The effect of arsenate,and of transitioń-metal ions,on the precipitation of phosphate as ammonium 12-molybdophosphate

The radionuclides phosphorus-32, arsenic-74, iron-59 and molybdenum-99 were used to determine the effect-of arsenate and some transition-metal ions on the precipitation of phosphorus as ammonium 12-molybdophosphate. Under the conditions necessary for the quantitative precipitation of phosphorus, arsenic is also precipitated by ammonium molybdate. The presence of iron(III) nitrate inhibits the precipitation of phosphorus and, particularly, arsenic, although the precipitates contain more molybdenum, and are heavier, than when iron is absent. Chromium (111) nitrate, nickel(II) nitrate and manganese(II) nitrate do not inhibit the precipitation of phosphorus and arsenic to the same extent as iron (III) nitrate.     

Stability of Lead(II) Arsenates

 Predictions of lead arsenate solubility and thermodynamic stability have been based on the value of the solubility constant for a precipitate with the general composition Pb₃(AsO₄)₂. The solubility of this precipitate is high and lead arsenate is considered to be unsuitable for lead and arsenic control in the environment. Standard Gibbs energy of formation for bayldonite, duftite, mimetite, philipsbornite, and schultenite can be found in the literature from solubility studies. From these data, stability diagrams were established for the environmentally relevant lead containing solid phases – anglesite, cerussite, schultenite, and mimetite. The diagrams lead to the conclusion that mimetite is a lead arsenate that can be used for remediation techniques.     

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.     

Adsorption of As (V) on iron oxide nanoparticle films studied by in situ ATR-FTIR spectroscopy

Stabilization of arsenic contaminated soils by iron oxides has been proposed as a remediation technique to prevent leaching of arsenate into the environment. Fundamental studies are needed to establish under which conditions the complexes formed are stable. In the present work, a powerful technique, viz. ATR-FTIR spectroscopy, is adapted to the studies of adsorption of arsenate species on iron oxides. This technique facilitates acquisition of both quantitative and qualitative in situ adsorption data.In the present work, about 800 nm thick films of 6-lineferrihydrite were deposited on ZnSe ATR crystals. Arsenate adsorption on the ferrihydrite film was studied at pD values ranging from 4 to 12 and at an arsenate concentration of 0.03 mM in D₂O solution. The amount of adsorbed arsenate decreased with increasing pD as a result of the more negatively charged iron oxide surface at higher pD values. The adsorption and desorption kinetics were also studied. Arsenate showed a higher adsorption rate within the first 70 min and a much lower adsorption rate from 70 to 300 min. The low adsorption rate at longer reaction times was partly due to a low desorption rate of already adsorbed carbonate species adsorbed at the surface. The desorption of carbonate species was evidenced by the appearance of negative absorption bands. The desorption of adsorbed arsenate complexes was examined by flushing with D₂O at pD 4 and 8.5 and it was found that the complexes were very stable at pD 4 suggesting formation of mostly inner-sphere complexes whereas a fraction of the complexes at pD 8.5 were less stable than at pD 4, possibly due to the formation of outer-sphere complexes.In summary, the ATR technique was shown to provide in situ information about the adsorption rate, desorption rate and the speciation of the complexes formed within a single experiment, which is very difficult to obtain using other techniques.     

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.     

Analytical investigations of phenyl arsenicals in groundwater

Phenylic arsenic compounds are the main contaminants in groundwater at abandoned sites with a history of arsenic containing chemical warfare agents (CWA). A fast and sensitive HPLC-ICP-MS method was developed to determine inorganic arsenic compounds like arsenite and arsenate as well as the degradation products of the arsenic containing warfare agents (phenylarsonic acid, phenylarsine oxide, diphenylarsinic acid). Beside these arsenic species the groundwater samples contained also high iron contents (up to 23 mg/l as Fe(II)) which led to precipitates in the samples after coming into contact with the atmosphere. Preservation immediately after sampling by phosphoric acid has shown that a successful avoidance of any losses of any arsenic species between sampling and analysis was possible. The suggested analytical method was applied to groundwater samples taken from different depths at a polluted site. The main contaminant in the water samples was diphenylarsinic acid (up to 2.1 mg/l) identified by ESI-MS, but also elevated concentrations of inorganic arsenic (up to 240 microg/l) were found.     

