Effect Of Other Anions Research Articles

Accumulation of Vanadium by Nanoscale Zero-Valent Iron Supported by Activated Carbon under Simulation Water Conditions: A Batch Study

Vanadium (V(V)) removal from simulation water (SW) was successfully accomplished using nanoscale zero-valent iron that was immobilized by activated carbon (NZVI/AC) which was used as an adsorbent. We investigated the effects of different parameters on V(V) removal, such as pH, dissolved oxygen (DO), common ions and adsorption kinetics for SW. The intraparticle diffusion model fits this study well (R2 > 0.9) according to the results of the kinetics investigation which showed that the adsorption of vanadium by NZVI/AC was rapid in the first 12 h and that equilibrium was reached in about 72 h. The amount of V(V) that was removed from the solution increased when it was subjected to pH 2 to pH 8, and this decreased after pH 8. While the effects of other anions and humic acid were negligible, the elimination of V(V) was significantly reduced by using phosphate and silicate. Fe2+ and Al3+, two common metal cations, improved the V(V) adsorption. High oxygen levels impeded the vanadium elimination, while anoxic conditions encouraged it. Elution with 0.1 M NaOH can be used to renew NZVI/AC in an efficient manner.

Effect of other anions on reduction of nitrate in water over Pd–In catalyst loaded on various supports

The effect of the presence of other anions on nitrate reduction was investigated using catalysts supported by TiO2 and nitrate adsorbents (calcium-chloride-treated charcoal and an anion exchange resin). When the TiO2-supported catalyst was used, the nitrate decomposition rate was greatly reduced in the presence of Cl−, SO42−, and PO43−, and the decrease was large for Cl− and PO43−. The activity of the nitrate-adsorbent-supported catalysts in the presence of SO42− and PO43− showed a smaller decrease than that of the TiO2-supported catalyst. In the presence of SO42−, the amount of nitrate adsorbed on the supports was correlated with the decrease in activity, and calcium-chloride-treated charcoal, which has high nitrate adsorption selectivity, showed the smallest decrease in activity in the presence of SO42−. By contrast, in the presence of PO43−, no clear correlation was found between the decrease in the amount of nitrate adsorption on the supports and the decrease in activity.

Galvanic displacement reaction of nickel to form one-dimensional trigonal tellurium structures in acidic solutions

Trigonal tellurium micro-wires and tubes were synthesized by galvanic displacement of nickel in acidic sulfate solutions where the growth mechanism was elucidated using various electroanalytical methods and material characterization. The effects of solution composition, including concentrations of tellurium precursor and sulfate, were studied. The transition from micro-wires to tubes with an increase in HTeO2+ concentration was observed, which might be attributed to the comparable diffusion length scale of tellurium on the cylindrical seed surface to the radius of the seed. On the other hand, increasing H2SO4 concentration led to transformation of microtubes to microwires owing to reduction deposition rate and limited mass transfer of HTeO2+ ions. The effect of other anions (i.e., Cl− and NO3−) on galvanic displacement reaction was also studied. As a strong oxidant, HNO3 dissolved nickel faster than SO4−2 and Cl−, but showed slower tellurium deposition tellurium nanowires, which might be due to co-reduction of nitrate ions. The preferential adsorption of Cl− increased both dissolution of nickel and the deposition of tellurium, resulting in larger tellurium microtubes.

The Inhibitive Effect of Artificial Seawater on Magnesium Corrosion

The corrosion behavior of pure magnesium (Mg) immersed in 3.5 wt% NaCl and artificial seawater is evaluated by immersion test, electrochemical impedance spectroscopy (EIS), polarization curve, scanning electrochemical microscopy (SECM), and corrosion morphology analysis. The results show that the corrosion rate of the pure Mg in the artificial seawater is nearly a half of that in the 3.5 wt% NaCl, and the serious localized corrosion of Mg in the NaCl is inhibited in the artificial seawater. The main constituents MgCl2 and Na2SO4 in artificial seawater are found to be inhibitive for the corrosion of Mg. The presence of Mg2+ ions could facilitate the formation of Mg(OH)2 film and thus to some extent retard the dissolution of Mg. The SO42– ions in the artificial seawater might be absorbed competitively against Cl− on the Mg surface to retard the corrosion of Mg. The corrosive and inhibitive effects of other anions and cations on Mg dissolution in the artificial seawater were also briefly analyzed.

