A.c. conductivity studies on the silver molybdo-arsenate glassy system

A new quaternary fast-ion conducting silver molybdo-arsenate [Agl-Ag2O-(MoO3 + As2O5)] (SMA) glassy system has been prepared using the melt-quenching technique for various dopant salt (Agl) concentrations by fixing the formers (MoO3 + As2O5) composition and the modifier (Ag2O) to formers (M/F) ratio. The prepared compounds were characterized by X-ray diffraction. The impedance measurements were made on different Agl compositions of the SMA glasses as a function of frequency (6.5 Hz-65 kHz) and temperature (303-343 K), using the Solatron frequency-response analyser(model 1250). The bulk conductivity and the appropriate physical model (equivalent circuit) of the SMA glass were obtained from the impedance analysis. The a.c. conductivity was calculated for different Agl compositions of SMA glasses at various temperatures and the obtained a.c. conductivity results were analysed using Jonscher's Universal Law. The conduction mechanism for the highest conducting SMA glassy compound has been explained using the diffusion path model.

A new open-framework zinc arsenate [C4N3H16](2)[Zn-5(AsO4)(4)(HAsO4)(2)]

A three-dimensional zinc arsenate with an interrupted zeolitic framework (-IIO), [C4N3H16](2)[Zn-5(AsO4)(4)(HAsO4)(2)], I has been synthesized solvothermally. The structure is built up from ZnO4, AsO4 and HAsO4 tetrahedral units connected alternatively through their vertices forming the 3-D structure possessing one-dimensional channels bound by 10 T-atoms (T = Zn, As), The framework density of the structure is 10.4 T-atoms which indicates considerable openness in its structure. (C) 2009 Elsevier B.V. All rights reserved.

Coupled substitution of niobium and silicon in potassium titanyl phosphate and arsenate (KTiOPO4 and KTiOAsO4. Synthesis and nonlinear optical properties of KTi1-xNbxOX1-xSixO4 (X = P, As)

Coupled substitution of Nb(V) and Si(IV) for Ti(IV) and P(V)/As(V) in KTiOP04 (KTP) and KTiOAsO4 (KTA) giving new series of nonlinear optical materials, KTi1-xNbxOX1-xSixO4 (X=P,As), has been investigated. Substitution up to x = 0.40 readily occurs, the members retaining the orthorhombic (Pna2(1)) structure of KTP. The second harmonic generation (SHG) property of the parent KTP and KTA is not adversely affected by the coupled substitution. SHG intensity of the powder samples of the X = P series shows a slight increase with x up to x = 0.15; for 0.15 < x less-than-or-equal-to 0.40, there is a decrease in SHG intensity as compared to that for KTP. A similar trend in SHG intensity is seen for the arsenic analogs.

Microbially induced separation of arsenopyrite and bioremediation of arsenic

This paper discusses the role of the mineral-adapted acidiphilic microorganism. Acidithiobacillus ferrooxidans in the beneficiation of arsenopyrite-containing multisulfides (pyrite and chalcopyrite) and the bioremediation of the resulting arsenical waste water. It was found that adaptation to minerals alters the surface properties of the microorganism. Bacterial adaptation to arsenopyrite and controlled bacterial adhesion to mineral surfaces lead to selectivity in arsenopyrite separation. Bioremoval of arsenic ions (both arsenite and arsenate ions) by Acidithiobacillus ferrooxidans is also discussed.

Enhanced adsorption capacity of activated alumina by impregnation with alum for removal of As(V) from water

Alum-impregnated activated alumina (AIAA) was investigated in the present work as an adsorbent for the removal of As(V) from water by batch mode. Adsorption study at different pH values shows that the efficiency of AIAA is much higher than as such activated alumina and is suitable for treatment of drinking water. The adsorption isotherm experiments indicated that the uptake of As(V) increased with increasing As(V) concentration from 1 to 25 mg/l and followed Langmuir-type adsorption isotherm. Speciation diagram shows that in the pH range of 2.8–11.5, arsenate predominantly exists as H2AsO4− and HAsO42− species and hence it is presumed that these are the major species being adsorbed on the surface of AIAA. Intraparticle diffusion and kinetic studies revealed that adsorption of As(V) was due to physical adsorption as well as through intraparticle diffusion. Effect of interfering ions revealed that As(V) sorption is strongly influenced by the presence of phosphate ion. The presence of arsenic on AIAA is depicted from zeta potential measurement, scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) mapping study. Alum-impregnated activated alumina successfully removed As(V) to below 40 ppb (within the permissible limit set by WHO) from water, when the initial concentration of As(V) is 10 mg/l.

