Search

Abstract: The aqueous phase oxidation of gaseous elemental mercury (Hg0) by potassium persulfate (K2S2O8, KPS) catalyzed by Ag+ and Cu2+ was investigated using a glass bubble column reactor. Concentrations of gaseous Hg0 and aqueous Hg2+ were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg0 inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg0 increased with increasing concentration of potassium persulfate and catalysts Ag+, Cu2+ and Ag+ provided better catalytic effect than Cu2+. For example, in the presence of 5.0mmoll−1 KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag+ concentration of 0.1 and 0.3mmoll−1, respectively, and 69.8 and 81.9% for 0.1 and 0.3mmoll−1 Cu2+. On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg0 was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag+ and Cu2+, and high Hg0 inlet concentration also has positive impact on the removal efficiency of Hg0. The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed. [Copyright &y& Elsevier]

Abstract: The bioremediation was employed to treat perchlorate-contaminated water. All enrichments and growth of mixed cultures were performed in anaerobic acetate medium. Enrichment cultures were started with activated sludge obtained from a local wastewater treatment plant where it predominantly treats domestic wastewater. Several parameters affecting perchlorate removal were examined through batch experiments, these include the amount of domesticated sludge, the acetate concentration, pH, the C/N ratio and the reaction temperature. The results indicated that acetate was an effective carbon source and electron donor. Under the selected conditions, namely 1.0g domesticated sludge, an acetate concentration of 1.2gl−1, pH 8.0, a C/N ratio of 20 at 40°C, 50mgl−1 perchlorate could be rapidly reduced to non-detectable levels within 24h. [Copyright &y& Elsevier]

Graphical abstract Highlights • TiC doped palladium/nickel foam cathode was synthesized via electroless deposition. • Pd/TiC/Ni foam show superior activity for 2,4-DCBA dechlorination to Pd/Ni foam. • Optimized conditions on 2,4-DCBA dechlorination were investigated. • Possible promotion mechanism by doped TiC over Pd/Ni foam cathode was proposed. Abstract Titanium carbide (TiC) with excellent electrical conductivity, chemical and thermal stabilities has been recognized as one of the most promising electrocatalysts. A novel cathode, titanium carbide doped palladium/nickel foam (TiC-Pd/Ni foam), was synthesized via electroless deposition to improve the performance of Pd/Ni foam in electrocatlytic hydrodechlorination (ECH). TiC can be co-precipitated onto the surface of cathode during galvanic replacement reaction between Pd(II) solution and Ni foam. Both constant potential and constant current tests proved that TiC-Pd/Ni foam cathode performed remarkably higher activity for 2,4-dichlorobenzoic acid (2,4-DCBA) than Pd/Ni foam cathode, owing to the excellent conductivity of TiC and enhanced water dissociation over TiC-Pd/Ni foam cathode. Under the optimized reaction conditions of –0.85 V (vs Ag/AgCl), electrolyte of 10 mM and initial pH of 4, 99.8% of aqueous 2,4-DCBA (0.2 mM) was removed within 90 min. The removal process of the aqueous 2,4-DCBA obeyed first-order decay kinetic model. Over 86.3% of 2,4-DCBA can still be removed by TiC-Pd/Ni foam cathode in the fifth consecutive run within 120 min, which was much higher than that of Pd/Ni foam cathode (37.5%). Consequently, TiC-Pd/Ni foam cathode was a promising design for enhanced ECH activity and reduced operation cost. [ABSTRACT FROM AUTHOR]

Polychlorinated dibenzo- p -dioxins (PCDDs), as a group of notorious anthropogenic environmental toxicants, are arguably ubiquitous in nature. In this study, we investigated the photocatalytic reductive dechlorination of 2-chlorodibenzo- p -dioxin (2-CDD) over Pd/g-C 3 N 4 catalysts under UV–vis irradiation. The g-C 3 N 4 and a series of Pd/g-C 3 N 4 catalysts were prepared by thermal polymerization and mechanical mixing-illumination method and characterized by XRD, TEM, BET, SEM and UV–vis DRS analyses. Among all the samples, the Pd/g-C 3 N 4 (5 wt%) yielded the optimal dechlorination activity with a total 2-CDD conversion of 54% within 4 h, and 76% of those converted 2-CDD were evolved to dibenzo- p -dioxin (DD). The kinetics of dechlorination could be described as pseudo-first-order decay model (R 2  > 0.84). Corresponding rate constants (k) increased from 0.052 to 0.17 h −1 with Pd contents up to 5 wt% and decreased to 0.13 h −1 with a 10 wt% of Pd. The enhanced activities originated from the surface plasmonic resonance (SPR) effect of Pd nanoparticles and the formation of Schottky barrier between Pd and g-C 3 N 4 , which extend the spectrum responsive range and suppress the charge recombination of g-C 3 N 4 . This is the first report on the photocatalytic reductive removal of PCDDs and may provide a new approach for PCDDs pollution control. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe0-Fe3O4 nanocomposites are embedded in polyvinyl alcohol/sodium alginate beads;. [•] Acidification and reduction after bead molding greatly improve beads performance;. [•] High stability, Cr(VI) removal efficiency and reusability of these beads;. [•] Easy and complete separation after reaction. [Copyright &y& Elsevier]

