Adsorption studies of arsenic on Mn-substituted iron oxyhydroxide

Mn-substituted iron oxyhydroxide (Mn(0.13)Fe(0.87)OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m2 g(-1) and a pore volume of 0.35 cm3 g(-1). Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 degrees C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g(-1), respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases, adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15-24 and 45-67 kJ mol(-1) for arsenate and arsenite, respectively.     

An approach to physical characterization of fundamental ion exchange and adsorption behaviours of tuffaceous minerals in aqueous solutions of some environmental pollutants

Adsorption was measured and compared for the uptake of zinc, iron, lead, copper and ammonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian and Chinese origin for both the natural and near homoionic Na form as well, using the radioanalytical and spectrometric determination. The higher quality of Slovakian clinoptilolite-rich tuff has been proven to be effective for a potential lead and ammonium removal in native form, while parent tuff in Na exchanged variety may be proposed for even Fe(III) species removal out of water. The raw and Na-exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity, however lower adsorption capacity. Chinese clinoptilolite-rich tuff has not proved any exceptional high adsorption performance towards Fe(III) species. The data obtained from the adsorption experiments at 7–75 °C were used for calculation of some thermodynamic parameters—Gibbs free energy, activation energy, standard enthalpy and entropy, too.     

Arsenic adsorption onto pillared clays and iron oxides

Arsenic adsorption was carried out on simple materials such as goethite and amorphous iron hydroxide, and more complex matrices such as clay pillared with titanium(IV), iron(III), and aluminum(III). These matrices were synthesized from a bentonite whose montmorillonitic fraction was pillared according to optimized parameters. These sorbents were characterized by various methods: XRD, FTIR, BET, DTA/TGA, surface acidity, and zetametry. Elimination of arsenite and arsenate as a function of pH was studied. Arsenate elimination was favored at acidic pH, whereas optimal arsenite elimination was obtained at 4相似文献   

Selective Adsorption of Arsenic Ions on Silica Gel Impregnated with Ferric Hydroxide

Abstract

Selective adsorption of trace arsenite- and arsenate anions in an aqueous solution by ferric hydroxyde supported on silica gel particles was investigated. Silica gel particles were loaded with ferric hydroxide of the range of 1 – 3 wt. % in terms of Fe based on the dry gel, and the extent of adsorption of arsenite or arsenate ion measured by batch- and column processes, being the highest at pH 6 in the presence of diverse foreign ions. With the use of silica gel containing 3.3 wt. % Fe, as much as 0.07 m mol of arsenic per gram of dry gel was adsorbed.     

Characterization of intercalated iron(III) nanoparticles and oxidative adsorption of arsenite on them monitored by x-ray absorption fine structure combined with fluorescence spectrometry

This paper first deals with the screening and optimization of Fe(III)-based adsorbents for arsenic adsorption from 0.2 to 16 ppm test solutions of arsenite/arsenate. The best adsorption capacity has been reported on alpha-FeO(OH) on an adsorbent weight basis. Better results were found on intercalated Fe-montmorillonites for arsenite adsorption below the equilibrium dissolved As concentration of 310 ppb and for arsenate adsorption in all of the concentrations studied. Next, the speciation of As adsorbed was performed by As K-edge x-ray absorption fine structure (XAFS) combined with high-energy-resolution fluorescence spectrometry. Major oxidative adsorption of arsenite was observed on Fe-montmorillonite from the 0.2-16 ppm test solutions. The reasons for the higher capacity of arsenic adsorption and oxidative adsorption of arsenite on Fe-montmorillonite are discussed.     

Speciation and oxidation kinetics of arsenic in the thermal springs of Wiesbaden spa, Germany

Since 1886 arsenic has been known to be present as a trace component in the Wiesbaden thermal waters at concentrations of over 100 microg L(-1). In this study for the first time molecular level speciation of arsenic was measured both in the water (by HG-AAS) and in wellstone scale deposits (by XANES). Most of the arsenic in the anoxic NaCl-type waters is in the reduced arsenite form. Hydrous ferric oxide (HFO) precipitates in the scale deposits scavenge only the minor dissolved arsenate portion which is, however, accumulated up to 3% w/w. Isothermal precipitation experiments at in-situ temperatures showed a difference between the progress of both arsenic and iron oxidation and precipitation. This can be explained in terms of adsorption of the aqueous arsenite and heterogeneous oxidation on the HFO surface, but subsequently rapid release of the arsenate thereby formed back into the aqueous phase at enhanced temperature and increased pH. Such relatively rapid pseudo-homogeneous arsenite oxidation is too slow to efficiently retard the As(III) load already on the wellhead, but fast enough to prevent arsenic seepage into ground water aquifers.     

