Arsenic Removal Rate Research Articles

Study on the integrated technology of arsenic removal and tungsten extraction based on the formation and decomposition of arsenotungstic acid

Arsenic is an accompanying element in sulfide minerals and distributed in dusts, solutions and slags during the metallurgical process. Particularly, arsenic removal from acidic solutions has long challenged hydrometallurgy. Herein, an integrated technology for arsenic removal and tungsten extraction based on the formation and decomposition of arsenotungstic acid is proposed. By leaching scheelite with H3AsO4-H2SO4 solution, arsenotungstic acid was formed with a tungsten leaching rate of 99.9 %. The arsenic content in the resulting gypsum was 0.003 wt%, which was lower than the initial 0.2 wt% in scheelite. Afterwards, the arsenotungstic acid can be selectively extracted by dodecanol, and the extraction rate increases with decreasing temperature and increasing acidity. It is also for this reason that the loaded organic phase can be easily stripped with hot water above 70 °C to obtain a pure arsenotungstic acid solution. When arsenotungstic acid reacted with ammonium, the resulting AAT precipitate has a particle size of less than 2 µm, which is much smaller than that of conventional ammonium paratungstate and reaches the ultrafine level. In the hydrogen reduction process of ammonium arsenotungstate, arsenic had an inhibitory effect on the growth of tungsten grains, resulting in the formation of tungsten powder with nanograins. Meanwhile, arsenic was reduced, volatilized, and finally condensed into elemental arsenic with metallic luster. The arsenic content in tungsten powder was 0.009 wt%, and the arsenic removal rate was 99.7 %. This work utilized arsenic acid and sulfuric acid as leaching agents for scheelite, and finally prepared two products of ultrafine tungsten powder and elemental arsenic, which provided a new approach for arsenic removal from highly acidic solutions and resource utilization of waste arsenic acid solution.

Green and efficient removal of arsenic and recovery of tin from hazardous waste tin refined copper slag

Arsenic contamination and low tin yields pose significant challenges in the utilization of copper slag for tin refining. Typically, tin in copper slag can be converted into a tin-rich concentrate or metallic tin via electrolysis, oxidation roasting, and acid leaching, facilitating tin resource recovery. However, copper slag roasting results in significant arsenic volatilization and environmental pollution. Herein, a novel copper slag treatment strategy for efficient tin recycling and arsenic removal. The thermodynamics of sulfuration reaction between copper slag and sulfur indicate that in the presence of sulfur, arsenic in copper slag can be converted into arsenic sulfide, effectively enhancing the arsenic thermostability. In addition, tin, cuprous sulfide, and iron are transformed into stable metal sulfides. The saturated vapor pressure of arsenic sulfide is higher than that of stannous sulfide, cuprous sulfide and iron sulfide. The conditions of sulfuration pretreatment were observed to be 1.6 times more sulfur, sulfuration temperature 573 K, and contact time of 4 h. The single vacuum distillation experiments for sulfides were carried out at 10 Pa and 1273 K held for 4 h to separate SnS, As2S3, and FeS, Cu2S. One-factor-at-a-time method was used to optimize operational parameters of secondary vacuum distillation, which include temperature and time. The optimum separation conditions of arsenic sulfide and stannous sulfide were 973 K and 2 h. The removal rate of arsenic is about 100%, and the purity of stannous sulfide is 99.9%. Arsenic is recovered as arsenic sulfide. This study will shed light on the development of new technologies for the treatment of arsenic-containing solid waste.

Separation of arsenic from tin anode slime by vacuum distillation

Tin anode slime (TAS) is a high-value waste produced by electrolytic refining of crude tin. In order to reduce the discharge of harmful waste and realize rational recycling, a process of removing arsenic from TAS by vacuum distillation was proposed, and theoretical and experimental studies were carried out. The saturated vapor pressure of each element in TAS and the activation energy of arsenic evaporation during vacuum distillation was calculated. The evaporation temperature and holding time of vacuum distillation for arsenic removal were investigated. The effects of evaporation temperature and holding time on arsenic removal were discussed. The results showed that the residual arsenic content is 0.32–0.19%, and the removal rate of arsenic is 84.87–91.90% at 1153 K and the range of holding time is 30–120min. When the temperature is 1353 K and the holding time from 30 to 120 min, the residual arsenic content is 0.029–0.025% and the removal rate is 99.43–99.59%. The activation energy for the evaporation of arsenic from TAS in vacuum distillation is EAs = 52.76 kJ/mol. The removal of arsenic improves the recycling value of TAS, and provides ideas for treating harmful substances from industrial wastes and recovering valuable metals.

