地学前缘 ›› 2020, Vol. 27 ›› Issue (5): 227-237.DOI: 10.13745/j.esf.sf.2020.5.40

• 表生成因矿物学:地表环境及其修复 • 上一篇    下一篇

砷在石膏中固定机制:掺杂态和表面吸附沉淀态以及其在砷污染控制中的作用

Jinru LIN, Ning CHEN, Yuanming PAN   

  1. 1. Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
    2. Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, 
    Shenyang, Liaoning 110016, P. R. China
    3. Canadian Light Source, University of Saskatchewan, Saskatoon, SK S7N 0X4, Canada
  • 收稿日期:2020-03-21 修回日期:2020-05-19 出版日期:2020-09-25 发布日期:2020-09-25
  • 通讯作者: 潘元明,男,教授,博士生导师,主要从事矿物学和地球化学
  • 作者简介:林金如,女,副研究员,研究方向为环境地球化学

Uptake mechanisms of arsenate in gypsum: Structural incorporation versus surface adsorption and implications for remediation of arsenic contamination

Jinru LIN, Ning CHEN, Yuanming PAN   

  1. 1. Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada
    2. Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences,
    Shenyang, Liaoning 110016, P. R. China
    3. Canadian Light Source, University of Saskatchewan, Saskatoon, SK S7N 0X4, Canada
  • Received:2020-03-21 Revised:2020-05-19 Online:2020-09-25 Published:2020-09-25
  • Contact: yuanming.pan@usask.ca
  • Supported by:

    The Natural Science and Engineering Research Council (NSERC) of Canada Discovery Grants (RGPIN 169994-201 and 2018-04106)

摘要:

石膏是矿山开采及冶炼等工业过程产生的大宗固体废弃物。工业活动产生的废液普遍有高含量的砷等有毒元素,这导致所产生的石膏也含有较高浓度的砷等有毒元素。研究砷在石膏中地球化学行为和归趋对含砷石膏的砷污染控制具有重要的理论和实际意义。然而目前对含砷石膏中不同形态的砷的定量测定和分析尚存在问题。本文在不同pH值的条件下共沉淀砷和石膏,利用电感耦合等离子体质谱(ICP-MS)、同步辐射X-射线吸收近边光谱(XANES)和电子顺磁共振(EPR)对石膏中掺杂态和表面吸附沉淀态的砷进行定量分析。ICP-MS的结果表明随着pH从2升高到12 和14,石膏中砷的含量由57×10-6 增加到 67 470×10-6和63 980×10-6。同步辐射X-射线吸收近边光谱和电子顺磁共振光谱分析表明石膏样品中主要含有五价砷。在2≤pH≤7.5时,固体样品中同步辐射吸收边后的峰形状和掺杂态砷的形状类似,而在pH≥8时,其边后峰的形状发生明显的变化;粉末电子顺磁共振(EPR)定量分析表明在2≤pH≤7.5时砷在石膏中的含量和ICP-MS的分析结果一致,而在pH≥8时其含量明显小于ICP-MS的分析结果。这些结果揭示了在2≤pH≤7.5时,砷在石膏中主要以掺杂态的形式存在,而在pH≥8时大部分砷是以吸附态或表面沉淀的形式存在。五价砷在石膏中的含量和固定机制随着pH值的变化而变化,其研究对了解尾矿中石膏对砷污染的控制作用具有重要作用。此外,研究石膏中由辐射导致的g约为2.33的[AsO32-自由基电子顺磁共振特征峰,有助于补充和完善石膏的电子顺磁共振特征谱在地质测年及辐射剂量学中的应用。

关键词: 石膏, 矿山尾矿, 砷污染, 结构掺杂, 表面吸附, pH作用

Abstract:

Gypsum (CaSO4·2H2O) as the most common and abundant secondary mineral in diverse types of mine tailings potentially plays important roles in the stability and bioavailability of heavy metal(loid)s, including As. Understanding on the behavior of As in gypsum-rich mine tailings and development of effective strategies for remediating related As contamination all require knowledge about the speciation and uptake mechanisms of this metalloid in the dominant mineral. However, quantitative determination of arsenic speciation and uptake mechanisms in gypsum-rich mine tailings at trace levels is analytically challenging. In this contribution, we use combined inductively coupled plasma mass spectrometry (ICP-MS), X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy to quantitatively determine structural incorporation and surface adsorption of arsenate in synthetic gypsum. Gypsum coprecipitated from aqueous solutions containing 0.02 M sodium hydrogen arsenate heptahydrate (Na2HAsO4·7H2O) at ambient conditions has As contents increasing from 57 ppm at pH=2 to 67470 and 53980 ppm at pH=12 and 14, respectively. Synchrotron As K-edge XANES and powder EPR spectra confirm that arsenate is the dominant species in coprecipitated gypsum. Specifically, As K-edge XANES spectra exhibit systematic variations in post-edge features as a function of pH, consistent with structure-bound arsenate at pH from 2 to 7.5 but different uptake mechanisms at pH from 9 to 14. Similarly, arsenic contents estimated from the structure-bound [AsO32- radical in powder EPR spectra are in agreement with those determined from ICP-MS analyses for gypsum synthesized at pH from 2 to 7.5, but show large discrepancies for the pH=9, 12 and 14 samples, indicative of a large fraction of non-structure-bound As at high pH. The marked pH dependence of arsenate uptake mechanisms in gypsum has important implications for both understanding the roles of this material in mine tailings and developing its optimal applications for remediation of arsenic contamination in aqueous environments. In addition, the radiation-induced [AsO3]2- radical in gypsum with a diagnostic peak at g=~2.33 is potentially useful for EPR/ESR dating and retrospective dosimetry.

Key words: Gypsum, Mine tailings, Arsenic contamination, Structural incorporation, Surface adsorption, pH control

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