Sorption Characteristics of Glyphosate on Colloids Extracted from Coal Dust

Coal dust samples were collected from Huolihe coal mining group in Inner Mongolia,China and the colloid was extracted from the sample using centrifugation process.The batch experiments were performed to investigate sorption kinetic characteristics of glyphosate on the coal colloid,and the sorption isotherms,as well as the effects of temperature(35 ℃,25 ℃ and15 ℃)and pH(4,6and 9)on the sorption.Results indicate that the sorption process of glyphosate on the coal colloid could be divided into two steps,i.e.,rapid sorption step(the first 120min)and slow sorption step(the second 120min).The sorption would be equilibrium in 360 min.The sorption kinetics of glyphosate on the coal colloids was discussed using three kinetic models,the pseudo-first-order,the pseudo-second-order and the intra-particle diffusion model.The experimental data fitted very well the pseudo-first-order kinetic model.Experimental results were also regressed with the Henry,Langmuir and Freundlich isotherm equations at different temperatures and pH.The isothermal was well described by Langmuir and Freundlich equations.Maximum sorption capacity was from 40.91mg/g to 48.08mg/g.The sorption was affected by temperature and pH obviously.When temperature rose,sorption capacity was increased and sorption rate was quickened.Sorption capacity was decreased and sorption rate was slowed down as the increase of pH.