Abstract: An equilibrium method was used to study the characteristics of P adsorption and desorption in slag containing silicon.The result showed that when P concentration increased,the adsorbing capacity increased,but the increasing rate slowed down gradually.However,with increasing adsorbing capacity of P,the desorption rate of adsorbed P decreased gradually.The adsorption and desorption capability of slag varied greatly due to their differences in chemical components.Adding urea,potassium chloride and their compounds in the slag could reduce the adsorption of P and increase the desorption rate of adsorbed P significantly,and the effect of urea was best.The adsorbing capacity of P increased and the desorption rate of adsorbed P decreased along with minishing particle diameter of slag.The adsorption isotherm of P was well described by using Langmuir and Freundlish equations(P0.01),whose parameters(K,MBC,a,b) could reflect the adsorption characteristics.Therefore,P fixation in slag and its controlling factors should been taken into consideration when using slag containing silicon as fertilizers to improve soil fertility or producing multivariate compound fertilizers containing silicon.