熱水環境における天青石の炭酸塩化：炭酸水素ナトリウム溶液を用いた実験 [in Japanese] Carbonation of celestine under hydrothermal condition: an experiment with sodium bicarbonate solution [in Japanese]
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In order to understand the processes and mechanism for the formation of strontianite from celestine under the existence of bicarbonate, chemical reaction of celestine with sodium bicarbonate solution was experimentally examined. Natural celestine grains between 1.00 and 1.18 mm in diameter were sealed in the teflon bottle which contains aqueous NaHCO<sub>3</sub> solution. A series of experiment with 1/900 mineral/solution weight ratio was carried out with changing temperature (100, 125 and 150°C), initial NaHCO<sub>3</sub> concentration (0.01, 0.05, 0.10, 0.50 and 1.00 mol/l), and reaction time (2, 4, 8, 12, 24 and 96 hours). The run products were filtered by 0.20 μm membrane filters, and the filtrate and residual solid were analyzed. In addition, a series of experiment with 1/450 mineral/solution weight ratio with celestine grains between 2.36 and 4.75 mm in diameter was also carried out for observation of solid profiles.<br>Regardless of the various conditions, the only identified reaction product was strontianite, which is well correlated with the equilibrium calculation results. Amount of strontianite relative to celestine increases with the increase in temperature, initial NaHCO<sub>3</sub> concentration and reaction time, in the range of ~0% for the condition of initial NaHCO<sub>3</sub> 0.01 mol/l-100°C-2 hours and 90.0% for 1mol/l-150°C-96 hours. Strontianite develops as aggregates or layers of crystals on the surface of initial celestine grains. The depth of strontianite layer increases with the increase in reaction time, suggesting that the reaction occurs at the interface between solid and solution. The crystal habits of strontianite on the surface differ with the initial NaHCO<sub>3</sub> concentration: granular, platy and bladed crystals with cauliflower-like aggregates in increasing order. The rate of strontianite formation from celestine for 24 hours increases with the increase of temperature and initial NaHCO<sub>3</sub> concentration, in the range of 2.95x 10-6 mol·s<sup>-1</sup>·m<sup>-2</sup> for the condition of initial NaHCO<sub>3</sub> 0.01 mol/l-100°C and 6.88 x 10-5 mol·s<sup>-1</sup>·m<sup>-2</sup> for 1.00 mol/l-150°C. Thus, formation of strontianite from celestine proceeds under the existence of bicarbonate even at low temperature.
Shigen-Chishitsu 65(1), 13-22, 2015
The Society of Resource Geology