Electrochemical reduction of hexavalent chromium on titania nanotubes with urea as an anolyte additive

The present study reports an energy efficient electrochemical strategy to remediate hexavalent chromium Cr(VI) to less toxic Cr(III). The novelty in this system is the use of titania nanotubes (TNT) synthesized by anodization as cathode for the reduction of Cr(VI) with alkaline urea as an anolyte additive. The electrochemical reduction of Cr(VI) was evaluated using bare Ti and porous TNT/Ti cathodes, both with and without urea as an anolyte additive. The experimental results showed that the dual combination of alkaline urea oxidation at anode and acidic Cr(VI) reduction on TNT cathode showed the best performance, with enhanced degradation efficiency up to 97% at 5 V within 15 min for an initial concentration of 100 mg L−1 Cr. The optimized urea-TNT combination was evaluated for the effect of catholyte pH, temperature, initial metal ion concentration and the effect of other anions, such as Cl−, NO3−, PO42− and CO32−, which are commonly present in wastewater discharged from tannery or electroplating industries. Furthermore, the performance when evaluated with cow urine as an anolyte additive confirmed that the dual combination could be a promising in-situ treatment technique for simultaneous urine oxidation and Cr(VI) reduction.

Hydrodynamic cavitation and activated persulfate oxidation for degradation of bisphenol A: Kinetics and mechanism

Bisphenol A (BPA) is an endocrine disruptor and is toxic at low concentrations. Furthermore, in order to oxidize BPA at the water treatment, an economical treatment method is required. This study was the first study to apply hydrodynamic cavitation/persulfate (HC/PS) processes to degrade BPA and investigated the effects of important operating parameters, such as HC inlet pressure, PS loading, pH, temperature and other anions. The results showed that the optimal pressure of HC was 0.5 MPa and the rate constant increased as the PS load concentration increased. The contribution of OH and SO4− to BPA oxidation using HC/PS processes was 10.3% and 89.7%, respectively. The reaction rate constant decreased with increasing pH and the reaction rate constant increased with increasing temperature. The activation energy was 69.62 kJ mol−1. The effects of other anions on BPA degradation were in the following order: Cl−> NO3−> HCO3−. Five major intermediates were formed in the HC/PS processes and they were obtained during 120 min of operation. Based on this, this study described the decomposition pathway of BPA. The kinetic study and economic evaluation of the HC/PS processes can be used as basic data for the real wastewater treatment process in the future.

Competing Effects of Chloride, Nitrate, and Sulfate Ions on the Removal of Fluoride by a Modified Zeolitic Tuff

Natural zeolitic tuff was modified with FeCl3 solution for the removal of fluoride, and the effect of chloride, nitrate, and sulfate ions was examined on fluoride sorption from solutions and drinking water. The unmodified zeolitic tuff (Z) and the iron-modified zeolitic tuff (Fe(III)-Z) were characterized by scanning electron microscopy and X-ray diffraction analysis. The elemental composition, the specific surface area, and the point of zero charge of the zeolitic material were also determined. The fluoride adsorption was carried out in a batch system considering the effect of contact time, the initial concentration of fluoride ions, and the effect of other anions naturally present in the drinking water. The kinetic and isotherm results were adjusted to the pseudo-second-order and Freundlich models, respectively, which indicated that the sorption mechanism was chemisorption on a heterogeneous material. The fluoride sorption capacity was higher in solutions (2.7 mg/g) than in drinking water (0.41 mg/g), and this could be attributed to the presence of other anions. Overall, the presence of chloride ions significantly diminished the fluoride adsorption capacity, while the presence of nitrate and sulfate ions did not show any significant effect; the anion removal efficiency by Fe(III)-Z followed the order F− > > Cl− > NO3 − > SO4 2−.

