| Contaminants from industrial wastewater rich in heavy metal ions remain an important environmental issue with the fast-growing economies of China.Although control technologies have been applied to many industrial and municipal wastewater sources,the total quantity of these agents released to the environment remains staggering.In addition,phosphorus is one of the essential limiting factors for the eutrophication of surface waters,while the phosphorus removal efficiency of conventional biological wastewater treatment plants is often low due to mechanical,financial,and limited personnel reasons.A wide range of treatment technologies,such as chemical precipitation,ion-exchange,membrane separation,electrocoagulation,solvent extraction,reduction,reverse osmosis and adsorption,have been developed to remove heavy metals and phosphorus from water and wastewater.Adsorption has been considered as an alternative approach for the removal of heavy metals and phosphorus since the adsorption process can be operated simply,produces little sludge,and enables phosphorus recovery.Considerable attention has been paid to the development of effective and low-cost sorbents and to evaluate their adsorption capacity.If inexpensively alternative sorbents can be developed,it would be beneficial to the environment and have attractive commercial value.The morphology of bioorganic plant materials is characterized by a hierarchically built anatomy with microstructural features ranging from the millimeter to the micrometer-scale(cellulose fibre structures).Converting biological structures into oxide/carbide based composite materials can overtake these advantages and represents an alternative material manufacturing route compared to the conventional powder processing technologies and has recently become a matter of increasing interest.Guangxi is the largest bamboo cultivation region in China,and its output ranked second in the whole country in 2010.As one of the three fast-growing trees,Eucalyptus is the largest source of timber tree species in Guangxi.They both are the common raw materials for pulp and paper industry.In this study,two kinds of porous biomorph-genetic composites of a-Fe2O3/Fe3O4/C were prepared with bamboo wood template(PBGC-Fe/C-B)and eucalyptus wood template(PBGC-Fe/C-E),which were selected as new adsorbents for the adsorption removal of Cr(VI),As(V)and P(V)from aqueous solution.The adsorption mechanism was investigated by materials preparation,adsorption effects,liquid analysis and materials characterization.The main researches and results are follows:1.The optimum conditions for preparing the PBGC-Fe/C adsorbents were determined.Rectangular specimens(30×10×3 mm3)of plant wood template were heated in boiling 5%dilute ammonia for 6h,impregnated through 1.2 mol/L ferric nitrate for 5 days at 60?(repeated three times),and then sintered for 3 hours at 600?.2.SEM,XRD and FT-IR analyses were used to monitor structural changes and phase formation processes during the treatment.The experimental results show that the PBGC-Fe/C materials were mainly consisted of a-Fe2O3,Fe3O4 and carbon,and retained the hierarchical porous structure of plant wood template with three different pore sizes.The BET surface area,the pore volume and the point of zero charge pHpZC were determined to be 93.06m2/g,0.12cm3/g and 3.1 for the PBGC-Fe/C-B,59.20m2/g,0.1 1cm3/g and 3.2 for the PBGC-Fe/C-E,respectively.3.Adsorption of Cr(VI),As(V)and P(V)from aqueous solution onto the PBGC-Fe/C adsorbent has been investigated to evaluate the effects of contact time,initial concentration and temperature,initial solution pH,adsorbent dose and adsorbent grain size on the removal systematically.