Presence Of Oxyanions Research Articles

Goethite and Hematite Nucleation and Growth from Ferrihydrite: Effects of Oxyanion Surface Complexes.

The presence of oxyanions, such as nitrate (NO3-) and phosphate (PO43-), regulates the nucleation and growth of goethite (Gt) and hematite (Hm) during the transformation of ferrihydrite (Fh). Our previous studies showed that oxyanion surface complexes control the rate and pathway of Fh transformation to Gt and Hm. However, how oxyanion surface complexes control the mechanism of Gt and Hm nucleation and growth during the Fh transformation is still unclear. We used synchrotron scattering methods and cryogenic transmission electron microscopy to investigate the effects of NO3- outer-sphere complexes and PO43- inner-sphere complexes on the mechanism of Gt and Hm formation from Fh. Our TEM results indicated that Gt particles form through a two-step model in which Fh particles first transform to Gt nanoparticles and then crystallographically align and grow to larger particles by oriented attachment (OA). In contrast, for the formation of Hm, imaging shows that Fh particles first aggregate and then transform to Hm through interface nucleation. This is consistent with our X-ray scattering results, which demonstrate that NO3- outer-sphere and PO43- inner-sphere complexes promote the formation of Gt and Hm, respectively. These results have implications for understanding the coupled interactions of oxyanions and iron oxy-hydroxides in Earth-surface environments.

Effect of water-soluble polymers on the transport of functional group-modified polystyrene nanoplastics in goethite-coated saturated porous media

The research on the impact of water-soluble polymers (WSPs) on the migration and fate of plastic particles is extremely limited. This article explored the effects of polyacrylic acid (PAA, a common WSP) and physicochemical factors on the transport of polystyrene nanoparticles (PSNPs-NH2/COOH) with different functional groups in QS (quartz sand) and FOS (goethite-modified quartz sand, simulates mineral colloids). Research has shown that PAA can selectively adsorb onto the surface of PSNPs-NH2, forming ecological corona heterogeneous aggregates. This process increased the spatial hindrance and elastic repulsion, resulting in the recovery of PSNPs-NH2 always exceeding that of PSNPs-COOH. Overall, PAA can hinder the migration of PSNPs in QS but can promote their migration in FOS. When multivalent cations coexist with PAA, the transport of PSNPs in the media is primarily affected by cation bridging and CH-cation-π interaction. The presence of oxyanions and PAA prevents PSNPs from following the Hofmeister rule and promotes their migration (PO43-: 82.34 ± 0.16% to 94.63 ± 2.82%>SO42-: 81.38 ± 2.73% to 91.15 ± 0.93%>NO3-: 55.85 ± 0.70%−87.16 ± 3.80%). The findings of this study contribute significantly to a better understanding of the migration of WSPs and group-modified NPs in complex saturated porous media.

Nano-size plastics inhibited Cr(VI) species transformation during facilitated transport of green synthesized nano-iron in the presence of oxyanions

Remediating hexavalent chromium (Cr(VI))-contaminated soils using green synthesized nano-iron (g-nZVI), which merits high reactivity, low cost, and environmental friendliness, has attracted significant attention. However, the broad existence of nano plastics (NPs) could adsorb Cr(VI) and subsequently influence in situ remediation of Cr(VI)-contaminated soil by g-nZVI. To clarify this issue and improve the remediation efficiency, we investigated the co-transport between Cr(VI) and g-nZVI coexisting with sulfonyl-amino-modified nano plastics (SANPs) in water-saturated sand media in the presence of oxyanions (i.e., phosphate and sulfate) at environmentally relevant conditions. This study found that SANPs inhibited the Cr(VI) reduction to Cr(III) (i.e., Cr2O3) by g-nZVI, attributed to nZVI-SANPs hetero-aggregates and Cr(VI) adsorption on SANPs. Notably, “nZVI-[SANPs•••Cr(III)]” agglomerate happened via complexation of [–NH3•••Cr(III)] between Cr(III) from Cr(VI) reduced by g-nZVI and amino group on SANPs. Further, the co-presence of phosphate (stronger adsorption on SANPs than g-nZVI) remarkably suppressed Cr(VI) reduction. Then, it promoted the co-transport of Cr(VI) with nZVI-SANPs hetero-aggregates, which could potentially threaten underground water. Fundamentally, sulfate would instead concentrate on SANPs, hardly impacting the reactions between Cr(VI) and g-nZVI. Overall, our findings provide crucial insights into understanding the Cr(VI) species transformation during co-transport with g-nZVI in ubiquitous complexed soil environments (i.e., containing oxyanions) contaminated by SANPs.