Two- and Three-Dimensional Open-Framework Uranium Arsenates: Synthesis, Structure, and Characterization

Hydrothermal reactions between uranium salts and arsenic pentoxide in the presence of two different amines yielded six new uranium arsenate phases exhibiting open-framework structures, ethylenediamine (en): [C2N2H9]-[(UO2)(ASO(4))] I; [C2N2H10][(UO2)F(HASO(4))]2 center dot 4H(2)O, II; [C2N2H9][U2F5(HASO(4))(2)], III; [C2N2H9][UF2(ASO(4))], IV; diethylenetriamine (DETA), [C4N3H16][U2F3(ASO(4))(2)(HAsO4)] V; and [C4N3H16][U2F6(AsO4)(HAsO4)], VI. The structures were determined using single crystal studies, which revealed two- (I, II, V) and three-dimensional (III, IV, VI) structures for the uranium arsenates. The uranium atom, in these compounds, exhibits considerable variations in the coordination (6 to 9) that appears to have some correlation with the synthetic conditions. The water molecules in [C2N2H10][(UO2)F(HAsO4)](2 center dot)4H(2)O, II, could be reversibly removed, and the dehydrated phase, [C2N2H10][(UO2)F(HAsO4)](2), IIa, was also characterized using single crystal studies. The observation of many mineralogical structures in the present compounds suggests that the hydrothermal method could successfully replicate the geothermal conditions. As part of this study, we have observed autunite, Ca[(UO2)(PO4)](2)(H2O)(11), metavauxite, [Fe(H2O)(6)][Al(OH)(H2O)(PO4)](2), finarite, PbCU(SO4)(OH)(2), and tancoite, LiNa2H[Al(PO4)(2)(OH)], structures. The repeated observation of the secondary building unit, SBU-4, in many of the uranium arsenate structures suggests that these are viable building units. Optical studies on the uranium arsenate compound, [C4N3H16][U2F6(AsO4)(HASO(4))), VI, containing uranium in the +4 oxidation state indicates a blue emission through an upconversion process. The compound also exhibits antiferromagnetic behavior.

Effect of associating anions on phosphorus retention in soil II. Under variable anion concentration

The results of the present investigation reveal that the presence of anions in the reacting medium greatly modify the reactions between soil and solution P. Associating anions reduce considerably the retention of phosphate in soils. Citrate, tartrate, and silicate are found to be superior to arsenate, oxalate, and fluoride in reducing phosphate retention in soil. The performance of associating anions depends on the pH and P concentration of the reacting medium. The nature and properties of soil also play a highly significant role on the effectiveness of associating anions.

Studies on nucleotide pyrophosphatase I. Partial purification and properties of a sheep liver enzyme that catalyzes the hydrolysis of dinucleotides

A partially purified sheep liver enzyme that hydrolyzed dinucleotides at the pyrophosphate bond was obtained by solubilizing the 18,000g sediment with n-butanol and fractionating the solubilized enzyme with acetone. The enzyme activity when measured using FAD as substrate, (FAD → FMN + AMP), was optimal at pH 9.7 and temperatures between 30 °–36 ° and at 60 °. The rate of release of FMN with time occurred with an initial lag of 30 sec, a linear increase for 1 min, and a subsequent irregular rate. In the presence of orthophosphate (Pi; 10 μImage ), FMN was released at an uniformly continuous and enhanced rate. 32Pi was not incorporated into the substrate or products. Sodium arsenate counteracted the effects of Pi. The apparent Km and Vmax were 0.133 mImage and 100 units; and 0.133 mImage and 200 units, in the absence and presence of Pi, respectively. The temperature optimum was 42 ° in the presence of Pi.Negative cooperative interactions observed at low concentrations of FAD were abolished by the addition of Pi. The inhibition by AMP was sigmoid and Pi abolished this sigmoidal response. The enzyme hydrolyzed in addition to FAD, NAD+ and NADP+. Nucleoside triphosphates were potent inhibitors of the enzyme activity. The partial inhibition of the enzyme by o-phenanthroline and by p-hydroxymercuribenzoate could be reversed by Fe2+ ions and by reduced glutathione, respectively.

