Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
Environ Sci Technol. 2013 May 7;47(9):4197-203. doi: 10.1021/es304824n. Epub 2013 Apr 4.
An important issue in mercury (Hg) biogeochemistry is to explore the influence of aqueous Hg(II) forms on bacterial uptake, and subsequent methyl mercury formation, under iron(III) and sulfate reducing conditions. The success of this is dependent on relevant information on the thermodynamic stability of Hg-sulfides. In the present study, we determined the solubility of a commercially available HgS(s) phase, which was shown by X-ray diffraction to be a mixture of 83% metacinnabar and 17% cinnabar. At aqueous sulfide concentrations between 0.060 and 84 μM, well below levels in previous studies, we report a solubility product (log Ksp ± SE) of -36.8 ± 0.1 (HgS(s) + H(+) = Hg(2+) + HS(-), I = 0, T = 25 °C, pH 6-10, n = 20) for metacinnabar. This value is 0.7 log units higher than previous estimates. Complementing our data with data from Paquette and Helz (1997), we took advantage of a large data set (n = 65) covering a wide range of aqueous sulfide (0.06 μM-140 mM) and pH (1-11). On the basis of this, we report refined formation constants (±SE) for the three aqueous Hg(II)-sulfide species proposed by Schwarzenbach and Widmer (1963): Hg(2+) + 2HS(-) = Hg(SH)2(0); log K = 39.1 ± 0.1, Hg(2+) + 2HS(-) = HgS2H(-) + H(+); log K = 32.5 ± 0.1, Hg(2+) + 2HS(-) = HgS2(2-) + 2H(+); log K = 23.2 ± 0.1. Our refined log K values differ from previous estimates by 0.2-0.6 log units. Furthermore, at the low sulfide concentrations in our study we could rule out the value of -10.0 for the reaction HgS(s) + H2O = HgOHSH(aq) as reported by Dyrssén and Wedborg (1991). By establishing a solubility product for the most environmentally relevant HgS(s) phase, metacinnabar, and extending the range of aqueous sulfide concentrations to sub-micromolar levels, relevant for soils, sediments, and waters, this study decreases the uncertainty in stability constants for Hg-sulfides, thereby improving the basis for understanding the bioavailability and mobility of Hg(II) in the environment.
在汞（Hg）生物地球化学中，一个重要的问题是探索水合 Hg(II)形态对铁(III)和硫酸盐还原条件下细菌摄取和随后形成甲基汞的影响。这一成功取决于与 Hg-硫化物热力学稳定性相关的信息。在本研究中，我们确定了一种市售 HgS(s) 相的溶解度，X 射线衍射表明该相是 83%辰砂和 17%朱砂的混合物。在低于先前研究水平的 0.060 至 84 μM 水合硫化物浓度下，我们报告了一个溶度积（log Ksp ± SE）为-36.8 ± 0.1（HgS(s) + H(+) = Hg(2+) + HS(-)，I = 0，T = 25 °C，pH 6-10，n = 20），用于 metacinnabar。这一数值比先前的估计值高 0.7 个对数单位。我们利用 Paquette 和 Helz（1997）的数据补充了我们的数据，该数据涵盖了广泛的水合硫化物（0.06 μM-140 mM）和 pH（1-11）范围，共 65 个数据点。基于此，我们报告了 Schwarzenbach 和 Widmer（1963）提出的三种水合 Hg(II)-硫化物物种的改进形成常数（±SE）：Hg(2+) + 2HS(-) = Hg(SH)2(0)；log K = 39.1 ± 0.1，Hg(2+) + 2HS(-) = HgS2H(-) + H(+)；log K = 32.5 ± 0.1，Hg(2+) + 2HS(-) = HgS2(2-) + 2H(+)；log K = 23.2 ± 0.1。我们的修正 log K 值与先前的估计值相差 0.2-0.6 个对数单位。此外，在我们的研究中，在低硫化物浓度下，我们可以排除 Dyrssén 和 Wedborg（1991）报道的反应 HgS(s) + H2O = HgOHSH(aq)的-10.0 值。通过建立最具环境相关性的 HgS(s)相 metacinnabar 的溶度积，并将水合硫化物浓度扩展到亚微米水平，这对于土壤、沉积物和水是相关的，本研究降低了 Hg-硫化物稳定性常数的不确定性，从而提高了理解环境中 Hg(II)生物利用度和迁移性的基础。
