Effect of precipitation pH and coexisting magnesium ion on phosphate adsorption onto hydrous zirconium oxide

To understand the effect of precipitation pH and coexisting Mg~(2+) on phosphate adsorption onto zirconium oxide(ZrO_2), ZrO_2 particles precipitated at pH 5.3, 7.1 and 10.5, i.e., ZrO_2(5.3), ZrO_2(7.1)and ZrO_2(10.5), respectively were prepared and characterized, then their adsorption performance and mechanism in the absence and presence of Mg~(2+) were comparatively investigated in this study. The results showed that the Elovich, pseudo-second-order and Langmuir isotherm models correlated with the experimental data well. The adsorption mechanism involved the complexation between phosphate and zirconium. Coexisting Mg~(2+) slightly inhibited the adsorption of phosphate on ZrO_2(5.3), including the adsorption capacity and rate, but coexisting Mg~(2+) greatly increased the adsorption capacity and rate for ZrO_2(7.1)and ZrO_2(10.5). The enhanced adsorption of phosphate on ZrO_2(7.1) and ZrO_2(10.5) in the presence of Mg~(2+) was mainly due to the formation of Mg~(2+)-HPO_4~(2-) ion pair(MgHPO_4~0) in the solution and then the adsorption of MgHPO_4~0 on the adsorbent surface, forming the phosphatebridged ternary complex Zr(OPO_3H)Mg. In the absence of Mg~(2+) , the maximum phosphate adsorption capacity at pH 7 calculated from the Langmuir isotherm model decreased in the order of ZrO 2(7.1)(67.3 mg/g) ZrO_2(5.3)(53.6 mg/g) ≈ ZrO_2(10.5)(53.1 mg/g), but it followed the order of Zr O2(7.1)(97.0 mg/g) ZrO_2(10.5)(79.7 mg/g) ZrO_2(5.3)(51.3 mg/g) in the presence of Mg~(2+) . The results of this work suggest that ZrO_2(7.1) is more suitable for use as an adsorbent for the effective removal of phosphate from municipal wastewater than ZrO_2(5.3) and ZrO_2(10.5),because Mg~(2+) is generally present in this wastewater.     

Investigation of adsorption/desorption behavior of Cr(VI) at the presence of inorganic and organic substance in membrane capacitive deionization (MCDI)

The adsorption and desorption behavior of Cr(VI) in membrane capacitive deionization (MCDI) was investigated systematically in the presence of bovine serum albumin (BSA) and KCl with different concentrations, respectively. Results revealed that Cr(VI) absorption was enhanced and the adsorption amount for Cr(VI) increased from 155.7 to 190.8?mg/g when KCl concentration increased from 100 to 200?mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2?mg/g when KCl concentration reached up to 1000?mg/L suggesting the negative effect for Cr(VI) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr (VI) significantly declined to 78.3?mg/g and pH was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(VI) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy (EDS). Based on above analysis, the enhanced removal mechanism for Cr(VI) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(VI) into Cr(III) and precipitation, which was demonstrated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM).     

Synthesis,characterization and application of Lagerstroemia speciosa embedded magnetic nanoparticle for Cr(Ⅵ)adsorption from aqueous solution

Lagerstroemia speciosa bark(LB) embedded magnetic nanoparticles were prepared by co-precipitation of Fe~(2+) and Fe~(3+) salt solution with ammonia and LB for Cr(Ⅵ) removal from aqueous solution.The native LB,magnetic nanoparticle(MNP),L.spedosa embedded magnetic nanoparticle(MNPLB) and Cr(Ⅵ) adsorbed MNPLB particles were characterized by SEM-EDX,TEM,BET-surface area,FT-IR,XRD and TGA methods.TEM analysis confirmed nearly spherical shape of MNP with an average diameter of 8.76 nm and the surface modification did not result in the phase change of MNP as established by XRD analysis,while led to the formation of secondary particles of MNPLB with diameter of 18.54 nm.Characterization results revealed covalent binding between the hydroxyl group of MNP and carboxyl group of LB particles and further confirmed its physico-chemical nature favorable for Cr(Ⅵ) adsorption.The Cr(Ⅵ) adsorption on to MNPLB particle as an adsorbent was tested under different contact time,initial Cr(Ⅵ) concentration,adsorbent dose,initial pH,temperature and agitation speed.The results of the equilibrium and kinetics of adsorption were well described by Langmuir isotherm and pseudo-second-order model,respectively.The thermodynamic parameters suggest spontaneous and endothermic nature of Cr(Ⅵ)adsorption onto MNPLB.The maximum adsorption capacity for MNPLB was calculated to be 434.78 mg/g and these particles even after Cr(Ⅵ) adsorption were collected effortlessly from the aqueous solution by a magnet.The desorption of Cr(Ⅵ)-adsorbed MNPLB was found to be more than 93.72%with spent MNPLB depicting eleven successive adsorption-desorption cycles.     

