Abstract: As a kind of high-effect, low-cost, environment-friendly and recyclable PO₄^3- adsorbent intended for use in farmlands, La-containing cornstalk based biochar was prepared for the first time for analysis of phosphate adsorption characteristics with thermodynamic, isothermic and kinetic methods. During the adsorption process, its Gibbs free energy declined below zero, while enthalpy and entropy both rose above zero.Its adsorption isotherm fitted the Langmuir model and its adsorption peaked up to 78.36 mg·g^-1 at 25℃.Its kinetics fitted the pseudo-second-order kinetic model with its adsorption rate constant being 23.19×10^-2 mg·g^-1·min^-1 when the  initial phosphate concentration was 50 mg·L^-1.The straight line fitted with the intra-particle diffusion model failed to pass the origin of the coordinates, but was displayed in a two-section line; When soil pH lingered in the range of 3–7,its phosphate adsorption capacity was quite high and not affected by any of the coexisting ions, except 200 mg·L^-1 of CO₃^2- and 2000 mg·L^-1 of CO₃^2-and F^-. Its phosphate adsorption was a kind of spontaneous endothermic reaction, and physical adsorption dominated monolayer adsorption. Its adsorption process was governed mainly by surface diffusion and intra-particle diffusion and its adsorption rate by thickness of the boundary layer. The La-containing cornstalk-based biochar is extensively applicable to farmlands with pH in a wide range, quite strong in disturbance resisting ability and quite high in phosphate adsorption and adsorption rate. The La-containing cornstalk-based biochar enjoys a broad application prospect in the future in remedying eutrophied bodies and purifying phosphorus-polluted wastewater.  

Key words: cornstalk-based biochar, adsorption thermodynamics, adsorption isotherm, adsorption kinetics, pH, coexisting ions