Recovery Of Arsenic Research Articles

Recovery of elemental arsenic from calcium arsenate slag by carbothermic reduction: Ca3(AsO4)2 → Ca3(AsO3)2 → As4(g) pathway

With the increasing application of As(0) in semiconductor, equipment manufacturing fields, recovery of As(0) from hazardous wastes-bearing arsenic has attracted great attention. As alkali leaching method is widely used for disposal of wastes-bearing arsenic, secondary arsenic pollution has become an inevitable environmental problem due to the generated calcium arsenate slag. To solve secondary arsenic contamination, a reduction roasting process was proposed to recover As(0) from calcium arsenate slag. Thermodynamic calculation suggested that reduction pathway Ca3(AsO4)2 → As4(g) is the most feasible, followed by As(s) and As(g). Increasing temperature is conducive to reduction of Ca3(AsO4)2(s) to As4(g). To achieve efficient reduction of Ca3(AsO4)2 and avoid generation of As4O6(g), the temperature should be 650 °C ∼ 952.88 °C and molar ratio of C/Ca3(AsO4)2 should be greater than 3.0. The optimum operating parameters were determined to be C dosage of 14 %, temperature of 900 °C, and reduction time of 2 h, arsenic recovery efficiency and purity of As(0) reached 99.22 % and 99.41 %, respectively. Besides, mechanism of reduction process was elucidated and the findings revealed that reduction process is carried out in steps by Ca3(AsO4)2 → Ca3(AsO3)2 → As4(g) pathway. Moreover, this method has been successfully applied for semi-industrial test, providing an alternative solution for treatment of arsenic-bearing wastes.

Efficient reductive recovery of arsenic from acidic wastewater by a UV/dithionite process

The removal of arsenic (As(III)) from acidic wastewater using neutralization or sulfide precipitation generates substantial arsenic-containing hazardous solid waste, posing significant environmental challenges. This study proposed an advanced ultraviolet (UV)/dithionite reduction method to recover As(III) in the form of valuable elemental arsenic (As(0)) from acidic wastewater, thereby avoiding hazardous waste production. The results showed that more than 99.9 % of As(III) was reduced to As(0) with the residual concentration of arsenic below 25.0 μg L−1 within several minutes when the dithionite/As(III) molar ratio exceeded 1.5:1 and the pH was below 4.0. The content of As(0) in precipitate reached 99.70 wt%, achieving the purity requirements for commercial As(0) products. Mechanistic investigations revealed that SO2·‒ and H· radicals generated by dithionite photolysis under UV irradiation are responsible for reducing As(III) to As(0). Dissolved O2, Fe(III), Fe(II), Mn(II), dissolved organic matter (DOM), and turbidity slightly inhibited As(III) reduction via free radicals scavenging or light blocking effect, whereas other coexisting ions, such as Mg(II), Zn(II), Cd(II), Ni(II), F(−I), and Cl(−I), had limited influence on As(III) reduction. Moreover, the cost of treating real arsenic-containing (250.3 mg L−1) acidic wastewater was estimated to be as low as $0.668 m−3, demonstrating the practical applicability of this method. This work provides a novel method for the reductive recovery of As(III) from acidic wastewater.

Alkali Extraction of Arsenic from Groundwater Treatment Sludge: An Essential Initial Step for Arsenic Recovery.

Arsenic (As)-bearing Fe(III) precipitate groundwater treatment sludge has traditionally been viewed by the water sector as a disposal issue rather than a resource opportunity, partly due to assumptions of the low value of As. However, As has now been classified as a Critical Raw Material (CRM) in many regions, providing new incentives to recover As and other useful components of the sludge, such as phosphate (P) and the reactive hydrous ferric oxide (HFO) sorbent. Here, we investigate alkali extraction to separate As from a variety of field and synthetic As-bearing HFO sludges, which is a critical first step to enable sludge upcycling. We found that As extraction was most effective using NaOH, with the As extraction efficiency increasing up to >99% with increasing NaOH concentrations (0.01, 0.1, and 1 M). Extraction with Na2CO3 and Ca(OH)2 was ineffective (<5%). Extraction time (hour, day, week) played a secondary role in As release but tended to be important at lower NaOH concentrations. Little difference in As extraction efficiency was observed for several key variables, including sludge aging time (50 days) and cosorbed oxyanions (e.g., Si, P). However, the presence of ∼10 mass% calcite decreased As release from field and synthetic sludges considerably (<70% As extracted). Concomitant with As release, alkali extraction promoted crystallization of poorly ordered HFO and decreased particle specific surface area, with structural modifications increasing with NaOH concentration and extraction time. Taken together, these results provide essential information to inform and optimize the design of resource recovery methods for As-bearing treatment sludge.