Preparation of Fe–Co based MOF-74 and its effective adsorption of arsenic from aqueous solution

To obtain a cost-effective adsorbent for the removal of arsenic in water,a novel nanostructured Fe–Co based metal organic framework(MOF-74)adsorbent was successfully prepared via a simple solvothermal method.The adsorption experiments showed that the optimal molar ratio of Fe/Co in the adsorbent was 2:1.The Fe_2Co_1MOF-74 was characterized by various techniques and the results showed that the nanoparticle diameter ranged from60 to 80 nm and the specific surface area was 147.82 m~2/g.The isotherm and kinetic parameters of arsenic removal on Fe_2Co_1MOF-74 were well-fitted by the Langmuir and pseudo-second-order models.The maximum adsorption capacities toward As(III)and As(V)were 266.52 and 292.29 mg/g,respectively.The presence of sulfate,carbonate and humic acid had no obvious effect on arsenic adsorption.However,coexisting phosphate significantly hindered the removal of arsenic,especially at high concentrations(10 mmol/L).Electrostatic interaction and hydroxyl and metal–oxygen groups played important roles in the adsorption of arsenic.Furthermore,the prepared adsorbent had stable adsorption ability after regeneration and when used in a real-water matrix.The excellent adsorption performance of Fe_2Co_1MOF-74 material makes it a potentially promising adsorbent for the removal of arsenic.     

Investigation of adsorption/desorption behavior of Cr(Ⅵ) at the presence of inorganic and organic substance in membrane capacitive deionization(MCDI)

The adsorption and desorption behavior of Cr(Ⅵ) in membrane capacitive deionization(MCDI) was investigated systematically in the presence of bovine serum albumin(BSA) and KCl with different concentrations, respectively. Results revealed that Cr(Ⅵ) absorption was enhanced and the adsorption amount for Cr(Ⅵ) increased from 155.7 to 190.8 mg/g when KCl concentration increased from 100 to 200 mg/L in the adsorption process, which was attributed to the stronger driving force. However, the adsorption amount sharply decreased to 90.2 mg/g when KCl concentration reached up to 1000 mg/L suggesting the negative effect for Cr(Ⅵ) removal that high KCl concentration had. As for the effect of BSA on ion adsorption, the amount for Cr(Ⅵ) significantly declined to 78.3 mg/g and p H was found to be an important factor contributing to this significant reduction. Then, the desorption performance was also conducted and it was obtained that the presence of KCl had negligible effect on Cr(Ⅵ) desorption, while promoted by the addition of BSA. The incomplete desorption was obtained and the residual chromium ions onto the electrode after desorption was detected via energy-dispersive X-ray spectroscopy(EDS). Based on above analysis, the enhanced removal mechanism for Cr(Ⅵ) in MCDI was found to be consisted of ion adsorption onto electrode surface, the redox reaction of Cr(Ⅵ) into Cr(III)and precipitation, which was demonstrated by X-ray photoelectron spectroscopy(XPS) and scanning electron microscope(SEM).     

