Co-precipitation Of Arsenic Research Articles

Removal of sulphate and arsenic from wastewater using calcium sulfoaluminate (ye’elimite)

Chemical precipitation is one of the most widely known methods for treatment of industrial wastewaters with high sulphate content, where sulphate can be precipitated as practically insoluble ettringite (Ca6Al2(SO4)3(OH)12·26H2O). This treatment method is also widely recognised for solidifying hazardous components and toxic elements e.g. arsenic in wastewater. In the ettringite precipitation process, lime and aluminium salts are typically used as starting materials, in stoichiometric amounts to form ettringite from the sulphate-containing water, leading to a pH rise to ∼11.5 and ettringite precipitation. In the current study, for the first time, ye’elimite mineral (Ca4Al6O12SO4), also known as calcium sulfoaluminate (CSA) in cements, is used in order to investigate its suitability to form ettringite precipitate from sulphate and arsenic containing synthetic wastewater and industrial wastewater solutions. The dissolution of ye’elimite prior to dosing, optimal precipitation pH, and arsenic co-precipitation were studied. The effluent and precipitates were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM-EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-OES). The results showed that high percentage of sulphate removal (98% in the synthetic wastewater and 87% in the industrial wastewater) can be achieved using ye’elimite as the aluminium source in ettringite precipitation. Additionally, up to 95% arsenic removal was achieved in arsenic co-precipitation experiments from the synthetic wastewater. The current developed technology can be used as a novel ecological and cost-effective approach for removal of sulphate and toxic elements from wastewater.

Procedure for the Precipitation of Iron, Chromium, Molybdenum, and Tungsten in the Determination of Arsenic and Antimony in Alloy Steels

A possibility of the separation of trace amounts of arsenic and antimony and macroquantities iron, chromium, molybdenum, and tungsten by the precipitation of the latter was investigated; regularities of the coprecipitation of arsenic and antimony are studied. The coprecipitation of arsenic and antimony in the precipitation of iron, chromium, molybdenum, and tungsten can be inhibited by introducing a certain amount of hydrofluoric acid. This decreases the specific surface and porosity of the precipitates and inhibits the coprecipitation process. A method is developed for the simultaneous determination of arsenic and antimony in alloy steels by inductively coupled plasma atomic emission spectrometry with preliminary separation of the main components of iron, chromium, molybdenum, and tungsten.

Mechanisms of arsenate removal and membrane fouling in ferric based coprecipitation–low pressure membrane filtration systems

Ferric based coprecipitation–low pressure membrane filtration is a promising arsenic (As) removal method, however, membrane fouling mechanisms are not fully understood. In this study we investigated the effect of feed water composition and membrane pore size on arsenate [As(V)] removal and membrane fouling. We observed that As removal efficiency was independent of the membrane pore size because the size of the Fe(III) particles was larger than the pore size of the membranes, attributed to a high calcium concentration in the feed water. Arsenic coprecipitation with Fe(III) (oxyhydr)oxides rapidly reached equilibrium before membrane filtration, within 1 min. Therefore, As removal efficiency was not improved by increasing residence time before membrane filtration. The removal of As(V) was strongly dependent on feed water composition. A higher Fe(III) dose was required to reduce As(V) to sub-µg/L levels for feed water containing higher concentration of oxyanions such as phosphate and silicate, and lower concentration of cations such as calcium. Cake-layer formation was observed to be the predominant membrane fouling mechanism.

A general strategy for the voltammetric trace determination of tellurium in geochemical and environmental matrices after arsenic coprecipitation and critical assessment of digestion schemes

Environmental contextAmong chemical elements classified as elements of strategic importance, tellurium is rapidly becoming an emergent contaminant. There is, however, no accurate and sensitive method for measuring tellurium concentrations in environmental and geological samples (e.g., soils, sediments), and thus it is not possible to determine whether an ecosystem is being polluted by human activities. This study provides a reliable answer to this problem. AbstractA general method is proposed for the determination of tellurium in environmental and geochemical samples. Samples may be digested by any technique (acid or fusion digestion). The tellurium in the resulting solution is reductively coprecipitated with added arsenite by hypophosphorous acid, and the precipitate is redissolved and analysed by catalytic anodic stripping voltammetry. Several sample digestion techniques (acid and fusion digestions) are critically assessed. The method is applied to ore certified reference materials, with tellurium concentrations spanning three orders of magnitude, and sediment certified reference materials (ocean, lake and estuarine). An overall limit of detection (LOD) of 5 ppb is achieved. Acid digestion by H2SO4 and by HClO4 or sintering with Na2O2 in glassy carbon crucibles are shown to be the most adequate sample digestion techniques.

