Study on aqueous speication of metals under supercritical hydrothermal conditions.

为了获得金属在热液溶液中的水相形态信息，这是阐明热液矿床形成机制不可缺少的信息之一，进行了实验研究。为此，研究了NaCl对矿物与水热溶液之间离子交换平衡的影响，并对结果进行了热力学分析。对锌、镉、铅和锡进行了实验。实验条件为500 ~ 700℃，1kb, 600℃，0.5kb。水热溶液的氯离子浓度固定为2M。实验采用冷密封型压力容器。实验表明，在实验条件下，中性和/或三氯配合物是主要的水相。通过热力学分析估计了金属三氯配合物的形成常数。三氯络合物（包括铁、锰、钴和镍）的形成常数与离子半径的关系曲线呈抛物线形，其中锰和镉之间的形成常数最大。然而，这条曲线的含义目前还不清楚。实验结果表明，金属在较高温度和较低压力下形成三氯配合物，因此溶解度随温度和压力的升高而增加。为了验证所得结果在更复杂的体系中是否有效，利用玄武岩进行了2M NaCl溶液阳离子浸出实验。实验温度分别为300 ~ 800℃、0.5 ~ 1.0kb、600℃。实验证实，在高温低压条件下，铁、锰、钴、镍和锌更容易从玄武岩中浸出到热液中。

Experiments were performed in order to obtain the information on aqueous speciation of metals in hydrothermal solutions, which is one of the informations indispensable for elucidating the formation mechanism of hydrothermal deposits. For the purpose, the effect of NaCl on ion exchange equilibria between minerals and hydrothermal solutions was examined and the results were analyzed thermodynamically. The experiments were carried out for zinc, cadmium, lead and tin. The experimental conditions were 500 to 700℃ at 1kb and 600℃ at 0.5kb. The chloride concentration of the hydrothermal solutions was fixed to be 2M.Cold seal type pressure vessels were used for the experiments.The experiments revealed that neutral species and/or tri-chloro complexes are dominant aqueous species under the experimental conditions. The formation constant of the tri-chloro complexes of the metals was estimated by the thermodynamic analysis. The plot of the formation constant of the tri-chloro complex including those for iron, manganese, cobalt and nickel previously obtained versus ionic radius shows a parabola-shaped curve with a maximun between manganese and cadmium. However the meaning of the curve is not clear at present.The experimental results show that the metals form tri-chloro complexes at higher temperatures and lower pressures and therefore the solubility increases with increasing temperature and decreasing pressure. In order to confirm whether the obtained results are effective in the more complex system or not, the experiment of cation leaching by 2M NaCl solution was carried out using basalt. The experiments were conducted at 300 to 800℃ under 1kb and at 600℃ under 0.5 to 1.0kb. It was confirmed by the experiments that iron, manganese, cobalt, nickel and zinc tends to be leached preferably from basalt into hydrothermal solutions at higher temperatures and lower pressures.