Aggregation and charging of natural allophane particles in the presence of oxyanions

Allophane is a typical clay mineral in young volcanic ash soil with special and complex structures and properties. The aggregation-dispersion and charging behaviors of natural allophane may have implications on sustainable agriculture and environment. Oxyanions, such as phosphate and arsenate, may also be related to many environmental resource problems. To investigate the aggregation and charging behaviors of allophane in the presence of oxyanions, the stability ratio (W) and electrophoretic mobility (EPM) of allophane were measured. The results of EPM, W and the values of CCCs show ion specific effect, which is not explicitly considered by the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. However, the relationship between critical coagulation ionic strength (CCIS) and surface charge density from EPM based on DLVO theory with the Debye-Huckel (DH) approximation is in good agreement with the experimental CCIS. This agreement indicates that the DLVO forces controlled by ionic strength and electrokinetic charge are the driving forces in the aggregation process of natural allophane particles in the presence of oxyanions.

Biodegradation of Highly Concentrated Phenol and Ammonia in the Presence of Oxyanions in Sequential A 2 /O MBBR System

Biodegradation of Highly Concentrated Phenol and Ammonia in the Presence of Oxyanions in Sequential A ² /O MBBR System

Competitive inhibition of catalytic nitrate reduction over Cu–Pd-hematite by groundwater oxyanions

The presence of various oxyanions in the groundwater could be the main challenge for the successive application of Cu–Pd-hematite bimetallic catalyst to aqueous NO3− reduction due to the inhibition of its catalytic reactivity and alteration of product selectivity. The batch experiments showed that the reduction kinetics of NO3− was strongly suppressed by ClO4−, PO43−, BrO3− and SO32− at low concentrations (>5 mg/L) and HCO3−, CO32−, SO42− and Cl− at high concentrations (20–500 mg/L). The presence of anions significantly changing the end-product selectivities influenced high N2 selectivity. The selectivity toward N2 increased from 55% to 60%, 60%, and 70% as the concentrations of PO43−, SO32−, and SO42− increased, respectively. It decreased from 55% to 35% in the presence of HCO3− and CO32− in their concentration range of 0–500 mg/L. The production of NO2− was generally not detected, while the formation of NH4+ was observed as the second by-product. It was found that the presence of oxyanions in the NO3− reduction influenced the reactivity and selectivity of bimetallic catalysts by i) competing for active sites (PO43−, SO32−, and BrO3− cases) due to their similar structure, ii) blockage of the promoter and/or noble metal (HCO3−, CO32−, SO42−, Cl− and ClO4− cases), and iii) interaction with the support surface (PO43− case). The results can provide a new insight for the successful application of catalytic NO3− reduction technology with high N2 selectivity to the contaminated groundwater system.

A Hexapodal Capsule for the Recognition of Anions.

