Experiments on the stability of aqueous metal chloro complexes in supercritical hydrothermal solutions

为了获得金属在超临界水热溶液中水相形态的信息，研究了在几乎互不相容的两相矿物共存时，氯化钠对矿物与氯化物水溶液之间离子交换平衡的影响。本文用CaWO_4-MeWO_4体系和CaTiO_3MeTiO_3体系分别对水相中的镁、锶、铁、锰、钴和镍的形态进行了实验研究。实验条件主要为600kb~(-1)C和1kb。对于Mg~(2+)&lt；~(2+)&gt；和Sr~(2+)~(lt；2+)~(gt；)而言，与两固相共存的氯化物水溶液的Ca/(Ca+Me)值不变，但ﾟ增加。这表明，在超临界水热溶液中，Mg^&lt；2+&gt；和Sr^&lt；2-&gt；以中性物种形式溶解，而不是以高阶氯络合物形式溶解。而对于Fe^&lt；2+&gt；，Mn^&lt；2+&gt；，Co^&lt；2+&gt；，Ni^&lt；2+&gt；和Zn^&lt；2+&gt；，随着盐浓度的增加，Ca/(Ca+Me)值显著降低。这可以归因于金属高阶氯络合物的形成。在本实验条件下，假设金属以三氯络合物形式存在，则三氯络合物的生成常数为Mn^&lt；2+&gt；&gt；Co^&lt；2+&gt；&gt；Fe^&lt；2+&gt；&gt；Ni^&lt；2+&gt；.量级根据配位场理论，推测金属在超临界水热溶液中形成低自旋态的四面体氯络合物，而对于锌离子和锌离子，分别在500~700ﾟC，1kb和600ﾟC，0.5kb条件下进行实验。结果表明，三氯络合物的生成常数随温度的升高而增大，随压力的升高而减小。这表明，在较高的温度和较低的压力下，过渡金属可以有效地从岩浆中浸出。

In order to obtain the information on the aqueous speciation of metals under supercritical hydrothermal solutions, the effect of NaCl on the ion exchange equilibria between minerals and aqueous chloride solution under the coexistence of two phase minerals almost immiscible to each other. In the present study, experiments on the aqueous speciation for Mg^<2+>, Sr^<2->, Fe^<2+>, Mn^<2+>, Co^<2+> and Ni^<2+> were carried out using the CaWO_4-MeWO_4, system and for Zn^<2+> using the CaTiO_3MeTiO_3 system. The experimental conditions are mainly 600ﾟC and 1kb.As for Mg^<2+> and Sr^<2+>, the Ca/(Ca+Me)ratios of the aqueous chloride solution coexisting with the two solid phases are constant in spite of the increase of NaCl. This indicates that under supercritical hydrothermal solutions, Mg^<2+> and Sr^<2-> dissolve as neutral species, but not as higher-order chloro complexes. On the other hand, for Fe^<2+>, Mn^<2+>, Co^<2+>, Ni^<2+>, and Zn^<2+> the Ca/(Ca+Me) ratios decreased significantly with the increases of NaCl. This can be attributed to the formation of the higher-order chloro complexes of the metals. On the assumption that the metals exist as tri-chloro complexes under the experimental conditions, the formation constants of the tri-chloro complexes are in the order of Mn^<2+>>Co^<2+>>Fe^<2+>>Ni^<2+>. Based on the ligand field theory, it is supposed that the metals form tetrahedral chloro complexes with low-spin state under supercritical hydrothermal solutions.As for Zn^<2+>, the experiments were performed at 500 to 700ﾟC,1kb and 600ﾟC,0.5kb. As a result, it is clarified that the formation constant of the tri-chloro complex incerases with the increase of temperature but decreases with the increase of pressure. This suggests that transition metals can be leached effectively from magmas under higher tempearature and lower pressures.