Quantitative trace-level speciation of arsenite and arsenate in drinking water by ion chromatography

We describe an improved method for the determination of inorganic arsenic in drinking water. The method is based on comprehensive optimization of the anion-exchange ion chromatographic (IC) separation of arsenite and arsenate with post-column generation and detection of the arsenate-molybdate heteropoly acid (AMHPA) complex ion. The arsenite capacity factor was improved from 0.081 to 0.13 by using a mobile phase (2.0 mL min(-1)) composed of 2.5 mM Na2CO3 and 0.91 mM NaHCO3 (pH 10.5). A post-column photo-oxidation reactor (2.5 m x 0.7 mm) was optimized (0.37 microM potassium persulfate at 0.50 mL min(-1)) such that arsenite was converted to arsenate with 99.8 +/- 4.2% efficiency. Multi-variate optimization of the complexation reaction conditions yielded the following levels: 1.3 mM ammonium molybdate, 7.7 mM ascorbic acid, 0.48 M nitric acid, 0.17 mM potassium antimony tartrate, and 1.0% (v/v) glycerol. A long-path length flow cell (Teflon AF, 100-cm) was used to measure the absorption of the AMHPA complex (818 +/- 2 nm). Figures of merit for arsenite/arsenate include: limit of detection (1.6/0.40 microg L(-1)): standard error in absorbance (5.1 x 10(-3)/3.5 x 10(-3)); and sensitivity (2.9 x 10(-3)/2.2 x 10(-3) absorbance units per ppb). Successful application of the method to fortified surface and ground waters (100 microL samples) is also described.     

原位水热合成Ce(Ⅳ)-X分子筛及对噻吩的吸附性能

通过原位水热合成方法直接制备出不同载Ce量的Ce(Ⅳ)-X分子筛,并考察了其对模拟汽油中噻吩的吸附性能。采用粉末X射线衍射(XRD)、傅里叶变换红外(FT-IR)、紫外-可见漫反射(UV-vis DRS)、全谱直读等离子体原子发射光谱(ICP-AES)、氮气吸附和NH₃程序升温热脱附(NH₃-TPD)等方法对分子筛进行表征。结果表明,合成分子筛均具备典型的X型分子筛结构,同时Ce(Ⅳ)被较好地引入到分子筛的骨架结构中;载Ce分子筛的酸性大于X分子筛,而且Ce(Ⅳ)-X分子筛的酸性随着Ce掺杂量的增加而增强。吸附实验表明,载Ce分子筛对噻吩的吸附性能明显好于X分子筛。其中,n(Ce)/n(Si)=0.05的分子筛脱硫效果最佳,饱和吸附容量达到52.541 9 mg/g。再生实验表明,加热再生的Ce(Ⅳ)-X分子筛对噻吩仍具有理想的吸附效果。n(Ce)/n(Si)=0.05的分子筛再生后饱和吸附容量为47.512 1 mg/g,约为新鲜吸附剂的90.43％。     

Sorption of As(V) on aluminosilicates treated with Fe(II) nanoparticles

Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, three samples of clay minerals (natural metakaoline, natural clinoptilolite-rich tuff, and synthetic zeolite) in both untreated and Fe-treated forms were used for the sorption of arsenate from model aqueous solution. The treatment of minerals consisted of exposing them to concentrated solution of Fe(II). Within this process the mineral surface has been laden with Fe(III) oxi(hydroxides) whose high affinity for the As(V) adsorption is well known. In all investigated systems the sorption capacity of Fe(II)-treated sorbents increased significantly in comparison to the untreated material (from about 0.5 to >20.0 mg/g, which represented more than 95% of the total As removal). The changes of Fe-bearing particles in the course of treating process and subsequent As sorption were investigated by the diffuse reflectance spectroscopy and the voltammetry of microparticles. IR spectra of treated and As(V)-saturated solids showed characteristic bands caused by Fe(III)SO(4), Fe(III)O, and AsO vibrations. In untreated As(V)-saturated solids no significant AsO vibrations were observed due to the negligible content of sorbed arsenate.     