We herein describe the preparation, characterization, and recognition characteristics of novel hexapodal capsule 1 composed of two benzenes joined by six hydrogen bonding (HB) groups to encircle space. This barrel-shaped host was obtained by reversible imine condensation of hexakis-aldehyde 2 and hexakis-amine 3 in the presence of oxyanions or halides acting as templates. Fascinatingly, capsule 1 includes 18 HB donating (Csp2-H and N-H) and 12 HB accepting groups (C═O and C═N) surrounding a binding pocket (78 Å3). In this regard, the complexation of fluoride, chloride, carbonate, sulfate, and hydrogen phosphate was probed by NMR spectroscopy (DMSO) and X-ray diffraction analysis to disclose the adaptive nature of 1 undergoing an adjustment of its conformation to complement each anionic guest. Furthermore, the rate by which encapsulated chloride was substituted by sulfate or hydrogen phosphate was slow (>7 days) while the stability of [SO4⊂1]2- was greatest in the series with Ka > 107 M-1 in highly competitive DMSO. With facile access to 1, the stage is set to probe this modular, polyvalent, and novel host to further improve the extraction of tetrahedral oxyanions from waste and the environment or control their chemistry in living systems.

Impact of Elevated Nitrate and Perchlorate in Irrigation Water on the Uptake, Speciation, and Accumulation of Arsenic in Rice (Oryza sativa L.)

In the absence of adequate molecular oxygen in a continuously flooded soil, other oxidizing anions can potentially oxidize arsenite (As(III)) into arsenate (As(V)) and reduce the bioavailability of arsenic (As) to rice while maintaining high rice yield. We conducted a greenhouse study to evaluate the effect of two prevalent oxyanions (10 mg/L nitrate and/or 50 μg/L perchlorate) on the As uptake, speciation, and accumulation in a hybrid rice (XL753) at the heading and maturity stages. The presence of nitrate and/or perchlorate at the used concentrations increased the rice grain yield by 35–93% to16.6–23.8 g/pot while lowering the total As in rice grains by 34–45% to 0.81–0.97 mg/kg dry weight. Perchlorate alone led to the greatest decrease in total As. Organic As was the predominant species in rice grains, with dimethylarsinic acid (DMA) accounting for 66–76% of total As in all treatments. In contrast, inorganic As was the dominant As form in rice straws and roots, with As(V) accounting for 62.4–91.4% of total As in all treatments. The translocation and accumulation of different As species in rice tissues varied at different growth stages in the presence of two tested oxyanions, as indicated by the ratios of inorganic vs organic As and inorganic As(III) vs As(V). Overall, the presence of oxyanions in irrigation water at the tested concentrations significantly decreased the total As accumulation in rice grains, while enhancing the rice yield.

Interpreting competitive adsorption of arsenate and phosphate on nanosized iron (hydr)oxides: effects of pH and surface loading.

Arsenate and phosphate have similar properties due to their electrochemical structures, but their environmental impacts are unique. The abundance and competition of arsenate and phosphate determine their bioavailability and leachability; thus, it is essential to understand their fate in the soil environment. In this study, the effects of pH and surface loading on the competitive adsorption of arsenate and phosphate on four iron (hydr)oxides were evaluated by employing the Langmuir isotherm, competitive sorption ratio (CSR), and competition effect (CE). The stability and transformation of the iron (hydr)oxides were also assessed. Various adsorption patterns were observed in the single and mixed treatments by controlling the addition of oxyanions, pH, surface loading, and type of iron (hydr)oxides. Arsenate was preferentially adsorbed at a low pH, whereas phosphate showed the opposite trend. The CEAs(V),P(V) was close to zero at low surface density (no competition) and sequentially changed to negative or positive values with increasing surface density, indirectly indicating the sequential development of promotive and competitive effects. Transformation in goethite was identified at a high pH with the presence of oxyanions, except that no transformation was observed upon the addition of oxyanions and with pH change. However, the stability of the iron (hydr)oxides decreased at a low pH and with the presence of phosphate, arsenate, or both. The hematite showed a significant promotive effect regardless of the pH. Our study revealed that the pH, surface loading, and type of iron (hydr)oxides are intercorrelated and simultaneously affect the adsorption characteristics of oxyanions and the stability of iron (hydr)oxides.

