Study on aqueous speication of metals under supercritical hydrothermal conditions.

热液中金属的水相形态信息是阐明热液矿床形成机制不可缺少的信息之一。为此，研究了NaCl对矿物与热液之间离子交换平衡的影响，并对结果进行了分析。对锌、镉、铅和锡进行了实验。实验条件为1 kb时500 ~ 700℃，0.5kb时600℃。水热溶液中氯离子浓度为2 M，采用冷封式压力容器进行实验，实验结果表明，在实验条件下，水热溶液中的氯离子主要以中性物种和/或三氯络合物为主。通过热力学分析估算了金属三氯配合物的形成常数。三氯络合物的形成常数（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，在锰和镉之间有一个最大值。实验结果表明，在较高的温度和较低的压力下，金属形成三氯配合物，因此溶解度随温度的升高和压力的降低而增加。为了验证所获得的结果是否在更复杂的体系中有效，用玄武岩进行了2 M NaCl溶液的阳离子浸出实验。实验在300 ~ 800℃、1 kb和600℃、0.5 ~ 1.0kb条件下进行。实验证实，在较高温度和较低压力下，铁、锰、钴、镍和锌倾向于优选地从玄武岩浸出到热液溶液中。

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.