Novel functional fiber loaded with carbon dots for the deep removal of Cr(VI) by adsorption and photocatalytic reduction

A novel functional fiber (PAN-CDs) loaded with carbon dots (CDs) with excellent photoreduction and adsorption properties for Cr(VI) was prepared via an amidization reaction between the CDs' carboxyl groups and amine groups on polyacrylonitrile (PAN)-based ion exchange fibers, which could completely preserve the fluorescence properties of the CDs. The photoluminescence (PL), photocatalysis and adsorption properties of PAN-CDs were characterized and analyzed. The PAN-CDs possess high adsorption capacity (297.6?mg/g) and excellent kinetic behavior (attaining adsorption equilibrium in 30?min) for Cr(VI) adsorption. Furthermore, the residual Cr(VI) (approximately 3?mg/L) after adsorption could be removed completely by subsequent photoreduction by the PAN-CDs. The Cr-saturated PAN-CDs could be easily separated by filtering and regenerated, with no observable decay of removal efficiency after five regeneration cycles. In addition, due to the PL quenching action of Cr(VI), the PAN-CDs can also be used as sensor for quantitative detection of trace Cr(VI) in aqueous solution.     

Nb_2O_5 nanowires in-situ grown on carbon fiber: A high-efficiency material for the photocatalytic reduction of Cr(Ⅵ)

Niobium oxide nanowire-deposited carbon fiber(CF) samples were prepared using a hydrothermal method with amorphous Nb_2O_5·nH_2O as precursor. The physical properties of the samples were characterized by means of numerous techniques, including X-ray diffraction(XRD), energy-dispersive spectroscopy(EDS), scanning electron microscopy(SEM), transmission electron microscopy(TEM), selected-area electron diffraction(SAED), UV–visible spectroscopy(UV–vis), N_2 adsorption–desorption, Fourier transform infrared spectroscopy(FT-IR), and X-ray photoelectron spectroscopy. The efficiency for the removal of Cr(VI) was determined.Parameters such as pH value and initial Cr(VI) concentration could influence the Cr(VI) removal efficiency or adsorption capacity of the Nb_2O_5/carbon fiber sample obtained after hydrothermal treatment at 160°C for 14 hr. The maximal Cr(VI) adsorption capacity of the Nb_2O_5 nanowire/CF sample was 115 mg/g. This Nb_2O_5/CF sample also showed excellent photocatalytic activity and stability for the reduction of Cr(VI) under UV-light irradiation: the Cr(VI) removal efficiency reached 99.9% after UV-light irradiation for 1 hr and there was no significant decrease in photocatalytic performance after the use of the sample for 10 repeated cycles. Such excellent Cr(VI) adsorption capacity and photocatalytic performance was related to its high surface area,abundant surface hydroxyl groups, and good UV-light absorption ability.     

Sequestration of toxic Pb(Ⅱ) ions by chemically treated rubber(Hevea brasiliensis) leaf powder

Rubber leaf powder(an agricultural waste) was treated with potassium permanganate followed by sodium carbonate and its performance in the removal of Pb(Ⅱ) ions from aqueous solution was evaluated.The interactions between Pb(Ⅱ) ions and functional groups on the adsorbent surface were confirmed by Fourier transform infrared(FT-IR) spectroscopy,scanning electron microscopy(SEM) coupled with X-ray energy dispersive spectroscopy(EDX).The effects of several important parameters which can affect adsorption capacity such as pH,adsorbent dosage,initial lead concentration and contact time were studied.The optimum pH range for lead adsorption was 4-5.Even at very low adsorbent dosage of 0.02 g,almost 100% of Pb(Ⅱ) ions(23 mg/L) could be removed.The adsorption capacity was also dependent on lead concentration and contact time,and relatively a short period of time(60-90 min) was required to reach equilibrium.The equilibrium data were analyzed with Langmuir,Freundlich and Dubinin-Radushkevich isotherms.Based on Langmuir model,the maximum adsorption capacity of lead was 95.3 mg/g.Three kinetic models including pseudo first-order,pseudo second-order and Boyd were used to analyze the lead adsorption process,and the results showed that the pseudo second-order fitted well with correlation coefficients greater than 0.99.     

