Calcite Formation in Calcium Chloride Rich Water

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1 Jap. J. Limnol. 45, 1, 1-5, Calcite Formation in Calcium Chloride Rich Water Chisato TOMIYAMA and Yasushi KITANO Abstract C alcite was found in the sediment of the Don Juan basin in the Dry Valleys region of Antarctica. In order to clarify the chemical composition of the past pond water, the crystal formation of calcium carbonate from calcium chloride rich solution was studied. The transformation of aragonite into calcite in a calcium chloride solution was also investigated. The experimental results suggest that calcite in the sediments of the Don Juan basin was formed from calcium chloride water through inorganic processes. 1. Introduction Calcium carbonate is contained in the sediment of the Don Juan basin, the south fork of the right Valley in the Dry Valleys region of Antarctica (latitude 77 34' S, longitude ' E) (ToMIYAMA and KITANO, 1982). Its content ranges from 0.2 to 8%. The distribution of carbonate is quite characteristic (see Fig. 1) : The carbonate-rich layer (8% content) was found only in DJ 14 sediment core. The other cores, DJ 2, 3, 5, 10, 12 and DVDP 13, contained only small amounts of carbonate. It is helpful for the investigation on the Fig. 1. Sampling location of sediment cores in the Don Juan basin and the distribution of carbonate-ca in each sediment core. Fig. 2. X-ray diffraction patterns of DJ 14-4 sampe; (A) original and (B) after HC1 treatment.

2 2 Calcite Formation in Calcium Chloride Rich Water origin of salt in the Don Juan basin to clarify the process by which calcium carbonate is formed in DJ 14. Two sources for calcium carbonate are supposed; calcium carbonate formed from the pond water and detrital calcium carbonate. The authors proposed that the inorganic formation of calcite from the pond water is a reasonable explanation for the calcium carbonate in DJ 14 (TOMIYAMA et al., 1983). The crystal form of calcium carbonate may yield useful information for the formation process (KITANO, 1962; KITANO and HooD, 1962; ToKUYAMA et al., 1973; KITANO et al., 1979) : When calcium carbonate is precipitated inorganically from seawater, an aragonite formation is most likely, because of the presence of magnesium ions in seawater (KITANO and HOOD, 1962). If the salt origin in the Don Juan basin was seawater, aragonitic calcium carbonate should be precipitated from the pond water. However, the calcium carbonates contained in DJ 14 core and the other cores were identified as calcite by X-ray diffractometry (Fig. 2). To clarify the calcite formation process, the present authors have studied the crystal form of calcium carbonate precipitated from calcium rich solutions containing, and they also have investigated the transformation of aragonite to calcite in calcium chloride type brine. 2. Experimental 1. Calcium carbonate synthesis from calcium chloride solution containing magnesium ions 1-a. CaC12 + NaHCO3 + MgCl2 + (NaCI) -~ Carbonate Table 1. CaC12-NaHC03-MgCl2- (NaCI) system (A) Chemical composition of the parent solution (B) Crystal form and Mg content of the formed calcium carbonate and final ph of the parent solution (after standing for 2 days) *1 The value for the difference in spacing of (014) reflection between pure calcite and precipitated calcite *2 GLOVER and SIPPEL (1967) and OHDE and KITAxo (1978) reported that magnesium carbonate content in magnesian calcite precipitated from CaCl2-MgCl2-NaHC03-NaCI solution increases with increasing NaCI concentration in the parent solution. This trend was recognized in the present experiment.

