Study On The Phosphate Removal By La- Modified Rice Husk Biochars

In order to prevent water pollution caused by eutrophication and make full use of the agricultural waste of rice husk,the concept of"green waste recycling"is achieved.In this paper,the rice husk-based biochar（RHC,RHC3,RHC9）with large specific surface area,abundant mesoporous numbers,and superior properties was prepared as a support material by means of CO2 activation and boiling in NaOH solution under normal pressure.La（OH）3 was loaded onto rice husk-based biochar by co-precipitation method to prepare three kinds of composite adsorbents（RHC-La,RHC3-La,RHC9-La）with good phosphate removal efficiency.A variety of characterization methods were used to study the physicochemical properties of La loaded onto rice husk-based biochar,the effects of initial phosphate concentration,temperature,pH,and coexisting ions on phosphate removal were investigated,and the main phosphate removal reaction mechanism was further analyzed.With this preparation process,the pore diameter of the rice husk-based biochar is mainly distributed between 2-6nm,which is a typical mesoporous material.The surface area of the alkaline-boiled biochar can be up to 603.61 m2/g than the unboiled biochar.The loading of lanthanum is transformed from amorphous state into a rod of La（OH）3crystal,and the capacity of lanthanum-loaded is about 12.0%,12.6%and 12.9%,respectively.With the time of alkaline-boiled increased,the metal stability of RHC-La,RHC3-La and RHC9-La increased gradually.In the pH range of 3.0-9.0,the lanthanum hydroxide-loaded composite adsorbent can effectively remove phosphate,and basically negligible La³⁺leaching were observed.The adsorption process was in line with the Langmuir adsorption isotherm model（R²=0.99）and the maximum adsorption capacity of RHC-La,RHC3-La and RHC9-La was 41.32mg/g,43.29mg/g and 46.51mg/g,respectively.The reaction kinetics followed pesudo-second-order kinetic model（R²=0.999）.Thermodynamic studies indicated that the adsorption of phosphate by the lanthanum hydroxide-loaded composite adsorbent were spontaneous endothermic process.The coexisting ions of SO4^2-had insignificant effect on the phosphate removal by the composite adsorbent,while HCO3^-and F^-had a significant effect on that.The possible mechanism of phosphate removal by the lanthanum hydroxide-loaded composite adsorbent were mainly included electrostatic attraction and ligand exchange.The La-modified rice husk biochars were demonstrated to be a selective and efficient adsorbent for the removal of the phosphate in wastewater.