Quinolinium and lutidinium molybdates as reagents for the precipitation of phosphate

The precipitation of phosphate with quinolinium molybdate was studied by means of radioactive tracers, in relation to the excess of reagent, temperature of precipitation, etc. Precipitation is almost quantitative (99.3%) even with a stoichiometric amount of reagent added but an excess helps to minimise the inhibitory effects of certain ions, notably Fe³⁺ ; inhibitory effects are eliminated by digesting the solution for 2 h. Chromium(III) nitrate, nickel(II) nitrate and manganese(II) nitrate have relatively little effect on the precipitation of quinolinium molybdophosphate. Under the conditions required for the quantitative precipitation of phosphorus, arsenic is also quantitatively precipitated.Phosphate can be precipitated as lutidinium molybdophosphate using 2,4-, 2,5- or 2,6-lutidinium molybdate; the reagents are less efficient than quinolinium molybdate but can be used to precipitate phosphate under conditions which leave arsenate in solution.     

Environmental bioremediation for organometallic compounds: Microbial growth and arsenic volatillization from soil and retorted shale

Nutrient effects on microbial growth and arsenic volatilization from retorted oil shale and soil were evaluated in a laboratory study. Dimethylarsinic acid (DMAA), methanearsonic acid (MAA) and sodium arsenate amendments were used with added nutrients, or with retort process water added to simulate possible co-disposal conditions. In experiments with soil and retorted shale, dimethylarsinic acid showing the highest cumulative arsenic releases, in comparison with added inorganic sodium arsenate (SA). Low but detectable amounts of innate arsenic present in retorted shale could be volatilized with added organic matter. In soil, arsenic volatilization showed a direct relationship to nutrient levels and microbial growth. With shale, in comparison, a threshold response to available nutrients was evident. Distinct increases in fungal community development occurred with nutrients available at a level of 2.5% w/v, which also allowed incresed arsenic volatization. Codisposal of retort process waters with shale allowed arsenic volatilization without the addition of other nutrients. The presence of retort process water limited arsenic volatilization from the added organometallic compounds DMAA and MAA, but not from SA or innate arsenic. These differences should be useful in the definition of permissive and non-permissive environmental conditions for arsenic volatilization in bioremediation programs.     

Determination of the oxidizing capacity of manganese ores

An accurate method is described for determining the amount of active oxygen in manganese ores, based on the oxidation-reduction reaction between the ore and arsenic(III) in presence of ammonium molybdate, followed by the back-titration of excess of arsenic(III) with cerium(IV), using osmium tetroxide as catalyst and Disulphine Blue V as indicator. A survey has been made of the applicability of this method to various pyrolusite ores containing less than 0.2% phosphorus. Aluminium(III), copper(II), iron(III), manganese(II), and molybdenum(VI) do not interfere. Up to 30% phosphorus(V) causes no interference.     

Determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples by gas chromatography of their 2,3-dimercaptopropanol (bal) complexes

Procedures are described for the determination of arsenite, arsenate and monomethylarsonic acid in aqueous samples. The arsenicals (after reduction of arsenic to the tervalent state) readily react with 2,3-dimercaptopropanol (BAL) to yield their BAL complexes. The products are extracted with benzene and introduced into a gas Chromatograph equipped with a flame-photometric detector for sulphur. One aliquot of sample is treated with stannous chloride solution and potassium iodide solution to reduce arsenate and monomethylarsonic acid, then BAL is added and the complexes are extracted with benzene. The extract is analysed for total inorganic As plus monomethylarsonic acid. Magnesia mixture and phosphate solution are added to another aliquot to remove arsenate by co-precipitation with magnesium ammonium phosphate. The precipitate is filtered off and arsenite determined in the filtrate. The detection limits are 0.02 ng of As for arsenate and arsenite and 0.04 ng of As for monomethylarsonic acid.     

溶剂热法合成纯单斜和四方晶相氧化锆中的溶剂效应

在以水或甲醇为溶剂, 通过溶剂热反应合成纯单斜相或四方相氧化锆的前期工作基础上, 利用X射线衍射手段研究了硝酸氧锆(ZrO(NO3)2·2H2O)和尿素的溶剂热反应产物——水合ZrO2的物相结构在不同反应温度、反应时间及后处理温度等条件下的变化过程, 提出了不同晶相氧化锆的形成、转变以及稳定的可能机理. 不论在水还是甲醇溶液中, 最初水解得到的水合ZrO2沉淀即晶相氧化锆前体都具有四方对称性结构. 在水热反应条件下, 氧化锆沉淀物发生Ostwald熟化(溶解-沉淀)过程, 四方对称性结构转变为热力学稳定的单斜对称性结构. 而在甲醇热反应条件下, 氧化锆沉淀物不溶于甲醇, 从而Ostwald熟化过程被抑制, 使得四方对称性结构得以保持; 同时, 尿素与水合锆沉淀物反应脱除所含的结晶水, 形成更刚性的四方对称性结构, 这样使得高温热处理(400 ℃)只能促进其晶化过程, 但不改变其对称性. 因而, 不同溶剂对氧化锆沉淀物溶解性的差异以及造成的氧化锆沉淀物与尿素反应性能的差异可能是溶剂热反应合成单一晶相氧化锆的关键因素.     

