Complexation of arsenate to humic acid with different molecular weight fractions in aqueous solution.

Natural organic matter (NOM) has been considered a critical substance in the transport and transformation of arsenic. NOM is a complex mixture of multifunctional organic components with a wide molecular weight (MW) distribution, and it is necessary to understand the complexation of arsenic with MW-dependent NOM fractions. In this study, humic acid (HA) was chosen as the representative fraction of NOM to investigate the complexation mechanism with arsenic. The bulk HA sample was fractionated to five fractions by ultrafiltration technology, and the complexing property of HA fractions with arsenic was analyzed by the dialysis method. We observed that the acidic and neutral conditions favor the complexation of HA fractions with arsenate (As(V)). The HA fractions with molecular weight > 100 kDa, 1-10 kDa, and <1 kDa have the stronger complexing capacity of As(V) than the other HA fractions. The bound As(V) percentage was positively associated with carboxyl content, phenolic content, and especially total acidity. A two-site ligand-binding model can describe the complexing capacity of arsenic onto HA fractions. The results can provide some fundamental information about the complexation of arsenic with MW-dependent HA fractions quantitatively.

The long-term stability of calcium arsenates: Implications for phase transformation and arsenic mobilization.

It is well known that calcium arsenates may not be a good choice for arsenic removal and immobilization in hydrometallurgical practices. However, they are still produced at some plants in the world due to various reasons. Furthermore, calcium arsenates can also naturally precipitate under some specific environments. However, the transformation process of poorly crystalline calcium arsenates (PCCA) and the stability of these samples under atmospheric CO2 are not yet well understood. This work investigated the transformation process of PCCA produced by using different neutralization reagents (CaO vs. NaOH) with various Ca/As molar ratios at pH 7-12 in the presence of atmospheric CO2. After aging at room temperature for a period of time, for samples neutralized with NaOH and precipitated at pH 10 and 12, release of arsenic back into the liquid phase occurred. In contrast, for the samples precipitated at pH 8, the aqueous concentration of arsenic was observed to decrease. XRD, Raman, and SEM results suggested that the formation of various types of crystalline calcium carbonates and/or calcium arsenates controls the arsenic behavior. Moreover, the application of lime may enhance the stability of the generated PCCA. However, no matter what neutralization reagent is used, the stability of the generated PCCA is still of concern.

Thermomechanical Characterization and Modeling of NiTi Shape Memory Alloy Coil Spring.

Today, shape memory alloys (SMAs) have important applications in several fields of science and engineering. This work reports the thermomechanical behavior of NiTi SMA coil springs. The thermomechanical characterization is approached starting from mechanical loading-unloading tests under different electric current intensities, from 0 to 2.5 A. In addition, the material is studied using dynamic mechanical analysis (DMA), which is used to evaluate the complex elastic modulus E* = E' - iE″, obtaining a viscoelastic response under isochronal conditions. This work further evaluates the damping capacity of NiTi SMA using tan δ, showing a maximum around 70 °C. These results are interpreted under the framework of fractional calculus, using the Fractional Zener Model (FZM). The fractional orders, between 0 and 1, reflect the atomic mobility of the NiTi SMA in the martensite (low-temperature) and austenite (high-temperature) phases. The present work compares the results obtained from using the FZM with a proposed phenomenological model, which requires few parameters for the description of the temperature-dependent storage modulus E'.

Partitioning and transformation behavior of arsenic during Fe(III)-As(III)-As(V)-SO42- coprecipitation and subsequent aging process in acidic solutions: Implication for arsenic mobility and fixation.

The coprecipitation and subsequent aging of Fe(III)-As(III)-As(V)-SO42- play an important role in controlling As behavior in acidic systems, such as acid mine drainage and hydrometallurgical acid waste. In this study, we investigated the redistribution and transformation of As in the Fe(III)-As(III)-As(V)-SO42- system (As(III)/As(V) ≈ 1) at different Fe/As molar ratios (i.e., 0.25, 0.5, and 1) and pH (1.2 and 1.8) at 60 °C. The results showed that As(III) and SO42- can be incorporated into the amorphous ferric arsenate and scorodite host phases by forming a Fe(AsO4)x(AsO3)y(SO4)z solid solution. As(III) contents in the freshly coprecipitated solids increased with pH and initial As(III) concentrations. During aging process, As(III) contents in the solid products with Fe/As molar ratios of 0.5 and 1 increased with aging time at pH 1.8. In contrast, As(III) was gradually expelled from aging products with aging time at pH 1.2, regardless of Fe/As molar ratio. X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Raman spectroscopy characterization results showed that an As(III)-SO42--doped scorodite was formed at Fe/As molar ratio ≤0.5 during the aging process. It was also found that As(III) had an inhibitory effect on the transformation of poorly crystalline ferric arsenate to scorodite. The present study may have important implications for understanding the geochemical cycle of As, Fe, and SO42- in acidic solutions and give further understanding on the mechanisms involved in As removal and fixation in hydrometallurgical unit operations.