Effectiveness of Arsenic Co-Precipitation with Fe-Al Hydroxides for Treatment of Contaminated Water

ABSTRACT Wastewater treatment is a challenging problem faced by the mining industry, especially when mine effluents include acid mine drainage with elevated arsenic levels. Iron (hydr)oxides are known to be effective in removal of As from wastewater, and although the resulting compounds are relatively unstable, the presence of structural Al enhances their stability, particularly under reducing conditions. The purpose of this study was to assess the effectiveness of Al-Fe (hydr)oxide co-precipitates for the removal of As from wastewater and to assess the chemical stability of the products. Different Al-Fe (hydr)oxides were synthesized at room temperature from ferrous and aluminum salts using three different Fe:Al molar ratios (1:0.0, 1:0.3, and 1:0.7) and aged for 90 days (sulfate experiments) or 120 days (chloride experiments) in the presence of arsenic. At the end of the aging periods, the precipitated sludges were dried and characterized in order to evaluate their stability and therefore potential As mobility. All treatments were effective in reducing As levels in the water to below 10 µg L-1, but the presence of Al impaired the effectiveness of the treatment. Aluminum decreased the chemical stability of the precipitated sludge and hence its ability to retain As under natural environmental conditions.

Arsenic Removal from Groundwater by Solar Driven Inline-Electrolytic Induced Co-Precipitation and Filtration-A Long Term Field Test Conducted in West Bengal.

Arsenic contamination in drinking water resources is of major concern in the Ganga delta plains of West Bengal in India and Bangladesh. Here, several laboratory and field studies on arsenic removal from drinking water resources were conducted in the past and the application of strong-oxidant-induced co-precipitation of arsenic on iron hydroxides is still considered as the most promising mechanism. This paper suggests an autonomous, solar driven arsenic removal setting and presents the findings of a long term field test conducted in West Bengal. The system applies an inline-electrolytic cell for in situ chlorine production using the natural chloride content of the water and by that substituting the external dosing of strong oxidants. Co-precipitation of As(V) occurs on freshly formed iron hydroxide, which is removed by Manganese Greensand Plus® filtration. The test was conducted for ten months under changing source water conditions considering arsenic (187 ± 45 µg/L), iron (5.5 ± 0.8 mg/L), manganese (1.5 ± 0.4 mg/L), phosphate (2.4 ± 1.3 mg/L) and ammonium (1.4 ± 0.5 mg/L) concentrations. Depending on the system setting removal rates of 94% for arsenic (10 ± 4 µg/L), >99% for iron (0.03 ± 0.03 mg/L), 96% for manganese (0.06 ± 0.05 mg/L), 72% for phosphate (0.7 ± 0.3 mg/L) and 84% for ammonium (0.18 ± 0.12 mg/L) were achieved—without the addition of any chemicals/adsorbents. Loading densities of arsenic on iron hydroxides averaged to 31 µgAs/mgFe. As the test was performed under field conditions and the here proposed removal mechanisms work fully autonomously, it poses a technically feasible treatment alternative, especially for rural areas.

Removal of Arsenic from Aqueous Solution by <i>Aeromonas</i> <i>hydrophila</i>

Arsenic contamination is considered as a global environmental problem. This metalloid is known to be carcinogenic in some forms, and is mostly found in the environment as arsenate As (V) and arsenite As (III). Several chemical methods have been established for decontamination of arsenic from ground water including biological treatments. In the present work, the effect of the anaerobic bioreduction of soluble Fe (III) by the strain Aeromonashydrophila on arsenic immobilization has been investigated. The tolerance of this strain to arsenic concentration and the effect of the iron concentration in arsenic immobilization have been studied. The release of ferrous ion indicated the bioreduction of iron and promoted the subsequent arsenic co-precipitation, leading to the formation of various iron-bearing minerals. This precipitate has been observed and identified by Scanning Electron Microscopy and X-ray diffraction analysis as Fe3(AsO4)2(H2O)8.