Preparation of ionic liquid modified graphene composites and their adsorption mechanism of arsenic (V) in aqueous solution.

Graphene (GR) is a new type of carbon-based material that combines many excellent properties. In order to give full play to the excellent properties of graphene and expand its application scope, this study used ionic liquid SbF6 to modify it and successfully prepared ionic liquid modified graphene composites (H/GR), and studied its adsorption mechanism of arsenic in aqueous solution. By investigating the effects of reaction temperature, reaction time, pH, adsorbent (H/GR) dosage, and humic acid concentration on the removal rate of arsenic in aqueous solution, the experimental results showed that when the reaction temperature was 30°C, reaction time was 1h, pH was 6, H/GR dosage was 0.1g·L-1, and humic acid (HA) concentration was 10mg·L-1, the best arsenic removal effect was achieved with a maximum. The removal rate was 99.4%. The equilibrium adsorption capacity was well modeled by the Langmuir, Freundlich, and Tenkin models at 30°C. The Langmuir adsorption isotherm was the most consistent, with a calculated maximum value of 137.95 mg·g-1, which is higher than most adsorbents in the field. In addition, it was determined that the graphene surface was indeed immobilized with the ionic liquid [Hmim]SbF6 by SEM mapping and EDS energy spectroscopy observation, and the adsorption isotherms and pore size distribution maps of graphene before and after the loading of the ionic liquid were analyzed by BET, which further confirmed a significant increase in the microporosity and porosity of the modified H/GR, and furthermore, it was demonstrated that the arsenic ions are chemically bonded with and indeed adsorbed on the surface of the H/GR by FT-IR and XPS characterization analyses. The results of all experimental data studies indicate that the main mechanism of As(V) removal from water by H/GR is due to electrostatic adsorption, ion exchange, and complexation between the modified graphene itself and the ionic liquid [Hmim]SbF6 itself.

Thermodynamic Behavior of Pyrite and Arsenopyrite in Preoxidation for Chlorination Leaching of Refractory Gold Concentrate

Recently, preoxidation is an effective pretreatment method of refractory gold ore, which has been widely used due to the high desulfurization, arsenic removal, low environmental pollution, and rapid reaction rate. In this paper, we describe the thermodynamic considerations of preoxidation of pyrite and arsenopyrite, the main minerals of the refractory gold ore, and the effect of the pressure oxidation, one of the preoxidation processes on the chlorination leaching. The thermodynamic results indicated that arsenopyrite under acidic conditions is easier to oxidize compared to pyrite and the oxidation decomposition of pyrite and arsenopyrite-type gold ore can be considered mainly for pyrite. The experiment has shown that the arsenic removal rate was higher than the desulfurization rate; it is confirmed that the thermodynamic conclusion of the oxidation of pyrite and arsenopyrite was correct. Comparing the XRD, SEM, and EDX analyses of gold concentrate and pressurized oxidation residue, it can be seen that the surface of pressurized oxidation residue is a fine porous structure and the dense and durable structure of sulfide ore is mainly destroyed.

Fe electrocoagulation technology for highly-efficient p-arsanilic acid removal from water: Feasibility and mechanisms

Conventional oxidation methods are effective for the removal of p-arsanilic acid (p-ASA) in water but are limited by complicated process. Herein, Fe electrocoagulation with Fe as anodes was used to efficiently remove p-ASA with 100% total arsenic removal within 60 min (1.75–20 A/m2). Current density significantly influenced sludge production, anode loss, and energy consumption (p-value < 0.05). Kinetic analyses showed a decline in arsenic removal rate with increasing initial pH (4.0–10.0). The changes in main elements of p-ASA (As and N) were analyzed to identify intermediate products using UPLC-Q-TOF-MS, HPLC-ICP-MS, and spectrometry. Hydroxyl radicals were confirmed as the primary reactive oxygen species. The active sites of p-ASA molecules were predicted by theoretical calculations and reaction paths were proposed. The toxicity of Fe-EC effluent was effectively reduced according to the analyses of ECOSAR and E. coli colonies method. The possible mechanisms of p-ASA removal, including oxidative degradation, electrostatic attraction, and ligand complexation, were proposed. Real water containing a p-ASA concentration of 250 μg/L was treated for 48 h using continuous-flow Fe-EC and arsenic concentrations of 2–30 μg/L in effluent were obtained. Overall, Fe-EC was a simple, cost-effective, and eco-friendly technology for the removal of p-ASA.

Deep Removal of Arsenic from Arsenic-Iron Slag by Carbothermal Reduction Method (CTR Method)

In order to remove arsenic from arsenic-iron slag, CTR method was used. CaO in arsenic-iron slag reacted with As2O3 to form CaAsO4, which hindered the removal of arsenic, adding SiO2 to arsenic-iron slag can generate CaSiO3, it can effectively avoid the production of CaAsO4. The CTR method can effectively remove arsenic from arsenic-iron slag, arsenic can be used in the form of As2O3 and iron can be used in the form of Fe3O4. The removal rate of arsenic was 99.56%, and the arsenic remained in the slag was only 0.08%, under the conditions of temperature of 600 °C, reductant addition of 20%, and time of 150 minutes.

Three-year monitoring of the efficacy and improvement of the most popular arsenic removal filter in Nepal

This paper presents the monitoring results of the arsenic removal efficacy of 27 Kanchan Arsenic Filters (KAF) in Nepal over a 3-year period. The average arsenic removal rate was 57%; however, 84% of the filtered water samples exceeded WHO guideline values. Arsenic removal capacities declined from over 90% to below 30% within approximately 1 year. Replacement of iron nails improved the arsenic removal capacities of two different testing groups by 10% and 23%, respectively, whereas changing all filter media, i.e., sand, gravel, and iron nails, with a limited budget of USD 17 per unit, improved the arsenic removal capacity by over 90% on average. The results of this study revealed that one reason for the reduced arsenic removal capacity of the KAF was the change in the type of iron nails used by the manufacturer, the substitution of non-galvanized with galvanized nails. An analysis of the different stages of the arsenic removal process using KAFs with already declined arsenic removal capacity revealed that the average arsenic removal rate from the supernatant to filtered water was −24%. In contrast, on average, most of the total iron (91%) from the supernatant water was removed from the filtered water. Based on these results, it was suggested that natural sand compounds may play a role in arsenic removal, and is recommended that the filter sand of the KAF be replaced every 3–4 months to maintain the effectiveness of the KAF in rural areas of developing countries, considering its maintenance and monitoring issues.

Arsenic removal from aqueous solution by chitosan loaded with Al/Ti elements

ABSTRACT In the process of removing arsenic in an arsenic-containing aqueous solution, a large amount of harmful arsenic-containing waste is usually discharged. In this paper, a recyclable and environmentally friendly method of removing arsenic with Al/Ti-supported chitosan (ATC) was proposed. The results show that ATC has the best adsorption effect on arsenic at pH 8 at room temperature. In addition, the ratio of Al and Ti to chitosan (CB) affects the adsorption effect of ATC on arsenic. When Al: Ti: CB is 1:1:10, the removal rate of arsenic is as high as 99%. ATC can rapidly adsorb arsenic within 30 min. The adsorption kinetics shows that the adsorption of ATC on arsenic follows the joint action of physical adsorption and chemical precipitation. The adsorption isotherm shows that the adsorption process is multilayer adsorption. Finally, ATC has good recycling ability and is an efficient arsenic-removing agent in the treatment of arsenic-containing aqueous solutions. It shows great potential in the remediation of heavy metal-containing aqueous solutions.

Mechanism of removal of toxic arsenic (As) from zinc sulfate solution by ultrasonic enhanced neutralization with zinc roasting dust

Arsenic in zinc sulfate solution greatly hinders the zinc hydrometallurgy process, and the treatment of arsenic residue with lime also generates large cost due to the large amount of residue. Herein, a new process of neutralization by zinc roasting dust (ZRD) and ultrasound (US) field enhancement of arsenic removal was proposed. The process includes the following steps:one-stage neutralization, KMnO4 oxidation and two-stage neutralization to remove arsenic. The process has the advantages of a good arsenic removal effect, no introduction of new impurities, and less residue. The effects of the ZRD dosage, temperature and US power on arsenic removal were investigated. The optimal conditions were 12 g/L, 70 ℃ and 300 W, respectively, and the arsenic removal rate reached 99.3%. The X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM-EDS) were utilized to analyze the raw materials and residue. The results showed that, compared with conventional conditions, US strengthening treatment led to more complete reaction of ZRD. The arsenic removal residue after US treatment mainly existed in the form of ZnFe2O4, Fe3O4 and ZnS, which exhibited low reactivity. Ultrasound could effectively destroy the wrapper on the surface of ZRD, and enhance the liquid–solid reaction, which reduced the amount of residue and improved the arsenic removal efficiency. Interestingly, we found that ultrasound could enhance arsenic removal by increasing the ligand exchange between arsenate and sulfate. Compared with the lime and conventional ZRD neutralization, the wet residue weight after US treatment was reduced by 46.8% and 16.3%, respectively.

Effect of injection of different gases on removal of arsenic in form of dust from molten copper smelting slag prior to recovery process

In order to reduce the environmental risks caused by arsenic in copper smelting slag, a method of dearsenisation from molten slag based on gas injection was proposed. It was expected to enrich arsenic in the form of dust prior to copper recovery process. The effects of inert, oxidising, and reducing gas on the removal of arsenic from molten slag were compared. When CO2 was injected, the removal of arsenic was mainly attributed to the oxidation of Cu—As inclusions and arsenic sulphide in the slag. Based on the injection of CO, the removal rate of arsenic reached more than 60%. Based on the injection of reducing gas, arsenic oxide in the FeOx—SiO2 slag was reduced and volatilised into the gas phase, resulting in the removal of arsenic. This study provides a reference with respect to the establishment of strategies for the mitigation of arsenic pollution caused by smelting slag.

Arsenic removal from acidic industrial wastewater by ultrasonic activated phosphorus pentasulfide

Arsenic is one of the main harmful elements in industrial wastewater. How to remove arsenic has always been one of the research hotspots in academic circles. In the process of arsenic removal by traditional sulfuration, the use of traditional sulfurizing agent will introduce new metal cations, which will affect the recycling of acid. In this study, phosphorus pentasulfide (P2S5) was used as sulfurizing agent, which hydrolyzed to produce H3PO4 and H2S without introducing new metal cations. The effect of ultrasound on arsenic removal by P2S5 was studied. Under the action of ultrasound, the utilization of P2S5 was improved and the reaction time was shortened. The effects of S/As molar ratio and reaction time on arsenic removal rate were investigated under ultrasonic conditions. Ultrasonic enhanced heat and mass transfer so that the arsenic removal rate of 94.5% could be achieved under the conditions of S/As molar ratio of 2.1:1 and reaction time of 20 min. In the first 60 min, under the same S/As molar ratio and reaction time, the ultrasonic hydrolysis efficiency of P2S5 was higher. This is because P2S5 forms ([(P2S4)])2+ under the ultrasonic action, and the structure is damaged, which is easier to be hydrolyzed. In addition, the precipitation after arsenic removal was characterized and analyzed by X-ray diffraction, scanning electron microscope-energy dispersive spectrometer, X-ray fluorescence spectrometer and X-ray photoelectron spectroscopy. Our research avoids the introduction of metal cations in the arsenic removal process, and shortens the reaction time.

A novel strategy for arsenic removal from acid wastewater via strong reduction processing.

Due to the high-acidic arsenic-containing wastewater pollution greatly threatening human health and ecological safety, a simple and efficient method for reducing arsenic was proposed in this paper to solve this problem. By using potassium borohydride (KBH4) as a reducing agent, the soluble arsenic was converted into the gaseous arsine (AsH3) or solid arsenic (As0) to achieve the purpose of removing arsenic in wastewater. By exploring the reaction kinetics of the arsenic removal process, it was found that the fast reaction stage (0-2min) conformed to pseudo-first-order kinetics. The removal rate of arsenic increased to over 73% in 0.5min, and reaction equilibrium was reached after 30min. Various influence factors including arsenic valence, aeration, addition method, concentrations of reducing agent, and hydrogen ion (H+) were investigated. The results showed that As(III) was easier to be removed by reduction than As(V), while adding KBH4 in multiples and aeration were both favorable to the removal of arsenic. Increased concentration of KBH4 also enhanced the removal of arsenic. Appropriate H+ concentration contributed to the arsenic removal, but excessive H+ concentration conversely has an inhibitory effect. The maximum removal rate of arsenic was 95.87%, with the maximum removal capacity of 45.50mg/g. Based on the XRD and SEM-EDS analysis of residue, amorphous arsenic (As0) with a mass ratio of more than 94.52% was generated after the reduction of soluble arsenic. Our study demonstrated that the reaction mechanism of reductive degradation is soluble arsenic with hydrogen radicals (H•) to form arsenic (As0) and arsine (AsH3) (in the molar ratio of 6:1). Although the generated solid arsenic (As0) is convenient for the soluble arsenic removal from wastewater, attention must be paid to the formation of AsH3, and strategies for AsH3 treatment should be considered.

Effects of Pretreatment and Polarization Shielding on EK-PRB of Fe/Mn/C-LDH for Remediation of Arsenic Contaminated Soils

In this study, coupling electrokinetic (EK) with the permeable reactive barriers (PRB) of Fe/Mn/C-LDH composite was applied for the remediation of arsenic-contaminated soils. By using self-made Fe/Mn/C-LDH materials as PRB filler, the effects of pretreatment and polarization shielding on EK-PRB of Fe/Mn/C-LDH for remediation of arsenic contaminated soils were investigated. For the pretreatment, phosphoric acid, phosphoric acid and water washing, and phosphate were adopted to reduce the influence of iron in soil. The addition of phosphate could effectively reduce the soil leaching toxicity concentration. The removal rate of the soil pretreated with phosphoric acid or phosphoric acid and water washing was better than with phosphate pretreatment. For the polarization shielding, circulating electrolyte, electrolyte type, anion and cation membranes, and the exchange of cathode and anode were investigated. The electrolyte circulates from the cathode chamber to the anode chamber through the peristaltic pump to control the pH value of the electrolyte, and the highest arsenic toxicity removal rate in the soil reaches 97.36%. The variation of total arsenic residue in soil using anion and cation membranes is the most regular. The total arsenic residue gradually decreases from cathode to anode. Electrode exchange can neutralize H+ and OH- produced by electrolyte, reduce the accumulation of soil cathode area, shield the reduction of repair efficiency caused by resistance polarization, enhance current, and improve the removal rate of arsenic in soil.

Multi-cycle regeneration of arsenic-loaded iron-coated cork granulates for water treatment

The chemical desorption of arsenic from saturated iron-coated cork granulates (ICG) and the regeneration capacity of this adsorbent for further reuse was investigated in batch and continuous modes. Different types of eluents were tested at different concentrations for evaluating their desorption capacity, and leaching of total organic carbon (TOC), iron content, and characterization by SEM/EDS were used to assess the eluents' attack on the adsorbent structure. The NaOH 0.1 M solution achieved the highest arsenic removal rate from saturated media; however, it was aggressive to the adsorbent structure, as reflected in high TOC values found in the eluate, higher iron leaching from the adsorbent, and degradation of cork cellular structure. The Elovich model fitted best (r2 > 0.98) the desorption kinetics when using NaOH as eluent. The less basic solution of NaOH 0.01 M proved to be less aggressive to ICG and allowed media regeneration for at least four adsorption-desorption cycles, while remaining an arsenic adsorption capacity of 1 mg g−1 in both batch and continuous modes. ICG's adsorption capacity was less affected after various cycles than other adsorbents, so this material proved to be potentially applicable as an alternative green solution for arsenic removal from water. The adsorbent was also successfully applied in continuous mode to remove arsenic from real groundwater and was able to maintain arsenic concentration under 10 and 50 μg L−1 for 140 and 341 bed volumes, respectively. This work provided good insights on arsenic desorption from ICG and its further application in similar real scenarios.

Effective removal of arsenic (V) from aqueous solutions using efficient CuO/TiO2 nanocomposite adsorbent

The groundwater is one of the biggest natural resources for providing drinking water to millions of people all around the globe. However, the presence of large amount of arsenic(V) in water causes serious health hazards to the consumers which necessitates the development of cost-effective remediation. The CuO/TiO2 nanocomposites were prepared by the precipitation-deposition method for the removal of the arsenate ion (AsO43-) from water. The prepared samples were characterized by powder X-ray diffraction, Fourier transform infrared, and scanning electron microscopy to examine crystallite size and structure, material purity, textural features, morphology, and surface area. The effect of different operating parameters such as pH, contact time, initial concentration of arsenic(V) and nanocomposite dose on the removal rate of arsenic(V) was examined to optimize the adsorption performance of the CuO/TiO2 nanocomposite. In addition, the adsorption mechanism was studied by employing Langmuir and Freundlich adsorption isotherms to gain better understanding of the adsorption mechanism. The Freundlich adsorption isotherm fits well with the experimental data and the maximum adsorption capacity of the Langmuir model was found to be 90 mg/g for arsenic(V). The CuO/TiO2 nanocomposite shows remarkable adsorption performance for the treatment of arsenic(V) contaminated water samples. This study provides a cost-effective solution for the safe use of groundwater contaminated with arsenic.

Fundamental research on selective arsenic removal from high-salinity alkaline wastewater

The alkaline leaching process of arsenic-containing solid waste discharged during nonferrous metal smelting affords typical high-salinity alkaline arsenic-containing wastewater (HSAW). In this study, for the first time, Me (Ca2+ and Mg2+)–AsO43−–OH−–H2O and Me (Ca2+ and Mg2+)–AsO43−–CO32−–H2O systems are studied based on a thermodynamic equilibrium diagram and an arsenic removal experiment, proving that the removal of arsenic using single metal ions in the presence of CO32− is infeasible because of carbonate coprecipitation. Based on this observation, a new method that uses magnesium ammonium complex salts (MACSs) for HSAW treatment is proposed. Based on the thermodynamic calculations of the Mg2+–AsO43−–NH4+–CO32−–H2O system and the arsenic removal experiment, carbonate and arsenate can be selectively separated by the formation of magnesium ammonium arsenate (NH4MgAsO4·6H2O). In an arsenic solution containing 150-g/L Na2CO3, the arsenic removal rate and the arsenic grade of the precipitation product reach 90.16% and 27.13%, respectively, when the molar ratios of Mg2+/NH4+:As(V) are 1.8:1 and 2:1, respectively. The proposed method is successfully employed for treating a leaching solution of alkaline arsenic slag discharged during antimony smelting. The findings of this study will broaden the basic theory of HSAW treatment and lay a foundation for the resource treatment of arsenic-containing solid waste.

Arsenite to Arsenate Oxidation and Water Disinfection via Solar Heterogeneous Photocatalysis: A Kinetic and Statistical Approach

Arsenic (As) poses a threat to human health. In 2014, more than 200 million people faced arsenic exposure through drinking water, as estimated by the World Health Organization. Additionally, it is estimated that drinking water with proper microbiological quality is unavailable for more than 1 billion people. The present work analyzed a solar heterogeneous photocatalytic (HP) process for arsenite (AsIII) oxidation and coliform disinfection from a real groundwater matrix employing two reactors, a flat plate reactor (FPR) and a compound parabolic collector (CPC), with and without added hydrogen peroxide (H2O2). The pseudo first-order reaction model fitted well to the As oxidation data. The treatments FPR–HP + H2O2 and CPC–HP + H2O2 yielded the best oxidation rates, which were over 90%. These treatments also exhibited the highest reaction rate constants, 6.7 × 10−3 min−1 and 6.8 × 10−3 min−1, respectively. The arsenic removal rates via chemical precipitation reached 98.6% and 98.7% for these treatments. Additionally, no coliforms were detected at the end of the process. The collector area per order (ACO) for HP treatments was on average 75% more efficient than photooxidation (PO) treatments. The effects of the process independent variables, H2O2 addition, and light irradiation were statistically significant for the AsIII oxidation reaction rate (p &lt; 0.05).

Nature of surface interactions among Fe3O4 particles and arsenic species during static and continuous adsorption processes

This study explored the mechanistic approaches to understand the adsorptive removal of arsenic species from aqueous medium in static and continuous adsorption processes. Fe3O4, an adsorbent is this study, is synthesized by reverse coprecipitation method using iron oxide waste of steel industry as a starting material. The surface properties of Fe3O4 were confirmed by several characterization techniques including XRD, XPS, SEM, TEM, FTIR, EDS, Raman, and zeta potential. The arsenic removal rate was found to be dependent on the synthesis pathway of Fe3O4 especially, the pH during reverse coprecipitation. Beside synthesis conditions, the adsorbent size, adsorbent quantity, an initial concentration of arsenic species, contact time, and the solution pH also influenced the arsenic removal rate. Over 90% arsenate and arsenite concentrations were effectively removed from the solution in initial 10 min of contact between Fe3O4 and arsenic solution. The adsorption sites of Fe3O4 were successfully reclaimed by regeneration of used particles with 0.1N NaOH solution. To assess the practicability of the Fe3O4 particles in continuous adsorption process, particles were used in column and plug flow reactors and the adsorption profile is examined under different operational conditions (operational scheme, influent flow direction, contact time, initial arsenic concentration, etc.). The operational performances of reactors confirmed that the synthesized particles have the potential to be successfully applied for arsenic removal from water.

Effective Remediation of Arsenic-Contaminated Soils by EK-PRB of Fe/Mn/C-LDH: Performance, Characteristics, and Mechanism.

Arsenic is highly toxic and carcinogenic. The aim of the present work is to develop a good remediation technique for arsenic-contaminated soils. Here, a novel remediation technique by coupling electrokinetics (EK) with the permeable reactive barriers (PRB) of Fe/Mn/C-LDH composite was applied for the remediation of arsenic-contaminated soils. The influences of electric field strength, PRB position, moisture content and PRB filler type on the removal rate of arsenic from the contaminated soils were studied. The Fe/Mn/C-LDH filler synthesized by using bamboo as a template retained the porous characteristics of the original bamboo, and the mass percentage of Fe and Mn elements was 37.85%. The setting of PRB of Fe/Mn/C-LDH placed in the middle was a feasible option, with the maximum and average soil leaching toxicity removal rates of 95.71% and 88.03%, respectively. When the electric field strength was 2 V/cm, both the arsenic removal rate and economic aspects were optimal. The maximum and average soil leaching toxicity removal rates were similar to 98.40% and 84.49% of 3 V/cm, respectively. Besides, the soil moisture content had negligible effect on the removal of arsenic but slight effect on leaching toxicity. The best leaching toxicity removal rate was achieved when the soil moisture content was 35%, neither higher nor lower moisture content in the range of 25–45% was conducive to the improvement of leaching toxicity removal rate. The results showed that the EK-PRB technique could effectively remove arsenic from the contaminated soils. Characterizations of Fe/Mn/C-LDH indicated that the electrostatic adsorption, ion exchange, and surface functional group complexation were the primary ways to remove arsenic.