Performance Of Ce-MOFs Composite Gel Beads Adsorption Coupled With Electrochemical Precipitation For Phosphorus Recovery In Water

Developing a new technology that can remove and recover excess phosphorus from water is currently of great importance to control eutrophication in water bodies and to recycle phosphorus resources.Adsorption is considered as a potential technology for the removal of phosphorus from water due to its simplicity,high removal efficiency and fast removal rate,as well as the potential recovery of phosphorus and reuse of adsorbent through desorption after adsorption.However,it is crucial to find suitable and efficient adsorbent materials for the practical application of adsorption.In recent years,lanthanide based metals(e.g.lanthanum and cerium)have become a hot research topic for adsorbent preparation due to their high affinity for phosphates and lower prices.Among them,cerium-based metal-organic frameworks(Ce-MOF)have received a lot of attention due to their good adsorption effect and high selectivity towards phosphates.However,Ce-MOF is in the form of powder,which is easy to agglomerate and difficult to separate in aqueous solution and cannot be applied on a large scale.Combining metal-organic frameworks(MOF)with natural organic polymers such as chitosan can overcome the shortcomings of MOF for practical applications,while achieving functionalisation of CS to further improve the adsorption capacity.In order to make the active component of Ce-MOF uniformly dispersed on the CS carrier substrate,this study used the in situ generation method to prepare chitosan gel spheres encapsulated with Ce-MOF,modified with PDA on this basis to further enhance its adsorption performance and stability,and carried out a study on its performance and mechanism of phosphate removal from water.In addition,in view of the fact that most of the previous studies on phosphorus recovery by adsorption have been confined to the study of efficient removal rate,although high phosphorus solution can be obtained by regeneration of adsorbent analysis,but not in the real sense of phosphorus resource recovery.Therefore,in this study,we propose to use guanoite electrochemical precipitation method to recover phosphate from the resolved solution,to investigate the effect of different test conditions on the phosphorus recovery effect,and to provide a new technology for recovering phosphorus resources from wastewater.The main findings of the study are as follows:(1)CS was used as the carrier material to prepare cerium hydroxide cross-linked chitosan gel spheres by the conventional drop method,and this was used as the MOF precursor to make in situ generation of Ce-MOF on the surface of CS gel spheres to form chitosan-cerium metal-organic framework composite gel spheres(CS-Ce-MOF)by solvothermal method,and then modified by PDA to successfully prepare dopamine-modified chitosan-cerium metal-organic framework gel spheres(CS-Ce-MOF@PDA)were successfully prepared.The morphological characteristics,functional groups,crystal properties,elemental energy spectra and specific surface areas of CS-Ce-MOF and CS-Ce-MOF@PDA gel spheres were characterized using SEM,FTIR,XRD,XPS and BET to investigate the adsorption mechanism of the gel spheres.Adsorption experiments were carried out under different operating parameters,such as solution p H,initial phosphate concentration,coexisting anions and temperature.The adsorption kinetics,equilibrium isotherms and adsorption stability of both adsorbents were examined,as well as reusability studies.The two adsorbents were also evaluated by column experiments using simulated P solutions as feedstock.In the Langmuir model,the maximum adsorption capacities of CS-Ce-MOF and CS-Ce-MOF@PDA gel spheres were 83.1mg-P/g and 168.59 mg-P/g.Compared to CS-Ce-MOF,CS-Ce-MOF@PDA has a stronger phosphate adsorption capacity,which is related to the higher amount of amino groups after the introduction of dopamine.By characterisation results such as FTIR and XPS and adsorption data,the adsorption mechanisms of CS-Ce-MOF and CS-Ce-MOF@PDA were electrostatic adsorption and ligand exchange-internal sphere complexation.CS-Ce-MOF and CS-Ce-MOF@PDA gel spheres showed better stability and reusability during phosphate adsorption,as well as synthetic wastewater with good columnar adsorption properties,making them promising for phosphate fixation in practice.(2)By comparing the reusability performance of CS-Ce-MOF and CS-Ce-MOF@PDA gel spheres sorbents.CS-Ce-MOF was used as a representative desorption regeneration test to obtain a highly concentrated phosphate enriched solution by multiple desorptions,and then used a guanoite electrochemical precipitation device to recover phosphate from the resolving solution.The effect of different initial p H and current density on the phosphate recovery performance was investigated in a phosphate-only simulated solution.The results showed that the best recovery was achieved at I=2m A/cm~2 and an initial p H=7.In order to verify the feasibility of the coupled"Ce-MOF composite gel sphere adsorption-electrochemical precipitation"method for the recovery of simulated phosphorus-containing wastewater,CS-Ce-MOF was used to treat the phosphorus-containing wastewater by repeated adsorption-desorption and to obtain a high phosphorus solution,and then guanoite was used to treat the high phosphorus solution by electrochemical precipitation according to the above optimal test parameters.Finally,the effect of organic matter on the phosphate recovery was investigated.The results show that the presence of organic matter inhibits the formation and growth of guanoite crystals,thus reducing the recovery efficiency,while an appropriate increase in initial p H can effectively alleviate the inhibitory effect of organic matter such as HA on the recovery of phosphorus by guanoite electrochemical precipitation.The results confirm that a more satisfactory guanoite recovery product can be obtained and the method may provide a new idea for the sustainable use of phosphorus resources.