Optimization of desorption parameters using response surface methodology for enhanced recovery of arsenic from spent reclaimable activated carbon: Eco-friendly and sorbent sustainability approach

Desorption and adsorbent regeneration are imperative factors that are required to be taken into account when designing the adsorption system. From the environmental, economic, and practical points of view, regeneration is necessary for evaluating the efficiency and sustainability of synthesized adsorbents. However, no study has investigated the optimization of arsenic species desorption from spent adsorbents and their regeneration ability for reuse as well as safe disposal. This study aims to investigate the desorption ability of arsenic ions adsorbed on hybrid granular activated carbon and the optimization of the independent factors influencing the efficient recovery of arsenic species from the spent activated carbon using central composite design of the response surface methodology. The activated carbon before the sorption process and after the adsorption-desorption of arsenic ions have been characterized using SEM-EDX, FTIR, and TEM. The study found that all the investigated independent desorption variables greatly influence the retrievability of arsenic ions from the spent activated carbon. Using the desirability function for the optimization of the independent factors as a function of desorption efficiency, the optimum experimental conditions were solution pH of 2.00, eluent concentration of 0.10 M, and temperature of 26.63 ℃, which gave maximum arsenic ions recovery efficiency of 91 %. The validation of the quadratic model using laboratory confirmatory experiments gave an optimum arsenic ions desorption efficiency of 97 %. Therefore, the study reveals that the application of the central composite design of the response surface methodology led to the development of an accurate and valid quadratic model, which was utilized in the enhanced optimization of arsenic ions recovery from the spent reclaimable activated carbon. More so, the desorption isotherm and kinetic data of arsenic were well correlated with the Langmuir and the pseudo-second-order models, while the thermodynamics studies indicated that arsenic ions desorption process was feasible, endothermic, and spontaneous.

Application of the liquid-liquid extraction method and subsequent icp-ms detection for speciation analysis of arsenic in wastewater samples

The current paper describes a method for determining As(III) and As(V) concentrations in wastewater samples. The approach is based on the extraction of As(III) from water samples using a non-polar organic solvent in a 10-12 M HCl medium. The extract contains As(III), while the raffinate contains As(V). Distilled water can be used to re-extract As(III) from the organic solvent. ICP-MS was used to analyze As concentrations in the reextract and the raffinate. The average recovery of arsenic by the proposed method is 99.6 %. It was calculated as the sum of As(III) and As(V) concentrations. The collected data demonstrated high repeatability. The standard addition procedure demonstrated the selectivity and accuracy of the employed method. The relative error of recovery of the standard As(III) addition is about 2 %, which is similar to the RSD found under repeatability conditions.

Separation and recovery of arsenic, germanium and tungsten from toxic coal ash from lignite by sequential vacuum distillation with disulphide

Large amount of coal ash is produced as industrial waste during the electricity generation through the combustion of lignite. Toxic elements arsenic exists in the coal ash, which hinders the subsequent recycling processes. Moreover, coal ash could be recycled further to retrieve scattered metals germanium and tungsten. It is believed that traditional recycling methods present barriers to scaled application, especially serious secondary pollution, such as toxic residue and waste liquid. In this work, a novel sequential vacuum distillation with disulphide method is proposed to separate arsenic, germanium and tungsten from coal ash. First, arsenic can be volatilized completely out of the reaction system at temperatures below 550 °C. Subsequently, Ge and W volatilized in the form of sulfide in the presence of Na2S2O3. The optimal condition was 1050 °C, the mass ratio of 0.6 with reaction a pressure of 1 Pa and a time duration of 120 min demonstrated the best evaporation ratio. For coal fly ash, chemical species As2S3, GeS, and WOx (x < 3)/WS2 were the main condensed products. For coal bottom ash, As2S3, GeS, and WO3/WS2 were dominant chemical components. Mechanisms for the process of release and evaporation of As, Ge, and W from coal ash, vacuum reaction, evaporation, and condensation were analyzed. In summary, the vacuum distillation method deserves to be further developed as it provides an eco-friendly method to recycle coal ash.