Aggregation and charging of sulfate and amidine latex particles in the presence of oxyanions

Electrophoretic mobility and time resolved light scattering are used to measure the effect on charging and aggregation of amidine and sulfate latex particles of different oxyanions namely, phosphate, arsenate, sulfate, and selenate. In the case of negatively charged sulfate latex particles oxyanions represent the coions, while they represent counterions in the case of the positively charged amidine latex. Repulsive interaction between the sulfate latex surface and the coions results in weak ion specific effects on the charging and aggregation. On the other hand the interaction of oxyanions with the amidine latex surface is highly specific. The monovalent dihydrogen phosphate ion strongly adsorbs to the positively charged surface and reverses the charge of the particle. This charge reversal leads also to the restabilization of the amidine latex suspension at the intermediate phosphate concentrations. In the case of dihydrogen arsenate the adsorption to amidine latex surface is weaker and no charge reversal and restabilization occurs. Similar differences are seen between the sulfate and selenate analogues, where selenate adsorbs more strongly to the surface as compared to the sulfate ion and invokes charge reversal. The present results indicate that ion specificity is much more pronounced in the case of counterions.

Synthesis of Birnessite in the Presence of Phosphate, Silicate, or Sulfate.

Layered manganese (Mn) oxides, such as birnessite, are versatile materials in industrial applications and common minerals mediating elemental cycling in natural environment. Many of birnessite properties are controlled by Mn(III) concentration and particle sizes. Thus, it is important to synthesize birnessite nanoparticles with controlled Mn(III) concentrations and sizes so that one can tune its properties for many applications. Birnessite was synthesized in the presence of oxyanions (phosphate, silicate, or sulfate) during reductive precipitation of KMnO4 by HCl and characterized using multiple synchrotron X-ray techniques, electron microscopy, and diffuse reflectance UV-vis spectroscopy. Results indicate that all three anions decrease MnO6 sheet sizes, attributed to oxyanion adsorption on edges of the sheets, inhibiting their lateral growth. As a result of decreased sizes, sheets undergo significant structural contraction. Meanwhile, Mn(III) concentration significantly increases with increasing oxyanion/Mn ratio. The increased Mn(III) concentration, along with the decreased size, enlarges both direct and indirect band gaps of birnessite. Phosphate imposes the strongest influence, followed by silicate and then by sulfate, consistent with their decreasing adsorption affinity. Reacting with 1 M KOH solution effectively removed the adsorbed oxyanions while leading to increased sheet sizes, probably due to oriented attachment-driven particle growth mechanisms. The results have important implications for developing highly performed birnessite materials, for example, small size Mn(III)-rich birnessite for photochemical and catalytic applications, as well as for understanding chemical compositional variations of naturally occurring birnessite.

Spectroscopic and Thermodynamic Analysis of Cd2+ Ion Sorption Kinetics by Manganese Dioxide in the Presence of Oxyanions

The present study reports the effect of contact time, nature of electrolyte, and temperature on the sorption kinetics of Cd2+ by manganese dioxide, which is the most active oxide in soils and sediments. The sorption kinetics of Cd2+ by manganese dioxide is evaluated at pH 6 in different electrolytes in the temperatures range 293-323 K. The solid samples are equilibrated in 0.45 mmol.L−1 Cd2+ and different electrolytes at pH 6. The results indicate that sorption of Cd2+ increases with time and temperature and the system attains equilibrium within 60 min in KNO3 as the electrolyte. However, in the presence of 0.001 M KH2PO4 sorption of Cd2+ increases and the time for equilibrium shifts to 90 min. The data second-order kinetics model and the calculated rate constant k and initial sorption rate h increases with increasing temperature phosphate treatment. Among the calculated thermodynamic activation parameters the positive values of ΔH‡ and ΔG‡ show the sorption process to be endothermic and nonspontaneous, while the ΔS‡ being negative indicates a decrease in randomness of the system during sorption process at the solid-liquid interface. The free energy of activation decreases from 15.95 kJ.mol−1 in nitrate to 8.76 kJ.mol−1 in phosphate. These observations suggest that the rate controlling step in Cd2+ sorption is diffusionally controlled, a fact that has been proved by application of Fick’s law.

Corrosion inhibition performance of polypyrrole Al flake composite coatings for Al alloys

Polypyrrole (PPy) was deposited on Al flakes in the presence of oxyanions (molybdate, phosphate or vanadate) as inhibiting dopants and the PPy modified Al flakes were incorporated into an epoxy primer as protection pigments for AA 2024-T3. The protection performance of the PPy Al flake coating was assessed by electrochemical evaluations including Scanning Vibrating Electrode Technique (SVET), Electrochemical Impedance Spectroscopy (EIS) and salt spray test. The oxyanion doped PPy Al flake coating shows enhanced protection performance for AA 2024-T3. An oxygen scavenger protection mechanism is suggested for PPy in the composite coating, and the roles of Al flake and oxyanions in the formulation are discussed.

Arsenic(III, V) adsorption on a goethite-based adsorbent in the presence of major co-existing ions: Modeling competitive adsorption consistent with spectroscopic and molecular evidence

Adsorption of the two oxyanions, arsenate (As(V)) and arsenite (As(III)), on a common goethite-based granular porous adsorbent is studied in the presence of major co-existing ions in groundwater (i.e., phosphate, silicic acid, sulfate, carbonate, magnesium, and calcium) and predicted using the extended triple layer model (ETLM), a dipole modified single-site triple layer surface complexation model consistent with spectroscopic and molecular evidence. Surface species of all ions were selected according to the previous ETLM studies and published experimental spectroscopic/theoretical molecular information. The adsorption equilibrium constants for all ions were determined using adsorption data obtained in single-solute systems. The adsorption equilibrium constants referenced to the site-occupancy standard state (indicated by Kθ) were compared with those for goethite in the literature if available. The values of these constants for the goethite-based adsorbent are found to be close to the values for goethite previously studied. These “constrained” adsorption equilibrium constants determined in single-solute systems were used in the ETLM to predict the competitive interactions of As(III, V) with the co-existing ions in binary-solute systems. The ETLM is capable of predicting As(III, V) adsorption in the presence of oxyanions (phosphate, silicic acid, sulfate, and carbonate). This study presents the first successful and systematic prediction of the competitive interactions of As(III, V) with these oxyanions using the ETLM. The ETLM prediction of surface (and aqueous) speciation also provides insights into the distinct adsorption behavior of As(III, V) in the presence of the oxyanions. Magnesium and calcium significantly enhanced As(V) adsorption at higher pH values, while they had little effect on As(III) adsorption. The enhanced adsorption of As(V), however, could not be predicted by the ETLM using the surface species proposed in previous ETLM studies. Further studies are necessary to identify ternary complexes, especially at high pH. Adsorption isotherms of As(V), a dominant form of arsenic in adsorptive water treatment systems, in the presence of the co-existing ions under relevant conditions of water treatment systems are also obtained and predicted by the ETLM to study and compare the effect of the co-existing ions on As(V) removal.

Removal of oxyanions from synthetic wastewater via carbonation process of calcium hydroxide: Applied and fundamental aspects

