A new method for the study of trace element partitioning between calcium carbonate and aqueous solution: A test case for Sr and Ba incorporation into calcite

Abstract

A new experimental method (evaporation method) for calcium carbonate precipitation in aqueous solution was attempted in order to develop a convenient and controllable experimental technique for obtaining precise trace element partition coefficients. Calcite crystals were formed by evaporation of H 2 O from the aqueous mother solution using a dehumidifier, and the consumed Ca ions were supplied from a refill solution to maintain supersaturation. This method has been tested for Sr and Ba partition coefficients using NaCl (3.5%) solution under room temperature and pressure. The results of two runs give Sr partition coefficients of 0.0585 and 0.0546, and Ba partition coefficients of 0.0302 and 0.0275 for growth rates of 152 and 499 µmol·m -2 ·hr -1 , respectively. It was found that this method has several merits for partitioning experiments: (1) pH of the solution is close to the natural ones, for example, pH of 8.08 in the present case is close to that of seawater; (2) chemical composition of the mother solution can be chosen to imitate natural composition; (3) the crystal growth rate is controllable in a relatively small range and is measurable; and (4) temperature and P CO2 pressure can be controlled. The relative errors of the partition coefficients in the present study were estimated to be about 5%. The results seem to be promising, and suggest that more precise determination of partition coefficients could be possible via more careful experimental handling and improving the apparatus.

Groundwater geochemistry observations in littoral caves of Mallorca (western Mediterranean): implications for deposition of phreatic overgrowths on speleothems

“…To that end, the greater Sr:Ca, Ba:Ca, and Sr:Mg ratios observed in this study suggest that higher relative abundances of Sr 2+ and Ba 2+ may also encourage aragonite precipitation and/or inhibit calcite precipitation (Lippmann, 1973;Terakado & Taniguchi, 2006;Sunagawa et al, 2007).…”

The effects of temperature and water concentration on the otolith incorporation of barium and manganese in black rockfish Sebastes melanops

“…Although researchers note that it is not necessary to fully understand the mechanisms regulating elemental incorporation to use otoliths as natural tags (Thorrold et al ., 2002; Martin & Thorrold, 2005), laboratory validation will advance understanding of abiotic (temperature, salinity and water concentration) and biotic (growth rate and osmoregulatory differences) effects on the incorporation rate of metals in biogenic carbonates. Variation in processes that regulate elemental incorporation among animal species and carbonate forms (vaterite, calcite and aragonite) appears extensive (Lorens & Bender, 1980; Zacherl et al ., 2003; Terakado & Taniguchi, 2006) and the need for validation studies remains. A common metric, the partition coefficient ( D Me ), is used to quantify the partitioning of metals (Me) in carbonates at equilibrium and is described by the following equation (Morse & Bender, 1990): …”

Experimental study of rare earth element partitioning between calcite and sodium chloride solution at room temperature and pressure

“…The calcite crystals were synthesized by using the "evaporation method" modified after Terakado and Taniguchi (2006). The parent solution (4 litters) was placed in the reaction container made of acrylic resin.…”

“…Moreover, the REE partition coefficients obtained in the previous studies are considerably variable with respect to the absolute values and the REE pattern shape. In the present study, we would like to report the REE partition coefficients between calcite and aqueous solution using the evaporation method (Terakado and Taniguchi, 2006) which can maintain pH, REE concentration level and crystal growth rate similar to those in seawater environments.…”