Arsenic Solution Research Articles

Redox reaction of aqueous selenite with As-rich pyrite from Jiguanshan ore mine (China): Reaction products and pathway

The interaction of an As-rich natural pyrite (FeS2.08As0.043) with aqueous Se(IV) was investigated as a function of pH, ferrous iron concentration, and reaction time. Arsenic is often the most abundant minor constituent of natural pyrite, and is believed to substitute for S in the pyrite structure. EXAFS measurements confirmed the presence of AsS dianion group, with arsenic in the same local configuration as in the arsenopyrite. Speciation studies indicated that Se(0) was the unique reduction product in the pH range 5.05–8.65 over a reaction period of >1month, while trace amounts of FeSeO3 might be formed at pH⩾6.10. At pH>6.07, the formation of Fe(III)-(oxyhydr)oxide is kinetically favored, and it consumed nearly all the aqueous iron, including the extra added Fe2+, thereby inhibiting the formation of the thermodynamically most stable product: FeSe2. After oxidation by Se(IV), the occurrence of surface S0, significant aqueous sulfur deficit, and excessive leaching of arsenic in solution, indicate the preferential release of As impurity via arsenopyrite oxidation. The data suggest that the polysulfide-elemental sulfur pathway, which prevails in acid-soluble metal sulfides, is an important pathway in the oxidation of As-rich pyrite, in addition to the thiosulfate pathway for acid-insoluble pyrite. Control experiments on As-free natural pyrite further support this mechanism. This study confirms the potential of reductive precipitation to attenuate the mobility of Se in the environment and demonstrates that minor elements commonly present in natural pyrite can play a significant role on its dissolution pathway.

Extraction of arsenic from arsenic-containing cobalt and nickel slag and preparation of arsenic-bearing compounds

The arsenic extraction from the arsenic-containing cobalt and nickel slag, which came from the purification process of zinc sulfate solution in a zinc smelting factory, was investigated. The alkaline leaching method was proposed according to the mode of occurrence of arsenic in the slag and its amphoteric characteristic. The leaching experiments were conducted in the alkaline aqueous medium, with bubbling of oxygen into the solution, and the optimal conditions for leaching arsenic were determined. The results showed that the extraction rate of arsenic was maximized at 99.10% under the optimal conditions of temperature 140 °C, NaOH concentration 150 g/L, oxygen partial pressure 0.5 MPa, and a liquid-to-solid ratio 5:1. Based on the solubilities of As2O5, ZnO and PbO in NaOH solution at 25 °C, a method for the separation of As in the form of sodium arsenate salt from the arsenic-rich leachate via cooling crystallization was established, and the reaction medium could be fully recycled. The crystallization rate was confirmed to reach 88.9% (calculated on the basis of Na3AsO4) upon a direct cooling of the hot leachate down to room temperature. On the basis of redox potentials, the sodium arsenate solution could be further reduced by sulfur dioxide (SO2) gas to arsenite, at a reduction yield of 92% under the suitable conditions. Arsenic trioxide with regular octahedron shape could be prepared successfully from the reduced solution, and further recycled to the purification process to purify the zinc sulfate solution. Also, sodium arsenite solution obtained after the reduction of arsenate could be directly used to purify the zinc sulfate solution. Therefore, the technical scheme of alkaline leaching with pressured oxygen, cooling crystallization, arsenate reduction by SO2 gas, and arsenic trioxide preparation, provides an attractive approach to realize the resource utilization of arsenic-containing cobalt and nickel slag.