Effect of replacing a hydroxyl group with a methyl group on arsenic (V) species adsorption on goethite (alpha-FeOOH)

Arsenate and methylated arsenicals, such as dimethylarsinate (DMA) and monomethylarsonate (MMA), are being found with increasing frequency in natural water systems. The mobility and bioavailability of these arsenic species in the environment are strongly influenced by their interactions with mineral surface, especially iron and aluminum oxides. Goethite (alpha-FeOOH), one of the most abundant ferric (hydr)oxides in natural systems, has a high retention capacity for arsenic species. Unfortunately, the sorption mechanism for the species is not completely understood, which limits our ability to model their behavior in natural systems. The purpose of this study is to investigate the effect of replacing a hydroxyl group with a methyl group on the adsorption behaviors of arsenic (V) species using adsorption edges, the influence of the background electrolyte on arsenic adsorption, and their effect on the zeta potential of goethite. The affinity of the three species to the goethite surface decreases in the order of AsO4=MMA>DMA. The uptake of DMA and MMA is independent of the concentration of background electrolyte, indicating that both species form inner-sphere complexes on the goethite surface and the most charge of adsorbed DMA and MMA locates at the surface plane. Arsenate uptake increases with increasing concentrations of background electrolyte at pH above 4, possibly due to that the charge of adsorbed arsenate is distributed between the surface plane and another electrostatic plane. DMA and lower concentrations of MMA have small effect on the zeta potential, whereas the zeta potential of goethite decreases in the presence of arsenate. The small effect on zeta potential of DMA or MMA adsorption suggests that the sorption sites for the anions is not important in controlling the surface charge. This observation is inconsistent with most adsorption models that postulate a singly coordinated hydroxyls contributing to both the adsorption and the surface charge, but supports the thesis that the charge on the goethite surface comes primarily from protonation of the triply bound oxygen atoms on the surface.     

氢化物发生电加热石英管原子吸收法测定包头铁矿中的砷、锑、铋

研究了氢化物发生原子吸收法测定包头矿中痕量砷、锑、铋的分析方法,试验确立了反应条件,建立了以KI、抗坏血酸、硫脲为还原体系,消除试样中共存元素的干扰,利用KMnO4消除锑对砷的干扰.砷、锑、铋的检出限可分别达到:0.15,0.28,0.15 ng/mL.方法已用于包头矿分析.     

Methylation of arsenic by anaerobic microbial consortia isolated from lake sediment

Anaerobic enrichment cultures, isolated from arsenic–contaminated lake sediment in the Canadian sub–arctic and grown in five selective media, methylated arsenate/arsenite to produce mono?, di? and tri–methyl arsenicals. The extent of methylation and methylarsenic species produced varied with the type of enrichment. Iron–reducing, manganese–reducing, sulfate–reducing and broad–spectrum anaerobic heterotrophic mixed cultures all produced methylarsenicals. Sulfate–reducing cultures produced higher concentrations of methylarsenicals (especially trimethyl species) than iron- or maganese–reducers. There is evidence that several of the methylarsenicals, which were hydride–reactive at pH 6, were methylarsenic(III) thiols. The organoarsenicals produced by enrichment cultures were the same as those detected in the porewater of the lake sediments used to initiate the enrichment cultures. Overall, this study demonstrates that microbes from anaerobic lake sediments can methylate (and demethylate) arsenic, a capability shared by manganese?, iron?, and sulfate–reducing microbial consortia.     

重铬酸钾滴定法测定废杂铜中的铁含量

研究了废杂铜中铁含量的测定方法.试料采用盐酸、硝酸、高氯酸溶解,加入过量氨水生成氢氧化铁沉淀与铜、铬等干扰元素分离,沉淀用热盐酸溶解后,用氯化亚锡还原至溶液呈浅黄色,重铬酸钾滴定法测定铁含量.探讨了溶样方式、氯化铵用量、氨水过量的体积、硫磷混酸用量对测定结果的影响.对4个废杂铜样品中的铁含量进行测定,测定结果的相对标准...     