Further understanding of the adsorption mechanism of N719 sensitizer on anatase TiO2 films for DSSC applications using vibrational spectroscopy and confocal Raman imaging.

Vibrational spectroscopic studies of N719 dye-adsorbed TiO(2) films have been carried out by using SERRS, ATR-FTIR, and confocal Raman imaging. The high wavenumber region (3000-4000 cm(-1)) of dye adsorbed TiO(2) is analyzed via Raman and IR spectroscopy to investigate the role of surface hydroxyl groups in the anchoring mode. As a complementary technique, confocal Raman imaging is employed to study the distribution features of key dye groups (COO-, bipyridine, and C=O) on the anatase surface. Sensitized TiO(2) films made from two different nanocrystalline anatase powders are investigated: a commercial one (Dyesol) and our synthetic variety produced through aqueous synthesis. It is proposed the binding of the N719 dye to TiO(2) to occur through two neighboring carboxylic acid/carboxylate groups via a combination of bidentate-bridging and H-bonding involving a donating group from the N719 (and/or Ti-OH) units and acceptor from the Ti-OH (and/or N719) groups. The Raman imaging distribution of COO(-)(sym) on TiO(2) was used to show the covalent bonding, while the distribution of C=O mode was applied to observe the electrostatically bonded groups.

Long-term stability of the Fe(III)-As(V) coprecipitates: Effects of neutralization mode and the addition of Fe(II) on arsenic retention.

The coprecipitation of arsenic with Fe(III) by lime neutralization is widely used in industrial practices to treat arsenic-containing waste waters generated from mineral processing operations. In this work, coprecipitation was conducted directly at pH 8 to simulate the operations in hydrometallurgical practices, which differed from the conventional laboratory operations. Moreover, although ferric is the major species of iron in arsenic-containing waste waters, the coexistence of ferrous ions cannot be ignored. Therefore, the effect of different neutralization modes, as well as the effect of ferrous ions on the removal of arsenic and the stability of the generated arsenic-bearing wastes, was systematically investigated. The result showed that arsenic was still released back into the liquid phase under alkaline conditions even for the samples formed directly at alkaline pH. It was found that the extra addition of Fe(II) may exert negative effect on the stability of the as-formed Fe(II)-Fe(III)-As(V) coprecipitates at pH 7 - 10. The concentration of ferrous ions in the liquid/solid phase decreased with increasing pH for each sample formed at different Fe(II)/Fe(tot). The results indicated that complete oxidation of the ferrous ions before coprecipitation with arsenic should be conducted to achieve optimal stability of the arsenic-bearing wastes for hydrometallurgical practice and waste disposal.

The long-term stability of FeIII-AsV coprecipitates at pH 4 and 7: Mechanisms controlling the arsenic behavior.

Hydrometallurgical FeIII-AsV coprecipitates, which are amorphous in nature, could re-crystallize gradually and pose risks of contamination to the environment. However, the mechanisms controlling the As behavior when the FeIII-AsV coprecipitates stored at different pHs is still not fully understood. This work systematically investigated the fate of As and the transformation process of the coprecipitates (Fe/As = ˜4) at different pHs and temperatures. XRD, EXAFS, HRTEM, and chemical extraction methods were employed to characterize the crystallinity degrees and the transformation products of the coprecipitates. The results showed that the coprecipitates are more stable at acidic pH than at neutral pH. For those samples aged at pH 4, the arsenic speciation includes poorly crystalline ferric arsenate (PCFA) and As adsorbed on 2-line ferrihydrite (Fh). Due to the presence of PCFA, the Fe/As molar ratio for the latter phase is much higher than the bulk Fe/As molar ratio (˜4 in this work) of the coprecipitates and controls As release. However, for those samples aged at pH 7, due to the fact that 2-line Fh is the major As-bearing phase, slight changes of the crystallinity degrees of 2-line Fh will trigger As release.