Water‐soluble polymer and photocatalysis for arsenic removal

ABSTRACTIn this study, the photocatalytic oxidation of hazardous arsenite (As(III)) to arsenate (As(V)) and the sequential removal of arsenate from aqueous solution by liquid‐phase polymer‐based retention (LPR) were investigated. The photocatalytic oxidation of arsenite was performed using TiO2 (P25 Degussa, Germany) under UV‐A light. The optimal photocatalytic conditions to oxidize 10 mg L−1 of arsenite solution were achieved using a 0.5 g L−1 of catalyst at a pH value of 2. The As(III) oxidation reached 100% after 30 min of illumination with UV‐A light. A water‐soluble polymer containing quaternary ammonium groups, poly(3‐acrylamidopropyl)trimethylammonium chloride (P(ClAPTA)), was used as an extracting reagent in the LPR process. To obtain the optimized conditions, the removal experiments were performed at various polymer : As(V) molar ratios using 10 mg L−1 of arsenate solutions. After the oxidation of As(III) to As(V), the removal of arsenate by P(ClAPTA) was obtained in a 99% yield using a 20 : 1 polymer : As(V) molar ratio at a pH value of 9. The results demonstrate that the combination of these methods is highly useful for potential applications related to the treatment of wastewater contaminated with As(III). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40871.

Behaviour of kaolinite intercalation compounds with selected ammonium salts in aqueous chromate and arsenate solutions

The removal of aqueous Cr(VI) and As(V) oxyanions from waters by different materials with sorption properties is of environmental importance. In this study, a methoxy-kaolinite derivative was intercalated with benzyltrimethylammonium (B1), tetramethylammonium (TMA), and benzyldimethylhexadecylammonium (B5) chlorides and the interaction of the obtained materials with oxyanions was examined. The PXRD (powder X-ray diffraction) and IR (Infrared spectroscopy) analyses indicated a monolayer arrangement of the B1 and TMA molecules in the interlayer space of the mineral, while a tilted arrangement was noticed in the case of B5. A complete or partial deintercalation of introduced molecules was observed in the reactions with aqueous solutions of Cr(VI) and As(V). In all studied systems a significant improvement of the oxyanions removal was observed as compared to the pure kaolinite. The highest uptake of oxyanions was noticed in the reaction with B5-intercalated material. This was due to precipitation of organic alkyl salts. The formation of alkylchromate was confirmed using FTIR spectroscopy. The lower uptake of oxyanions by the B1- and TMA-intercalated materials was due to lack of new solid precipitation and resulted from the ion-exchange of chlorides initially compensating the ammonia nitrogen charge. The experimental sorption isotherms for all the reactions were best represented by Langmuir equation. A gradual, two-step removal process of Cr(VI) and As(V) by B1- and TMA-intercalated materials was observed. In turn, the precipitation of alkyl salts in reaction with B5-intercalated material resulted in a rapid immobilization of the oxyanions. The kinetic data modelled using pseudo-second order equation showed very good agreement with experimental results.

Multivariate spatial modeling of conditional dependence in microscale soil elemental composition data

The mobility and environmental impacts of toxic trace elements are regulated by their reactions with soils, which are complex heterogeneous mixtures of minerals and organic matter. We describe an experiment that maps the composition of elements on an individual soil sand grain using X-ray fluorescence microprobe analyses, after the grain is treated with arsenic solutions, resulting in multivariate spatial lattice maps of elemental abundance. To understand the behavior of arsenic in soils, it is important to disentangle the complex multivariate relationships among the elements in the sample. The abundance of most elements, including arsenic, correlates strongly with that of iron; but conditional on the amount of iron, some elements mitigate or potentiate the accumulation of arsenic. This problem motivates our work to define conditional correlation in spatial lattice models and give general conditions under which two components are conditionally uncorrelated given the rest. We describe how to enforce that two components are conditionally uncorrelated given a third in parametric models, which provides a basis for likelihood ratio tests for conditional correlation between arsenic and chromium given iron. We show how to apply our results to big datasets using the Whittle likelihood, and we demonstrate through simulation that tapering improves Whittle likelihood parameter estimates governing cross covariance.

Spectrometric characterisation of the solid complexes formed in the interaction of cysteine with As(III), Th(IV) and Zr(IV)

The aminoacids play important roles in biological systems as they participate in key chemical reactions for life, usually involving complexation with metal and metalloid {metal(loid)} ions. In this work, the solid complexes prepared after mixing arsenic(III), thorium(IV) and zirconium(IV) solutions with l-cysteine at pH 8.0 were spectrometrically characterised. The X-ray diffraction, together with secondary electron microscopy/energy dispersive-X ray spectrometry, allowed us to obtain information about the crystallinity, morphology and elemental composition of the solid metal(loid)–cysteine complexes. Photoluminescence of the prepared solid complexes was also evaluated by confocal microscopy. The functional groups responsible of the complexation processes were elucidated by Raman and infrared spectrometry. The participation of the thiol group from the l-cysteine molecule in the complexation of As(III) was effectively noted by Raman spectrometry. Nonetheless, Th(IV) and Zr(IV) were bound to l-cysteine through the oxygen atoms of the carboxylate group, according to the FT-IR results.

Evaluation of a new dielectric barrier discharge excitation source for the determination of arsenic with atomic emission spectrometry

A low power dielectric barrier discharge excitation source was developed to determine arsenic in a cost-effective manner. Arsenic in water was reduced to AsH₃ by hydride generation (HG), which was transported to the miniature dielectric barrier discharge (DBD) excitation source for excitation and optical detection at As 193.7 nm atomic line. The DBD source consists of a quartz tube, a tungsten rod electrode, and a copper coil electrode. The main operation parameters and the potential interferences affecting the determination were investigated. The detection limit for arsenic with the proposed DBD-AES was 4.8 μg L(-1) when the HG products were dried with concentrated H₂SO₄ before introducing to DBD. Repeatability, expressed as the relative standard deviation of the spectral peak height, was 2.8% (n=11) for 0.1 mg L(-1) arsenic solution. The proposed method was successfully applied to the determinations of certified reference material (GBW08605) and nature water samples.

REMOVAL OF As(III) AND As(V) FROM AQUEOUS SOLUTION USING MODIFIED SOLID WASTE VEGETABLE OIL INDUSTRY AS A NATURAL ADSORBENT

This paper presents the results of the removal of arsenite and arsenate ions from an aqueous solution using Fenton modified solid waste vegetable oil industry (SWVOI). Several factors (such as pH, contact time and Fe2+/H2O2 ratio, initial arsenic ion concentration and adsorbent concentration) that affect the arsenic ion adsorption on the SWVOI adsorbent material were investigated. The sorption characteristics of the adsorbent material before modification were also studied and compared with those after sorbent modification. Additionally, the influence of experimental conditions on equilibrium Isotherms were observed. The equilibrium adsorption data were fitted to Langmuir and Freundlich adsorption models, and model parameters were evaluated. The adsorption capacity of the adsorbent and arsenic removal efficiency decreased with increasing pH values up to 7. Maximum removal of 84 for As(III) at pH 7 and 78 for As(V) at pH 4 were obtained from arsenical aqueous solutions of 150 μg L-1 using one gram of modified SWVOI.

Influence of humidity, temperature, and the addition of activated carbon on the preparation of cellulose acetate membranes and their ability to remove arsenic from water

ABSTRACTSeveral composite membranes have been prepared from cellulose triacetate (CTA) and activated carbon (AC) by solvent casting, varying temperature from 35 to 55°C and relative humidity (RH): 10–70%. Some conditions promoted AC particle agglomeration which is evidenced by SEM and IFME® program. In those membranes, where homogeneity is attained, a deep characterization has been carried out by DMA, MDSC, thermoporometry, solute transport, and AFM. When AC is added in films, Tg is lowered and the fraction of pores with bigger size is augmented. Molecular weight cut off calculated by solute transport, increases from 801.15 to 1194.29 kDa using 1% AC at RH 70% and T 35°C. Water flux is of 5.23 Lm−2 h−1 bar−1. Arsenic removal has been performed, achieving a 45% tested from a 500 ppb arsenic solution, where several factors such as electrical rejection, adsorption and exclusion, could contribute to the total membrane nanofiltration process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40134.

Tracer study of pore initiation in anodic alumina formed in phosphoric acid

Arsenic species are utilized as tracers in a study of pore initiation in anodic films that were formed at constant potentials on aluminium in phosphoric acid. The films were grown first in sodium arsenate solution and then in phosphoric acid, and examined using ion beam analysis and scanning and transmission electron microscopies. The analysis of the arsenic content of specimens indicates that the growth mechanisms of incipient and major pores involve mainly field-assisted dissolution and field-assisted flow of the alumina, respectively. The transition between incipient and major pore formation is suggested to be initiated by preferential growth of certain incipient pores, leading to a locally increased current density at the pore bases. The major pores subsequently develop by the flow oxide away from the pore bases, which is evident from the behaviour of the arsenic tracer. The results suggest that the flow is associated with the non-uniform distribution of ionic current and a relatively low volume of formed film material compared with the volume of oxidized aluminium.

Oxidation and adsorption of arsenic species by means of hybrid polymer containing manganese oxides

ABSTRACTThe aim of this work was a comprehensive study of the oxidative and sorptive properties of a hybrid polymer containing manganese oxide toward As(III) and As(V). A poly(styrene‐divinylbenzene) copolymer containing oxidative functional groups (SO2NBrNa) was used as the supporting material for MnO2. The inorganic component was deposited as a result of the oxidation reaction of Mn(II) with oxidative groups of the host polymer. The surface of the polymer matrix was evenly covered with a thin layer of manganese oxide. The obtained product (R/S/Mn) exhibited high oxidative capacity over a wide pH range (2–12); however, under acidic and neutral conditions, the reaction ran significantly faster. The studied material shows some sorption properties but its sorption capacity is much lower than its oxidation capacity. The treatment, in a column regime, of the arsenic solution containing 1 mg As(III) dm−3 and coexisting ions in concentrations similar to those in natural waters, confirmed the excellent oxidation capacity of the obtained product. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39489.

Removal of fluoride and arsenate from aqueous solution by hydrocalumite via precipitation and anion exchange

Hydrocalumite was used to treat fluoride and arsenate solutions with a wide range of initial concentrations. A marked decrease in solution fluoride and arsenate to below 0.05 and 0.005mmol/L was observed when their initial concentrations were not higher than 30 and 5mmol/L respectively. However, a sharp increase occurred to equilibrium F and As concentrations over these critical initial concentrations. The mechanisms for fluoride and arsenate removal were investigated by comparison between measured chemical compositions of solution samples and their PHREEQC simulation along with XRD, SEM and EDX analyses for solid samples. The solution defluoridation was primarily a result of hydrocalumite dissolution and subsequent precipitation of fluorite and fluoride-bearing bayerite, although the anion exchange between fluoride in solution and chloride in interlayers of hydrocalumite functioned as well provided that not all hydrocalumite added to solution was dissolved. In contrast, the principal approach for arsenate removal was through the formation of johnbaumite and other arsenic-bearing minerals or solid–solution series. Solution pH value has little effect on defluoridation and dearsenication by hydrocalumite due to its pH buffering effect, while the coexistence of competitive anions and the variation of reaction temperature affected the fluoride and arsenate removal significantly. The maximum uptake capacities of hydrocalumite for fluoride and arsenate are 719.1 and 361.7mg/g respectively, much better than other types of layered double hydroxides. It is promising for treatment of not only naturally occurring poor-quality groundwater with not very high fluoride and arsenic concentrations but also industrial wastewater enriched highly in fluoride or arsenic.

Elimination of arsenic contamination from water using chemically modified wheat straw

