A Combined Precipitation-Adsorption Method for Harmless Treatment of Glyphosate Mother Liquor

A large amount of glyphosate mother liquor containing high concentrations of several phosphorous-based compounds, namely glyphosate, phosphorous acid, and glyphosine at a concentration of 34 g/L, is generated in the production of the most widely used organophosphorus herbicide and poses a grave threat to the envi-ronment. In this study, a combined method of precipitation and resin adsorption was used for the harmless treatment of the mother liquor. Firstly, most of the phosphorous-based compounds in the mother liquid were precipitated by metal ions of Ca2+, and then the excess metal ions and the remained phosphorous compounds in the supernatant were removed by using 001*7 and D301 resin, respectively. Results showed that 98.9% of the phosphorous compounds could be precipitated by Ca2+, and the residual concentration of Ca2+ and total phosphorus were 1.2 and 0.4 g/L, respectively, after this treatment. Adsorption experiment results showed that the 001*7 resin had the high adsorption capacity of 52.9 mg/g for Ca2+, and it almost did not absorb glyphosate, phosphorous acid, and glyphosine (adsorption capacity of them all <0.1 mg/g) in the investigated pH range from 1.0 to 8.0. The D301 resin performed well under dynamic adsorption conditions, with adsorption capacities of 233.3, 90.3, and 89.6 mg/g for glyphosine, phosphorous acid, and glyphosate, respectively, at a flow rate of 7.2 mL/min. When using tandem columns fixed with 001*7 and D301 resins to treat the supernatant from the precipitation step, the concentrations of Ca2+ and total phosphorus decreased significantly to 1.5 and 0.5 mg/L, respectively, and reached the discharge standards for industrial wastewater. The technology proposed in this study has great application potential in the glyphosate production industry.