Enhancement of phosphate removal from water by TiO2/Yemeni natural zeolite: Preparation, characterization and thermodynamic

In order to develop an effective technique for enhancing the efficiency of phosphate ion (PO43−) removal, a novel composition of TiO2/Zeolite (TZ) adsorbent was prepared and investigated systematically. The characteristics of TZ and its mechanism for PO43− removal were investigated and compared with that of natural zeolite (NZ). Important parameters which affect adsorption, such as contact time, pH, dosage, temperature, initial PO43− concentration and the presence of competing anions were investigated. Almost 100% removal efficiency was achieved by the TZ composite at low initial PO43− concentrations. The specific surface area and PO43− adsorption capacity of the composite material reached 166.5m2/g and 37.6mg/g, respectively. Moreover, Maximum adsorption occurred at around pH 2–4 and 35°C. The results of zeta potential, FTIR, XRF and EDS analyses indicated that electrostatic attraction and replacement of surface hydroxyl groups (T/OH) by phosphate were the main adsorption mechanism. Arsenate and silicate markedly decreased the removal of PO43− whereas the effect of other anions was insignificant. The adsorption isotherm results illustrated that Freundlich model (FM) provided the best fit for the equilibrium data. In addition to that, the change in free energy (ΔG○), enthalpy (ΔH○) and entropy (ΔS○) revealed that the adsorption of PO43− ion by zeolite is spontaneous and endothermic at 25 and 35°C. It was concluded that a TiO2/Zeolite composite is a highly efficient and economic adsorbent material with good regeneration and can be utilized in the remediation of environmental pollution.

Hydrogeochemistry and arsenic contamination of groundwater in the Jianghan Plain, central China

Although high arsenic groundwater has been reported in the northwest of China, no data describing groundwater arsenic in the river plains of central China have been published to date. In this study, 186 groundwater samples were collected from the Jianghan Plain between the Yangtze and Han rivers. Major constituents, trace elements, dissolved organic carbon (DOC), and stable hydrogen and oxygen isotopic compositions were analyzed to characterize groundwater chemistry and evaluate the factors controlling arsenic concentration and distribution in the plain. The results show that the groundwater is mainly HCO3–CaMg type with circum-neutral pH and moderate to high electrical conductivity. Negative Eh and high concentrations of DOC clearly indicate strongly reducing conditions with abundant organic matter in the groundwater aquifers. The characteristics of H/O stable isotopes demonstrate that the groundwater in the study area is recharged by local precipitation and there is a slow evaporation effect. Groundwater with high arsenic was found in wells at depths of 10 to 45m along rivers. About 87% of the groundwater samples had As concentrations exceeding the WHO recommended value of 10μg/L, up to 2330μg/L. High concentrations of dissolved Fe (maximum value, 23mg/L), Mn (maximum value, 5mg/L) and P (maximum value, 4mg/L) were also observed in groundwater. Among the wells, 89% and 98% exceeded the WHO guideline for Fe and Mn, respectively. The concentrations of total As measured in sediments from the Jianghan Plain were much higher than the global average, ranging from 11 to 108mg/kg. All of the sediments had high Fe (Fe2O3 4–9%) and Mn (504–1064mg/kg) levels, which is consistent with Fe and Mn oxides/hydroxides considered to be the dominant minerals containing As in sediments and the main sources for As in groundwater of the Jianghan Plain. The main potential mechanism for the release of As is the reductive dissolution of Fe and Mn oxides/hydroxides under reducing conditions, while microbial degradation of organic matter may also facilitate the release of arsenic into groundwater. The competitive effects of other anions may also be important factors since the concentrations of DOC, HCO3− and dissolved P were high in many of the groundwater samples.

Predicting perchlorate uptake in greenhouse lettuce from perchlorate, nitrate, and chloride irrigation water concentrations.

