Study On Phosphate Adsorption By Lanthanum Doped Wetland Plants Biochars (La-CB)

Agricultural runoff and industrial discharges have caused ever-increasing levels of phosphorus in waterbodies,which has aggravated eutrophication.The aquatic ecosystem is facing a severe crisis.To find a new type of material with low cost,environmentally friendly and highly adsorption of phosphorus,discarded lignocellulosic biochar loaded with lanthanum was applied for phosphate adsorption.A new way to reduce the phosphorus in sewage and alleviate the eutrophication of water was provided in this paper.In this study,the Box–Behnken experimental design-based response surface methodology?RSM?was used to further optimize the preparation conditions of adsorbents.With the strategy of wt?La?/wt?biomass?of 12.1%,pyrolyzing La-biomass at 491°C for 67 minutes,the biochar obtained?simplified as La-CB?has 5 times phosphate adsorption capacity that of unmodified biochar.The results of SEM,BET,XPS,XRD and FT-IR analysis demonstrated that the lanthanum particles were loaded in the pore channel and external surface of biochar,which reduced its specific surface area but raised adsorption capacity due to many new phosphate adsorption sites and positive charged on the surface.In this paper,the static adsorption and dynamic adsorption of phosphate were studied on La-CB adsorbent prepared under optimized conditions,and the adsorption mechanism was explored.Additionaly,the feasibility of La-CB in practical engineering was analyzed.Batch experiments were conducted to investigate the effects of temperature,initial phosphorus concentration and pH values on the phosphate adsorption by La-CB.As the environmental temperature increased or the initial phosphorus concentration increased,the higher the phosphate adsorption capacity of La-CB.The maximum adsorption capacity was appeared at pH=3,and the removal efficiency of 50 mg P/L phosphate reached 99.0%.Adsorption isothermal experiments showed that Langmuir isotherm model fitted the experimental data quite well.The results indicated that La-CB was dominated by single-molecule adsorption,and the adsorption sites were evenly distributed.The maximum adsorption capacity was calculated to be 36.1 mg P/g?25°C?.The adsorption kinetics of La-CB perfectly matched the pseudo-second-order model,which demonstrated that chemisorption was the main limiting factor.Adsorption thermodynamic analysis showed that phosphate adsorption of La-CB was an endothermic entropy reaction.Column experiments were carried out to explore the effects of the height of the adsorbent layer and the influent flow rate on the adsorption of phosphate by La-CB.The penetration curve of La-CB indicated that the height of La-CB fill was positively correlated with breakthrough time,exhausted time,phosphate adsorption capacity and removal efficiency,while influent flow rate was negatively correlated with the breakthrough time,exhausted ime,phosphate adsorption capacity and removal efficiency.Compared with Adams-Bohart model,Thomas model was more suitable for describing the penetration curve of La-CB via nonlinear fitting.Combined with the pH effect test and XPS characterization results,the adsorption of phosphate by La-CB included three mechanisms:ligand exchange,electrostatic interaction and complexation reaction.The practical application feasibility of La-CB was investigated by desorption and regeneration,phosphorus dissolution,coexisting ions competitive adsorption and adsorption experiments of actual phosphorus-containing wastewater.La-CB adsorbent could be regenerated efficiently and conveniently with NaOH-NaCl binary solution for reuse,with adsorption performance of phosphorus on La-CB after five cycles remaining about 85%of the maximum adsorption amount and 92.3%of the phosphorus desorption efficiency.At pH33,La-CB could stay good stability in solution.La-CB indicated favorable selectivity to phosphate with weak effects by foreign ions(Cl^-,SO₄^2-and NO₃^-),yet the the influence of coexisting ions CO₃^2-and HCO₃^-on phosphate adsorption was more significant.The secondary effluent from WWTP that meet the primary B standard c onducted the actual phosphorus-containing wastewater adsorption experiment.TP dropped to zero by static adsorption after 20min and the phosphate removal efficiency was 93.5%after 5 h of dynamic adsorption.Overall,La-CB adsorbents have certain potentials to be applied to engineering practice.