Synthesis and distribution coefficient of low-magnesium calcites

Assessing the effect of on scale formation–bulk precipitation and surface deposition

“…The distribution coefficient reflects the distribution of the ratio of Mg/Ca in the surface deposit and Mg/Ca ratio in the bulk solution. In dynamic conditions (under 1500 rpm), the distribution coefficient is 0.028, 0.033, 0.031 for different Mg/Ca ratios of 0.227, 0.445, 0.667, respectively, which is broadly in agreement with the value of D ¼ 0:030 AE 0:005 at 25 1C has been determined by Howson [19] for Mg/Ca o1. It is shown that the distribution coefficient is a constant and is independent of the concentration of Mg 2þ ions in the bulk solution.…”

Complex speleothem growth processes revealed by trace element mapping and scanning electron microscopy of annual layers

“…This effect is not noticed in calcites grown from solutions with Mg/Ca ratios above 7.5 as in this situation, the amount of Mg adsorbed onto non-lattice sites is constant (sites are saturated) and small compared with the amount of Mg taken up into lattice sites which is proportional to the fluid Mg/Ca ratio (Mucci and Morse, 1983). Subsequent studies (Howsen et al, 1987; also found elevated D Mg values (ϳ0.02-0.03) for solutions with low Mg/Ca ratios, close to those typical of cave waters, although the experimental range investigated by Howson et al (1987) and was not broad Fig. 7.…”

Mg isotope fractionation during calcite precipitation: An experimental study

“…This value is in agreement with published data obtained from experiments performed at equilibrium under similar conditions (of pH, solution composition and temperature). Indeed, Mucci and Morse (1983), Howson et al (1987), and Huang and Fairchild (2001) found an equilibrium D Mg value of 0.029 ± 0.008 at 25°C. Huang and Fairchild (2001) found a D Mg value of 0.020 ± 0.006 at 15°C.…”

“…The equilibrium D Mg,eq during calcite formation is estimated to be 0.029 ± 0.008 at 25°C and 0.020 ± 0.006 at 15°C from previous experimental studies (Mucci and Morse, 1983;Howson et al, 1987;Huang and Fairchild, 2001) for the solution Mg/Ca and chemical composition used in these experiments. The Mg enrichments, defined as D Mg,apparent /D Mg,eq , range from $1.5 to $8 (Fig.…”

“…Previous studies have examined some of the parameters which could influence D Mg such as temperature (Katz, 1973;Fü chtbauer and Hardie, 1976;Howson et al, 1987;Mucci, 1987;Oomori et al, 1987;Nü rnberg et al, 1996;Huang and Fairchild, 2001;Chen et al, 2005), salinity (Zhong and Mucci, 1989), pH (Oomori et al, 1987;Burton and Walter, 1991;Hartley and Mucci, 1996), calcite growth rate (Given and Wilkinson, 1985a,b) or Mg/Ca of the solution (Devery and Ehlmann, 1981;Mucci and Morse, 1983;Busenberg and Niel Plummer, 1989). However, no consensus has been reached on the key controls on the equilibrium D Mg value.…”