Removal of oxyanions (selenite, selenate, arsenate, phosphate and nitrate) during calcite formation was experimentally studied using aqueous carbonation of calcium hydroxide under moderate pressure (P CO2 ≅ 20 bar) and temperature (30 °C). The effects of Ca(OH) 2 dose (10 and 20 g), Ca(OH) 2 source (commercial pure material or alkaline paper mill waste) and oxyanion initial concentration (from 0 to 70 mg atom/L) were investigated for this anisobaric gas–liquid–solid system. The Ca(OH) 2 carbonation reaction allowed successfully the removal of selenite (>90%), arsenate (>78%) and phosphate (≅100%) from synthetic solutions. Conversely, nitrate and selenate had not any physicochemical affinity/effect during calcite formation. The rate of CO 2 transfer during calcite formation in presence of oxyanions was equal or slower than for an oxyanion-free system, allowing to define a retarding kinetic factor RF that can vary between 0 (no retarding effect) to 1 (total inhibition). For selenite and phosphate RF was quite high, close to 0.3. A small retarding effect was detected for arsenate ( RF ≈ 0.05) and no retarding effect was detected for selenate and nitrate ( RF ≈ 0). In general, RF depends on the oxyanion initial concentration, oxyanion nature and Ca(OH) 2 dose. The presence of oxyanions could also influence the crystal morphology and aggregation/agglomeration process. For example, a c-axis elongation of calcite crystals was clearly observed at the equilibrium, for calcite formation in presence of selenite and phosphate. The oxyanions removal process proposed herein was inspired on the common physicochemical treatment of wastewater using calcium hydroxide (Ca(OH) 2). The particularity, for this novel method is the simultaneous calcium hydroxide carbonation with compressed carbon dioxide in order to stabilise the solid matter. This economical and ecological method could allow the removal of various oxyanions as well as the ex situ mineral sequestration of CO 2; particularly, when the Ca(OH) 2 source comes from alkaline solid waste.

Stifling of Crevice Corrosion in Alloy 22 During Constant Potential Tests

Artificially creviced Alloy 22 (N06022) may be susceptible to crevice corrosion in the presence of high-chloride aqueous solutions, especially at higher temperatures and at anodic potentials. The presence of oxyanions in the electrolyte, particularly nitrate, inhibits the nucleation and growth of crevice corrosion. The current results show that crevice corrosion will develop in Alloy 22 when a constant potential above the crevice repassivation potential is applied to a creviced specimen. The analyses of the current output showed the presence of three characteristic domains: (1) passivation or induction time, (2) nucleation and growth, and (3) stifling and arrest. That is, under the tested conditions, crevice corrosion did initiate but after it reached a critical stage of growth, further damage stalled and the output anodic current returned to the passive values before the nucleation of the attack.

Mechanisms of Inhibition of Crevice Corrosion in Alloy 22

ABSTRACTAlloy 22 may be susceptible to crevice corrosion in chloride-containing environments, especially at temperatures above ambient. The presence of oxyanions, especially nitrate, minimizes or eliminates the susceptibility of Alloy 22 to crevice corrosion. Other anions such as sulfate, carbonate and fluoride were also reported as inhibitors of crevice corrosion in Alloy 22. It is argued that the occurrence of crevice corrosion is due to the formation of hydrochloric acid solution in the creviced region. Inhibitors act by eliminating the occurrence of hydrochloric acid or by hampering its action.

A MODEL FOR THE ION-PAIRS OF TRIS(TRIMETHYLENEDIAMINE)COBALT(III) WITH POLYOXYANIONS. THE ORIGINS OF THE CIRCULAR DICHROISM CHANGES

Abstract Through structural and circular dichroism spectral comparison, 1,1,1-tris(3′-aminopropylaminomethyl)-ethanecobalt(III), Co(spn)3+, has been determined to be a model for the oxyanion ion-pairs of Co(tn)3 3+. The CD spectral changes of δ-Co(spn)3+ in the presence of oxyanions in conjunction with previous investigations suggest that conformational changes of the six-membered rings cause the intensities of the Ea and A2 components of the octahedral T1 g band to change in a direction opposite to that observed when only asymmetric nitrogens are generated, either by oxyanion hydrogen bonding or by means of an alkyl cap. It appears that when both effects occur together it is the conformational change that dominates the CD spectral changes. In the absence of conformational change the asymmetric nitrogens cause the Ea component to decrease while the A2 component increases, as was found in previous studies. The nickel(II) and copper(II) complexes of spn are reported also.