of La 3+ and Al 3+ with O atoms of the phosphonate group of glyphosate. At a NaCl concentration range of 0–16%, R‐Al featured excellent salt tolerance and highly stable glyphosate adsorption capacity than 330, D301, R‐La, and the 14 adsorbents reported in the literature.