Preparation Of La/Ca-SA-FA Microspheres And Atudy On Their Removal Performance For Low Concentration Phosphorus In Water

The eutrophication as well as low-concentration phosphorus wastewater has become one of the urgent environmental problems to be solved.Among existing phosphorus removal methods,the adsorption has been widely used because of its high removal efficiency,high adsorption capacity and good removal efficiency for low concentration phosphorus-containing wastewater,but most of commonly used phosphorus removal adsorbents are powder-like at present.They are easy to lose and not easy to be recovered in practical application,so it is urgent to develop a kind of adsorption material with high removal efficiency and easy recovery for phosphorus with low concentration.Fly ash,as industrial waste,would lead to an adverse environmental impact on our surroundings and thus endanger public health and welfare if it is disposed at liberty.Sodium alginate has good gel performance and is environmentally friendly.The calcium and lanthanum not only have a good affinity to phosphorus,but also can be used as the metal cross-linking agent to prepare gel microspheres.For above items,sodium alginate and fly ash are used as raw materials and cross-linked by two metallic elements of calcium and lanthanum to prepare La/Ca-SA-FA microspheres of phosphorus removal adsorbent in the study.Besides,preparation parameters were optimized to study the adsorption performance of low-concentration phosphate and the mechanism of phosphorus removal in static and dynamic adsorption processes.Main conclusions are as follows:?1?Optimized preparation parameters of La/Ca-SA-FA microspheres are as follows:the concentration of sodium alginate was 2%,the mass ratio of sodium alginate to fly ash was 1:3,the cross-linking time was 8 h,the concentration of cross-linking agent was 5%and the ratio of calcium to lanthanum was 7:3.?2?Effects of adsorbent dosage,pH value and coexistent ions on phosphorus removal by La/Ca-SA-FA microspheres are respectively investigated in static adsorption experiments.When the initial phosphorus concentration is 1 mg/L,the optimal dosage of microspheres is 0.75 g/L.When the initial pH value of the solution is in 4.9¹1.01,La/Ca-SA-FA microspheres have a removal efficiency of more than 96%for phosphate.The process for phosphorus removal by La/Ca-SA-FA microspheres is greatly disturbed by SO₄^2-and F^-in the solution coexisting anions.The adsorption kinetics study shows that the adsorption process of La/Ca-SA-FA microspheres on the phosphate conforms to the quasi-second order kinetic model and belongs to chemisorption.The results of adsorption isotherm show that the temperature increased is beneficial to the adsorption for removal of phosphorus.The maximum adsorption capacity of the microspheres obtained by the Langmuir model was 4.59 mg/g.The Freundlich isotherm model shows that the adsorption process of microspheres on phosphorus is between monolayer and multilayer adsorption.?3?The characterization results of SEM,EDS,XRD and FTIR show that La/Ca-SA-FA microspheres had been prepared successfully and lanthanum and calcium have been cross-linked successfully inside microspheres.The precipitation of Ca₂P₄O₁₂·4H₂O,Ca₃?PO₄?₂ and LaPO₄ is formed by the reaction of La³⁺and Ca²⁺on the surface of microspheres.The phosphorus removal mechanism is mainly chemisorption.?4?The effects of filling layer height,inflow rate and initial phosphate concentration on phosphorus removal efficiency of La/Ca-SA-FA microspheres are investigated in fixed-bed dynamic adsorption experiments.The results show that the filling layer height is positively correlated with the adsorption column penetration,depletion time and adsorption capacity.The increase of flow rate and initial phosphate concentration will lead to the adsorption column penetration,decrease of depletion time and decrease of adsorption capacity.BDST model,Thomas model and Yoon-Nelson model can be used for dynamic adsorption and phosphorus removal by La/Ca-SA-FA microspheres.The fitting parameters of Thomas model show that the high efficiency of La/Ca-SA-FA microspheres can be realized in the fixed-bed dynamic adsorption experiment.?5?In the static and dynamic adsorption experiments of practical wastewater,La/Ca-SA-FA microspheres showed good selective adsorption performance,which shows the potential of application in the treatment of low-concentration phosphorus-containing wastewater.