Treatment of Wastewater from New Copper Smelter RTB Bor

RTB Bor smelter and sulfuric acid plant modernization project includes reconstruction of an old wastewater treatment plant (WWTP). The task for a team from the Innovation Center of TMF was technical-technological solution for the reconstruction of WWTP with a new wastewater treatment process. Wastewater from the primary copper smelter is very acidic, with a high content of dissolved heavy metals and arsenic. Treatment of wastewater includes the neutralization of the acid, precipitation of the heavy metals in the form of hydroxides by using hydrated lime, and the arsenic co-precipitation with iron(III) hydroxide. Material and energy balances of the process are determined by simulating the wastewater treatment in Superpro Designer software package with thermodynamic parameters defined in HSC Chemistry program. The simulation results were confirmed by experimental tests at the pilot plant level. The designed process is applied in WWTP exploitation within the new copper smelter RTB Bor. Treatment of 8,7 m2/h of wastewater generates 7,2 m2/h of treated wastewater and 10,3 t/h of wastewater treatment (WWT) sludge. The WWT sludge is characterized as hazardous waste requiring treatment prior to disposal. A proposed treatment for WWT sludge is solidification/stabilization (S/S) using a mixture of fly ash and hydrated lime. Results of laboratory scale tests, which included standard leaching tests EN 12457 and TCLP, as well as the compressive strength testing of obtained solidificates, shows that the S/S treatment leads to stabilization of more than 99% of the heavy metals and more than 90% of arsenic. The treated sludge has the characteristics of non-hazardous waste and is suitable for disposal.

Comparison of arsenic co-precipitation and adsorption by iron minerals and the mechanism of arsenic natural attenuation in a mine stream

Mine stream precipitate collected from Ilkwang mine, Korea, contained high concentrations of arsenic (As), while water collected from the same site had negligible As concentrations, indicating natural attenuation of As occurred in the mine stream. The mechanism of attenuation was explained by comparison of X-ray absorption near edge structure (XANES) of As(V) co-precipitated with or adsorbed to iron (Fe) minerals in mine precipitates. Arsenic in the mine precipitate was present as As(V) and schwertmannite was the main Fe mineral. Arsenic co-precipitation with schwertmannite was the major mechanism of As removal in the mine stream, followed by As adsorption by goethite and As co-precipitation with ferrihydrite. Schwertmannite and ferrihydrite were formed in acid mine drainage and As was incorporated in their structure during formation. Additionally, schwertmannite and ferrihydrite may transform to goethite with As adsorbed onto the goethite surface. Based on the results of batch experiments of As co-precipitation and adsorption, co-precipitation of As with ferrihydrite and schwertmannite was the most effective As sequestration mechanism in the removal of As(V) from acid mine drainage.

In situ treatment of arsenic contaminated groundwater by aquifer iron coating: Experimental study

In situ arsenic removal from groundwater by an aquifer iron coating method has great potential to be a cost effective and simple groundwater remediation technology, especially in rural and remote areas where groundwater is used as the main water source for drinking. The in situ arsenic removal technology was first optimized by simulating arsenic removal in various quartz sand columns under anoxic conditions. The effectiveness was then evaluated in an actual high-arsenic groundwater environment. The arsenic removal mechanism by the coated iron oxide/hydroxide was investigated under different conditions using scanning electron microscopy (SEM)/X-ray absorption spectroscopy, electron probe microanalysis, and Fourier transformation infrared spectroscopy.Aquifer iron coating method was developed via a 4-step alternating injection of oxidant, iron salt and oxygen-free water. A continuous injection of 5.0mmol/L FeSO4 and 2.5mmol/L NaClO for 96h can form a uniform goethite coating on the surface of quartz sand without causing clogging. At a flow rate of 7.2mL/min of the injection reagents, arsenic (as Na2HAsO4) and tracer fluorescein sodium to pass through the iron-coated quartz sand column were approximately at 126 and 7 column pore volumes, respectively. The retardation factor of arsenic was 23.0, and the adsorption capacity was 0.11mol As per mol Fe. In situ arsenic removal from groundwater in an aquifer was achieved by simultaneous injections of As(V) and Fe(II) reagents. Arsenic fixation resulted from a process of adsorption/co-precipitation with fine goethite particles by way of bidentate binuclear complexes. Therefore, the study results indicate that the high arsenic removal efficiency of the in situ aquifer iron coating technology likely resulted from the expanded specific surface area of the small goethite particles, which enhanced arsenic sorption capability and/or from co-precipitation of arsenic on the surface of goethite particles.

