Adsorption and desorption characteristics of cyromazine on Aldrich humic acid

Batch equilibrium experiments were conducted to investigate adsorption and desorption characteristics of cyromazine(CYR) on and from Aldrich humic acid(HA).Results show that the adsorption and desorption of CYR on and from HA consisted of a rapid,a medium rapid and a slow processes.Adsorption kinetics curves at different temperatures were well fitted with a pseudo second-order kinetic model,suggesting that the adsorption was determined by the availability of sorption sites on the HA surfaces rather than the CYR concentration in the bulk solution.The adsorption rate of CYR in the rapid process increased with rise in temperature,but the adsorption amount at sorption equilibrium decreased with rise in temperature.Adsorption and desorption isotherms fitted Freudlich and Langmuir models well.The desorption rate of CYR from humic acid was lower than the sorption rate,implying a hysteresis occurred during the desorption of CYR from humic acid.The negative values of Ho,Soand Go before and after the adsorption revealed that the CYR adsorption on humic acid was a spontaneous,entropy decrease and exothermic processes.The absolute value of Go was less than 40 kJ.mol-1,indicating physical sorption predominated in the adsorption of CYR on humic acid.