Perchlorate (ClO) has been detected in edible leafy vegetables irrigated with Colorado River water. The primary concern has been the ClO concentration in lettuce ( L. var. L.). There has been a limited number of studies on ClO uptake, but the interactive effect of other anions on ClO uptake is not known in detail. We conducted a greenhouse ClO uptake experiment using two types of lettuce (iceberg and butterhead) to investigate the interaction of uptake of ClO, Cl, and NO on ClO uptake under controlled conditions. We examined three concentrations of ClO, 40, 220, and 400 nmol/L; Cl at 2.5, 13.75, and 25 mmol/L; and NO at 2, 11, and 20 mmol/L. Perchlorate was taken up the most in lettuce when ClO was the greatest and NO and Cl were lowest in concentration in the irrigation water. More ClO was detected in leafy material than in root tissue. In general, the outer leaves of iceberg and butterhead lettuce contained more ClO than did the inner leaves. The results indicate that selective ClO uptake occurs for green leaf lettuce. A predictive model was developed to describe the ClO concentration in lettuce as related to the Cl, NO, and ClO concentration in the irrigation water. Research results can be utilized to elucidate the effect of salts on the accumulation and uptake of ClO by edible leafy vegetables.

Kinetic, isotherm and thermodynamic study of nitrate adsorption from aqueous solution using modified rice husk

In this article, we prepared anionic sorbent using rice husk (RC). Anionic rice husk (ARC) structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated. The sorption of NO 3 − by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.4 g in 100 mL of NO 3 − solution, contact time of 90 min, pH = 7. In optimum condition, removal efficiency was 94.3% for the NO 3 −. The nitrate adsorption process was well described by the pseudo-second-order kinetic model, and the experimental isotherm data fitted well with the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated and the results showed that the adsorption of nitrate on ARC was spontaneous and exothermic in nature. The effect of other anions were also studied and was found that the anions reduced the nitrate adsorption in the order of carbonate > chloride > phosphate > sulphate. ARC was used for the removal of NO 3 − from real wastewater (urban wastewater) that high performance of adsorbent was considerable.

Study effect of different parameters on the sulphate sorption onto nano alumina

The aim of this research work is to investigate sorption characteristic of modified nano alumina (n-Al) for the removal of SO 4 2− from aqueous solutions and wastewater. The sorption of SO 4 2− by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.3 g in 100 ml of SO 4 2−, contact time of 35 min, pH = 5. In optimum condition, removal efficiency was 85.6% for the SO 4 2−. Three equations, i.e. Morris–Weber, Lagergren and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich and D–R are subjected to sorption data to estimate sorption capacity. It can be concluded that n-Al has potential to remove SO 4 2− ions from aqueous solutions at different concentrations. It was found that the temperature has positive effect on the process and negative Δ G values indicated thermodynamically feasible and spontaneous nature of the sorption. Positive value of Δ S reveals the increased randomness at the solid–solution interface during the fixation of the ion on the active sites of the sorbent. The effect of other anions was studied and it was found the existence of them in the solution has considerable effect on the sulphate removal.

Perchlorate Uptake in Spinach As Related to Perchlorate, Nitrate, And Chloride Concentrations in Irrigation Water

Several studies have reported on the detection of perchlorate (ClO(4)(-)) in edible leafy vegetables irrigated with Colorado River water. However, there is no information on spinach as related to ClO(4)(-) in irrigation water nor on the effect of other anions on ClO(4)(-) uptake. A greenhouse ClO(4)(-) uptake experiment using spinach was conducted to investigate the impact of presence of chloride (Cl(-)) and nitrate (NO(3)(-)) on ClO(4)(-) uptake under controlled conditions. We examined three concentrations of ClO(4)(-), 40, 220, and 400 nmol(c)/L (nanomoles of charge per liter of solution), three concentrations of Cl(-), 2.5, 13.75, and 25 mmol(c)/L, and NO(3)(-) at 2, 11, and 20 mmol(c)/L. The results revealed that ClO(4)(-) was taken up the most when NO(3)(-) and Cl(-) were lowest in concentration in irrigation water. More ClO(4)(-) was detected in spinach leaves than that in the root tissue. Relative to lettuces, spinach accumulated more ClO(4)(-) in the plant tissue. Perchlorate was accumulated in spinach leaves more than reported for outer leaves of lettuce at 40 nmol(c)/L of ClO(4)(-) in irrigation water. The results also provided evidence that spinach selectively took up ClO(4)(-) relative to Cl(-). We developed a predictive model to describe the ClO(4)(-) concentration in spinach as related to the Cl(-), NO(3)(-), and ClO(4)(-) concentration in irrigation water.