Arsenic Removal and Transformation by Pseudomonas sp. Strain GE-1-Induced Ferrihydrite: Co-precipitation Versus Adsorption

Hundreds of millions of people are at risk from drinking arsenic (As)-contaminated groundwater in the world, making As removal from aquatic systems of utmost importance. However, characteristics of As removal by bacteria-induced ferrihydrite and coupled with redox processes are still not clear. Two-line ferrihydrite was formed in the presence of aerobic Fe(II)-oxidizing bacterium, Pseudomonas sp. strain GE-1. Arsenic co-precipitation with and adsorption onto ferrihydrite induced by Pseudomonas sp. strain GE-1 and redox processes of As were investigated. Results demonstrated that co-precipitation performed better in As(V) removal than As(III) removal, while adsorption showed higher capacity for As(III) removal. X-ray absorption near-edge spectroscopy (XANES) indicated that As(III) oxidation occurred in solid phases during co-precipitation and adsorption. Detection of As species in solution showed that As(V) was reduced to As(III) during co-precipitation, although no As(V) reduction occurred during adsorption. Arsenic immobilization by Pseudomonas sp. strain GE-1-induced ferrihydrite in the presence of the strains may be applied as an alternative remediation strategy.

Anoxic, ethanolic, and cool – An improved method for thioarsenate preservation in iron-rich waters

Preservation of thioarsenates is challenging, especially in the presence of iron. Flash-freezing and cryo-storage, which was considered to be the best available technique, led to arsenic co-precipitation with iron upon thawing and transformation of thioarsenates to arsenite with further oxidation to arsenate. Even in the absence of iron, flash-freezing was found to be problematic when water samples were in disequilibrium. In arsenite solutions with excess sulfide increasing formation of thioarsenates was observed as an artifact upon storage. High ionic strengths were found to have a similar effect of pushing thioarsenate distribution towards equilibrium which renders it difficult to transfer a preservation method developed with synthetic thioarsenate solutions in the laboratory to any type of natural water chemistry. Addition of EDTA to complex excess iron also led to arsenite oxidation and artificial thioarsenate formation. An effective method that required minimal logistic effort was to use anoxic septum vials and store the samples at 4°C in 1% ethanol to reduce any remaining oxygen. This method preserved (thio)arsenic speciation in both synthetic and natural waters in the absence and presence of iron or excess sulfide up to one week. With the new method we were able to show that iron-rich mineral waters in Czech Republic had a much higher share of thioarsenates (up to 50%) than previously reported and that up to 26% trithioarsenate existed – a species which has not been described from iron-rich waters before.

Continuous circuit coprecipitation of arsenic(V) with ferric iron by lime neutralization: The effect of circuit staging, co-ions and equilibration pH on long-term arsenic retention

This article presents the results of an investigation on the impact of the continuous neutralization circuit and solution parameters on the stability of Fe(III)–As(V) coprecipitates produced from acidic sulfate solutions by lime neutralization. The work was undertaken to better understand the link between the process of arsenic removal via continuous circuit coprecipitation as practiced in industrial effluent treatment and the stability of arsenic in the resulting coprecipitates. In particular the work sought to establish the effects of circuit staging (1–3 stages, with and without recycling) and the presence of Ni2+ and Al3+ co-ions on coprecipitate stability. The latter was monitored during long-term laboratory aging (300–400days and in some cases for ~1500days) at various temperatures (4, 22, 40 and 70°C) under fixed (pH8) or drift pH oxic environment. Of the different circuit configurations the two-stage neutralization/coprecipitation circuit operating at pH=4 (stage 1) and pH=8 (stage 2) yielded the most stable coprecipitate in terms of arsenic retention. Recycling had no apparent effect on stability. It is proposed that stage-wise neutralization promotes the formation of ferric arsenate in addition to arsenate-bearing ferrihydrite resulting in enhanced arsenic retention. Furthermore arsenic retention was found to improve under pH drift aging conditions, where coprecipitates rapidly attained equilibrium values (<0.2mg/L As and pH~7.2 at 22°C). Coprecipitates aged under drift pH condition exhibited resistance to arsenic release upon pH elevation. Finally, arsenic release was found to be further suppressed in the case of coprecipitates produced in the presence of Ni2+ and Al3+.