Hierarchy of structures in the family of amine templated open-framework gallium arsenates

Five new gallium arsenate compounds C2N2H10]Ga(H2AsO4)(HAsO4)(2)]center dot H2O, I; C2N2H10]Ga(OH)(AsO4)](2), II; C2N2H10]GaF(AsO4)](2), III; C3N2H12]Ga(OH)(AsO4)](2), IV; Ga2F3(AsO4)(HAsO4)]center dot 2H(3)O, V, have been synthesized under hydrothermal conditions and the structures determined employing single crystal X-ray diffraction studies. All the structures consist of octahedral gallium and tetrahedral arsenate units connected together forming a hierarchy of structures. Thus, one- (I), two- (II and IV) and three-dimensionally (III and V) extended structures have been observed. The Ga-O(H)/F-Ga connectivity in some of the structures suggests the coordination requirements posed by the octahedral gallium in these compounds. The observation of only one type of secondary building unit in the structures of III (SBU-4) and V (spiro-5) is unique and noteworthy. All the compounds have been characterized by a variety of techniques that include powder XRD, IR, and TGA. (C) 2010 Elsevier B. V. All rights reserved.

Removal of As(V) by adsorption onto mixed rare earth oxides

Arsenic pollution of water is a major problem faced worldwide. Arsenic is a suspected carcinogen in human beings and is harmful to other living beings. In the present study, a novel adsorbent was used to remove arsenate [As(V)] from synthetic solutions. The adsorbent, which is a mixture of rare earth oxides, was found to adsorb As(V) rapidly and effectively. The effect of various parameters such as contact time, initial concentration, pH, and adsorbent dose on adsorption efficiency was investigated. More than 90% of the adsorption occurred within the first 10 min and the kinetic rate constant was found to be about 3.5 mg min(-1). Adsorption efficiency was found to be dependent on the initial As(V) concentration, and the adsorption behavior followed the Langmuir adsorption model. The optimum pH was found to be 6.5. The presence of other ions such as nitrate, phosphate, sulphate, and silicate decreased the adsorption of As(V) by about 20-30%. The adsorbed As(V) could be desorbed easily by washing the adsorbent with pH 12 solution. This study demonstrates the applicability of naturally occurring rare earth oxides as selective adsorbents for As(V) from solutions.

Synthesis of zero valent iron nanoparticles and application to removal of arsenic(III) and arsenic(V) from water

Recently nano scale zero valent iron particles (nZVI) have been considered as smart adsorbent for environmental and groundwater remediation. Although several synthetic methods are available for the preparation of nZVI, air stable nZVI are not available for remediation works. Further, challenges demand synthesis of nZVI without stabilizers and capping agents. A modified methodology for the synthesis of air stable nZVI has been developed without any capping agents and characterized by powder X-Ray Diffraction (XRD), Scanning Electron Microscopy Energy-dispersive X-Ray (SEM-EDS), Transmission Electron Microscopy (TEM) and X-Ray Photoelectron Spectroscopy (XPS). The results of the present study suggest that the synthetic nZVI are air-stable over a period of one year and consists of particles of 30-40 nm in diameter. Although a layer of less than 3 am thick oxide/hydroxide is observed by TEM and XPS, it appears to be due to oxidation of outer surface during analysis. Adsorption study has shown that the synthetic nZVI are more effective adsorbent than the commercial nZVI and can remove simultaneously arsenite As-III] and arsenate As-V] from water without prior reduction of As-V to As-III. The removal process is adsorptive rather than precipitative and the removal of As-III is greater than that of As-V.