XPS and XAS studies of copper(II) sorbed onto a synthetic pyrite surface

Pyrite-activated persulfate to degrade 3,5,6-trichloro-2-pyridyl in water: Degradation and Fe release mechanism

TCP (3,5,6-trichloro-2-pyridinol), the main recalcitrant degradation product of chlorpyrifos, poses a high risk to human health and ecological systems. This study provided a comprehensive exploration of the pyrite-activated persulfate (PS) system for the removal of TCP in water and placed particular emphasis on the pyrite oxidation process that releases Fe. The results showed that the pyrite-activated PS system can completely degrade TCP within 300 min at 5.0 mmol/L PS and 1000 mg/L pyrite at 25 °C, wherein small amounts of PS (1 mmol/L) can effectively facilitate TCP removal and the oxidation of pyrite elements, while excessive PS (>20 mmol/L) can lead to competitive inhibitory effects, especially in the Fe release process. Aimed at the dual effects, the evident positive correlation (R2 > 0.90) between TCP degradation (kTCP) and Fe element release (kFe), but the value of k (0.00237) in the pyrite addition variable experiment was less than that in the PS experiment (k = 0.00729), further indicating that the inhibition effect of excessive addition consists of PS but not notably pyrite. Moreover, the predominant free radicals and non-free radicals produced in the pyrite/PS system were tested, with the order of significance being •OH < Fe (Ⅳ) < SO4•- < •O2- < 1O2, wherein 1O2 emerged as the principal player in both TCP degradation and Fe release from the pyrite oxidation process. Additionally, CO32- can finitely activate PS but generally slows TCP degradation and inhibit pyrite oxidation releasing Fe process. This study provides a theoretical basis for the degradation of TCP using pyrite-activated PS.

Interfacial N-Cu-S coordination mode of CuSCN/C3N4 with enhanced electrocatalytic activity for hydrogen evolution

Nitrogen/carbon layer coordinated transition metal complexes are the most important alternatives to improve the catalytic performance of catalysts for energy storage and conversion systems, which require systematic investigation and improvement. The coordination mode of transition metal ions can directly affect the catalytic performance of catalysts. Herein, this paper reports that two kinds of Cu-based composites (CuSCN and CuSCN/C3N4) are prepared by in situ controllable crystallization of copper foam (CF) through electropolymerization and calcination. As a comparison, it is clarified that the different coordination modes of Cu1+ ions determine the different catalytic properties. The samples can be switched freely by tuning the electropolymerization period, which leads to different coordination modes of Cu1+ ions dramatically, thus affecting the electrocatalytic performance of composite materials for the hydrogen evolution reaction (HER) in turn. Thorough characterization using techniques, including X-ray photoelectron spectroscopy (XPS) and synchrotron-based near edge X-ray absorption fine structure (EXAFS) spectroscopy, reveals that strong interactions between CuSCN and C3N4 of CuSCN/C3N4 facilitate the formation of subtle coordinated N-Cu-S species, of which electronic structures are changed. Density Functional Theory (DFT) calculations indicate that the electrons can penetrate from CuSCN to N atoms present in C3N4. As a result, CuSCN/C3N4 demonstrates a better catalytic performance than the conventional transition-metal-based electrocatalysts. Besides, CuSCN/C3N4 reflects almost identical hydrogen evolution reaction (HER) activity and stability in an acid electrolyte with Pt/C.

Enhanced sulfidation xanthate flotation of malachite using ammonium ions as activator

In this study, ammonium ion was used to enhance the sulfidation flotation of malachite. The effect of ammonium ion on the sulfidation flotation of malachite was investigated using microflotation test, inductively coupled plasma (ICP) analysis, zeta potential measurements, and scanning electron microscope analysis (SEM). The results of microflotation test show that the addition of sodium sulfide and ammonium sulfate resulted in better sulfidation than the addition of sodium sulfide alone. The results of ICP analysis indicate that the dissolution of enhanced sulfurized malachite surface is significantly decreased. Zeta potential measurements indicate that a smaller isoelectric point value and a large number of copper-sulfide films formed on the malachite surface by enhancing sulfidation resulted in a large amount of sodium butyl xanthate absorbed onto the enhanced sulfurized malachite surface. EDS semi-quantitative analysis and XPS analysis show that malachite was easily sulfurized by sodium sulfide with ammonium ion. These results show that the addition of ammonium ion plays a significant role in the sulfidation of malachite and results in improved flotation performance.

A new adsorbent of Pb(ii) ions from aqueous solution synthesized by mechanochemical preparation of sulfonated expanded graphite

After the mechanochemical modification, sulfonated functional groups were able to be attached on the surface of SEG effectually, acted a significant role in the adsorption process, the schematic diagram of SEG interacted with Pb(ii) showing as below.

Evaluation of metal partitioning and mobility in a sulfidic mine tailing pile under oxic and anoxic conditions

Mining-influenced water emanating from mine tailings and potentially contaminating surface water and groundwater is one of the most important environmental issues linked to the mining industry. In this study, two subsets of Callahan Mine tailings (mainly comprised of silicates, sulfides, and carbonates) were collected using sealed containers, which allowed keeping the samples under anoxic conditions during transportation and storage. Among the potential contaminants, in spite of high concentrations of Cu, Mn, Pb, and Zn present in the solid mine tailings, only small amounts of Mn and Zn were found in the overlying pore water. The samples were subjected to leaching tests at different reduction-oxidation (redox) conditions to compare metal and S mobilization under oxic and anoxic conditions. It was observed that Cd, Cu, Mn, Pb, S, and Zn were mobilized at higher rates under oxic conditions, while Fe was mobilized at a higher rate under anoxic conditions in comparable constant pH experiments. These results suggest that metal mobilization is significantly impacted by redox conditions. When anoxic metal mobilization assessment is required, it is recommended to always maintain anoxic conditions because oxygen exposure may affect metal mobilization. A sequential extraction performed under oxic conditions revealed that most of the metals in the samples were associated with the sulfidic fraction and that the labile fraction was associated with Mn and moderate amounts of Pb and Zn.

Selenide retention onto pyrite under reducing conditions

Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it turns out to be a sorption sink for certain radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize selenide (Se(-II)). Due to the fact that pyrite surface oxidizes readily, potentials were applied in order to minimise its surface evolution, and ensure the reducing conditions necessary for stabilizing Se(-II). The sorption experiments were carried out in NaCl electrolyte and were amperometrically controlled. After only several minutes of reaction, at least 97% of Se(-II) initially present in solution was disappeared. The K d values vary from 7–65 L/g and the isotherm curve shows site saturation at higher initial selenide concentrations and no pH-dependence. By means of several spectroscopic techniques, the reaction mechanism was investigated. The XRD and in situ XANES results indicate the presence of Se(0) on pyrite surface, which explain the rapid disappearance of Se observed in the sorption experiments. Moreover, XPS results obtained from Se-reacted pyrite particles reveal cleavage of S–S bonding which resulted in formation of S2− on pyrite surface. Thus, we conclude that Se(-II) can be immobilized by pyrite via surface redox reaction:

≡FeS2 + HSe− ⇔ ≡FeS + Se(0) + HS−.