Flower-, wire-, and sheet-like MnO_2-deposited diatomites:Highly efficient absorbents for the removal of Cr(Ⅵ)

Flower-, wire-, and sheet-like MnO2-deposited diatomites have been prepared using a hydrothermal method with Mn(Ac)2, KMnO4and/or MnSO4 as Mn source and diatomite as support. Physical properties of the materials were characterized by means of numerous analytical techniques, and their behaviors in the adsorption of chromium(VI) were evaluated.It is shown that the MnO2-deposited diatomite samples with different morphologies possessed high surface areas and abundant surface hydroxyl groups(especially the wire-like MnO2/diatomite sample). The wire-like MnO2/diatomite sample showed the best performance in the removal of Cr(VI), giving the maximum Cr(VI) adsorption capacity of 101 mg/g.     

Interference of iron as a coagulant on MIB removal by powdered activated carbon adsorption for low turbidity waters

Powered activated carbon (PAC) is widely used in water treatment plants to minimize odors in drinking water. This study investigated the removal of 2-methylisoborneol (MIB) by PAC adsorption, combined with coagulation using iron as a coagulant. The adsorption and coagulation process were studied through different case scenarios of jar tests. The analysis evaluated the effect of PAC dosing in the liquid phase immediately before or after the coagulant addition. Ferric sulphate was used as the coagulant with dosages from 10 to 30 mg/L, and PAC dosages varied from 10 to 40 mg/L. The highest MIB removal efficiency (about 70%) was achieved without the coagulant addition and with the highest PAC dosage (40 mg/L). Lower MIB removal efficiencies were observed in the presence of coagulant, showing a clear interference of the iron precipitate or coagulant in the adsorption process. The degree of interference of the coagulation process in the MIB removal was proportional to the ratio of ferric hydroxide mass to the PAC mass. For both cases of PAC dosing, upstream and downstream of the coagulant injection point, the MIB removal efficiency was similar. However, MIB removal efficiency was 15% lower when compared with experiments without the coagulant application. This interference in the MIB adsorption occurs potentially because the coagulant coats the surface of the carbon and interferes with the MIB coming in contact with the carbon’s surface and pores. This constraint requires an increase of the PAC dosage to provide the same efficiency observed without coagulation.     

Strong enhancement of methylene blue removal from binary wastewater by in-situ ferrite process

Dye wastewater containing heavy metal ions is a common industrial effluent with complex physicochemical properties.The treatment of metal–dye binary wastewater is difficult.In this work,a novel in-situ ferrite process(IFP) was applied to treat Methylene Blue(MB)–Cu(II)binary wastewater,and the operational parameters were optimized for MB removal.Results showed that the optimum operating conditions were OH/M of 1.72,Cu~(2+)/Fe~(2+)ratio of 1/2.5,reaction time of 90 min,aeration intensity of 320 mL/min,and reaction temperature of40°C.Moreover,the presence of Ca~(2+)and Mg~(2+)moderately influenced the MB removal.Physical characterization results indicated that the precipitates yielded in IFP presented high surface area(232.50 m2/g) and a multi-porous structure.Based on the Langmuir model,the maximum adsorption capacity toward MB was 347.82 mg/g for the precipitates produced in IFP,which outperformed most other adsorbents.Furthermore,IFP rapidly sequestered MB with removal efficiency 5 to 10 times greater than that by general ferrite adsorption,which suggested a strong enhancement of MB removal by IFP.The MB removal process by IFP showed two different high removal stages,each with a corresponding removal mechanism.In the first brief stage(5 min),the initial high MB removal(~95%)was achieved by predominantly electrostatic interactions.Then the sweep effect and encapsulation were dominant in the second longer stage.     

Degradation of sulfonamides and formation of trihalomethanes by chlorination after pre-oxidation with Fe(Ⅵ)

