Optimization of Glyphosate Adsorption Conditions on Pyrophyllite

The aim of this work is to find the optimal conditions for the adsorption of glyphosate on pyrophyllite. The adsorption of glyphosate on pyrophyllite from aqueous solutions was quantified spectrophotometrically with ninhydrin and sodium molybdate. Studied conditions were mass of adsorbent (100–1000 mg), pH (1–13), contact time (10–180 min) and temperature (24–55 ℃). The results are expressed by adsorption capacity (qe), removal efficiency (R) and the partition coefficient (Kd). Initial glyphosate concentrations were 15, 20 and 25 mg/L. Adsorption of glyphosate was most effective when the dosages of pyrophyllite were lower: 100, 250 and 500 mg and at contact times of 60, 120 and 180 min (R = 69.25% to R = 74.04 at 60 min). Due to different ionic species of glyphosate at different pH values, the adsorption was highly pH-dependent and showed the best results in the basic pH range from 11 to 13.5 (R ≈ 73%). Results for influence of temperatures shows that at 45 ℃ adsorption efficiency (R = 43.07%; R = 28.08% and R = 13.73%) increases for all tested concentrations, but the highest is achieved at 55 ℃ (R = 45.85%; R = 44.30% and R = 40.61%). The process of glyphosate adsorption onto pyrophyllite was fitted to the Freundlich adsorption isotherm model isotherm (R2 = 0.9994) and the kinetics were best described by a pseudo-second-order model (R2 = 0.9676). Based on the obtained data, the chemical type of adsorption is present.