Molecular-scale characterization of groundwater treatment sludge from around the world: Implications for potential arsenic recovery

Iron (Fe)-based treatment methods are widely applied to remove carcinogenic arsenic (As) from drinking water, but generate toxic As-laden Fe (oxyhydr)oxide waste that has traditionally been ignored for resource recovery by the water sector. However, the European Commission recently classified As as a Critical Raw Material (CRM), thus providing new incentives to re-think As-laden groundwater treatment sludge. Before As recovery techniques can be developed for groundwater treatment waste, detailed information on its structure and composition is essential. To this end, we comprehensively characterized sludge generated from a variety of As-rich groundwater treatment plants in different geographic regions by combining a suite of macroscopic measurements, such as total digestions, leaching tests and BET surface area with molecular-scale solid-phase analysis by Fe and As K-edge X-ray absorption spectroscopy (XAS). We found that the As mass fraction of all samples ranged from ∼200–1200 mg As/kg (dry weight) and the phosphorous (P) content reached ∼0.5–2 mass%. Notably, our results indicated that the influent As level was a poor predictor of the As sludge content, with the highest As mass fractions (940–1200 mg As/kg) measured in sludge generated from treating low groundwater As levels (1.1–22 µg/L). The Fe K-edge XAS data revealed that all samples consisted of nanoscale Fe(III) precipitates with less structural order than ferrihydrite, which is consistent with their high BET surface area (up to >250 m2/g) and large As and P mass fractions. The As K-edge XAS data indicated As was present in all samples predominantly as As(V) bound to Fe(III) precipitates in the binuclear-corner sharing (2C) geometry. Overall, the similar structure and composition of all samples implies that As recovery methods optimized for one type of Fe-based treatment sludge can be applied to many groundwater treatment sludges. Our work provides a critical foundation for further research to develop resource recovery methods for As-rich waste.

Investigating the selective flotation of auriferous arsenian pyrite from refractory ores using thionocarbamate

Thionocarbamate, specifically modified Isopropyl Ethyl Thionocarbamate (IPETC) is selective in the separation of pyrite from arsenopyrite, following copper activation. In this work, the flotation response of a refractory gold (Au) ore containing arsenic (As) mainly in the form of arsenian pyrite is investigated to reject gold-barren sulphidic phases. The recovery of Au increased with an increase in CuSO4 concentration to 0.3 kg/t, beyond which further increase in concentration yielded no significant recovery. Variations of IPETC concentration between 0.2 and 1.5 kg /t of ore influenced both gold and arsenic recovery. It was surmised that the high collector dosage may have resulted from competitive adsorption between arsenian pyrite and other gangue minerals in the ore. 0.3 kg/t CuSO4 and 1.2 kg/t IPETC concentration at pH 11 gave the best results of 86% Au and 83% As recovery at an Au and As grade of 8.14 g/t and 2436 ppm respectively. LA-ICP-MS analysis of the concentrate showed a positive correlation between gold and arsenic. The technique also revealed arsenic-rich zones in pyrite which was further confirmed by SEM/BSD imaging to be rims of arsenian pyrite encapsulating Au-barren pyrite. MLA mineral maps of concentrates obtained at different times also showed that there is no relationship between the arsenic content of pyrite and the flotation rate. The deportment of arsenic in the rims of pyrite presents a complex mineralogical association which results in a decrease in concentrate grade.

Soil Arsenic Toxicity Impact on the Growth and C-Assimilation of Eucalyptus nitens

The selection of adequate plants that can cope with species that can live in contaminated/degraded and abandoned mining areas is of utmost importance, especially for environmental management and policymakers. In this framework, the use of a fast-growing forestry species, such as Eucalyptus nitens, in the recovery of arsenic (As) from artificially contaminated soils during a long-term experiment was studied. Roots can accumulate to levels ranging between 69.8 and 133 μg g−1 for plants treated with 100 and 200 µg As mL−1, respectively, while leaves between 9.48 μg g−1 (200 As) and 15.9 μg g−1 (100 As) without apparent morphological damage and toxicity symptoms. The C-assimilation machinery performance revealed a gradual impact, as evaluated through some gas exchange parameters such as the net photosynthetic rate (Pn), stomatal conductance to H2O (gs), and transpiration rate (E), usually with the greater impacts at the highest As concentration (200 As), although without significantly impacting the PSII performance. The As effects on the uptake and translocation of Ca, Fe, K, and Zn revealed two contrasting interferences. The first one was associated with Zn, where a moderate antagonism was detected, whereas the second one was related to Fe, where a particular enrichment in leaves was noted under both As treatments. Thus, it seems to exist a synergistic action with an impact on the levels of the photosynthetic pigments in As-treated plant leaves, compared with control plants. E. nitens must be considered as an alternative when phytoremediation processes are put into practice in our country, particularly in areas with cool climatic conditions.