Sulfonamides are used in human therapy,animal husbandry and agriculture but are not easily biodegradable,and are often detected in surface water.Sulfamethazine(SMZ) and sulfadiazine(SDZ) are two widely used sulfonamide antibiotics that are used heavily in agriculture.In this study,they were degraded in an aqueous system by chlorination after pre-oxidation with ferrate(VI)(FeVIO42-,Fe(VI)),an environmentally friendly oxidation technique that has been shown to be effective in degrading various organics.The kinetics of the degradation were determined as a function of Fe(VI)(0–1.5 mg/L),free chlorine(0–1.8 mg/L) and temperature(15–35°C).According to the experimental results,SMZ chlorination followed second-order kinetics with increasing Fe(VI) dosage,and the effect of the initial free chlorine concentration on the reaction kinetics with pre-oxidation by Fe(VI) fitted a pseudo-first order model.The rate constants of SDZ and SMZ chlorination at different temperatures were related to the Arrhenius equation.Fe(VI) could reduce the levels of THMs formed and the toxicity of the sulfonamide degradation systems with Fe(VI) doses of 0.5–1.5 mg/L,which provides a reference for ensuring water quality in drinking water systems.     

Preparation, characterization and performance of an electrospun carbon nanofiber mat applied in hexavalent chromium removal from aqueous solution

Hexavalent chromium, Cr(VI), a highly toxic oxyanion known as a carcinogen and mutagen,is an issue of concern due to its adverse impact on human health. Therefore, development of effective technologies and/or materials for Cr(VI) removal from water has been of great interest for researchers. In this study, an electrospun carbon nanofiber(CNF) mat was prepared via electrospinning polyacrylonitrile(PAN), followed by thermal pre-oxidation and carbonization. Scanning electron microscopy(SEM) observation showed that the fiber diameter of the CNF with carbonization temperature of 950°C(CNF_(950)) was about 266 nm.Potentiometric titration analysis demonstrated that the point of zero charge p H(pHpzc) of CNF_(950) was around 7.93. CNF_(950) demonstrated high adsorption capacity and fast adsorption kinetics for Cr(VI) at pH 3. Langmuir isotherm calculations showed that the maximum adsorption capacity of Cr(VI) on CNF_(950) was 118.8 mg/g at pH 2. The adsorption isotherm of Cr(VI) on CNF_(950) was well described by the Redlich–Peterson model, revealing that Cr(VI)adsorption was the result of a combination of monolayer and multilayer adsorption,depending on the initial Cr(VI) concentration. Solution pH greatly affected Cr(VI) adsorption onto CNF_(950) due to the electrostatic interaction, and the adsorption capacity was relatively high when pH was below 3. X-ray photoelectron spectroscopy(XPS) analysis revealed that the removal of Cr(VI) might be the result of a combination of redox reaction and electrostatic adsorption. The adsorption-saturated CNF_(950) could be regenerated by NaOH solution. This study extends the potential applicability of electrospun CNF mats for Cr(VI)-contaminated water purification.     

Cr(VI) removal from aqueous solution with bamboo charcoal chemically modified by iron and cobalt with the assistance of microwave

Bamboo charcoal (BC) was used as starting material to prepare Co-Fe binary oxideloaded adsorbent (Co-Fe-MBC) through its impregnation in Co(NO3)2 , FeCl3 and HNO3 solutions simultaneously, followed by microwave heating. The low-cost composite was characterized and used as an adsorbent for Cr(VI) removal from water. The results showed that a cobalt and iron binary oxide (CoFe2O4 ) was uniformly formed on the BC through redox reactions. The composite exhibited higher surface area (331 m2/g) than that of BC or BC loaded with Fe alone (Fe-MBC). The adsorption of Cr(VI) strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed the Langmuir isotherm model well, and the maximum adsorption capacities for Cr(VI) at 288 K and pH 5.0 were 35.7 and 51.7 mg/g for Fe-MBC and Co-Fe-MBC, respectively. The adsorption processes were well fitted by the pseudo second-order kinetic model. Thermodynamic parameters showed that the adsorption of Cr(VI) onto both adsorbents was feasible, spontaneous, and exothermic under the studied conditions. The spent Co-Fe-MBC could be readily regenerated for reuse.     

