Institute of Resource Ecology, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany.
The Rossendorf Beamline (ROBL), 71, Avenue des Martyrs, 38043 Grenoble, France.
Environ Sci Technol. 2020 Mar 3;54(5):2678-2687. doi: 10.1021/acs.est.9b05341. Epub 2020 Feb 10.
Tc(VII) uptake by synthetic pure pyrite at 21 °C was studied in a wide pH range from 3.50 to 10.50 using batch experiments combined with scanning electron microscopy, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and Raman microscopy. We found that pyrite removes Tc quantitatively from solution (log = 5.0 ± 0.1) within 1 day at pH ≥ 5.50 ± 0.08. At pH < 5.50 ± 0.08, the uptake process is slower, leading to 98% Tc removal (log = 4.5 ± 0.1) after 35 days. The slower Tc uptake was explained by higher pyrite solubility under acidic conditions. After 2 months in contact with oxygen at pH 6.00 ± 0.07 and 10.00 ± 0.04, Tc was neither reoxidized nor redissolved. XAS showed that the uptake mechanism involves the reduction from Tc(VII) to Tc(IV) and subsequent inner-sphere complexation of Tc(IV)-Tc(IV) dimers onto a Fe oxide like hematite at pH 6.00 ± 0.07, and Tc(IV) incorporation into magnetite via Fe(III) substitution at pH 10.00 ± 0.04. Calculations of Fe speciation under the experimental conditions predict the formation of hematite at pH < 7.50 and magnetite at pH > 7.50, explaining the formation of the two different Tc species depending on the pH. XPS spectra showed the formation of TcS at pH 10.00 ± 0.04, being a small fraction of a surface complex, potentially a transient phase in the total redox process.
采用批实验结合扫描电子显微镜、X 射线吸收光谱（XAS）、X 射线光电子能谱（XPS）和拉曼显微镜研究了在 21°C 下，pH 值范围为 3.50 至 10.50 时，合成纯黄铁矿对 Tc(VII)的吸附作用。我们发现黄铁矿在 pH 值≥5.50±0.08 时，1 天内可定量从溶液中去除 Tc（log Kd=5.0±0.1）。在 pH 值<5.50±0.08 时，吸附过程较慢，35 天后 98%的 Tc 被去除（log Kd=4.5±0.1）。在酸性条件下，由于黄铁矿的溶解度较高，导致 Tc 的吸附速度较慢。在 pH 值为 6.00±0.07 和 10.00±0.04 下与氧气接触 2 个月后，Tc 既未被再氧化也未被重新溶解。XAS 表明，吸附机制涉及 Tc(VII)被还原为 Tc(IV)，随后 Tc(IV)-Tc(IV)二聚体在 pH 值为 6.00±0.07 时与赤铁矿等 Fe 氧化物发生内配位络合，在 pH 值为 10.00±0.04 时通过 Fe(III)取代进入磁铁矿。根据实验条件下的 Fe 形态计算，预测在 pH 值<7.50 时形成赤铁矿，在 pH 值>7.50 时形成磁铁矿，这解释了两种不同 Tc 物种的形成取决于 pH 值。XPS 谱表明，在 pH 值为 10.00±0.04 时形成 TcS，这是表面络合物的一小部分，可能是总氧化还原过程中的一个瞬态相。