Water-assisted-mechanical activation of copper pyrometallurgical tailings for molybdenum leaching and selective removal of environmentally-hazardous elements

Fayalite-rich and elemental crystalline blockade of copper pyrometallurgical slag flotation tailings (CSFT) make it difficult to dispose of safely and limits high-value reutilization. Water-assisted milling, a waste-free method, is exploratively employed for activation of CSFT and to improve elemental leachability. In comparison to traditional milling, water-assisted milling reduces the time required for amorphous transition and amorphous nano-mesoporous materials were obtained in 4 h-activated CSFT (SBET increased to 12.25 m2·g−1 from 0.99 m2·g−1; pore size: 2–50 nm). Formation and re-removal of strongly-bound water promoted the hydration expansion of mineral particles and generation of tetrahedral or octahedral silicon defects and vacancies, which provided a large number of active sites and effectively promoted the rapid diffusion and transfer of ions. Water-assisted milling improves the leachability of high-value-added Mo (from 53.09 to > 95 %). During the water-assisted milling process, the dissociation and REDOX reaction of Mo were accelerated by the co-effect of reactive metals (Ca and Al) and the electron migration in the friction environment. This procedure exposed and morphologically changed Mo, facilitated the separation of the iron phase from Mo, and enhanced its solubility in diluted H2SO4 agents. The separation and leaching recovery of high-toxicity arsenic (As) and cadmium (Cd) was enhanced and a preliminary process was proposed for selective leaching of As (>96.99 %) and Cd (96.15 %) by NaOH solution.

Adsorptive recovery of arsenic (III) ions from aqueous solutions using dried Chlamydomonas sp.

The present study aimed to descry the effectiveness of dried microalga Chlamydomonas sp. for disposing of arsenic from aqueous solution. The study included examining the impact of some factors on algae’s adsorption capacity (optimization study), such as initial concentrations of heavy metal, biosorbent doses, pH and contact time. All trials have been performed at constant temperature 25 °C and shaking speed of 300 rpm. The optimization studying indicated the pH 4, contact time at 60 min, temperature 25 °C and biomass concentration of 0.6 g/l were the best optimum conditions for the bioremediation activity with maximum removal percentage 95.2% and biosorption capacity 53.8 mg/g. Attesting of biosorption by applying FTIR (Fourier transfigure infrared), XRD (X-ray diffraction), SEM-EDX (Scanning Electron Microscope - Energy Dispersive X-ray), DLS (Dynamic light scarring) and ZP (Zeta Potential) was conducted. Also, Kinetics, isotherm equilibrium and thermodynamics were carried out to explain the plausible maximum biosorption capacity and biosorption rate of biosorbent q maximum.

Quantitation and speciation of inorganic arsenic in a biological sample by capillary ion chromatography combined with inductively coupled plasma mass spectrometry

The toxicity and biological activity of arsenic depend on its chemical form. In particular, inorganic arsenics are more toxic than organic ones. Apart from the determination of total arsenics, their accurate speciation is important for toxicity assessment. To separate arsenic species using a cation or an anion separation column, at least 0.5–1.0 mL of sample is required because conventional ion chromatography columns use a sample loop of 100–200 μL. It is thus difficult to analyze samples with small volumes, such as clinical and biological samples. In this study, a method for separating arsenic species using a 5-μL sample loop combined with a capillary ion exchange column has been developed for analyzing small volume of samples. The separated arsenics were determined by inductively coupled plasma mass spectrometry. By oxidizing As(III) to As(V) prior to analysis, the total inorganic arsenics, As(III) and As(V), could be well separated from the organic ones. Linear calibration curves (0.5–50 μg/kg) were obtained for total inorganic arsenics dissolved in water. Sub-picogram-level detection limit was obtained. The analytical capability of this method was successfully validated for certified reference materials, namely water and human urine, with total inorganic arsenic recovery efficiencies of 100% and 121%, respectively. Our method requires less than ~ 10 μL of sample and will be very useful to analyze valuable samples available in limited amounts.