Dissolution of Nickel Ferrite in Aqueous Solutions Containing Oxalic Acid and Ferrous Salts

The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate-oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages, the first one corresponding to the dissolution of the ferric oxide outer layer and the second one being the dissolution of Ni(1.06)Fe(1.96)O(4). The kinetics of dissolution during this first stage is typical of ferric oxides: in oxalic acid, both a ligand-assisted and a redox mechanism operates, whereas in the presence of ferrous ions, redox catalysis leads to a faster dissolution. The rate dependence on both oxalic acid and on ferrous ion is described by the Langmuir-Hinshelwood equation; the best fitting corresponds to K(1)(ads)=25.6 mol(-1) dm(-3) and k(1)(max)=9.17x10(-7) mol m(-2) s(-1) and K(2)(ads)=37.1x10(3) mol(-1) dm(-3) and k(2)(max)=62.3x10(-7) mol m(-2) s(-1), respectively. In the second stage, Langmuir-Hinshelwood kinetics also describes the dissolution of iron and nickel from nickel ferrite, with K(1)(ads)=20.8 mol(-1) dm(3) and K(2)(ads)=1.16x10(5) mol(-1) dm(3). For iron, k(1)(max)=1.02x10(-7) mol of Fe m(-2) s(-1) and k(2)(max)=2.38x10(-7) mol of Fe m(-2) s(-1); for nickel, the rate constants k(1)(max) and k(2)(max) are 2.4 and 1.79 times smaller, respectively. The factor 1.79 agrees nicely with the stoichiometric ratio, whereas the factor 2.4 implies the accumulation of some nickel in the residual particles. The rate of nickel dissolution in oxalic acid is higher than that in bunsenite by a factor of 8, whereas hematite is more reactive by a factor of 9 (in the absence of Fe(II)) and 27 (in the presence of Fe (II)). It may be concluded that oxalic acid operates to dissolve iron, and the ensuing disruption of the solid framework accelerates the release of nickel. Copyright 2000 Academic Press.     

The effect of copper on the precipitation of scorodite (FeAsO4·2H2O) under hydrothermal conditions: evidence for a hydrated copper containing ferric arsenate sulfate-short lived intermediate

The effect of copper sulfate on scorodite precipitation and its mechanism of formation at 150 °C was investigated. Scorodite was determined to be the dominant phase formed under all conditions explored (0.61 < Fe(III)/As(V) < 1.87, 0.27-0.30 M Fe(SO(4))(1.5), 0-0.3 M CuSO(4), 0-0.3 M MgSO(4), at 2.5 h and 150 °C). The produced scorodite was found to incorporate up to 5% SO(4) and ≤1% Cu or Mg in its structure. The precipitation of scorodite was stoichiometric, i.e. the Fe/As molar ratio in the solids was equal to one independent of the starting Fe/As ratio in the solution. The presence of excess ferric sulfate in the initial solution (Fe/As>1) was found to slow down the ordering of the H-bond structure in scorodite. Precipitation under equimolar concentrations (As = Fe = Cu = 0.3 M), short times and lower temperatures (30-70 min and 90-130 °C) revealed the formation of a Cu-Fe-AsO(4)-SO(4)-H(2)O short lived gelatinous intermediate that closely resembled the basic ferric arsenate sulfate (BFAS) type of phase, before ultimately converting fully to the most stable scorodite phase (96 min and 138 °C). This phase transition has been traced throughout the reaction via elemental (ICP-AES, XPS), structural (PXRD, TEM) and molecular (ATR-IR, Raman) analysis. ATR-IR investigation of an arsenic containing industrial residue produced during pressure leaching of a copper concentrate (1 h and 150 °C) found evidence of the formation of an arsenate mineral form resembling the intermediate basic ferric arsenate sulfate phase.     

Polarographic determination of total iron content using a Fe(2+/3+)-Methylthymol Blue-NO2- system.

In the buffer solution of NH3-NH4Cl (pH = 8.5, 0.04 mol l(-1)), iron-Methylthymol Blue (MTB) can produce a sensitive polarographic wave at -1.10 V (vs. SCE) in the NaNO2. The peak current is linear with the concentration of the iron in the range of 3 x 10(-8)-5 x 10(-6) mol l(-1), and the detection limit is 1 x 10(-8) mol l(-1). By studying the characteristics of the wave and the electrode reaction mechanism, we can prove that the catalytic wave is an adsorption wave and that the peak current comes from the reduction of Fe(II). The molar ratio of iron to ligand was found to be 1:1. Adsorption particles are neutral molecules, the saturated adsorption quantity of the complex on the mercury electrode is 1.92 x 10(-9) mol cm(-2), according with the Frumkin isothermal formula. In the experiments, the adsorption coefficient (beta) is 4.05 x 10(5); the adsorption factor (gamma) is 0.70: the electron transfer number (n) is 2; the free energy (deltaG(o)) is 31.99 kJ mol(-1); the transfer coefficient of the irreversible adsorption is 0.42-0.45; and the reaction velocity constant (Ks) is 1.35 s(-1). This method, whose result is satisfying, can be applied to the detection of trace total iron contents in medicinal products.     

