Simultaneous Removal Of Phosphorus And Fluoride From Acidic Wastewater By Polystyrene Based Ce-La Bimetallic Oxides Composite Nanomaterial

Excess phosphorus and fluoride in waters triggers a severe threat to the safety of aquatic ecosystem and human health.Industrial production is one of the main reasons for the increase of phosphorus and fluoride concentration in aquatic environment,in which the semiconductor industry,phosphate fertilizer industry and mining and metallurgical industry will produce a large number of acidic production wastewater containing phosphate and fluoride.These wastewaters have the characteristics of complex composition,strong toxicity and high acidity,conventional sewage treatment technology for these wastewaters can not meet the discharge standards steadily.As a consequence,it is an urgent need to develop efficient new technology for simultaneous removal of phosphate and fluoride from acid wastewater.Adsorption has been regarded as the most dominant technology for phosphate and fluoride removal from wastewater,but some of the available adsorbents are subject to the weaknesses of high dissolution rate,narrow applicable pH ranges,or low adsorption capacity in complex water circumstance,which greatly astrict their practical application.To solve the above problems,a novel Ce-La bimetal oxides nano-adsorbent(Ce-La Bimetal Oxides,CLBOs)capable of simultaneous adsorption of phosphate and fluoride were prepared by coprecipitation method in this paper.The results showed that the CLBOs existed mainly in the form of nanoparticles or nanoclusters with a particle size of 20-50 nm and a specific surface area of 117.9 m2/g.The CLBOs exhibited excellent chemical stability against pH variation(4-12),and the acidic condition was beneficial to the adsorption of phosphate and fluoride.Under the conditions of pH=4.0,the initial concentration of phosphate and fluoride was 30 mg/L and 10 mg/L respectively,the maximum adsorption capacity of phosphate and fluorine could reach to 59.14 mg/g and 19.25 mg/g,respectively.Thanks to the synthetic effects of electrostatic attraction,ligand exchange and inner-sphere complexation,CLBOs showed excellent adsorption performance for co-removal of phosphate and fluoride,and the concomitant competing anions exerted negligible effect on the removal efficiency.The kinetic experiments showed that the adsorption processes of CLBOs for phosphate and fluoride agreed well with the pseudo-second-order kinetic model,and the adsorption rate of CLBOs on fluorine was significantly faster than that of phosphate,which the adsorption equilibrium time of fluoride only took 100 min,and the adsorption equilibrium time of phosphate was about 240 min.The exhausted CLBOs could be efficiently regenerated by a simple alkaline treatment for cyclic utilization with constant adsorption performance.The above results verified that CLBOs is an efficient adsorbent with practical application prospect for synchronous removal of phosphate and fluoride from acidic wastewater.In order to solve the problem that CLBOs nanoparticles are too fine to be applied in largescale engineering,this study prepared Ce-La bimetallic oxides nanocomposite CLBOs@201 suitable for large-scale engineering applications by using quaternary amine polystyrene microspheres D201 as the matrix and loading CLBOs into the pores of D201 through the method of "Ce-La precursor introduction-alkali addition in situ co-deposition".The study showed that CLBOs@201 were orange-yellow spherical particles with a specific surface area of 56.90 m2/g,an average pore size of 5.99 nm and a pore volume of 7·14×10-2 cm3/g.The SEM and TEM characterization showed that the loaded CLBOs nanoparticles were distributed in the peripheral pore domain of the carrier,mainly in the form of nanoparticles or nanoclusters,and the particle size ranged from 10 to 30 nm,among which the loading of Ce and La were 13.72%and 12.51%(mass percentage),respectively.The stability of CLBOs@201was excellent in the pH=3-12 range and no dissolution of Ce or La was found in long-term use.Under the conditions of pH=4.0,phosphate concentration of 30 mg/L and fluoride concentration of 10 mg/L,the maximum phosphate and fluoride adsorption capacity of CLBOs@201 could reach to 42.04 mg/g and 13.50 mg/g,respectively.This is related to the special structure of CLBOs@201 and the occurrence characteristics of phosphate and fluoride in different solution pH conditions.In the high concomitant competing anions system,CLBOs@201 exhibited excellent selective adsorption performance for phosphate and fluoride,which was attributed to the ligand exchange and inner-sphere complexation of the loaded CLBOs in the composites with phosphate and fluoride.The adsorption kinetics experiments showed that the phosphate and fluoride removal process of CLBOs@201 agreed well with the pseudo-second-order kinetic model and intra-particle diffusion model.In addition,the adsorption rates of CLBOs@201 for phosphate and fluoride were significantly enhanced compared with those of CLBOs nanoparticles,with the adsorption equilibrium time of about 150 min for phosphate and only 50 min for fluoride.This was attributed to the Donnan membrane pre-enrichment effect on phosphate and fluoride in solution by the quaternary amine-based polystyrene microsphere carriers.The adsorbed saturated CLBOs@201 can be regenerated effectively by NaOH-NaCl mixed solution,and the phosphorus and fluoride adsorption capacity did not decrease significantly after regeneration.CLBOs@201 maintained relatively stable phosphorus and fluoride removal capacity in the multi-batch "adsorptionregeneration" cycle.The fixed-bed adsorption experiments demonstrated that the effective treatment capacity of CLBOs@201 could reach 5000 BV for phosphate and 230 BV for fluoride in simulated phosphorus and fluoride wastewater(pH=4.0、P=5 mg/L and F=3 mg/L),and CLBOs@201 has high in situ desorption efficiency,which has good application potential for the deep treatment of acidic wastewater containing phosphorus and fluoride.