Selective Separation Recovery of Copper and Arsenic from the Leaching Solution of Copper Soot

Through the main chemical reaction of metal ions and S2−, a new type of sulfide precipitant was first prepared and used to realize the selective separation recovery of copper and arsenic from the leaching solution of copper soot. It is proven by experimental results that the prepared sulfide precipitant could realize the efficient separation recovery of copper and arsenic. Indeed, the copper sulfide slag with Cu grade of about 47% and arsenic trisulfide slag with As operation recovery of about 98% could be obtained. The results of chemical reaction energy calculation analysis and SEM images analysis illustrate that the selective separation recovery of copper and arsenic mainly depended on the chemical reactions of sulfide precipitation. The ions of S2− and HS− produced by the prepared sulfide precipitant could react with Cu2+ and arsenic components to form CuS and As2S, respectively, in the copper and arsenic recovery procedure. In addition, the smaller solubility of CuS and the lower rate of S2− engendered by the sulfide precipitant were key to achieving the efficient separation and recovery of copper and arsenic.

A feasible strategy for deep arsenic removal and efficient tungsten recovery from hazardous tungsten residue waste with the concept of weathering process strengthening

Tungsten residue waste (TRW), generated by tungsten hydrometallurgy, is classified as a hazardous solid waste by Chinese government due to its high content and leaching toxicity of arsenic, but is also a typical critical metal secondary resource of tungsten. Deep arsenic removal and tungsten recovery of TRW are beneficial to waste harmless treatment and circular economy. However, the occurrence state and weathering mechanism of arsenic in TRW have not been investigated and reported, which is the fundamental reason why the harmless treatment of TRW has become a bottleneck problem. In this paper, a feasible and novel strategy for deep arsenic removal and efficient tungsten recovery from TRW was proposed based on the concept of weathering process strengthening. The results show that arsenic in TRW mainly exists in the form of arsenopyrite, and ionically bound arsenic (V) generated by weathering of arsenopyrite directly leads to leaching toxicity of arsenic in TRW exceeding 5 mg/L. The environmental risk of arsenic in TRW can be completely eliminated by strengthening the uncontrollable and slow weathering process of TRW into a controllable and efficient process. Over 98 % of arsenic and 84 % of tungsten were simultaneously leached from TRW under optimal conditions via an enhanced pressure oxidation leaching process in alkaline solutions based on the leaching thermodynamic and kinetic, resulting in only 0.07 mg/L of arsenic leaching toxicity in the secondary leach residue. Hydrated ferric oxide (HFO) generated by the leaching process provides the possibility for the diffusion of reactants and products, so that arsenic and tungsten can be high-efficiently leached. The harmless secondary leach residue can be used as a raw material for the production of building materials, cement, and glass. Taking into account the reduction of alkali consumption and recovery of tungsten and arsenic, the leach solution was recycled. The closed-loop strategy shows great promise for the harmless treatment and tungsten recovery of TRW on an industrial scale to promote circular economy and environmental protection.

Mineralogical characteristics of copper smelting slag affecting the synchronous flotation enrichment of copper and arsenic

Synchronous enrichment of copper and arsenic has become a newly emerging and significant problem during copper smelting slag (CSS) flotation, which affects environmental safety and CSS utilization. This study on CSS and its flotation products revealed the factors that affect the flotation enrichment of copper and arsenic from a mineralogy perspective. Mineralogical characteristic studies revealed that copper existed primarily in the form of matte with excellent floatability, whereas arsenic was primarily dissolved or wrapped in glassy silicates without floatability. The second occurrence phase of copper and arsenic, copper–arsenic alloy, was closely embedded with gangue minerals, which increased the difficulty of enriching copper and arsenic. Sequential extraction and X-ray photoelectron spectroscopy analysis indicated that the floatability of copper was better than that of arsenic. Flotation tests showed that copper recovery could reach 82.79 %, whereas arsenic recovery was only 40.83 %, which further confirmed that copper and arsenic could not be enriched synchronously. Mineral phase reconstruction was proposed as a potential scheme to enhance arsenic recovery. Arsenic was released from glassy silicates and combined with a copper-bearing phase to form copper–arsenic alloy during mineral phase reconstruction, which significantly increased arsenic recovery by 39.34 % and slightly increased copper recovery. The synchronous enrichment of copper and arsenic effectively reduces the total arsenic emission during copper pyrometallurgy, thereby alleviating the pressure of environmental pollution caused by CSS flotation tailings. This work provides a scientific reference for CSS processing toward recycling and harmlessness.