The co-precipitation of manganese by iron(III) hydroxide

Radioactive manganese and iron were used to study the precipitation of iron(III) and managanese hydroxides at differentpH values from their pure solutions as well as in the presence of each other. It was noticed that there was always some entrainment of mangenese by iron(III) hydroxide even at lowpH values at which the iron itself was incompletely precipitated. The amount of manganese entrained at various concentrations of manganese and iron at the intermediatepH values from 3 to 7 were determined. There is a criticalpH value (i.e. between 4.5 and 4.7) at which there is a change in the course of entrainment from adsorption process to the incorporation phenomena. The effect of aging of the precipitate in its mother liquor to reduce the entrainment was also investigated.     

In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions

Adsorption methods have been developed for the removal of arsenic from solution motivated by the adverse health effects of this naturally occurring element. Iron exchanged natural zeolites are promising materials for this application. In this study we introduced iron species into a clinoptilolite-rich zeolitic tuff by the liquid exchange method using different organic and inorganic iron salts after pretreatment with NaCl and quantified the iron content in all trials by XRF spectroscopy. The materials were characterized by XRD, FTIR, FTIR-DR, UV-vis, cyclic voltammetry, ESR and M?ssbauer spectroscopies before and after adsorption of arsenite and arsenate. The reached iron load in the sample T+Fe was %Fe(2)O(3)-2.462, n(Fe)/n(Al)=0.19, n(Si)/n(Fe)=30.9 using FeCl(3), whereby the iron leachability was 0.1-0.2%. The introduced iron corresponded to four coordinated species with tetrahedral geometry, primarily low spin ferric iron adsorbing almost 12 mug g(-1) arsenite (99% removal) from a 360 mug(As(III)) L(-1) and 6 mug g(-1) arsenate from a 230 mug(As(V)) L(-1). Adsorption of arsenite and arsenate reached practically a plateau at n(Fe)/n(Si)=0.1 in the series of exchanged tuffs. The oxidation of arsenite to arsenate in the solution in contact with iron modified tuff during adsorption was observed by speciation. The reduction of ferric iron to ferrous iron could be detected in the electrochemical system comprising an iron-clinoptilolite impregnated electrode and was not observed in the dried tuff after adsorption.     

Ion-chromatographic screening method for monitoring arsenate and other anionic pollutants in ground waters of Northern Italy

A novel, rapid ion-chromatographic method for screening anionic pollutants in ground water, based on both conductivity and postcolumn spectrophotometric detection, has been developed. A relatively rapid separation of more than ten inorganic and polarizable anions was achieved by coupling an high capacity, hydroxide selective anion-exchange columns (Dionex IonPac AS16) supplied with an electrolytic eluent generator operating in gradient mode. The good control of the selectivity allowed the determination of polarizable anions including arsenate, thiocyanate, thiosulfate and perchlorate without interference from major components present at levels greater than 100 mg l⁻¹. This method was applied to the determination of arsenate in ground water samples collected in industrial and agricultural zones of Lombardia (Northern Italy). No traces of arsenate were detected in any sample, but added arsenate cannot be revealed by chromatographic analyses. This fact can be attributed to different causes, from reduction to the more reduced arsenic form to precipitation or dissolution in organic or inorganic based colloids. Oxidation with hydrogen peroxide seems to be useful for a partial recovery of added arsenate, but a stronger oxidation method, compatible with chromatographic separation, must be studied.     

Determination of dissolved arsenic in waters at μg l−1 levels by precipitation and energy-dispersive x-ray fluorescence spectrometry

Arsenic is precipitated as magnesium ammonium arsenate with magnesium ammonium phosphate as carrier. The precipitate is collected on a glass-fibre filter and arsenic is measured by energy-dispersive x-ray fluorescence spectrometry with a silver secondary target. With 200-ml water samples and 100-s counting times, the limit of detection is 0.7 μg As l^?1. The method is applicable to all types of natural water including sea waters.     

原子荧光光谱法测定固体废弃物——氧化皮中的砷

建立了固体废弃物——氧化皮中砷的测定方法。氧化皮粉末样品经盐酸溶解,在溶液中添加硫脲和抗坏血酸预还原砷,以盐酸(2+98)为载流,硼氢化钠(10g/L)和氢氧化钾(5g/L)混合溶液为还原剂,砷与硼氢化钠、盐酸反应生成砷化氢,砷化氢利用氩气导入石英炉原子化器中原子化,以空心阴极灯为激发光源,测量砷产生的荧光强度。测试氧化皮中砷含量的相对标准偏差为不大于4.8%,检出限为0.12μg/L,回收率为97%～103%,结果准确度较好。方法具有试剂消耗少、快速、检出限低的优点。