Cation Leaching from the Basalt JB–1a by 2M NaCl Hydrothermal Solutions

Abstract

Abstract:The basalt JB-1a was reacted with 2M NaCl solutions, and the leaching behavior of the cations Na, K, Ca, Mg, Fe, Mn, Zn and Co was monitored. The experiments were carried out using standard cold-seal pressure vessels in the temperature range from 300 to 800°C under the constant pressure of 1000 bars and also in the pressure range from 500 to 1000 bars at 600°C.The concentrations of Fe, Mn, Zn and Co in the hydrothermal solutions increased significantly with increasing temperature and with decreasing pressure. The thermodynamic analysis of the experimental results suggests that this is due to the formation of trichloro-complexes and also partly due to the temperature dependence of ion exchange between augite and aqueous chloride solution. The Na concentration in the aqueous solution decreases with increasing temperature and with decreasing pressure. On the other hand, the behavior of K, Ca and Mg is complex and their concentrations seem to be controlled by the coexisting minerals.Judging from the experimental results, it is concluded that the transition elements are effectively leached from the basalt under higher temperatures and lower pressures. This means that higher temperature and lower pressure conditions are preferable for the production of ore-forming hydrothermal solutions.

Experiments on the Element Distribution between the Granodiorite JG‐1a and 2M NaCl Hydrothermal Solution at Temperatures of 300 to 800°C and a Pressure of 1 kb

“…As the case of Uchida and Tsutsui (2000), 2M NaCl aqueous solution prepared from reagent grade NaCl was used as a reactant solution.…”

“…Uchida and Tsutsui, 2000). The dissociation or formation constants for the aqueous species were taken from Table 4 of Uchida and Tsutsui (2000).…”

“…Uchida and Tsutsui, 2000). The dissociation or formation constants for the aqueous species were taken from Table 4 of Uchida and Tsutsui (2000). The activity coefficient for the charged aqueous species was obtained using a Debye-Hückel equation and that for neutral species was assumed to be unity.…”

“…The activity coefficient for the charged aqueous species was obtained using a Debye-Hückel equation and that for neutral species was assumed to be unity. Details for the calculation are described in Uchida and Tsutsui (2000). Because of the deficiency in the thermodynamic data for 300°C, the calculation was conducted only for the experiments carried out at temperatures of 400 to 800°C.…”

“…However, few experimental studies on the element distribution between acidic rocks and hydrothermal solutions under supercritical conditions have been conducted until now (e.g., Whitney et al, 1985). Uchida and Tsutsui (2000) has carried out such an experiment using the basalt JB-1a, one of the geochemical standard rock samples prepared by the Geological Survey of Japan (Imai et al, 1995a(Imai et al, , 1995b, and demonstrated that transition elements such as Fe, Mn, Zn and Co are leached considerably from the rock by 2M NaCl aqueous solution and that their concentrations in the solution increase significantly with increasing temperature. Such results for the transition elements have been predicted by the experiments of Uchida et al (1995Uchida et al ( , 1998 dealing with the formation of tri-chloro complex of the transition elements under supercritical hydrothermal conditions.…”