Stability of manganese(II) chloride complexes from 25 to 300 degrees C
Stability of manganese(II) chloride complexes from 25 to 300 degrees C
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DOI：
10.1016/s0016-7037(96)00275-x
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发表时间：
1996-11-01
影响因子：
5
通讯作者：
Seward, TM
中科院分区：
文献类型：
--
作者：
Gammons, CH;Seward, TM
在25 ~ 300℃的温度范围内实验测定了Mn（II）氯络合物的稳定性和化学计量学。在固定HCl浓度（0.01 ~ 6.0 m）和变化Sigma Mn/Sigma Cl摩尔比（0.0 ~ 0.5）的溶液中测量了AgCl的溶解度(s)，这是对Ruaya和Seward（1986）方法的改进。对结果进行回归，得到Mn（II）氯化配合物的第一和第二累积缔合常数(分别为beta（1)和beta(2)）的平滑值如下：[图]我们的研究表明，Mn2+在25℃时是优势种，而MnCl+和MnCl20的稳定性随着温度的升高而迅速增加。在没有竞争配体的情况下，中性的MnCl20配合物应该在300℃或以上的富氯化物热液中主导Mn的运输。没有证据表明存在更高配体数的配合物（例如MnCl3-， MnCl42-）。我们的结果表明，Mn在高温下比Fe更强的络合。一些常见的含锰矿物的溶解度被计算为pH、a(Cl)（-）、Sigma CO3和温度的函数。矿物菱铁矿和菱铁矿在弱酸性溶液中是高度可溶的。因此，预计大多数活跃的地热系统在这些相方面是不饱和的，尽管它们可能因pH值的突然增加而局部沉淀（例如，在沸腾期间）。锰硅酸盐矿物将倾向于溶解在经过冷却的溶液中，而红锰矿则表现出顺溶性或逆行溶性，这取决于盐度。被热液流体动员的锰可以移动相当远的距离，直到最终与氧化环境接触，此时锰氧化物矿物将沉淀。
The stability and stoichiometry of the Mn(II) chloride complexes have been experimentally determined in the temperature range 25 to 300 degrees C. The solubility of AgCl(s) was measured in solutions of fixed HCl concentration (0.01-6.0 m) and varying Sigma Mn/Sigma Cl molar ratio (0.0-0.5), following a modification of the method of Ruaya and Seward (1986). The results were regressed to obtain the following smoothed values for the first and second cumulative association constants (beta(1) and beta(2), respectively)for the Mn(II) chloride complexes:[GRAPHICS]Our study indicates that Mn2+ is the dominant species at 25 degrees C, whereas the stabilities of MnCl+ and MnCl20 increase rapidly with temperature. In the absence of competing Ligands, the neutral MnCl20 complex should dominate Mn transport for chloride-rich hydrothermal fluids at or above 300 degrees C. No evidence was found for complexes of higher ligand number (e.g., MnCl3-, MnCl42-). Our results indicate that Mn is more strongly complexed than Fe at elevated temperature.The solubilities of some common manganese-bearing minerals have been calculated as a function of pH, a(Cl)(-), Sigma CO3, and temperature. The minerals rhodonite and rhodocrosite are highly soluble in mildly acidic solutions. Most active geothermal systems are, therefore, expected to be undersaturated with respect to these phases, although they may locally precipitate in response to sudden increases in pH (e.g., during boiling). Mn-silicate minerals will tend to dissolve in solutions undergoing cooling, whereas rhodocrosite exhibits either prograde or retrograde solubility, depending on salinity. Manganese mobilized by hydrothermal fluids may travel considerable distances until contact is ultimately made with an oxidized environment, at which point Mn-oxide minerals will precipitate.