Abstract: Mercury (II) (Hg2+) ion can be reduced by aqueous S(IV) (sulfite and/or bisulfite) species, which leads to elemental mercury (Hg0) emissions in wet flue gas desulfurization (FGD) systems. Numerous reports have demonstrated the high trapping efficiency of sodium dithiocarbamate over heavy metals. In this paper, a novel sodium dithiocarbamate, DTCR, was utilized as a precipitator to control Hg2+ reduction and Hg0 emission against S(IV) in FGD solutions. Results indicated that Hg2+ reduction efficiency decreased dramatically while precipitation rate peaked at around 91.0% in consistence with the increment of DTCR dosage. Initial pH and temperature had great inhibitory effects on Hg2+ reduction: the Hg2+ removal rate gradually increased and reached a plateau along with the increment of temperature and initial pH value. Chloride played a key role in Hg2+ reduction and precipitation reactions. When Cl− concentration increased from 0 to 150mM, Hg2+ removal rate dropped from 93.84% to 86.05%, and the Hg2+ reduction rate remained at a low level (<7.8%). SO4 2−, NO3 − and other common metal ions would affect the efficiency of Hg2+ reduction and precipitation reactions in the simulated desulfurization solutions: Hg2+ removal rate could always be above 90%, while Hg2+ reduction rate was maintained at below 10%. The predominance of DTCR over aqueous S(IV), indicated by the results above, has wide industrial applications in FGD systems. [Copyright &y& Elsevier]

Abstract: This paper describes the use of highly reactive magnetite (Fe3O4) nanoparticles-stabilized Fe0 nanocomposites for the reduction and mitigation of hexavalent chromium Cr(VI) species in aqueous solutions. Higher proportions of Fe3O4 in the nanocomposites could increase the rate of Cr(VI) reduction. In the absence of magnetite, the Cr(VI) mitigation rate was just 51.4% after 60min of reaction, while with an initial Fe3O4 mass loading of 3gl−1, the Cr(VI) mitigation rate was nearly 100% after 60min. The optimal ratio of Fe3O4:Fe0 for the mitigation of Cr(VI) was found to be 40:1. Otherwise, solution pHs significantly affected the rate of Cr(VI) reduction, with reactions occurring more rapidly under acidic or neutral than basic conditions. It is hypothesized that the high efficiency of the Fe3O4 nanoparticles-stabilized Fe0 nanocomposites for Cr(VI) reduction was a direct result of the attachment of Fe0 nanoparticles to the surface of magnetite, which prevents the aggregation of nano-Fe0, moreover, the electron transfer during the reduction process most likely takes place via Fe0 nanoparticles that are located at the magnetite octahedral sites, which are versatile redox centers as they can accommodate both Fe(III) and Fe(II), and this will promote the reduction of Cr(VI). Cr(VI) reduction is coupled with nano-Fe0 oxidation. Nano-Fe0 particles are located at the magnetite octahedral sites. Ions of Fe(II) and Fe(III) accommodated by magnetite octahedral sites are products of nano-Fe0 oxidation. Therefore, Cr(VI) reduction is mediated either by nano-Fe0 (direct reduction) or Fe(II) species (indirect reduction). Additionally, catalytic Cr(VI) reduction by molecular H2 (or atomic H) is possible. [Copyright &y& Elsevier]

Abstract: In this study, considering that Hg2+ in wet flue gas desulfurization (FGD) systems can easily be reduced and then released into atmosphere, causing secondary pollution, the researches about Hg2+ reduction and Hg0 re-emission mechanism were carried out. The effects of several experimental parameters on the reduction were studied, including initial pH, temperature, and concentrations of Cl− and S(IV). Our experimental results indicated that Cl− had a restraining effect on the Hg2+ reduction and Hg0 re-emission, after 24h reaction, only 20.5% of Hg2+ was reduced with 100mM Cl− in simulated desulfurization solution. Cl− can slow Hg2+ reduction and Hg0 re-emissions dramatically through changing reaction mechanism, with formation of new intermediate: ClHgSO3 −, which can decompose to Hg0, but much more slowly than Hg(SO3)2 2− or HgSO3. Simulating the conditions of the practical application (initial pH 5, T =50°C, S(IV)=5mM, Cl− =100mM), we also found that Ca2+, NO3 −, F−, etc. all had obvious effects on reduction rates. Based on the material balance and characteristic of the reactants, the reduction emission mechanism of Hg2+ has been established, providing theoretical basis for industrial application of mercury control in wet FGD systems. [Copyright &y& Elsevier]

The aqueous phase oxidation of gaseous elemental mercury (Hg(0)) by potassium persulfate (K(2)S(2)O(8), KPS) catalyzed by Ag(+) and Cu(2+) was investigated using a glass bubble column reactor. Concentrations of gaseous Hg(0) and aqueous Hg(2+) were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg(0) inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg(0) increased with increasing concentration of potassium persulfate and catalysts Ag(+), Cu(2+) and Ag(+) provided better catalytic effect than Cu(2+). For example, in the presence of 5.0 mmol l(-1) KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag(+) concentration of 0.1 and 0.3 mmol l(-1), respectively, and 69.8 and 81.9% for 0.1 and 0.3 mmol l(-1) Cu(2+). On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg(0) was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag(+) and Cu(2+), and high Hg(0) inlet concentration also has positive impact on the removal efficiency of Hg(0). The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed.