Adsorption Of As Research Articles

Innovative metal−phenolic nanocomposite sorbent: A groundbreaking solution for arsenic-free drinking water – Synthesis and characterization approaches

Arsenic (As) stands as one of the most alarming contaminants, presenting a formidable challenge in the realm of drinking water across numerous countries. To deal with this challenge, the sequestration of arsenic by Adsorption has been extensively investigated in the solid media. Here, a sorbent system based on a polyphenolic network with physical cross-linking using tannic acid and ZrIV ions is investigated for high binding, which is in the form of metal sequestration. The derived solvent system of nano adsorbent molecules was characterized using x-ray diffraction analysis (XRD), energy dispersive x-ray spectroscopic (EDS) and Fourier transform infrared (FTIR) spectroscopic techniques. Adsorption of As was studied under varying governing factors such as pH, adsorbent dosage, and metal ion concentration, and the effects of changing these parameters were documented. Maximum adsorption was observed at solution pH-7, 1 gL−1, and 20 mgL−1 metal ion concentration with removal efficiency reaching up to 95 % in 90 min. Adsorption isotherm and kinetics were studied to deduce the mechanism of adsorption as homogeneous monolayer chemisorption and were best fitted by the Langmuir isotherm model and pseudo-second-order kinetics. Considering the extent of As contamination in the groundwater and the associated health risk to the population, our work provides insides into the nanostructure-dependent capability for As adsorption applications.

Impact of silicate on the microstructure of β-FeOOH and its adsorption of As

The structural and chemical properties of iron oxides are usually pertinent to the high affinity of silicon and iron in the environment, which further influences the retention of As. Previous work mainly focused on the Fe-Si interactions in Si-rich environments, while there is a dearth of both structural alteration of iron oxide in low-silicate conditions and the mechanistic understanding on the adsorption As process in Si-Fe oxide (Si-FeOOH). Herein, we investigated the adsorption of As on Si-FeOOH, proceeding from the physical and chemical properties of low-silicate co-precipitated β-FeOOH. Additionally, the effect of initial concentration of arsenic, oxygen, pH, and electrolyte concentration were discussed. SEM, TEM, XPS, FTIR, XRD and Rietveld refinement, BET and Zeta potential were used to characterize the structure and surface properties of Si-FeOOH; atomic fluorescence spectrometer were used to determine the residual As solution. DFT-calculated adsorption energies and electron localization function distribution for (310) facet is consistent with the analytical results obtained from experiments, demonstrating that the little dopped silicate stabilized the crystal microstructure of β-FeOOH, and strengthened the combination of As by generating the intramolecular hydrogen bonding and promoting electron transfer.

The influence of carbonate on the adsorption performance and mechanism of LDHs toward Cd and As

The excellent adsorption performance of layered double hydroxides (LDHs) toward heavy metals (HMs) had been demonstrated. The carbonate contamination was one of the inherent problems for LDHs whether during the synthesis or application procedure, which significantly affected the adsorption performance of LDHs toward HMs. However, a few studies investigated the mutual effect and mechanism between HMs on LDHs with carbonate interference, especially for the coexistence system of cationic and anionic HMs. In this study, cadmium (Cd) and arsenate (As) were selected as typical cationic and anionic HMs to study the influences of carbonates on their adsorption performance on LDHs. The carbonate intercalated LDHs (CLDH) promoted Cd adsorption but inhibited As adsorption in single system. The adsorption capacity of Cd increased by ∼ 50 % while As adsorption decreased by half. CdCO3 precipitation contributed to ∼ 40 % of the adsorbed Cd whereas weaker electrostatic adsorption inhibited As adsorption due to lower surface zeta potentials of CLDH than LDH. In contrast, both adsorption capacities and rates of Cd and As on CLDH were promoted in binary system (the co-existence of Cd and As) compared with single system. The surface potentials of CLDH turned from positive to negative with As rapid occupation, facilitating Cd entrance into the interlayers. And then the opening of the interlayer space and rearrangement of CLDH enhanced CdCO3 precipitation and isomorphic substitution. With the increase of surface zeta potentials and rearrangement of CLDH, in turn, the adsorption of As was promoted via electrostatic adsorption (∼65 %) and surface complexation (∼35 %). The adsorption capacity of Cd increased by ∼ 15 % whereas As adsorption decreased by half with increasing pH from 4 to 9 in binary system. In contrast, temperature (15–35 ℃) had negligible influence on the adsorption of CLDH toward Cd and As. Herein, this study illustrated the influence mechanism of carbonate intercalation on the simultaneous immobilization of Cd and As on LDHs, providing an understanding for fates of Cd and As with LDHs in more realistic scenes.

Deep removal of arsenic from arsenic-bearing gypsum using a seed-induced crystal control technique and its mechanisms

Arsenic-bearing gypsum (ABG), a byproduct from the lime/ferric sulfate process in the waste acid treatment of the heavy non-ferrous industry, represents a substantial hazardous arsenic (As) waste issue in China. Due to the potential arsenic leakage, the disposal of ABG poses an urgent challenge to the surrounding environment. The elevated As content and the low-value-added recycling products are the primary hurdles hindering ABG recycling. In this study, precise control over the gypsum crystal and As species in Na2SO4-H2SO4 solutions under mild conditions facilitated the deep removal of As (with a leaching efficiency of 92.45 % and a final product As concentration of 80.32 ppm) and simultaneous preparation of high-strength α-bassanite (with a compressive strength of 35.38 MPa) from the pre-treated ABG. This process occurred during the recrystallization from dihydrate gypsum (CaSO4·2H2O, DH) to α-bassanite (α-CaSO4·0.5H2O, α-HH), involving DH dissolution followed by α-HH crystallization. The encapsulated As was fully released during the dissolution process, crucial for the efficient elimination of As impurities. H2SO4 dissolved the released As, transforming it into the protonated species (H3AsO4) with a distinct structure and a less negative binding energy (ΔEB) to SO42-. This transformation prevented the chemical incorporation of the released As during the α-HH crystallization process. Additionally, the morphology and size of α-HH were controlled by seeding in the mixed solutions. The formation of large short-columnar α-HH crystals with a low specific surface area significantly reduced the surface adsorption of As, further enhancing As leaching efficiency. Importantly, the large short-columnar α-HH was identified as high-strength gypsum with high added value. This study provided innovative guidance for efficiently removing impurities from gypsum and pioneered a cost-effective approach for the clean and high-value utilization of industrial gypsum residues.

Inhibiting effects of humic acid on iron flocculation hindered As removal by electro-flocculation on air cathode iron anode

Activated carbon air cathode combined with iron anode oxidation-flocculation synergistic Arsenic (As) removal was a new groundwater purification technology with low energy consumption and high efficiency for groundwater with high As concentration. The presence of organic matter such as humic acid (HA) had ambiguous effects on formation of organic colloids in the system. The effects of the particle size distribution characteristics of these colloids on the formation characteristics of flocs and the efficiency of As purification was not clear. In this work, we used five different pore size alumina filter membranes to separate mixed phase solutions and studied the corresponding changes in iron and arsenic concentrations in the presence and absence of humic acid conditions. In the presence of HA, the arsenic concentration of < 0.05 µm particle size components was 1.01, 1.28, 3.07, 7.69, 2.85 and 1.24 times of that in the absence of HA. At the same time, the arsenic content in 0.05–0.1 µm and 0.1–0.45 µm particle size components was also higher than that in the system without HA, which revealed that the presence of HA hindered the flocculation behavior of As distribution to higher particle sizes in the early stage of the reaction. The presence of HA affected the flocculation rate of iron flocs from small to large particle size fractions and it had limited effect on the behavior of large-size flocs in adsorption of As. These results provide a theoretical basis for targeted, rapid, and low consumption synergistic removal of arsenic and organic compounds in high arsenic groundwater.

Tuned bimetallic MOFs with balanced adsorption and non-radical oxidizing activities for efficient removal of arsenite

The removal of arsenic from contaminated water is important for environmental protection and drinking water safety worldwide. In this study, bimetallic metal–organic frameworks (MOFs) with catalytic and adsorptive effects were synthesized and combined with peroxymonosulfate (PMS) for efficient As(III) oxidation and As(III)/As(V) removal. The molar ratio of Fe and Mn precursor was adjusted to balance the adsorption and catalytic processes of As(III) in the system. The results showed that among the Fe/Mn-MOFs and MIL-88(Fe) tested, the Fe/Mn-MOFs with an Fe/Mn molar ratio of 1:1 (Fe0.3Mn0.3-MOFs) could achieve the best catalytic and adsorption performance with 98% removal of As(III). The performance of Fe0.3Mn0.3-MOFs in natural contaminated water was also verified. Electron spin resonance detection and quenching experiments have revealed that trivalent arsenic oxidation is facilitated primarily by a non-radical process through singlet oxygen. Density-functional theory, XPS and FTIR analyses reveal the structures, corresponding binding energies and binding sites for the adsorption of As(III)/As(V) by Fe0.3Mn0.3-MOFs. The coupling of Fe0.3Mn0.3-MOFs to the PMS system was still able to achieve 78% arsenic removal after five cycles, showing good reliability and effectiveness in arsenic removal. This study provides a new insight into the catalytic and adsorption mechanisms in MOFs/PMS systems and provides a theoretical basis for the application of MOFs in the remediation of arsenic contaminated water.

Native microalgae and Bacillus XZM remediate arsenic-contaminated soil by forming biological soil crusts

Biological soil crusts (BSCs) are a useful tool for immobilization of metal(loid)s in mining areas. Yet, the typical functional microorganisms involved in promoting the fast development of BSCs and their impacts on arsenic(As) contaminated soil remain unverified. In this study, As-contaminated soil was inoculated with indigenous Chlorella thermophila SM01 (C. thermophila SM01), Leptolyngbya sp. XZMQ, isolated from BSCs in high As-contaminated areas and plant growth-promoting (PGP) bacteria (Bacillus XZM) to construct BSCs in different manners. After 45 days of ex-situ culture experiment, Leptolyngbya sp. XZMQ and bacteria could form obvious BSCs. Compared to single-inoculated microalgae, the co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased soil pH and water content by 10% and 26%, respectively, while decreasing soil EC and density by 19% and 14%, respectively. The soil catalase, alkaline phosphatase, sucrase, and urease activities were also increased by 30.53%, 96.24%, 154.19%, and 272.17%, respectively. The co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM drove the formation of BSCs by producing large amounts of extracellular polymeric substances (EPS). The three-dimensional fluorescence spectroscopy (3D-EEM) analysis showed that induced BSCs increased As immobilization by enhancing the contents of tryptophan and tyrosine substances, fulvic acid, and humic acid in EPS. The presence of the –NH2 and –COOH functional groups in tryptophan residues were determined using Fourier Transform Infrared Spectroscopy (FTIR). X-Ray Diffraction (XRD) analysis showed that there were iron (hydrogen) oxides in BSCs, which could form ternary complexes with humic acid and As, thereby increasing the adsorption of As. Therefore, BSCs formed by co-inoculation of Leptolyngbya sp. XZMQ and Bacillus XZM increased the immobilization of As, thereby reducing the content of soluble As in the environment. In summary, our findings innovatively provided a new method for the remediation of As-contaminated soil in mining areas.

Investigation of factors affecting removal of arsenic from polluted water using iron-based particles: Taguchi optimization design

Intensive research efforts have been followed to remove arsenic (As) from contaminated water to provide potable water to millions living in different countries. Adsorption is a simple and efficient way for arsenic contamination purification in water, with a pressing challenge to find a cheap and efficient adsorbent. The present paper deals with optimizing various batch parameters for the adsorption of As from solution by synthesized iron-based particles (hematite, magnetite, and zero-valent iron (ZVI)) nanomaterials using Taguchi’s optimization methodology. Taguchi’s (L27) orthogonal design with six effective factors, namely: initial As concentration, pH, contact time, adsorbent type, size, and dose, was applied for the multivariate optimization in adsorption studies for As to maximize the adsorption capacity along with the signal-to-noise ratio. The equilibrium studies revealed that the data were well described by Freundlich isotherm. The results showed that initial As concentration was the most important parameter in the adsorption process.

Toxicity effects of polystyrene nanoplastics and arsenite on Microcystis aeruginosa

Despite the increasing research on the fate of nanoplastics (NPs, <100 nm) in freshwater systems, little is known about the joint toxic effects of metal(loid)s and NPs modified with different functional groups on microalgae. Here, we explored the joint toxic effects of two types of polystyrene NPs [one modified with a sulfonic acid group (PSNPs-SO3H), and one without this functional group (PSNPs)] and arsenic (As) on the microalgae Microcystis aeruginosa. The results highlighted that PSNPs-SO3H showed a smaller hydrodynamic diameter and greater potential to adsorb positively charged ions than PSNPs, contributing to the more severe growth inhibition, while both of them produced oxidative stress. Metabolomics further revealed that the fatty acid metabolism of the microalgae was significantly up-regulated under both NPs exposure, while PSNPs-SO3H down-regulated the tricarboxylic acid cycle (TCA cycle) of the microalgae. As uptake by algae was significantly reduced by 82.58 % and 59.65 % in the presence of 100 mg/L PSNPs and PSNPs-SO3H, respectively. The independent action model showed that the joint toxicity of both NPs with As was assessed as antagonistic. In addition, PSNPs and PSNPs-SO3H had dissimilar effects on the composition of the microalgae extracellular polymeric substances (EPS), resulting in different uptake and adsorption of As, thereby affecting the physiology and biochemistry of algae. Overall, our findings propose that the specific properties of NPs should be considered in future environmental risk assessments.

Natural Clay Minerals as Potential Arsenic Sorbents from Contaminated Groundwater: Equilibrium and Kinetic Studies

Arsenic (As) contaminated groundwater is a worldwide concern due to its chronic effects on human health. The objectives of the study were to evaluate natural inexpensive raw laterite (RL) and kaolinite (RK) for their potential use as As sorbents and to understand the As sorption on laterite and kaolinite by employing sorption and kinetic models. Raw laterite and RK were tested for EC, pH, XRF and CEC as basic parameters. Batch sorption and kinetic experiments data were fitted in the sorption (Langmuir and Freundlich) model and kinetic (pseudo-first and pseudo-second order) reaction equations, respectively. Morphological and structural changes were observed in RL and RK samples before and after As saturation by employing FTIR and SEM. The major constituent in RL was Fe and Al oxides while in RK major oxides were silica and Al. The Freundlich sorption model well explained the experimental data, indicating a greater sorption capacity of RL on a hetero-layered surface compared to RK. The kinetic reaction equations showed that equilibrium was achieved after a contact time of 240 min and the adsorption was chemisorption in nature. The RL and RK were found to be effective sorbents for As removal, however, RL showed maximum As adsorption and thus superior in comparison with RK. Structural and morphological characterization reveals the role of Fe and Al oxides in the case of RL, and Al oxides in the case of RK, in the adsorption of As. Hence this study concludes that these naturally occurring inexpensive resources can be used as sorbent agents for As-contaminated drinking water treatment.

The effect of extracellular polymeric substances (EPS) of iron-oxidizing bacteria (Ochrobactrum EEELCW01) on mineral transformation and arsenic (As) fate

Extracellular polymeric substances (EPS) are an important medium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron (oxyhydr) oxides production which reduced arsenic (As) availability. The main component of EPS secreted by iron-oxidizing bacteria (Ochrobactrum EEELCW01) was composed of polysaccharides (150.76-165.33 mg/g DW) followed by considerably smaller amounts of proteins (12.98–16.12 mg/g DW). Low concentrations of As (100 or 500 µmol/L) promoted the amount of EPS secretion. FTIR results showed that EPS was composed of polysaccharides, proteins, and a miniscule amount of nucleic acids. The functional groups including -COOH, -OH, -NH, -C=O, and -C-O played an important role in the adsorption of As. XPS results showed that As was bound to EPS in the form of As3+. With increasing As concentration, the proportion of As3+ adsorbed on EPS increased. Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp. At day 8, the minerals were composed of goethite, galena, and siderite. With the increasing mineralization time, the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite (FeCO3) or goethite (α-FeOOH), and the specific surface area and active sites of minerals were reduced. It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals. This study is potential to understand the biomineralization mechanism of iron-oxidizing bacteria and As remediation in the environment.

Ab initio calculation of the adsorption of As, Cd, Cr, and Hg heavy metal atoms onto the illite(001) surface: Implications for soil pollution and reclamation

Elucidating the mechanisms of heavy metal (HM) adsorption on clay minerals is key to solving HM pollution in soil. In this study, the adsorption of four HM atoms (As, Cd, Cr, and Hg) on the illite(001) surface was investigated using density functional theory calculations. Different adsorption configurations were investigated and the electronic properties (i.e., adsorption energy (Ead) and electron transfer) were analyzed. The Ead values of the four HM atoms on the illite(001) surface were found to be As > Cr > Cd > Hg. The Ead values for the most stable adsorption configurations of As, Cr, Cd, and Hg were −1.8554, −0.7982, −0.3358, and −0.2678 eV, respectively. The As atoms show effective chemisorption at all six adsorption sites, while Cd, Cr, and Hg atoms mainly exhibited physisorption. The hollow and top (O) sites were more favorable than the top (K) sites for the adsorption of HM atoms. The Gibbs free energy results show that the illite(001) surface was energetically favorable for the adsorption of As and Cr atoms under the influence of 298 K and 1 atm. After adsorption, there was a redistribution of positions and reconfiguration of the chemical bonding of the surface atoms, with a non-negligible influence around the upper surface atoms. Bader charge analysis shows electrons were transferred from the surface to the HM atoms, and a strong correlation between the valence electron variations and the adsorption energy was observed. HM atoms had a high electronic state overlap with the surface O atoms near the Fermi energy level, indicating that the surface O atoms, though not the topmost atoms around the surface, significantly influence HM adsorption. The above results show illite(001) preferentially adsorbed As among all four investigated HM atoms, indicating that soils containing a high proportion of illite might be more prone to As pollution.

Synergy of Fe and biogenic Mn oxide components mediated by a newly isolated indigenous bacterium to enhance As(III/V) immobilization in groundwater

Biogenic Fe–Mn oxides (BFMO) have shown potential to control As pollution. However, the immobilization of As(III/V) via BFMO generated in situ by indigenous bacteria in groundwater has received little attention. In this study, the oxidation and adsorption of As(III/V) by BFMO induced via a newly isolated indigenous bacterium (Comamonas sp. RM6) and the interaction between the components of BFMO were investigated in high arsenic groundwater by batch experiment combined with structural characterization. The results showed that strain RM6 exhibited high Mn(II) removal capacity (80%) and maximal Mn-oxidizing activity (45%) at the initial Mn(II) concentration of 15 mg/L. The BFMO formed by bacterial induction was a bacteria-mineral complex consisting of Fe oxides (2-line ferrihydrite) and biogenic Mn oxides (δ-MnO2). In the immobilization of BFMO to As(III) and As(V), the As(T) removal efficiencies were 83% and 82%, respectively, in which the Fe oxide component dominated the adsorption of As, while the biogenic Mn oxide component mainly acted as an oxidant. Furthermore, Fe and biogenic Mn oxide components synergistically promoted the immobilization of As(III/V) in groundwater. Therefore, the biostimulation of indigenous Mn oxidizing bacteria and the effective immobilization of As(III/V) via BFMO may be used as a potential strategy for in situ remediation of high arsenic groundwater.

“One-pot” synthesis of mesoporous ion imprinted polymer for selective adsorption and detection of As(V) in aqueous phase via cooperative extraction mechanism

The mesoporous As(V) ion imprinted polymer (M−IIP) was synthesized in aqueous environment by simple “one-pot” co-polycondensation with functional monomer 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane (AAAPTS) and functionalized ligand diethylenetriamine (DETA), which can effective and selective adsorption of As(V) ion throughcooperative mechanisms. The synthesized M−IIP with good nanoparticles structure and rough surface, exhibited excellent adsorption capacity and selectivity for As(V) with the saturated adsorption capacity of 78.74 mg / g and imprinting factor of 1.2. Additionally, the adsorption behavior of M−IIP was more consistent with the Langmuir model (R2 = 0.994) and pseudo-second-order model (R2 = 0.999), indicating a monolith homogeneous adsorption process with chemical interaction between As(V) and the M−IIP. The M−IIP demonstrated a highly selective adsorption, and the adsorption capacity of M−IIP retained 93.0% after 6 successive recycles. The M−IIP can be used in the treatment of actual water samples with the recovery rate of 81.8%-95.4% and the RSD of 0.9%-7.9%, and the limit of detection (LOD) can be as low as 0.64 μg·L−1 with a good linear relationship (R2 = 0.991) from 5 ∼ 200 μg·L−1. The synthesized M−IIP with favourable mesoporous structure, excellent adsorption capacity and selectivity, provides a prospect for selective adsorption, removal and trace detection of toxic As(V) in real water samples.

Adsorption behavior of arsenic onto lignin-based biochar decorated with zinc

This study evaluated the adsorption properties of arsenic (As) by lignin biochar (LBC) decorated with Zn (Z-LBC) derived from the impregnation reaction of ZnCl 2 colloid and the pyrolysis process. The carbon contents of LBC and Z-LBC were 92.8% and 80.2%, respectively. The carbon content in Z-LBC was lower than that of LBC, demonstrating that Zn was clearly deposited in Z-LBC. The surface area of Z-LBC (255 m 2 /g) was higher than that of LBC (244 m 2 /g) and showed a more well-developed pore structure. The adsorption amounts of As by pure lignin, LBC, and Z-LBC were 0.44, 1.50, and 18.3 mg/g, respectively, and Z-LBC showed a strong affinity for As. The optimal isotherm and kinetic models for predicting the adsorption of As by Z-LBC were the Langmuir isotherm and pseudo-second order kinetic model, respectively, and the maximum adsorption capacity derived from the Langmuir isotherm was 20.2 mg/g. The adsorption properties of As by Z-LBC were dominantly influenced by the initial pH and Z-LBC dose. In addition, FTIR analysis clearly showed a difference in the functional group of Z-LBC before and after As adsorption, which proved that As was adsorbed on the surface of Z-LBC. Overall, Z-LBC is derived from the impregnation reaction of the ZnCl 2 colloid, and the pyrolysis process is adequately utilized as an adsorbent for As removal. However, since the amount of As adsorbed by Z-LBC is greatly affected by the initial pH and Z-LBC dose, a management plan will be necessary. • Zinc-impregnated biochar (Z-LBC) was prepared by Zn impregnation and pyrolysis processes. • Z-LBC showed a strong affinity for arsenic with maximum adsorption capacity of 20.2 mg/g. • Chemisorption was the rate-limiting factor for the adsorption of arsenic onto Z-LBC. • Adsorption of As is dominantly influenced by the outer boundary of the Z-LBC surface. • FTIR results clearly demonstrated the adsorption of arsenic by Z-LBC.

Cu decorated functionalized graphene for Arsenic sensing in water: A first principles analysis

The pristine graphene (G) and copper decorated boron/nitrogen doped graphene (Cu-B/NG) nanosheets have been computationally analyzed and demonstrated for their detection ability towards Arsenic, presence in the aqueous environment. The sheet’s detection ability has been analyzed in terms of it’s interaction stability and the observed variations in electronic and transport properties. The results reveal that the interaction stability of As has improved significantly for the Cu-BG/NG sheets in comparison to the pristine graphene. The computed electronic properties deduce the adsorption of As, transforms the semiconducting behavior of the Cu-BG/NG sheets into metallic, leading to the variation in its conductance. The observed variation in conductance found to be 25% and 55% for Cu-BG and Cu-NG sheets, respectively, which are relatively higher than the one computed for its pristine (19%) counterpart. Thus, the above results confirm that the functionalization of graphene sheet via doping and decoration with nitrogen and copper, respectively (Cu-NG), enhances the sheet's response by 189%, compared to the pristine sheet. Therefore, Cu-NG nanosheet can be implemented as a potential candidate as Arsenic detector in the aqueous environment.

Efficient removal of arsenic from copper smelting wastewater via a synergy of steel-making slag and KMnO4

Copper smelting wastewater, one of the most significant sources of arsenic pollution from the copper extraction process of arsenic-associated minerals, seriously impedes the attainment of sustainable industrial development due its tremendous disposal cost and the potential risks it poses. Steel-making slag can effectively detoxify low arsenic-bearing wastewater, but its low removal rate, low adsorption capacity, and high arsenic concentration limit its large-scale application. In the study, we propose a cost-effective and feasible strategy for the disposal of high arsenic-bearing wastewater from copper smelting plant via a synergy of steel-making slag and permanganate (KMnO4). Steel-making slag dissolved in wastewater releases Fe, Ca, and Si ions while simultaneously increasing the pH value of the solution. Afterward, As(III) and Fe(II) are oxidized to As(V) and Fe(III) in situ through the permanganate, generating an amorphous FeAsO4 precipitate and As-adsorbing Fe(OH)3 flocs. The dissolution and oxidization reaction is driven by a mutually improved cycle of reduction-generated H+ and MnO2, ensuring the continuous precipitation and adsorption of As. In this study, the synergy between steel-making slag and KMnO4 successfully achieved an arsenic removal rate of 91.37% and an arsenic removal capacity of 32.37 mg/g with an initial arsenic concentration of 1834 mg/L and a sulfuric acid concentration of 2800 mg/L. In combination with the adjustment of the pH value, subsequently, residual Fe, Ca, and Si ions were further hydrolyzed in the form of new Fe(OH)3 flocs and a Ca2SiO4 gel, promoting the deep purification of the wastewater. The final residual arsenic concentration achieved was 1.54 mg/L at a pH value of 10. Based on this study case, a process by which cooper smelting wastewater can be successfully treated via the synergy of steel-making slag and KMnO4 is proposed, which is potentially feasible for industrial application.

Influence of Organic Fertilizers and Brassinosteroids on Accumulation and Uptake of as and Cd by Rice Seedlings (Oryza Sativa L.) Grown in Soil

ABSTRACT The influence of four organic fertilizers (OF) (rapeseed dregs (RD), sesame dregs (SD), bean dregs (BD), and peanut dregs (PD)), two brassinosteroids (Br) (24-epibrassinolide (Br24), and 28-homobrassinolide (Br28)), and their combination (RD+Br and BD+Br) on the accumulation and uptake of arsenic (As) and cadmium (Cd) by rice plants grown in paddy soil spiked with 40 mg kg−1 As and 5 Cd mg kg−1 was performed under waterlogged conditions. The results showed that OF, Br, and their combination significantly decreased Cd contents in shoot and root, but increased As contents in shoot of rice seedling. Iron (Fe) concentration in shoot showed a significant negative correlation with Cd concentration in shoot, but a positive correlation with As concentration in shoot. There was a positive correlation between the Fe content and As or Cd content in plaque. The application of SD, BD, and BD+Br increased the amount of iron plaque, which promoted the adsorption of As, manganese (Mn), copper (Cu), and zinc (Zn) on root surface of rice plant. These findings suggested that the application of OF, Br, and their combination in As-Cd-contaminated paddy soil was an effective approach to decrease Cd uptake by rice plant, but not for As reduction. This is a preliminary study, which has the potential for further enhancing the understanding of uptake mechanisms of As and Cd in rice plant in paddy fields.

Identification of pH-dependent removal mechanisms of lead and arsenic by basic oxygen furnace slag: Relative contribution of precipitation and adsorption

Removal mechanisms, precipitation and adsorption, of lead (Pb) and arsenic (As) by basic oxygen furnace (BOF) slag were studied at pH 7–pH 13 range. Specifically, the relative contribution of precipitation and adsorption on Pb and As removal was investigated. Pb was mainly removed by precipitation at the pH values tested, as evidenced by the presence of Pb-hydroxide precipitate confirmed by X-ray diffractometry. In contrast, As seemed to be removed mainly by adsorption at the pH range tested. But, precipitation of amorphous calcium (Ca) arsenate was observed at above pH 11. An experiment with Ca-reduced BOF slag provides a line of evidence implying the involvement of Ca2+ in the adsorption of As, probably by bridging between slag surface and As oxyanions. X-ray photoelectron spectroscopy and thermogravimetric analysis also elucidated that calcium hydroxide and calcium carbonate were coated on the slag surface at pH 13, which probably blocked As adsorption. When tested following the toxicity characteristic leaching procedure, the precipitation seemed more stable than the adsorption. The removal mechanism and efficiency demonstrated in this study would contribute to the reuse of BOF slags for Pb and As removal.

Experiment-based geochemical modeling of Arsenic(V) and Arsenic(III) adsorption onto aquifer sediments from an inland basin

Natural occurrence of groundwater arsenic (As) exists in many aquifers and threatens the health of hundreds of millions of people. Adsorption of As is critical to its distribution in aquifer groundwater, as it can lower dissolved As concentrations and provide a source for As mobilization. However, little is known about As adsorption onto aquifer sediments in inland basins. To fill this gap, we investigated As(V) and As(III) adsorption onto a brown sediment hosting low-As groundwater and two gray sediments hosting high-As groundwater sampled from an approximate flow path of the Hetao Basin, China. Those three sediments had total Fe contents of around 1.3% and As contents of around 9.0 μg/g. Arsenic(III) adsorption were kinetically faster than As(V) adsorption on the sediments. The characteristics of As(V) and As(III) adsorption both exhibited nonlinear isotherms, with adsorption decreasing with increases in pH from around 7 to 9 (typical ambient groundwater pH of inland basins). Generally, As(V) adsorption was greater than As(III) adsorption at pH < 7.5, whereas the opposite was true at pH > 7.5. Phosphate competed more strongly with As(V) adsorption than As(III) adsorption, while HCO3 competed more strongly with As(III) adsorption. Aqueous As(III) was oxidized to As(V) by interaction with the brown sediment, mainly due to its high content of extractable Mn(IV) oxides. Arsenic adsorption onto the sediments was primarily controlled by the content and crystallinity of their Fe(III) oxides. The brown sediment showed weaker affinity for As(V) and As(III) than the gray sediments, possibly due to the better crystallinity of the Fe(III) oxides in the brown sediment. In the two gray sediments containing Fe(III) oxides with similar crystallinities, the As adsorption capacity was related to the content of Fe(III) oxides. Geochemical models were developed to quantitatively simulate As(V) and As(III) adsorption onto aquifer sediments. Experimental data were approximated well by these models, indicating that As(V) adsorption decreases at elevated pH and PO4 concentration, while As(III) desorption is favored at high pH and concentrations of HCO3 and PO4. According to the models, the extent and kinetics of As(III) oxidation are controlled by the number of free oxidation sites in Mn(IV) oxides, pH, and As(III) concentration. This study suggests that the characteristics of As adsorption are highly dependent on the mineral phases existing in the sediments, which must be fully understood to quantify the reactive transport of groundwater As in aquifer systems.