Enhanced Glyphosate Removal by Montmorillonite in the Presence of Fe(III)

N-(Phosphonomethyl)­glycine (glyphosate, PMG) is an effective broad-spectrum organic phosphoric herbicide. The mass production and wide use of PMG presents a potential environmental hazard. This study evaluated the feasibility of using montmorillonite (MT) as an adsorbent to remove PMG from wastewater in the presence of Fe­(III) ions. The results showed that the PMG adsorption process is dependent on the Fe­(III) concentration. Adsorption was fast, and the adsorption kinetics were best described by a pseudo-second-order model. Adsorption of PMG was most effective over the pH range from 1.9 to 4.1. Ionic strength was found to have little effect on PMG removal at pH < 4.1 but to enhance PMG removal at pH > 4.1. Competing ions reduced the PMG removal at low pH (pH < 5.9) but increased the PMG removal at pH > 5.9. The adsorption capacity was found to be greater than 210 mg/g. The mechanism of this removal process is discussed in detail in terms of XRD and species calculations.