Synthesis of Nanostructures Using Gas-Diffusion Electrodes

Gas diffusion electrodes (GDEs) intertwine an ionically conducting liquid and a gas with an electrically conducting solid, supporting electrochemical reactions involving constituents linked to the three phases (i.e., chemical species, electrons). GDEs are broadly used in electrochemical energy-conversion devices, such as fuel cells and metal-air batteries, as well as in electrolyzers aiming at chemical synthesis, like in the chlor-alkali industry, hydrogen peroxide production, CO2 conversions to fuels and fine chemicals, or N2 reduction to ammonia. Recently, the use of GDEs was pioneered for metal recovery and the synthesis of nanostructures, in a process named gas-diffusion electrocrystallization (GDEx).[1–4] A liquid solution containing dissolved metal or metalloid ions (e.g., Cu2+, Fe3+, As3+, PtCl2 −6) flows through an electrochemical cell equipped with a GDE, filling in its porosity. The gas (e.g., O2, O2 in air, CO2, etc.) percolates through a hydrophobic backing (e.g., PTFE) on the GDE. After the gas diffuses to the electrically conducting layer acting as an electrocatalyst (e.g., hydrophilic porous activated carbon), the gas is electrochemically reduced. For instance, by imposing specific cathodic polarization conditions (e.g., at −0.145 VSHE O2 is reduced producing H2O2, H2O and OH–). As the highly abundant hydroxyl ions accompanied by redox reactive species spread to the bulk electrolyte, a reaction front develops throughout the hydrodynamic boundary layer. This creates local saturation conditions at the electrochemical interface, where metal ions precipitate in metastable or stable phases, depending on the operational variables. When O2 is the oxidizing gas, GDEx has been explained with an oxidation-assisted alkaline precipitation mechanism.[4] Conversely, when CO2 is used, the reaction front, rich in reducing species, yields elemental nanoparticles.This centennial celebration talk will explain the underlying principles of GDEx, portray reflections on its design and scale-up, and substantiate some of the experimental merits achieved. It will include the GDEx: (a) synthesis of iron oxide nanoparticles with high control of their magnetic susceptibility[1]; (b) recovery and immobilization of arsenic into crystalline scorodite[2]; (c) synthesis of nanoparticles with novel magnetic ground states (e.g., spin liquids and spin glasses)[3]; (d) synthesis of libraries of electrochemically-active materials[5] and (e) formation of elemental nanoparticles of platinum group metals (PGMs).

Evaluation of the effects of significant factors and interactions on the enrichment of arsenic and chromium by pipette tip solid phase extraction using novel P-ZrO2CeO2ZnO nanoparticles/alginate beads

The study seeks to determine the most significant factors affecting arsenic and chromium enrichment using novel P-ZrO2CeO2ZnO nanoparticles/alginate beads in order to minimize the total number of runs needed to successfully run the experiment. The effects of interactions between factors were also evaluated so that the optimum conditions which are not affected by the other factors are chosen for the experiments. The most significant factors on arsenic and chromium enrichment were screened for by using a half-factorial design, followed by the optimization of significant factors using the full-factorial design, and the interaction between factors was determined using ANOVA and interaction plots. The most significant factors for chromium recovery were sample volume, eluent flow rate, and sorbent dosage. For both chromium and arsenic recovery, interactions occurred between sample volume, dosage, and pH. The optimum conditions chosen for the experiment that gave favourable results for both metal ions were sample volume 5 mL, dosage 40 mg, pH = 7 and eluent flow rate 1 mL/min. This study showed that a preliminary screening step for the most significant factors for arsenic and chromium enrichment helps to reduce the number of total runs, and for the same experiment interactions between factors were present; hence, it is necessary to take this into account during the experimental design.

LCA of Disposal Practices for Arsenic-Bearing Iron Oxides Reveals the Need for Advanced Arsenic Recovery.

