2000 Fiscal Year Final Research Report Summary
Study on aqueous speication of metals under supercritical hydrothermal conditions.
| Project/Area Number |
09640576
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Waseda University |
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Principal Investigator |
UCHIDA Etsuo Waseda University, School of Science and Engineering, Professor, 理工学部, 教授 (40185020)
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| Project Period (FY) |
1997 – 2000
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| Keywords | aqueous speciation / supercritical / hydrothermal solution / ion exchange / tri-chloro complex / formation constant / basalt / cation leaching |
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| Research Abstract |
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.
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