Fluoride Ions Behavior in the Presence of Corrosion Products of Iron: Effects of Other Anions

The behavior of fluoride ions in the presence of corrosion products of iron in drinking and water solutions was analyzed and the adsorption capacities of the iron oxides (corrosion products of iron) for fluoride ions were determined. Drinking water containing naturally 2.45 mg of fluoride ions per liter was characterized and the concentrations of other anions were determined. The effect of contact time, the initial concentration of fluoride ions, and the effect of other anions naturally present in the drinking water were considered. The kinetic results could be adjusted to the pseudo-second order model, which indicated that the sorption mechanism was chemisorption and the equilibrium was reached in 24 hours. The presence of bicarbonate and chloride ions diminishes the removal efficiency of the fluoride ions, whereas other anions (sulfate, phosphate, and nitrate) did not show any significant effect. The results reflect that the iron oxides products from the corrosion of a hydraulic infrastructure allow the removal of fluoride ions from water.

Aggregation behavior of poly(methacrylic acid) with cucurbit[7]uril and the effect of ammonia ions on aggregation

The interaction between poly(methacrylic acid) (PMAA) and cucurbit[7]uril (CB[7]) in aqueous solution were investigated by dynamic light scattering (DLS), fluorescence techniques, UV-spectrophotometer, and resonance light scattering (RLS). The experimental results show that the aggregates were formed between CB[7] and H+ of PMAA by the hydrogen bonding interaction that increases with increasing the concentration of CB[7], which leads to the formation of the larger aggregates. Interestingly, PMAA has temperature sensitivity with the addition of CB[7] by UV-spectrophotometer and DLS. The pH of the solution of PMAA appears a inflection point with increasing the concentration of CB[7] comparing with the increase of the electrical conductivity all the time with the addition of CB[7]. In addition, in order to investigate the effect of cation on the size of the aggregates and avoid the effect of other anions at the same time, the dilute ammonia was added into the solution of PMAA. The experimental data show that the size of the aggregates increases with adding CB[7] because CB[7] could combine with both NH 4 + by the electrostatic and iondipole interactions and H+ by the hydrogen bonding interaction, and a possible model is proposed to explain the host-guest interactions between PMAA and CB[7].

A reply

A reply

Removal of arsenic from water by supported nano zero-valent iron on activated carbon

Nano-sized zero-valent iron is an effective adsorbent for arsenic removal from drinking water. However, its application may be limited in public water system and small scale water treatment system due to its tiny particle size. In the present work, nanoscale zero-valent iron was supported onto activated carbon (NZVI/AC) by impregnating carbon with ferrous sulfate followed by chemical reduction with NaBH 4. Approximate 8.2 wt% of iron was loaded onto carbon and SEM analysis showed that the iron particles in the pores of carbon were needle-shaped with the size of 30–500 × 1000–2000 nm. Kinetics study revealed that adsorption of arsenite and arsenate by NZVI/AC was fast in the first 12 h and the equilibrium was achieved in ∼72 h. The adsorption capacity of the synthesized sorbent for arsenite and arsenate at pH 6.5 calculated from Langmuir adsorption isotherms in batch experiments was 18.2 and 12.0 mg/g, respectively. Phosphate and silicate markedly decreased the removal of both arsenite and arsenate, while the effect of other anions and humic acid was insignificant. Common metal cations (Ca 2+, Mg 2+) enhanced arsenate adsorption but ferrous iron (Fe 2+) was found to suppress arsenite adsorption. NZVI/AC can be effectively regenerated by elution with 0.1 M NaOH.