Kinetics and mechanism of hexavalent chromium removal by basic oxygen furnace slag

Basic oxygen furnace slag(BOFS) has the potential to remove hexavalent chromium(Cr(VI))from wastewater by a redox process due to the presence of minerals containing Fe2+. The effects of the solution p H, initial Cr(VI) concentration, BOFS dosage, BOFS particle size, and temperature on the removal of Cr(VI) was investigated in detail through batch tests. The chemical and mineral compositions of fresh and reacted BOFS were characterized using scanning electron microscope(SEM) equipped with an energy dispersive spectrometer(EDS)system and X-ray diffractometer(XRD). The results show that Cr(VI) in wastewater can be efficiently removed by Fe2+released from BOFS under appropriate acidic conditions. The removal of Cr(VI) by BOFS significantly depended on the parameters mentioned above. The reaction of Cr(VI) with BOFS followed the pseudo-second-order kinetic model. Fe2+responsible for Cr(VI) removal was primarily derived from the dissolution of Fe O and Fe3O4 in BOFS. When H2SO4 was used to adjust the solution acidity, gypsum(Ca SO4·2H2O)could be formed and become an armoring precipitate layer on the BOFS surface, hindering the release of Fe2+and the removal of Cr(VI). Finally, the main mechanism of Cr(VI) removal by BOFS was described using several consecutive reaction steps.     

Enhanced removal of I− on hierarchically structured layered double hydroxides by in suit growth of Cu/Cu2O

To further improve the removal ability of layered double hydroxide(LDH) for iodide(I~-) anions from wastewater, we prepared hierarchically porous Cu_5Mg_(10)Al_5-LDH and used as a matrix for in suit growth of Cu/Cu_2O on its surface, forming Cu/Cu_2O-LDH, which was characterized and applied as an adsorbent.Results displayed high I~-saturation uptake capability(137.8 mg/g) of Cu/Cu_2O-LDH compared with Cu_5Mg_(10)Al_5-LDH(26.4 mg/g) even thermal activated LDH(76.1 mg/g).Thermodynamic analysis showed that the reaction between I~-anions and Cu/Cu_2O-LDH is a spontaneous and exothermic.Uptake kinetics analysis exhibited that adsorption equilibrium can be reached after 265 min.Additionally, the adsorbent showed satisfactory selectivity in the presence of competitive anions(e.g., SO_4~(2-)), and could achieve good adsorption performance in a wide pH range of 3–8.A cooperative adsorption mechanism was proposed on the basis of the following two aspects:(1) ion exchange between iodide and interlayer anions;(2) the adsorption performance of Cu, Cu(Ⅱ) and Cu_2O for I~-.Meanwhile, the difference between the adsorption mechanism of Cu/Cu_2O-LDH, Cu_5Mg_(10)Al_5-LDH and Cu_5Mg_(10)Al_5-CLDH adsorbents was also elaborated and verified.     

Rapid adsorption of toxic Pb(Ⅱ) ions from aqueous solution using multiwall carbon nanotubes synthesized by microwave chemical vapor deposition technique

Multiwall carbon nanotubes(MWCNTs) were synthesized using a tubular microwave chemical vapor deposition technique, using acetylene and hydrogen as the precursor gases and ferrocene as catalyst. The novel MWCNT samples were tested for their performance in terms of Pb(Ⅱ)binding. The synthesized MWCNT samples were characterized using Fourier Transform Infrared(FT-IR), Brunauer, Emmett and Teller(BET), Field Emission Scanning Electron Microscopy(FESEM) analysis, and the adsorption of Pb(Ⅱ) was studied as a function of p H,initial Pb(Ⅱ) concentration, MWCNT dosage, agitation speed, and adsorption time, and process parameters were optimized. The adsorption data followed both Freundlich and Langmuir isotherms. On the basis of the Langmuir model, Qmaxwas calculated to be 104.2 mg/g for the microwave-synthesized MWCNTs. In order to investigate the dynamic behavior of MWCNTs as an adsorbent, the kinetic data were modeled using pseudo first-order and pseudo second-order equations. Different thermodynamic parameters, viz., ΔH0, ΔS0and ΔG0were evaluated and it was found that the adsorption was feasible, spontaneous and endothermic in nature. The statistical analysis revealed that the optimum conditions for the highest removal(99.9%) of Pb(Ⅱ) are at p H 5, MWCNT dosage 0.1 g, agitation speed 160 r/min and time of 22.5 min with the initial concentration of 10 mg/L. Our results proved that microwave-synthesized MWCNTs can be used as an effective Pb(Ⅱ) adsorbent due to their high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.     