Presence of arsenic in natural water resource as a common contaminant has always been a great concern for the scientists. The objective of this study was to explore the possibility of wheat straw modified with sodium bicarbonate (NaHCO3) for removing arsenate from aqueous solution. Adsorption process was accomplished in a laboratory-scale batch with emphasis on the effect of various parameters such as pH, contact time, arsenic concentration, and adsorbent dosage on the adsorption efficiency. In order to understand the adsorption process, sorption kinetics and equilibrium isotherms were also determined. It was found that adsorption of the arsenic is influenced by several parameters such as arsenic initial concentration, adsorbent dosage, and solution pH. Maximum adsorption efficiency was achieved at a pH of 7. The equilibrium adsorbed amount also increased with the initial concentration of the metal ions, as expected. NaHCO3 was used to modify wheat straw and scanning electron microscopy images showed that all of the adsorbents have been affected and modified by NaHCO3 solution. Among the models tested, both the Langmuir and Freundlich models represented the experimental data well. According to the Dubinin–Radushkevich isotherm model, mean free energy of adsorption (15.2 kJ mol-1) indicates that adsorption of arsenic by wheat straw might follow a chemisorption mechanism. It was also found that adsorption of arsenic by wheat straw followed pseudo-second-order kinetics. It is concluded that adsorption using modified wheat straw is an efficient and reliable method for arsenate removal from liquid solutions.

Adsorption of Arsenic on MgAl Layered Double Hydroxide

Groundwater in the Eastern Croatia, as well in the South-eastern Hungary, contains relatively high concentrations of arsenic that can cause chronic toxicity to humans. Therefore, the aim to find an effective composite adsorbent that can be applied for arsenic water remediation by introducing it in the groundwater treatment is very important. The presented results were obtained using layered double hydroxide (LDH) as a sorbing system. MgAl LDH samples with a Mg:Al molar ratio of 2:1 were synthesized. Adsorption of arsenic anions from groundwater samples from Eastern Croatia, as well as adsorption of model aquatic arsenic sample solutions, on MgAl layered double hydroxide was investigated. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for determination of arsenic concentration after adsorption. It was shown that in both cases the adsorption process could be interpreted in terms of Kroeker adsorption isotherm regardless to the presence of other ions in the groundwater. Additionally, the influence of phosphate concentration on adsorption of model arsenic samples was examined and it was shown that (at least in examined range of arsenic and phosphate concentration) there is no significant influence of phosphate on adsorption of arsenic.

Indispensable or toxic? The phosphate versus arsenate debate

Indispensable or toxic? The phosphate versus arsenate debate

Effect of foulants on arsenic rejection via polyacrylonitrile ultrafiltration (UF) membrane

Arsenic rejection via modified polyacrylonitrile ultrafiltration (UF) membrane was found to be very high, however, the presence of commonly found foulants in arsenic solution affected membrane performance. The effect of commonly found foulants, such as ovalbumin, humic acid and egg white on arsenic rejection were studied. Experiments indicated that the As(V) rejection was affected by the total quantity of proteins and not the variety of proteins present in a solution. As(V) rejection was found to decrease with increasing proteins while fouling was found to increase from 25% for 0.1mg/ml to 33% for 0.5mg/ml egg white. The As(V) rejection was found to decrease with increasing concentration of humic acid for PAN membranes. Fouling studies showed that humic acid was a lesser foulant in comparison to egg white. However a combination of the two foulants led to a decrease in the overall fouling. pH was also found to be a very important factor for egg white dissolution and As(V) rejection.

Identification of Arsenic in the Water Using Energy Dispersive X-Ray Diffraction

The occurrence of arsenic in natural water has received significant attention during recent years. The arsenic plays an important role for its behavior and toxicity in the aqueous system. Arsenic is a toxic pollutant in water with serious health effects upon long-term intake of even low concentrations through drinking water consumption population. By means of the energy-dispersive X-ray diffraction (EDXRD) technique, confected different concentrations of sodium arsenate solution and reservoir water of Tuoketuo county in the Inner Mongolia, were analyzed. The result shows that arsenic is present within reservoir water of Tuoketuo county. But, fluorescence peak photons of arsenic in the solution are not in proportion to the concentration. So, it is difficulty to quantitatively decide the concentration of the arsenic in the water.