Arsenic removal by goethite and jarosite in acidic conditions and its environmental implications

Schwertmannite (Fe 8O 8(OH) 5.5(SO 4) 1.25), jarosite (KFe 3(SO 4) 2(OH) 6) and goethite (FeOOH) control natural attenuation of arsenic in acid mine drainage (AMD) impacted areas. Batch experiments were conducted to examine the sorption capacity of synthetic goethite and synthetic jarosite at highly acidic pH (1.5–2.5), at two ionic strengths (0.02–0.15 mol dm −3, NaCl) and at sulphate concentrations in the range of 5 × 10 −3 to 2.8 × 10 −1 mol dm −3. In the absence of competitive effects of other anions, K-jarosite presents better removal efficiency than goethite for As(V). The maximum sorption capacity is estimated to be 1.2 × 10 −4 and 7.0 × 10 −6 mol m −2 for jarosite and goethite, respectively, under similar experimental conditions. The variation of arsenic sorbed on goethite as a function of the equilibrium arsenic concentration in solution fits a non-competitive Langmuir isotherm. In the case of K-jarosite, sorption data could not fit a Langmuir or Freundlich isotherm since sulphate–arsenate anion exchange is probably the sorption mechanism. Ionic strength and pH have little effect on the sorption capacity of goethite and jarosite in the small range of pH studied. The presence of sulphate, which is the main anion in AMD natural systems, has a negative effect on arsenic removal since sulphate competes with arsenate for surface sorption sites. Moreover, mobilization of arsenic in the transformation of schwertmannite to jarosite or goethite at pH 2–3 is proposed since the sorption capacities of goethite and K-jarosite are considerably lower than those reported for schwertmannite.

Equilibrium, Kinetic and Mass Transfer Studies and Column Operations for the Removal of Arsenic(III) from Aqueous Solutions using Acid Treated Spent Bleaching Earth

In the present study, a new adsorbent was produced from spent bleaching earth by H2SO4 impregnation method. The sorption of arsenic(III) by acid treated spent bleaching earth was studied to examine the possibility of utilizing this material in water treatment systems. The effect of time, pH, initial concentration, temperature on the adsorption of arsenic(III) was studied. Maximum adsorption was found to occur at pH 9.0. The adsorption process followed the first order Lagergren equation. Mass transfer coefficients and rate constants of intraparticle diffusion were calculated. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacity (Q0) of the adsorbent and the value of Q0 was found to be 0.46 mmol g–1. In order to understand the adsorption mechanism, Dubinin-Radushkevich (DR) isotherm was used. The magnitude of E calculated from DR equation was found to be 5.12 kJ mol–1. The heat of adsorption (ΔH0 = –30367 J mol–1) implied that the adsorption was physical exothermic adsorption. The column studies were also carried out to simulate water treatment processes. The capacity values obtained in column studies were found to be greater than the capacity values obtained in batch studies. This result was explained by the difference between batch system and column system. The factors that affect the capacity values of column and batch systems were explained. The effect of other anions on the adsorption of arsenic(III) in the presence of NO3 –, SO4 2–, Cl–, Br– was studied. The presence of these anions did not affect the adsorption of arsenic(III) significiantly.

Sorption enhancement of phosphorus by chemically modified rice hull

Chemically modified rice hull was prepared through a single stage chemical reaction with N‐(3‐chloro‐2‐hydroxypropyl)‐trimethylammonium chloride. The sorption characteristics of this material were studied under batch and continuous flow conditions. Parameters investigated under batch conditions were different initial concentrations, agitation rates, temperature and the interfering effect of other anions. Maximum sorption of P(V) calculated from Langmuir isotherm model was 9.53 mg/g and this value is higher than that of unmodified rice hull which could sorb only 0.23 mg/g of P(V). Under continuous flow conditions, it was found that the time for 50% breakthrough showed a linear relationship with bed‐depth although it did not obey the Hutchin's bed‐depth service time model.