熱水条件(150℃)におけるカルサイトのマグネサイト化反応の条件とマグネサイトと熱水溶液間の希土類元素分配挙動(<特集>炭酸塩の地球化学)

概要

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Reagent grade calcite was reacted with MgCl_2 solutions doped with REE (Mg concentration of 0.089M-1.8M and REE concentration of about 0.3 ppm each) at 150℃ for 10 or 20 days. Solid products were identified by X-ray diffraction. Solid and liquid phases were analyzed for Mg, Ca and REE. The solid phases reacted with MgCl_2 solutions (0.89M and 1.8M of Mg^<2+>) were almost magnesite (about 95%). The molar ratios of Mg/(Mg + Ca) in solutions of the run products were consistent with the extrapolation of the reported experimental equations in the high temperature range from 275℃ to 420℃ to lower temperatures. The values of pH at room temperature of the final solutions are ranging from 5-7, and they show a decreasing trend with increasing Mg concentration. This is probably caused by the precipitation reaction of brucite, which is more likely to occur at 150℃ than at 25℃. The REE partition coefficients between solid and liquid phases defined by K_d(REE)={X_<REE>/(X_<Mg>+X_<Ca>)}_<solid>/{[REE]/([Mg]+[Ca])}_<liquid> have been determined experimentally. The series variation of logK_d (REE) in the run in which the solid phases were almost magnesite, shows a decreasing trend in LREE and a convex tetrad effect.
日本地球化学会の論文
2006-08-25