3 TOMIYAMA and KITANO 3 Calcium carbonate was formed by adding NaHCO3 solution to CaC12 solution containing. Table 1-A shows the concentrations of these chemical constituents. Selection of their concentrations in a parent solution was based on the chemical composition of the Don Juan Pond water (Table 2, ToRII et al., 1977). Table 2. Chemical composition of the Don Juan Pond water (TORII et al., 1977) 1-b. Ca (HCOs) 2 + CaC12 + MgC Carbonate Calcium bicarbonate solution was prepared by bubbling carbon dioxide gas into calcium carbonate suspended solution for one day and filtering off the suspended carbonate (KITANO, 1962). Five hundred ml of the calcium bicarbonate solution was added to 500 ml of calcium chloride (Ca2#, 0.3 to 50 g) plus magnesium chloride (Mg2+, 2 g) solutions. The chemical composition of these parent solutions are shown in Table 3-A. After these parent solutions were allowed to stand at 20 C for a few days, calcium carbonate was formed from the solution by the escape of carbon dioxide gas into air. The formed calcium carbonate was filtered off through No.5 B filter, washed with deionized water until free of chloride ions and dried in an air bath at 60 C. The crystal form of carbonate was identified by X-ray difractometry. The magnesium content of the carbonate was determined by atomic absorption spectrometry after it was dissolved with hydrochloric acid. 2. Transformation of aragonite into calcite Aragonite was synthesized from calcium bicarbonate solution containing magnesium ions (2.0 g.l-1) by the escape of carbon dioxide gas into air (KITANO et al., 1962). The synthesized pure aragonite was powdered. The powdered aragonite was added to the calcium chloride solution containing (Ca g - l-1, Mgt+2.Og-l-1). The suspension was allowed to stand at 20 C. After 1, 7, 17, 44 days, the carbonate was filtered off, washed with deionized water and dried. The crystal form was identified by X-ray diff ractometry. 3. Results and Discussion 1. Calcium carbonate synthesis from the calcium chloride solution containing 1-a. CaCl2 + NaHCO3 + MgC12 + (NaCI) --> Carbonate Table 1-B shows the crystal form of Table 3. Ca (HC03) 2-CaCl2-MgC12 system (A) Chemical composition of the parent solution (20 C) (B) Crystal form and Mg content of the formed calcium carbonate and final ph (after standing for 10 days)

4 Calcite Formation in Calcium Chloride Rich Water formed calcium carbonate. Aragonite alone is formed from general solutions containing 2 g l-1 of magnesium ions (KITANO and HOOD, 1962).

4 4 Calcite Formation in Calcium Chloride Rich Water formed calcium carbonate. Aragonite alone is formed from general solutions containing 2 g l-1 of magnesium ions (KITANO and HOOD, 1962). As seen from Nos. 2 to 6 in Table 1, however, calcitic calcium carbonate was formed from the solutions in the high calcium chloride concentrations (Ca g 11 -to 2 g 1') -in spite of the presence of (Mg2+2.Og-1-1). In the low calcium chloride concentrations (Nos. 7 and 8 of Table 1, Ca2+ lower than 1 g.1') -aragonite also was formed with calcite. Table 1-B shows the magnesium content of the formed calcium carbonate and the difference in spacing of (104) reflection between pure calcite and precipitated calcite. The values of Nos. 7 and 8 indicate that the magnesium carbonate in the formed carbonate is contained as a form of magnesian calcite (a solid solution between CaCO3 and MgCO3) (KITANO and KANAMORI, 1966). The effect of temperature on the crystal form was not significant as seen from Nos. 1 and 2 in Table 1. When the concentration of NaHCO3 in the parent solution was varied but the concentrations of magnesium and calcium ions were kept constant, only calcitic calcium carbonate was formed as seen from Nos. 9 to 14 in Table 1. The results indicate that the concentration of NaHCO3 in this solution system has no effect on the crystal form of calcium carbonate. It was reported that sodium chloride in a parent solution favors the formation of calcitic calcium carbonate (KITANO, 1962). The experimental results of Nos. 15 and 16 in Table 1 show that aragonitic calcium carbonate was precipitated from the solution containing a large amount of sodium chloride, a small amount of calcium chloride and (2.0 g.1'), -because of the strong influence of. These results indicate that the combination of calcium and chloride ions in a parent solution favors calcite formation very strongly as compared with that of sodium and chloride ions (KITANO, 1962). 1-b. Ca (HCO~) 2 CaCl MgCL > Carbonate The crystal form and the magnesium content of the formed calcium carbonate are shown in Table 3-B. The experimental results of Nos. 19 to 22 in Table 3 show aragonite formation, while the experimental results of Nos. 5 and 6 in Table 1 show calcite formation, although the calcium concentrations of Nos. 5 and 6 are the same as those of Nos. 19 and 20 respectively. This difference of the crystal form is considered to be caused by the absence or presence of sodium ions in the parent solution. KITANO (1962) reported that sodium ions in a parent solution favor calcite formation and inhibit aragonite formation. The effect of sodium ions on the crystal form seems to be significant when the calcium concentration was lower than 5 g.11 -, However, as seen from Nos. 17 and 18 in Table 3, calcitic calcium carbonate was formed at high calcium concentrations (higher than 10 g.11) -in spite of the absence of sodium ions in the parent solution. The experimental results in the above two solution systems (1-a, 1-b) show that calcite is formed from the calcium chloride rich solution (Ca2+ higher than log l-1) containing (Mg2+ 2 g l-1), owing to the high concentrations of calcium and chloride ions in a parent solution. 2. Transformation of aragonite to calcite For the calcite formation from a calcium chloride rich solution, the transformation of aragonite to calcite was examined in the laboratory. BIscHOFF and FYFE (1968) reported that the rate of transformation of aragonite to calcite in calcium chloride solution increases with the concentration of calcium chloride. KITANO et al. (1972) reported that the presence of magnesium ions in a solution strongly inhibits the transformation of aragonite into calcite. The present experimental results (Table 4) indicate that aragonite suspended in the calcium chloride rich solution containing was not transformed into calcite. Thus, calcite was not formed