Microbial Reduction of Arsenic-Doped Schwertmannite by Geobacter sulfurreducens

The fate of As(V) during microbial reduction by Geobacter sulfurreducens of Fe(III) in synthetic arsenic-bearing schwertmannites has been investigated. During incubation at pH7, the rate of biological Fe(III) reduction increased with increasing initial arsenic concentration. From schwertmannites with a relatively low arsenic content (<0.3 wt %), only magnetite was formed as a result of dissimilatory iron reduction. However, bioreduction of schwertmannites with higher initial arsenic concentrations (>0.79 wt %) resulted in the formation of goethite. At no stage during the bioreduction process did the concentration of arsenic in solution exceed 120 μgL(1), even for a schwertmannite with an initial arsenic content of 4.13 wt %. This suggests that the majority of the arsenic is retained in the biominerals or by sorption at the surfaces of newly formed nanoparticles. Subtle differences in the As K-edge XANES spectra obtained from biotransformation products are clearly related to the initial arsenic content of the schwertmannite starting materials. For products obtained from schwertmannites with higher initial As concentrations, one dominant population of As(V) species bonded to only two Fe atoms was evident. By contrast, schwertmannites with relatively low arsenic concentrations gave biotransformation products in which two distinctly different populations of As(V) persisted. The first is the dominant population described above, the second is a minority population characterized by As(V) bonded to four Fe atoms. Both XAS and XMCD evidence suggest that the latter form of arsenic is that taken into the tetrahedral sites of the magnetite. We conclude that the majority population of As(V) is sorbed to the surface of the biotransformation products, whereas the minority population comprises As(V) incorporated into the tetrahedral sites of the biomagnetite. This suggests that microbial reduction of highly bioavailable As(V)-bearing Fe(III) mineral does not necessarily result in the mobilization of the arsenic.

Conversion of agricultural residues into activated carbons for water purification: Application to arsenate removal

The conversion of two agricultural wastes, sugar beet pulp and peanut hulls, into sustainable activated carbons is presented and their potential application for the treatment of arsenate solution is investigated. A direct and physical activation is selected as well as a simple chemical treatment of the adsorbents. The material properties, such as BET surface areas, porous volumes, elemental analysis, ash contents and pHPZC, of these alternative carbonaceous porous materials are determined and compared with a commercial granular activated carbon. An adsorption study based on experimental kinetic and equilibrium data is conducted in a batch reactor and completed by the use of different models (intraparticle diffusion, pseudo–second-order, Langmuir and Freundlich) and by isotherms carried out in natural waters. It is thus demonstrated that sugar beet pulp and peanut hulls are good precursors to obtain activated carbons for arsenate removal.

Electrodeposition and stripping voltammetry of arsenic(III) and arsenic(V) on a carbon black–polyethylene composite electrode in the presence of iron ions

In this work, a new sensor is proposed for the stripping voltammetric determination (anodic stripping voltammetry—ASV) of total arsenic(V) or arsenic(III). The sensor is based on an Fe-modified carbon composite electrode containing 30 % carbon black–high-pressure polyethylene (CB/PE). The modification with iron is achieved by the addition of Fe(III) or Fe(II) ions to the sample solution and co-electrodeposition of iron and arsenic on the CB/PE electrode. In anodic stripping voltammetry, two peaks are observed: an Fe peak at −0.45 or −0.29 V and a peak at 0.12 ± 0.07 V which depends on the arsenic concentration and corresponds to the As(0) → As(III) oxidation, as is the case with other solid electrodes. The optimum conditions proposed for ASV determination of As(V) and As(III) in solutions in the presence of dissolved oxygen are the following: the background electrolyte is 0.005 M HCl containing 0.5–1 mg/ L Fe(III) for As(V) and containing 1.0–1.5 mg/ L Fe(III) for As(III), respectively; Edep = −2.3 V; rest period at −0.10 V for 3–5 s before the potential sweep from −0.2 to +0.4 V; scan rate is 120 mV/ s. The detection limit (LOD, t = 120 s) for As(III) and As(V) is 0.16 and 0.8 μg/ L, respectively. Various hypotheses on the effect of Fe ions and atoms on the electrodeposition and dissolution of arsenic are considered. The new method of determination of As(III) and As(V) differs from known analogues by its simplicity, low cost, and easy accessibility of the electrode material. It allows the voltammetric determination of total arsenic after chemical reduction of all its forms to As(III) or after their oxidation to As(V).