Arsenic associated with gypsum produced from Fe(III)-As(V) coprecipitation: Implications for the stability of industrial As-bearing waste.

Gypsum is a high-volume by-product of hydrometallurgical arsenic removal using the Fe(III)-As(V) coprecipitation technique. However, the role of gypsum in As fixation during the Fe(III)-As(V) coprecipitation process and the potential risk of As-bearing gypsum are still not well known. In this study, the fixation of As by gypsum was quantitatively investigated as a function of the initial As and H2SO4 concentrations, Fe/As molar ratio, pH, and neutralization mode. Column leaching tests were also performed to evaluate the potential risk of Fe(III)-As(V) coprecipitates. The results showed that the gypsum isolated from Fe(III)-As(V) coprecipitates by ascorbic acid (VC) treatment could fix up to 4.5% of the total As in the system at pH 8 in fixed-pH mode. The gypsum produced in fixed-pH mode contained a significantly higher concentration of As than that produced in acid-alkaline neutralization mode. The column leaching tests showed that a faster leaching rate could enhance the release of As from Fe(III)-As(V) coprecipitates. It seems that the presence of gypsum could prevent the release of As from Fe(III)-As(V) coprecipitates. Linear combination fits of the As and Fe K-edge XANES spectra suggested that As was likely to occur as adsorbed As and yukonite in VC-isolated gypsum.

Effects of nutrient and sulfate additions on As mobility in contaminated soils: a laboratory column study.

The effect of nutrient and sulfate additions on As mobility in contaminated soils was investigated under advective-flow anoxic columns in this study. The mobility of As in surface contaminated soils was investigated by the leaching of de-ionized water (DI-water), artificial ground water (AG-water) and AG-water+sulfate (Sulfate). After 144 d of experiments, compared to the DI-water column, the total As exported from the columns AG-water and Sulfate was enhanced by seven and eightfold, respectively. The results indicated that the nutrient and sulfate addition significantly enhanced the As mobility in contaminated soils. In low-sulfate soils (DI-water and AG-water systems), As mobilization was primarily attributed to As reduction and to the transformation of amorphous Fe(III) (oxy)hydroxides. In soil with sulfate addition (Sulfate system), besides As reduction and Fe(III) (oxy)hydroxides transformation, the dissolution of As sulfides and the formation of thioarsenic species under sulfidogenic condition were possibly important processes accelerating As release. In conclusion, the addition of the nutrient solution and sulfates may increase the mobility of As in contaminated soils, posing a potential threat to groundwater.

Checklist of tidepool fishes from Jericoacoara National Park, southwestern Atlantic, with additional ecological information / Inventário dos peixes de poças de mare do Parque Nacional de Jericoacoara, Atlântico sudoeste, com informações ecológicas adicionais

Ichthyofauna from 29 tidepools in Jericoacoara National Park (Ceará State, Brazil) was sampled. A total of 733 fishes, comprising 16 species belonging to 12 families, was collected. The three most abundant species were the frillfin goby Bathygobius soporator, the sergeant-majorAbudefduf saxatilis and the molly miller Scartella cristata. An invasive species from the Indo-Pacific, the Muzzled blenny Omobranchus punctatus, was also recorded. The known geographic distribution of the blenny Hypleurochilus fissicornis was extended approximately 2,500 km northward. These findings highlight the lack of knowledge of the rocky intertidal ecosystems along the Brazilian coast, an area that needs more sampling effort and ecological data.

Um total de 733 espécimes de peixes, pertencentes a 16 espécies (12 famílias), foi capturado em 29 poças de maré no Parque Nacional de Jericoacoara (Ceará, Brasil). As espécies mais numericamente abundantes foram o amboré Bathygobius soporator, o sargentinho Abudefduf saxatilis e o macaco-verdeScartella cristata. Uma espécie invasora originária do Indo-Pacífico, Omobranchus punctatus, foi registrada para a área. A ocorrência de Hypleurochilus fissicornis permitiu expandir sua distribuição geográfica em cerca de 2.500 km ao norte. Esses resultados demostram que diversos aspectos relacionados a ictiofauna do ecossistema entremarés em substrato consolidado ainda permanecem pouco estudados no Brasil, e portanto, mais levantamentos da biodiversidade e dados ecológicos são necessários.