| Arsenic(As),phosphorus(P)and antimony(Sb)belong to the same group 15(VA)of the periodic table of elements and share similar chemical properties.They are widespread pollutants in water environment and their removal are getting more and more attention.Adsorption has evolved as one of the most promising methodes for water decontamination owing to its low cost,high efficiency,ease in operation and no secondary pollution.Intensive studies have been made on developing various adsorbents with low costs,high efficiency and facilitatly packing column(bed)for practical application.Guangxi is one of the major provinces of planting and industrial application of fast-growing eucalyptus and bamboo.The resource utilization and new technologies for water pollution control are two important aspects for the ecological civilization construction in Guangxi,China.In the present work,a kind of novel porous modified composites of a-Fe2O3/Fe3O4/C(PMC-Fe/C)were firstly prepared using forestry residues such as the side shoots of eucalyptus and bamboo as biotemplates,which were then characterized by SEM-EDS,BET,XRD,XPS and FT-IR instruments.Simultaneously,the PMC-Fe/C materials were applied in the fix-bed column system to remove As(V),P(V)and Sb(III)from simulation wastewaters and an actual molasses alcohol wastewater,in which the dynamic adsorption performance,influencing factors and adsorption mechanism were investigated.The dynamic adsorption data were analyzed in detail by using several models such as the Thomas model model,the Yoon-Nelson model,the Adams-Bohart model,the Clark model and the Wolborska model.Based on the charaterization of the PMC-Fe/C surface and the Charge Distribution Multisite Complexation Model(CD-MUSIC)simulation with the program PHREEQC,the speciation distribution and the surface complexation on the PMC-Fe/C adsorbents during the As(V),P(V)and Sb(III)adsorption were analyzed to investigate the adsorption mechanism.The main conclusions were as follows:The characterization results by SEM-EDS,XRD,XPS,FT-IR and BET confirmed that the PMC-Fe/C composites retained accurately the hierarchical porous microstructure of the eucalyptus and bamboo biotemplates.The PMC-Fe/C-E and PMC-Fe/C-B block materials were measured for the porosities of 43.95%and 69.51%,the BET specific surface areas of 73.1516m2/g?121.6829m2/g and 138.17m2/g?186.66m2/g,the mesoporous rates of 79.4?86.1%and 74?81.3%,the average Fe contents of 23.65%and 67.05%,the pHPZC values of 3.3 and 3.2,respectively.The iron oxide crystal forms of the PMC-Fe/C were identified as a-Fe2O3 and Fe3O4.The PMC-Fe/C can be used to remove As(V),P(V)and Sb(III)effectively from the wastewater.Increasing in the PMC-Fe/C adsorbent amount(adsorption column height)and reducing in the particle size could effectively prolonged the break-through time and failure time and improved the quality of the column.The acid condition(pH 2-4)was favorable for adsorption of As(V)and P(V).Increasing in the influent As(V)concentration and the influent velocity could accelerate the column failure.Under the optimized experimental conditions of influent concentration of 20mg/L(As),10 mg/L(P),20 mg/L(Sb),the influent flow rate of 5.136mL/min,pH of 3(As,P)and 8(Sb),adsorbent particle size<100mesh and adsorption temperature of 35?,the PMC-Fe/C-E dosage of 2.0g or the PMC-Fe/C-B dosage of 0.5g,the breakthrough of PMC-Fe/C-E and PMC-Fe/C-B to As(V)occurred at 110min(257BV)and 50min(184BV),respectively.The qe,exp values of PMC-Fe/C-E and PMC-Fe/C-B were calculated to be 14.99mg/g and 21.0mg/g,respectively.The Thomas model and Yoon-Nelson model could well fit the adsorption experiment data of As(V)(R2>0.9).The breakthrough of PMC-Fe/C-E and PMC-Fe/C-B to P(V)occurred at 68min(159BV)and 21min(77BV),respectively.The qe,exp values of PMC-Fe/C-E and PMC-Fe/C-B were calculated to be 7.74mg/g and 12.36mg/g,respectively.The Thomas model,the Yoon-Nelson model and the Clark model could well fit the adsorption experiment data of P(V)(R2>0.9).The breakthrough of PMC-Fe/C-E and PMC-Fe/C-B to Sb(III)occurred at 78min(415BV)and 36min(132BV),respectively.The qe,exp values of PMC-Fe/C-E and PMC-Fe/C-B were calculated to be 18.47mg/g and 19.28mg/g,respectively.The Thomas model,the Yoon-Nelson model and the Clark model could well fit the adsorption experiment data of Sb(?)(R2>0.9).The Adams-Bohart model an d the Wolborska model could only fit to the early stage of the adsorption break-through vurves.Under the optimized experimental conditions of NaOH concentration of 1M,the influent flow rate of 5.136mL/min,the As(V),P(V)and Sb(III)adsorbed on PMC-Fe/C could be effectively desorbed.The desorption effiency bigger than 80%.The PMC-Fe/C-B can be used to remove As(?),P(?)and Sb(?)effectively from the molasses alcohol wastewater.Under the optimized experimental conditions of the influent flow rate of 5.136mL/min,pH of 3,adsorbent particle size<100mesh and adsorption temperature of 35? and the PMC-Fe/C-B dosage of 1.0g,the breakthrough occurred at 1247BV,880BV and 1834BV for the influent concentrations of 11.22pg/L As,2.4mg/L P and 25.13?g/L Sb,respectively.The corresponding qe,exp values were calculated to be 37.97?g/g As,6.98mg/g P,37.46?g/g Sb.The Adams-Bohart model,the Wolborska model and the Clark model could well fit the As(?)adsorption data;the Thomas model,the Yoon-Nelson and the Clark model could well fit the P(?)adsorption data,the Adams-Bohart model and the Wolborska model could well fit the Sb(?)adsorption data.The SEM-EDS,FT-IR,XRD and XPS analytical results of the PMC-Fe/C materials after the As(V),P(V)and Sb(III)adsorption revealed that As(V)and Sb(III)were mainly absorbed on the pits or micropores on the PMC-Fe/C.The Fe,O and C functional groups on the PMC-Fe/C surface were the major active sites for the As(V)adsorption.Phosphor existed as a group of phosphorus compounds and mainly deposited on the fiber wall and pits of the PMC-Fe/C.The iron and oxygen functional groups on the PMC-Fe/C were the major active sites for the P(V)adsorption.After the As(V),P(V)and Sb(III)adsorption,the crystal structure of the ferric oxides on the PMC-Fe/C-E surface was not changed,only the strength of main reflection peaks was reduced.The crystal structure of a-Fe2O3 on PMC-Fe/C-B was changed which inferred that a-Fe2O3 participated in the chemical reactions during the adsorption process.Therefore,a-Fe2O3 provided the main active sites for the As(V)adsorption onto PMC-Fe/C-B.As can be seen from the FT-IR spectrograms of the PMC-Fe/C after the As(V),P(V)and Sb(III)adsorption,the number of OH groups on the PMC-Fe/C surface increased,confirming that the PMC-Fe/C had an acid-base dissociation during the adsorption.The Fe-O stretching vibration peaks fluctuated or disappeared,and the metal oxide vibration peaks also changed,confirming that the groups corresponding to these peaks were the active adsorption sites on the PMC-Fe/C surface.When the PMC-Fe/C-E adsorbed As(V)ions,Fe and O accepted electrons,which acted as a Lewis acid.No oxidation-reduction reaction occured in related to As(V).When the PMC-Fe/C-B adsorbed As(V),no chemical reaction of O and Fe was involved.When the PMC-Fe/C-E adsorbed P(V),O acted as an electron acceptor and played the role of Lewis acid.Fe did not participate in chemical reaction.The P(V)adsorption onto the PMC-Fe/C-E was likely to be controlled by ion exchange reaction between HPO42-and-OH.When the PMC-Fe/C-B adsorbed P(V),O atoms acted as an electron donor and played the role of a Lewis base.Fe was not involved in the chemical reaction.After the PMC-Fe/C-B had adsorbed Sb(III),antimony existed in the form of Sb2O5,which indicated a redox reaction of Sb(III).Sb(III)and O provided the adsorpion system with electronics,and Fe accepted electronics.Fe and O played the role of Lewis acid and Lewis base,respectively.The surface characteristics of the PMC-Fe/C composites were simulated and analyzed by the CD-MUSIC model using the program PHREEQC.The surface densities of the PMC-Fe/C-E and PMC-Fe/C-B were estimated to be 0.8site/nm2 and 2.5site/nm2,respectively.The speciation distribution of the surface complexation at different pHs during the As(V),P(V)and Sb(III)adsorption onto PMC-Fe/C was simulated.The possible surface complexes for the As(V)adsorption onto the PMC-Fe/C were ?FeOAsO2OH,?Fe2O2AsOOH and ?Fe2O2AsO2.?FeOSbOOH was the dominant complex at pH of 2-13.The possible surface complexes for the P(V)adsorption onto the PMC-Fe/C were ?FeOPO3,?Fe2O2POOH and ?Fe2O2PO2.Fe2O2POOH mainly existed at pH<6.?FeOPO3 was the dominant complex at pH of 4-13.The possible surface complexes for the Sb(III)adsorption onto the PMC-Fe/C were =FeOSbOOH and =FeOSb(OH)2.When pH<5,?FeOSbOOH was the predominated complex.?FeOSb(OH)2 existed at pH of 2?13 and would be an dominant complex when pH>5.The CD-MUSIC model was effectively coulped with the TRANPORT model by using the program PHREEQC to simulate the reactive transport of As(V)and P(V)in the fixed-bed column and to predict the breakthrough curve for the column adsorption. |
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