Mechanistic modeling of arsenic retention on natural red earth in simulated environmental systems

Arsenic retention on natural red earth (hereafter NRE) was examined as a function of pH, ionic strength, and initial arsenic loading using both macroscopic and spectroscopic methods. Proton binding sites on NRE were characterized by potentiometric titrations yielding an average pH(zpc) around 8.5. Both As(III)- and As(V)-NRE surface configurations were postulated by vibration spectroscopy. Spectroscopically, it is shown that arsenite forms monodentate complexes whereas arsenate forms bidendate complexes with NRE. When 4相似文献   

生物质乙醇在 Fe-HZSM-5分子筛催化剂上脱水制乙烯

乙烯是一种重要的大宗化工原料.目前国内外乙烯的生产方法主要是石脑油裂解法.但是,随着全球性石油资源供求关系日趋紧张,以及该生产过程存在较大环境污染,该工艺面临严峻挑战.生物乙醇是一种可以通过生物质发酵获得的可再生资源.因此,生物质乙醇催化脱水制乙烯工艺受到越来越多研究者关注.该技术的关键在于高性能乙醇脱水制乙烯催化剂的开发.研究发现, Si/Al比大于40的 Fe改性 ZSM-5分子筛在乙醇转换制碳氢化合物的催化反应中具有较高活性,当反应温度大于400oC时,可生成 C1-C9的烷烃、烯烃和芳香烃,其中以 C3产物和芳香烃产物为主.本文研究了 Si/Al比为25-300的 Fe离子交换 ZSM-5分子筛在乙醇脱水制乙烯反应中的催化活性,并利用 XRD, NH3-TPD,吡啶吸附 FT-IR和DRS UV-VIS等表征手段,研究了催化剂的晶相结构、表面组成及酸性位点等,进而探究了该催化反应的反应机理.我们首先考察了 Si/Al比为25-300的 HZSM-5分子筛.随着分子筛 Si/Al比增大,乙醇转化率先增加后降低,在 Si/Al比为100时获得最高值;但是乙烯收率随着 Si/Al比的增加而持续下降, Si/Al比为25时有其最高值47%.经产物分析, HZSM-5(25)和 HZSM-5(300)虽具有相似的乙醇转化率,但前者产生大量 C3+产物,而后者产物只有乙烯和乙醚.据文献报道,乙醚是乙醇脱水制乙烯的中间产物,它的进一步脱水产生乙烯,而乙烯可进一步转化生成 C3+产物.因此,由于 HZSM-5(300)表面酸性较弱,主要生成反应中间体,而 HZSM-5(25)较强的表面酸性又导致乙烯进一步转化,生成 C3+产物.然后我们考察了经过3次离子交换处理的 Fe-ZSM-5催化剂.随着 Si/Al比上升(25-300),乙醇转化率和乙烯收率下降, Si/Al比为25时为其最高值;随着反应温度上升,乙醇转化率在260oC时达到近100%,之后维持不变,乙烯收率也在260 oC时为其峰值,温度继续上升造成乙烯收率再次下降;催化剂空速增大降低乙醇转化率和乙烯收率.经产物分析,温度较低和空速较大时产生大量的反应中间体乙醚,而温度较高时导致乙烯进一步转化生成 C3+产物.在反应温度为260oC、空速为0.81 h-1时, Fe-HZSM-5(25)催化剂上乙醇转化率为98%-99%、乙烯收率为97%-99%,并可实现长达1440 h的单程使用寿命,该值是 HZSM-5(25)催化剂的20余倍,具有很好的工业应用前景.为探究 Fe-ZSM-5(25)催化剂高催化活性和长催化寿命的原因,我们表征了催化剂.从 XRD结果可以看出,离子交换没有损坏 HZSM-5的晶体结构,也没有新的可检测到的物相产生.从 NH3-TPD结果看, HZSM-5(25)的CH/CL(强酸/弱酸)比为0.7, Fe-ZSM-5(25)的CH/CL比为0.29,可知 Fe离子交换降低了分子筛的表面酸性,特别是强酸性位.从吡啶吸附 FT-IR结果看, HZSM-5(25)的 B/L (Br?nsted酸性位/Lewis酸性位)比为1.42, Fe-ZSM-5(25)的 B/L比为0.25,可知 Fe离子交换主要减少的是分子筛表面的 Br?nsted酸性位.文献报道,乙醇脱水制乙烯主要发生在弱酸性位上,而乙烯进一步转化为 C3+产物发生在强酸性位上.所以,催化剂上强酸性位的减少有利于乙烯的生成反应.另据文献报道, Br?nsted酸性位是乙烯聚合、迅速覆盖催化活性位点产生积炭的催化活性中心.因此, Br?nsted酸性的降低可认为是 Fe-HZSM-5(25)催化剂单程使用寿命长较 HZSM-5(25)分子筛显著延长的原因.从 UV-VIS结果得知, Fe-ZSM-5上的 Fe物种主要以骨架内和骨架外 Fe3+为主,此外含有少量低聚合的 FexOy,但几乎没有 Fe2O3颗粒存在.文献记载, Fe3+物种是乙烯形成的活性物种,而 FeOx催化产生乙烯和乙醛.因此,催化剂中大量骨架内和骨架外 Fe3+物种的存在也可认为是该催化剂具有较强乙醇脱水制乙烯催化活性的原因之一.     