Exfoliated Mg–Al–Fe layered double hydroxides/polyether sulfone mixed matrix membranes for adsorption of phosphate and fluoride from aqueous solutions

Mg–Al–Fe layered double hydroxides(LDHs) were exfoliated and incorporated in polyether sulfone membranes for the removal of phosphate and fluoride for the first time. The exfoliation methods, coagulation bath, LDH amount, interfering ions, adsorption isotherm,desorption and reuse of the membranes were investigated. It was found that LDHs could be quickly exfoliated in formamide/N,N-dimethylformamide(DMF) solvent mixtures with sodium carboxymethyl cellulose as a stabilizer. The membranes displayed much higher adsorption capacity for phosphate(5.61 mg/g) and faster adsorption rate than the unexfoliated materials. With increased DMF content in the coagulation bath, the static and dynamic adsorption capacity rose. Interference from Cl-and SO_4~(2-)(50 mg/L) on adsorption of phosphates was not apparent. The membranes displayed excellent reusability in dynamic adsorption/desorption. The membranes also showed high adsorption capacity for fluorides(1.61 mg/g).     

Enhanced U(Ⅵ) bioreduction by alginate-immobilized uranium-reducing bacteria in the presence of carbon nanotubes and anthraquinone-2,6-disulfonate

Uranium-reducing bacteria were immobilized with sodium alginate, anthraquinone-2,6-disulfonate(AQDS), and carbon nanotubes(CNTs). The effects of different AQDS-CNTs contents, U(Ⅳ) concentrations, and metal ions on U(Ⅳ) reduction by immobilized beads were examined. Over 97.5% U(Ⅵ)(20 mg/L) was removed in 8 hr when the beads were added to 0.7% AQDS-CNTs, which was higher than that without AQDS-CNTs. This result may be attributed to the enhanced electron transfer by AQDS and CNTs. The reduction of U(Ⅵ) occurred at initial U(Ⅵ) concentrations of 10 to 100 mg/L and increased with increasing AQDS-CNT content from 0.1% to 1%. The presence of Fe(Ⅲ), Cu(Ⅱ) and Mn(Ⅱ)slightly increased U(Ⅵ) reduction, whereas Cr(Ⅵ), Ni(Ⅱ), Pb(Ⅱ), and Zn(Ⅱ) significantly inhibited U(Ⅵ) reduction. After eight successive incubation-washing cycles or 8 hr of retention time(HRT) for 48 hr of continuous operation, the removal efficiency of uranium was above 90% and 92%, respectively. The results indicate that the AQDS-CNT/AL/cell beads are suitable for the treatment of uranium-containing wastewaters.     

Simultaneous removal of chromium and arsenate from contaminated groundwater by ferrous sulfate: Batch uptake behavior

Chromium and/or arsenate removal by Fe(II) as a function of pH, Fe(II) dosage and initial Cr(VI)/As(V) ratio were examined in batch tests. The presence of arsenate reduced the removal e ciency of chromium by Fe(II), while the presence of chromate significantly increased the removal e ciency of arsenate by Fe(II) at pH 6–8. In the absence of arsenate, chromium removal by Fe(II) increased to a maximum with increasing pH from 4 to 7 and then decreased with a further increase in pH. The increment in Fe(II) dosage resulted in an improvement in chromium removal and the improvement was more remarkable under alkaline conditions than that under acidic conditions. Chromium removal by Fe(II) was reduced to a larger extent under neutral and alkaline conditions than that under acidic conditions due to the presence of 10 mol/L arsenate. The presence of 20 mol/L arsenate slightly improved chromium removal by Fe(II) at pH 3.9–5.8, but had detrimental e ects at pH 6.7–9.8. Arsenate removal was improved significantly at pH 4–9 due to the presence of 10 mol/L chromate at Fe(II) dosages of 20–60 mol/L. Elevating the chromate concentration from 10 to 20 mol/L resulted in a further improvement in arsenate removal at pH 4.0–4.6 when Fe(II) was dosed at 30–60 mol/L.