5 Table 4. Transformation experiment of aragonite (Ca,2} 100 g 1-1, Mg,2+2 g 1-1) through the transformation of aragonite suspended in the Don Juan Pond water. 4. Conclusion The experimental results show that calcite was formed in calcium-rich solution in spite of the presence of, and that aragonite was not transformed into calcite in calcium chloride rich solution containing. These results suggest that calcite has been formed from the Don Juan Pond water through inorganic processes and that the past pond water contained a large amount of calcium chloride and a rather small amount of as seen in the present pond water. TOMIYAMA and KITANO 5 of magnesium calcites. Geochim. Cosmochim. Acta, 31: KITANO, Y. (1962) : The behavior of various inorganic ions in the separation of calcium carbonate from a bicarbonate solution. Bull. Chem. Soc. Jpn., 35: KITANO, Y. and D. W. Hoon (1962) : Calcium carbonate crystal forms formed from sea water by inorganic processes. J. Oceano. Soc. Jpn., 18: KITANO, Y., K. PARK and D. W. Hoon (1962) : Pure aragonite synthesis. J. Geophys. Res., 67: KITANO, Y. and N. KANAMORI (1966) : Synthesis of magnesian calcite at low temperatures and pressures. Geochem. J., 1: KITANO, Y., S. YOSHIOKA, N. KANAMORI and T. TSUZUKl (1972) : The transformation of aragonite to calcite in aqueous solutions. Fossils, 23, 24: KITANO, Y., A. TOKUYAMA and T.ARAKAKI (1979) : Magnesian calcite synthesis from calcium bicarbonate solution containing magnesium and barium ions. Geochem. J., 13: OHDE, S. and Y. KITANO (1978) : Synthesis of protodolomite from aqueous solution at normal temperature and pressure. Geochem. J, 12: TOKUYAMA, A., Y. KITANO and N. KANAMORI (1973) : Crystal forms of calcium carbonate formed from calcium bicarbonate solution containing heavy metal ions. Bull. Science Engineering.Div., Univ. of the Ryuhyu (Math. and Nat. Sci.), 16: TOMIYAMA, C. and Y. KITANO (1982) : Partitioning of chemical elements into mineral species in core sediment from Don Juan Pond using selective chemical leaching technique. Antarct. Rec., 76: TOMIYAMA, C., Y. KITANO and T. TORII (1983) Sources of chemical constituents in the salts of the Don Juan basin. Antarct. Rec., 79: TORII, T., N. YAMAGATA, J. OSSAKA and S. MURATA (1977) : Salt balance in the Don Juan Basin. Antarct. Rec., 58: References BISCHOFF, J. L.. and W. S. FYFE (1968) : Catalysis, inhibition and the calcite-aragonite problem. I. The aragonite-calcite transformation. Am. J. Sci., 266: GLOVER, E. D. and R. F. SIPPEL (1967) : Synthesis Chisato TOMIYAMA and Yasushi KITANO, Water Research Institute, Nagoya University, Chikusa-ku, Nagoya 464) Accepted: 23 June 1983

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