[MIS07-P03] Crystal Growth of Norsethite BaMg(CO3)2 from aqueous solution
Keywords:Norsethite, Solution Growth, Carbonate
Hood et al., for the first time, has reported the artificial synthesis of norsethite in 1973.2) Recently, Pina reported that norsethite appears through the below two chemical reactions:3)
Like this way, the formation of norsethite is complicated. Hence, to control the growth of norsethite, understanding of the physical factor, which governs norsethite crystallization, is essential. In this study, we directly observed the precipitations obtained from BaCl2-MgCl2-NaHCO3 mixture solutions by optical microscopy and powder X-ray diffraction, and examined the crystallization of norsethite from aqueous solution.
0.3M BaCl2•2H2O, 0.3M MgCl2•6H2O, and 0.125M NaHCO3 were dissolved to pure water (200 mL) heated at 50-90 oC, and the mixture solution was stirred and heated for 3 weeks. The temporal course of the precipitation was observed by optical microscopy and powder X-ray diffraction.
First, the temporal course of the precipitations obtained at 60 oC was observed. Just after we added the chemical regents to the pure water, BaCO3 crystals with a needle shape (witherite) sedimented. In contrast, norsethite with a rhombohedral shape was obtained in 216 h. To quantify the crystallization of norsethite, we measured the longitudinal of witherite L and (104)-face diffraction intensity of norsethite I104. Witherite enlarged until 48 h. However, more than 48 h, L started to become small, and witherite gradually was dissolving. In contrast, the I104 increased over 200 h. These results demonstrate that norsethite is formed not by solid-solid transition, but by solution-mediated transition. At the other temperatures, norsethite also appears by solution-mediated transition. By extrapolate line of I104, we also revealed the induction period of norsethite obtained at 60 oC was 182 h. In this presentation, we are going to report the solution growth of norsethite at various temperature, regarding the rate-determining process.
(1) Shin-ichi Hirano and Ko-ichi Kikuta, J. Cryst. Growth, 351-356, 1989.
(2) Hood et al., Am. Mineral, 471-474, 1974.
(3) C.M.Pina and C.Pimentel, Dolomite, 115-139, 2017.