Ti-Si介孔分子筛的转晶与控制

以季铵盐型阳离子Gemini表面活性剂[C16H33(CH3)2N+(CH2)6N+(CH3)2C16H33]•2Br−(GEM16-6-16)为模板剂, 改变n(Ti)/n(Si)比值, 合成了系列Ti-Si介孔分子筛. X射线衍射(XRD)和透射电子显微镜(TEM)等表征结果表明, 在n(Ti)/n(Si)≤0.20时, 分子筛为高度有序六方介孔; 当 n(Ti)/n(Si)为 0.30时, 介孔转晶为立方相; 当n(Ti)/n(Si)为0.50时, 介孔转晶为层状相; n(Ti)/n(Si)为1.0时, 材料失去有序孔道结构. FT-IR分析表明, 在分子筛骨架间形成了Ti—O—Si键, 而且Ti—O—Si键的数目随n(Ti)/n(Si)的增加而增加, 达到一定饱和值后基本保持不变. 乙醇和丁醇对纯硅基介孔分子筛孔结构转晶控制作用呈现六方相→立方相→层状相递变规律, 因而钛酸正丁酯水解生成的丁醇对Ti-Si介孔分子筛转晶具有一定的控制作用.     

A linear comprehensive adsorption model of hydrogen on super activated carbon under supercritical conditions

The adsorption isotherms of hydrogen on super activated carbon were measured systematically, covering a temperature range of 93-293 K at 20 K intervals and pressures up to 7 MPa. All the experimental data were linearized by adopting the coordinates ln ln(n) vs 1/(ln P). The results indicate that the adsorption limit (P(lim), n(lim)) exists virtually at high pressure and has a certain physical meaning. Based on the adsorption limit, further analyses were carried out by modeling the adsorption isotherms in the coordinates ln(n(lim)/n) vs ln(RT(ln(P(lim)/P) and a linear comprehensive adsorption model was proposed in the form n (lim)=n.exp(psi T+lambda/T-c/) (beta).[RT ln( P (lim)P )] (b) which can predict the adsorption isotherm of hydrogen on activated carbon in supercritical conditions.     

Studies of iron(II) and iron(III) complexes with fac-N2O, cis-N2O2 and N2O3 donor ligands: models for the 2-His 1-carboxylate motif of non-heme iron monooxygenases

Enzymes in the oxygen-activating class of mononuclear non-heme iron oxygenases (MNOs) contain a highly conserved iron center facially ligated by two histidine nitrogen atoms and one carboxylate oxygen atom that leave one face of the metal center (three binding sites) open for coordination to cofactor, substrate, and/or dioxygen. A comparative family of [Fe(II/III)(N(2)O(n))(L)(4-n))](±x), n = 1-3, L = solvent or Cl(-), model complexes, based on a ligand series that supports a facially ligated N,N,O core that is then modified to contain either one or two additional carboxylate chelate arms, has been structurally and spectroscopically characterized. EPR studies demonstrate that the high-spin d(5) Fe(III)g = 4.3 signal becomes more symmetrical as the number of carboxylate ligands decreases across the series Fe(N(2)O(3)), Fe(N(2)O(2)), and Fe(N(2)O(1)), reflecting an increase in the E/D strain of these complexes as the number of exchangeable/solvent coordination sites increases, paralleling the enhanced distribution of electronic structures that contribute to the spectral line shape. The observed systematic variations in the Fe(II)-Fe(III) oxidation-reduction potentials illustrate the fundamental influence of differential carboxylate ligation. The trend towards lower reduction potential for the iron center across the [Fe(III)(N(2)O(1))Cl(3)](-), [Fe(III)(N(2)O(2))Cl(2)](-) and [Fe(III)(N(2)O(3))Cl](-) series is consistent with replacement of the chloride anions with the more strongly donating anionic O-donor carboxylate ligands that are expected to stabilize the oxidized ferric state. This electrochemical trend parallels the observed dioxygen sensitivity of the three ferrous complexes (Fe(II)(N(2)O(1)) < Fe(II)(N(2)O(2)) < Fe(II)(N(2)O(3))), which form μ-oxo bridged ferric species upon exposure to air or oxygen atom donor (OAD) molecules. The observed oxygen sensitivity is particularly interesting and discussed in the context of α-ketoglutarate-dependent MNO enzyme mechanisms.     

Mechanism of removal of arsenic by bead cellulose loaded with iron oxyhydroxide (beta-FeOOH): EXAFS study

Bead cellulose loaded with iron oxyhydroxide (BCF) with 47 mass% Fe content was prepared and was successfully applied to the elimination of arsenic from aqueous solutions. A clearer understanding of the arsenic removal mechanism will provide accurate prediction of the arsenic adsorptive properties of the new adsorbent. To study the mechanism of the adsorption process, we measured the extended X-ray absorption fine structure (EXAFS) spectra of arsenite and arsenate sorbed onto the adsorbent with different surface coverages. Both arsenite and arsenate were strongly and specifically adsorbed by akaganéite adsorptive centers on BCF by an inner-sphere mechanism. There was no change in oxidation state following interaction between the arsenic species and the BCF surface. The dominant complex of arsenic species adsorbed on akaganéite was bidentate binuclear corner-sharing ((2)C) between As(V) tetrahedra (or As(III) pyramids) and adjacent edge-sharing FeO(6) octahedra. On the basis of the results from EXAFS spectra, the adsorptive characteristics of arsenic, such as the effects of pH and competing anions, were satisfactorily interpreted.     

铁掺杂方沸石的合成及其磁性化

采用水热合成法, 按摩尔比n(SiO2):n(Al2O3):n(Na2O):n(Fe3+):n(H2O)=2.3:1:3.9:(0.02, 0.04, 0.08):185配料, 三乙胺为模板剂, 草酸为铁离子的络合剂, 经过室温搅拌成胶, 170 ℃下于不锈钢反应釜晶化60 h, 合成了三种掺杂铁量不同的方沸石, 为了解决粉末沸石分子筛难以从使用料液中分离问题, 对合成铁掺杂方沸石700 ℃下进行氢气还原制得了磁性沸石. 利用X射线衍射(XRD)、傅立叶变换-红外(FT-IR)光谱和扫描电子显微镜(SEM)对制得的产品进行表征. 结果表明, 合成的铁掺杂方沸石与纯方沸石结构相同, 磁性化沸石结构发生了变化. 考察样品对水中氟离子和铅离子的吸附性能发现, 铁掺杂方沸石和磁性沸石对它们的吸附性能没有促进作用.     

Increasing the arsenate adsorption capacity of neutralized red mud (Bauxsol)

The possibility of increasing the arsenate adsorption capacity of seawater-neutralized red mud (Bauxsol) through acid treatment, combined acid and heat treatment, and the addition of ferric sulfate (Fe(2)(SO(4))(3).7H(2)O) or aluminum sulfate (Al(2)(SO(4))(3). 18H(2)O) is investigated. The results show that acid treatment alone, as well as in combination with heat treatment increases the removal efficiency, with the combination providing the best removal. Adding ferric sulfate or aluminum sulfate, however, suppress the removal. The results also show that activated Bauxsol (AB) produced using combined acid and heat treatment can remove roughly 100% arsenate (at pH 4.5) with or without competing anions (i.e., phosphate, bicarbonate, and sulfate) when the initial arsenate concentration is < or = 2 mgl(-1). Furthermore, it is found that the adsorption process using AB is not accompanied by the release of unwanted contaminants, and TCLP results indicate that the spent AB is not hazardous. It is believed that the AB produced here has good potential as an alternative adsorbent to conventional methods for removing arsenate from water.