Amorphous calcium carbonate associated with biofilms in hot spring deposits
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Amorphous calcium carbonate
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Calcium carbonate has three different crystal forms, such as calcite, aragonite and vaterite. Calcite is the most common form of native calcium carbonate known and is one of the stable forms of carbonate on the earth's surface also. Authors have been summarized the research progress on heavy metals partitioning in carbonate calcium formation. The review is divided two parts. The topic for the part 1 is theoretic background and experimental methods. The topic for the part 2 is research progress and partitioning mechanism. Here is the part 1. In this paper,the equations for calculating partitioning coefficient of heavy metal ions were propo sed. The growth conditions and synthetic methods for calcite, aragonite and vaterite and its solid solution have been evaluated. The analytical methods for trace elements were summarized. The partitioning behaviors of heavy metal ions were discussed. The experimental results shown that: the presence of Mg 2+ inhibits vaterite formation; the presence of Sr 2+ favors aragonite formation; F - inhibits adsorption of Mg 2+ ions on calcite surface; the Sr 2+ distribution coefficients increases with increasing precipitation rate, while for Co 2+ , Mn 2+ , Cd 2+ , the distribution coefficients decrease with increasing precipitation rate.
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In this report, controls of polymorphism and morphology of calcium carbonate compounds were studied by suspending amorphous calcium carbonate hydrate (ACC) powder in water or MgCl2 solution. Characteristics of calcium carbonate compounds formed from ACC were determined by means of X-ray diffraction, thermal analysis (TG-DTA) and scanning electron microscopic observation. ACC was synthesized by adding 0.1mol⋅dm-3 CaCl2 solution into a mixed solution of 0.1mol⋅dm-3 NaOH and 0.1mol⋅dm-3 Na2CO3 at 0°C. The calcium carbonate compounds formed easily by suspending ACC in water and was affected remarkably by temperature (0-80°C) and pH (1.7-14.0). Thus ACC changed into hexagonal plate-like calcium carbonate hexahydrate at 0°C, rhombohedral calcite at 15-20°C, spherical vaterite at 30-50°C and needle-like aragonite above 80°C after aging for 1h. ACC was also changed into vaterite in the pH region of 7.0-9.5 and to basic calcium carbonate above pH 12.8 at 20-40°C. On the other hand, spherical calcium carbonate monohydrate was formed from ACC in MgCl2 solution (0.03-0.50mol⋅dm-3) and then changed finally to aragonite after long aging. For example, the amount of spherical monohydrate with a diameter of 30μm reached a maximum after aging for 3d, and it changed to needle-like aragonite with an average length of 50μm after 10d in 0.10mol⋅dm-3 MgCl2 solution. Accordingly, ACC changed easily to calcium carbonate anhydrides (calcite, aragonite, vaterite), calcium carbonate hydrates (monohydrate, hexahydrate) and basic calcium carbonate, when ACC was suspended in solutions of different conditions such as temperature, pH and concentration of MgCl2.
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Calcite, vaterite 그리고 aragonite가 혼합되어 있는 탄산칼슘을 X-선 회절로 분석하였다. 이것은 2성분 혼합물에서 X-선회질의 특성피크의 높이로부터 표준곡선을 작성하여 각각의 조성을 구하였다. 즉, calcite-vaterite 혼합물에서, vaterite의 양은 calcite의 특성피크인 2θ값이 29.32°의 높이에 대한 vaterite의 특성피크인 2θ값이 24.81°, 27.09° 그리고 32.75° 특성피크의 높이비로부터 구하였으며, 이 식의 실험오차는 약 3%이다. 그리고 calcite-aragonite의 호합물에서 aragonite의 양은 calcite의 특성피크인 2θ값이 29.32°의 높이에 대한 aragonite의 특성피크인 2θ값이 26.06°, 38.40° 그리고 45.81° 특성피크의 높이비로부터 구하였으며, 이 식의 실험오차는 약 3%이다. 위의 표준곡선으로부터 3성분의 혼합물의 조성비를 계산할 수가 있다. 합성된 순수한 입자의 혼합물을 위의 방법으로 계산한 결과 실험치와 계산치가 아주 잘 일치하였다.
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Abstract Calcium carbonate polymorphism is one of the most challenging problems in biomineralization. Calcium carbonate exists in three crystalline forms: calcite, aragonite and vaterite. Otoliths of teleost fishes are made of vaterite and aragonite, located in different sacs and never mixed together. This paper presents a biochemical characterization of the intracrystalline macromolecules associated to the vateritic and aragonitic phases of otoliths. Experimental evidences from calcium carbonate overgrowth on the surface of otoliths and in vitro crystallization on the chitin‐silk fibroin assembly organic matrix suggest that the intracrystalline macromolecules associated to the otolith influence the aragonite−vaterite polymorphism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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