(1)The PBGC-Fe/C could effectively remove Cr(VI)from aqueous solution.With increasing initial concentration from 10 to 400mg/L,the amounts of Cr(VI)adsorbed on the pulverized PBGC-Fe/C-B adsorbent(<100mesh)increased from 1.OOmg/g to 30.61 mg/g at 25?,from 1.00mg/g to 30.94mg/g at 35? and from 1.00mg/g to 32.88mg/g at 45?.With increasing initial concentration from 10 to 150mg/L,the amounts of Cr(VI)adsorbed on the pulverized PBGC-Fe/C-E adsorbent(<100mesh)increased from 1.00mg/g to 4.01mg/g at 25?,from 1.OOmg/g to 4.22mg/g at 35? and from 1.OOmg/g to 4.52mg/g at 45?.At the initial concentrations of 2,10 and 50mg/L,the adsorption capacities were determined to be 0.20,1.00 and 4.94mg/g for the unpulverized PBGC-Fe/C-B adsorbent,0.20,0.92 and 2.96mg/g for the unpulverized PBGC-Fe/C-E adsorbent,which exhibited a similar average values to those of fine particles or nanoparticles of iron oxides.(2)The PBGC-Fe/C could effectively remove As(V)from aqueous solution.With increasing initial As(V)concentration from 5mg/L to 100mg/L,the amounts of As(V)adsorbed on the pulverized PBGC-Fe/C-B sorbent(<100mesh)increased from 0.50mg/g to 4.55mg/g at 25?,from 0.50mg/g to 5.33mg/g at 35? and from 0.50mg/g to 4.89mg/g at 45?.The amounts of As(V)adsorbed on the pulverized PBGC-Fe/C-E sorbent(<100mesh)increased from 0.50mg/g to 4.01mg/g at 25?,from 0.50mg/g to 4.83mg/g at 35? and from 0.50mg/g to 4.19mg/g at 45?.At the initial concentrations of 5,10 and 50mg/L,the adsorption capacities were determined to be 0.45,0.86 and 3.02mg/g for the unpulverized PBGC-Fe/C-B adsorbent,0.50,0.99 and 2.49mg/g for the unpulverized PBGC-Fe/C-E adsorbent,which exhibited a similar average values to those of fine particles or nanoparticles of iron oxides.(3)The PBGC-Fe/C could effectively remove P(V)from aqueous solution.With increasing initial P(V)concentration from 2 to 50 mg/L,the amounts of P(V)adsorbed on the pulverized PBGC-Fe/C-B adsorbent(<100mesh)increased from 0.20 to 2.46 mg/g at 25?,from 0.20 to 2.64 mg/g at 35? and from 0.20 to 2.77 mg/g at 45?.The amounts of P(V)adsorbed on the pulverized PBGC-Fe/C-E adsorbent(<100mesh)increased from 0.20 to 1.56 mg/g at 25?,from 0.20 to 1.66 mg/g at 35? and from 0.20 to 1.72 mg/g at 45?.At the initial phosphorus concentrations of 2,5 and 10mg/L,the adsorption capacities were determined to be 0.18,0.36 and 0.66 mg/g for the unpulverized PBGC-Fe/C-B adsorbent,0.18,0.34 and 0.69 mg/g for the unpulverized PBGC-Fe/C-E adsorbent,which exhibited a similar average values to those of fine particles or nanoparticles of iron oxides reported in the literatures.(4)The adsorptions of Cr(VI),As(V)and P(V)on the PBGC-Fe/C followed Freundlich as well as Langmuir isotherms,and could well be described by the pseudo-second-order kinetic equation.Langmuir and Freundlich isotherms were used to analyze the equilibrium data at different temperatures and the equilibrium data of P(V)adsorbed on the PBGC-Fe/C were found to fit Freundlich isotherm equation better than Langmuir isotherm.4.The thermodynamic speciation analysis of Cr(VI),As(V)and P(V),SEM-EDS,XRD,FT-IR and XPS analysis of the PBGC-Fe/C before and after adsorption showed that most of the adsorbed elements were evenly distributed on the sample tube wall positions.The main mechanism of Cr(VI)removal was an adsorption-redox reaction between Cr(VI)and the PBGC-Fe/C adsorbents.The PBGC-Fe/C adsorbents have potential application in the conversion of toxic Cr(VI)into less toxic Cr(III).The adsorption processes of As(V)and P(V)include the electrostatic attraction and the chemical reaction with ferric oxides.Low solution pH favored the adsorption of Cr(VI),As(V)and P(V)onto the PBGC-Fe/C. |
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