Dynamic Microbial Community Associated with Iron–Arsenic Co-Precipitation Products from a Groundwater Storage System in Bangladesh

The prokaryotic community in Fe-As co-precipitation product from a groundwater storage tank in Bangladesh was investigated over a 5-year period to assess the diversity of the community and to infer biogeochemical mechanisms that may contribute to the formation and stabilisation of co-precipitation products and to Fe and As redox cycling. Partial 16S rRNA gene sequences from Bacteria and Archaea, functional markers (mcrA and dsrB) and iron-oxidising Gallionella-related 16S rRNA gene sequences were determined using denaturing gradient gel electrophoresis (DGGE). Additionally, a bacterial 16S rRNA gene library was also constructed from one representative sample. Biogeochemical characterization demonstrated that co-precipitation products consist of a mixture of inorganic minerals, mainly hydrous ferric oxides, intimately associated with organic matter of microbial origin that contribute to the chemical and physical stabilisation of a poorly ordered structure. DGGE analysis and polymerase chain reaction-cloning revealed that the diverse bacterial community structure in the co-precipitation product progressively stabilised with time resulting in a prevalence of methylotrophic Betaproteobacteria, while the archaeal community was less diverse and was dominated by members of the Euryarchaeota. Results show that Fe-As co-precipitation products provide a habitat characterised by anoxic/oxic niches that supports a phylogenetically and metabolically diverse group of prokaryotes involved in metal, sulphur and carbon cycling, supported by the presence of Gallionella-like iron-oxidizers, methanogens, methylotrophs, and sulphate reducers. However, no phylotypes known to be directly involved in As(V) respiration or As(III) oxidation were found.

Continuous circuit coprecipitation of arsenic(V) with ferric iron by lime neutralization: Process parameter effects on arsenic removal and precipitate quality

The coprecipitation of arsenic(V) with ferric iron was studied through the use of continuous circuit coprecipitation experiments that involved lime neutralization of acidic sulfate solutions (Fe/As molar ratio of 4) to pH 8. The influence of coprecipitation circuit design on arsenic removal was evaluated through one, two and three-stage experiments as well as the use of solids recycling in a two-stage circuit. The two-stage (operating respectively at pH 4 and 8) continuous circuit configuration produced the lowest residual arsenic concentration and the lowest specific surface area coprecipitate. Two-stage continuous experiments were also used to examine the influence of nickel and aluminum, co-ions that are common in industrial solutions. Nickel was not observed to significantly influence the residual dissolved arsenic under the conditions tested. Aluminum was found to be a suitable equimolar substitute for a portion of the ferric iron. X ray diffraction and Raman spectroscopic data indicated that the coprecipitates consisted of a mixture of gypsum, poorly crystalline ferric arsenate and (arsenic-bearing) ferrihydrite. Calculations based on the pH of point of zero charge (pH pzc) suggested that the content of ferric arsenate ranged from 24% to 57% and was influenced by the coprecipitation circuit design. The highest ferric arsenate content was observed with the two-stage coprecipitation circuit which also yielded the lowest residual arsenic concentration. The results indicated that subtle chemical differences induced in the coprecipitates by the process could be of significant influence to the geochemical stability of arsenic.

A performance assessment of arsenic-iron removal plants in the Manikganj District of Bangladesh

In Bangladesh, arsenic contamination of groundwater, microbial contamination of surface water and seasonally variable rainfall make reliable access to acceptable quality drinking water a challenge. Arsenic-iron removal plants (AIRPs) are a relatively inexpensive way of removing arsenic from groundwater for access to safer drinking water. This study evaluated the performance of 21 (of 105) AIRPs installed by a local non-governmental organization (Society for People's Action in Change and Equity) with financial assistance from the Australian High Commission, Dhaka, under the Direct Aid Program of the Australian Government. All AIRPs achieved the Bangladesh standard for arsenic in drinking water of 50 microg L(-1) and 17 achieved the World Health Organization guideline of 10 microg L(-1). The AIRPs removed 87% of influent arsenic, on average. After cleaning, poor arsenic and iron removal was observed for about 2 days due to inadequate residence time. Chemical processes that may influence AIRP performance are also discussed herein, including iron and arsenic oxidation, arsenic co-precipitation with iron, multiple iron additions, interference by organics, and iron crystallization. Effluent faecal coliform counts were generally low, though were slightly higher than influent counts. Overall, AIRPs were shown to possess considerable promise for use in areas with high natural iron where users are concerned about arsenic and/or iron in their drinking water.

Arsenic association and stability in long-term disposed arsenic residues

Long-term stability of arsenic residues is investigated by determining arsenic phases remaining in gold mining residues after two decades of impoundment. The residues, generated by arsenic coprecipitation with iron and lime, were disposed of in-lined sites for 9–16 years (pit C) and 16–23 years (pits A and B). Arsenic is present in the residues as As(V) species, predominantly in the form of amorphous iron arsenate (55–75% As total, pits A and B; 55–70% As total, pit C) and sorbed onto amorphous iron-oxyhydroxides (20–33% As total, pits A and B; 22–37% As total, pit C). The presence of minor Ca–arsenate phases (undefined composition) and Al–arsenate coprecipitates is also indicated. The passive enrichment of iron in pits A and B, and the relative low concentration of calcium, sulfur and arsenic if compared to those of pit C, suggest that a soluble Ca–arsenate phase (e.g. CaHAsO 4.H 2O), a fraction of gypsum and As(III) were dissolved along 16–23 years of residue disposal. The presence of As(V) only and excess iron demonstrates the importance of the oxidation state and high Fe/As ratio on long-term stability of arsenic residues.

Studies on the electrochemical decontamination of wastewater containing arsenic

The arsenic removal from aqueous solutions by electrocoagulation (EC) using mild steel electrodes was studied. Effect of electrolytes such as NaCl, NaNO 3 and Na 2SO 4 on anodic dissolution of iron and in turn the arsenic removal was deliberated. The arsenic removal was observed to be 98% in the presence of NaCl whereas it is around 75% in the presence of Na 2SO 4 and NaNO 3. The removal of arsenic by EC process was found to be almost similar irrespective of its oxidation state. Almost 95% of the total arsenic was removed within 5 min from its initial concentration of 10 mg L −1. The precipitates formed during EC were characterized using FT-IR, SEM-EDAX, XRD, XPS and magnetometer. The iron oxy-hydroxide precipitate formed during EC was identified as maghemite and lepidocrocite. The magnetic property, particle size and surface properties of the iron oxy-hydroxide precipitate were found to be influenced by arsenic adsorption. The oxidation state of arsenic and iron in EC products was ascertained by XPS. It was observed that some amount of As 3+ was converted to As 5+ during EC. The electrokinetic and FT-IR measurements revealed the co-precipitation of arsenic by specific chemical interaction between arsenic species and iron oxide precipitate. The effect of initial As 3+concentration and current density on arsenic removal was also discussed. The TCLP test (USEPA method-1311) was conducted on EC products to assess their toxicity. It was confirmed that the solid waste generated during EC process is non-hazardous and can be safely disposed.

Arsenic from Groundwater to Paddy Fields in Bangladesh: Solid–Liquid Partition, Sorption and Mobility

The arsenic contamination of Bangladesh groundwater involves heavy arsenic inputs to irrigated rice fields. Beside adsorption on soil colloids, iron–arsenic co-precipitation phenomena can affect arsenic retention in soils. In paddy fields of Satkhira District, Bangladesh, the study of the arsenic and iron forms in the irrigation waters and in soils at different times and distances from the irrigation well evidenced that a higher Fe/As ratio in the well water was related to a faster oxidation of Fe(II) and As(III) in water and to a close Fe–As association in soils, together with a greater accumulation of arsenic and poorly ordered iron oxides. The concentration of arsenic and of labile iron forms decreased with the distance from the well and with the depth, as well as the reversibility of arsenic binding. The fate of the arsenic added to the soils by irrigation hence resulted strongly influenced by iron–arsenic co-precipitation, depending on the Fe/As ratio in water. Irrigation systems favouring the sedimentation of the Fe–As flocks could help in protecting the rice from the adverse effects of dissolved arsenic.

Arsenic removal from aqueous solution using ferrous based red mud sludge

Ferrous based red mud sludge (FRS) which combined the iron–arsenic co-precipitation and the high arsenic adsorption features was developed aimed at low arsenic water treatment in rural areas. Arsenic removal studies shown that FRS in dosage of 0.2 or 0.3 g/l can be used effectively to remove arsenic from aqueous solutions when initial As(V) concentration was 0.2 or 0.3 mg/l. Meanwhile, turbidity of supernatant in disturbing water was lower than 2 NTU after 24 h. The pH range (4.5–8.0) for FRS in effective arsenic removal was applicable in natural circumstance. Phosphate can greatly reduce the arsenic removal efficiency while the presence of carbonate had no significant effect on arsenic removal. Arsenic fractionation experiments showed that amorphous hydrous oxide-bound arsenic was the major components. When aqueous pH was decreased from 8.0 to 4.5, arsenic in FRS was not obviously released. The high arsenic uptake capability, good settlement performance and cost-effective characteristic of FRS make it potentially attractive material for the arsenic removal in rural areas.