In-depth Phosphate Removal From Water Containing Low Phosphate By Calcined La-Ca-Co₃

Excess phosphorus??0.02mg/L?could lead to eutrophication of water bodies.On the other hand,phosphate rock will be running out in short future.Thus it is important to achieve the purpose both of removal and recycle of phosphate at low concentrations.Compared to methods of chemical coagulation,biology and membrane permeation,adsorption is highly efficient and appropriate for removal of phosphate at low concentrations.A novel environment and eco-friendly adsorbent,La-Ca-CO₃ was synthesized by co-precipitation method.This study investigated the behaviors and mechanisms of low concentrations of phosphorus?0.5²mg/L?adsorption onto La-Ca-CO₃.The minimal dosages of the material for reducing the residual phosphorus to lower than 20ug/L were found to be 0.1g/L,0.025g/L at 2mg/L and 0.5mg/L of initial phosphorus concentration,respectively.The phosphate adsorption isotherm was well described by Langmuir mode with the estimated maximum phosphate removal capacity of 137.9mg/g.The kinetic data of phosphorus adsorption onto La-Ca-CO₃ agree well with pseudo second-order model.Batch of static experiments were performed to investigate the effect of pH,ionic strength,and co-existing anions on phosphate adsorption onto La-Ca-CO₃.Little pH independence was observed in the range from 3 to 10 with initial phosphorus concentration of 2mg/L at sorbent dosage of 0.1g/L and 4 to 11 with initial phosphorus concentration of 0.5mg/L at sorbent dosage of 0.025g/L,respectively.In the presence of 1000-fold molar excess of fluoride,nitrate and sulfate anions,phosphate removal by La-Ca-CO₃ was not affected.Moderate impacts were observed with bicarbonate anions.And after phosphate adsorption,phosphate adsorbed could be almost totally desorbed from the P-loaded La-Ca-CO₃ by 0.1M H₂SO₄.Furthermore adsorption of phosphate onto La-Ca-CO₃ was characterized by FTIR,which confirmed the adsorption mechanism of ligand exchange betweenCO₃^2-andPO₄^-3.SEM-EDS,BET and XRD were also employed to characterize the adsorbent before and after phosphate adsorption.La-Ca-CO₃ demonstrated to be a selective and efficient adsorbent toward in-depth phosphate removal and recycle.