Iron (Fe)-based groundwater treatment removes carcinogenic arsenic (As) effectively but generates toxic As-rich Fe oxide water treatment residuals (As WTRs) that must be managed appropriately to prevent environmental contamination. In this study, we apply life cycle assessment (LCA) to compare the toxicity impacts of four common As WTR disposal strategies that have different infrastructure requirements and waste control: (i) landfilling, (ii) brick stabilization, (iii) mixture with organic waste, and (iv) open disposal. The As disposal toxicity impacts (functional unit = 1.0 kg As) are compared and benchmarked against impacts of current methods to produce marketable As compounds via As mining and concentrate processing. Landfilling had the lowest non-carcinogen toxicity (2.0 × 10-3 CTUh), carcinogen toxicity (3.8 × 10-5 CTUh), and ecotoxicity (4.6 × 103 CTUe) impacts of the four disposal strategies, with the largest toxicity source being As emission via sewer discharge of treated landfill leachate. Although landfilling had the lowest toxicity impacts, the stored toxicity of this strategy was substantial (ratio of stored toxicity/emitted As = 13), suggesting that landfill disposal simply converts direct As emissions to an impending As toxicity problem for future generations. The remaining disposal strategies, which are frequently practiced in low-income rural As-affected areas, performed poorly. These strategies yielded ∼3-10 times greater human toxicity and ecotoxicity impacts than landfilling. The significant drawbacks of each disposal strategy indicated by the LCA highlight the urgent need for new methods to recover As from WTRs and convert it into valuable As compounds. Such advanced As recovery technologies, which have not been documented previously, would decrease the stored As toxicity and As emissions from both WTR disposal and from mining As ore.

Reductive removal of As(V) and As(III) from aqueous solution by the UV/sulfite process: Recovery of elemental arsenic

The removal of arsenic (As(V) and As(III)) from contaminated water has attracted great attention. However, the generation of arsenic-containing hazardous waste by traditional methods has become an inevitable environmental problem. Herein, a UV/sulfite advanced reduction method was proposed to remove As(V) and As(III) from aqueous solution in the form of valuable elemental arsenic (As(0)), thus avoiding the generation of arsenic-containing hazardous waste. The results showed that greater than 99.9% of As(V) and As(III) were reduced to the high purity As(0) (> 99.5 wt%) with the residual arsenic concentration below 10 μg L−1. The hydrated electrons (eaq−), H• and SO3•− radicals are generated by the UV/sulfite process, of which eaq− and H• serve as reductants of As(V) and As(III) while the SO3•− radicals inhibit arsenic reduction by oxidizing arsenic. The effective quantum efficiency (Φ) for the formation of As(0) in the As(V) and As(III) removal process is approximately 0.0078 and 0.0055 mol/Einstein, respectively. The reduction of arsenic is favorable under alkaline conditions (pH > 9.0) due to the higher photolysis efficiency of SO32− than HSO3− (pKa = 7.2) and higher stability of eaq−/H• under alkaline conditions. The presence of dissolved oxygen (O2), NO2−, NO3−, CO32−, PO43− and humic acid (HA) inhibited arsenic reduction through light blocking or eaq−/H• scavenging effects while Cl−, SO42−, Ca2+ and Mg2+ had negligible effects on arsenic reduction. The proposed method can effectively remove and recover arsenic from contaminated water at a low cost, demonstrating feasibility for practical application. This study provides a novel technology for the reductive removal and recovery of arsenic from contaminated water.

Proton Self-Enhanced Hydroxyl-Enriched Cerium Oxide for Effective Arsenic Extraction from Strongly Acidic Wastewater.

Acid recycling and arsenic recovery from strongly acidic wastewater are goals of the metallurgical industry to reduce carbon emissions. In this study, arsenic was recovered using a hydroxyl-enriched CeO2 adsorbent, and the adsorption mechanism in a strongly acidic solution was investigated. The adsorption capacities of 88.59 mg/g for As(III) and 126.211 mg/g for As(V) at pH 1.0 are the highest reported values to date. It is revealed that the hydroxyl groups on the CeO2 surface can buffer hydrogen ions, and the isoelectric point of the material can be reduced to pH 1.52. The binding energy of arsenic is -1.25 eV for the hydroxyl-enriched CeO2 and -2.24 eV for CeO2 without hydroxyl groups. Additionally, the protonated hydroxyl groups reduce the oxidation energy of As(III) and promote the adsorption of arsenic by forming new active sites in the strongly acidic solution. Nearly 98.11% of arsenic (initial concentration is 886.8 mg/L) is removed within 24 h without pH adjustment, indicating the feasibility of hydroxyl-enriched CeO2 for recovering arsenic and acid. This work investigated the adsorption and proton-enhanced oxidation mechanism of arsenic by hydroxyl-enriched CeO2 in strongly acidic wastewater.