Coprecipitation of Sr/sup 2 +/ with calcite at 25/sup 0/C and 1 atm

Journal Article · Wed Oct 01 00:00:00 EDT 1986 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(86)90074-8· OSTI ID:6896643

Pingitore, Jr, N E; Eastman, M P

The incorporation of Sr/sup 2 +/ into calcite at earth surface aqueous conditions is affected by the absolute concentration of Sr/sup 2 +/, the presence of Ba/sup 2 +/ and NaCl in the solution, and the rate of precipitation. At solution ratios (molar) of Sr/sup 2 +/ to Ca/sup 2 +/ in the low 10/sup -3/ range, which yield calcites with several hundred ppm Sr/sup 2 +/, k/sub calcite//sup Sr/ typically assumes a value between 0.10 and 0.20. Above these concentrations the value of k/sub calcite//sup Sr/ drops to approximately 0.06. Furthermore, if minor amounts of Ba/sup 2 +/ or large amounts of Na/sup +/ (0.48 M) are added to a dilute Sr/sup 2 +/ solution, a value around 0.06 for k/sub calcite//sup Sr/ is found. This strontium concentration effect and the associated competitive cation effect suggest that small amounts of Sr/sup 2 +/ may be incorporated into a limited number of nonlattice sites in calcite. Incorporation of Sr/sup 2 +/ into these sites, presumably defects, noticeably affects k/sub calcite//sup Sr/ only at low Sr/sup 2 +/ concentrations and in the absence of competition from other large cations. An increase in k/sub calcite//sup Sr/ with rate of precipitation, qualitatively similar to that found in other studies, was observed only when precipitation times were decreased from days to hours. For many geologic settings a partition coefficient for Sr/sup 2 +/ into calcite of 0.06 appears appropriate, but there are situations - very low Sr/sup 2 +/ concentrations, the presence of Mg/sup 2 +/, and fast precipitation rates - in which a larger value might better approximate natural partitioning.

• Research Organization: Univ. of Texas, El Paso
• OSTI ID: 6896643
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 50:10; ISSN GCACA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
AQUEOUS SOLUTIONS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
COPRECIPITATION
DISPERSIONS
ELEMENTS
GEOCHEMISTRY
METALS
MINERALS
MIXTURES
OXYGEN COMPOUNDS
PRECIPITATION
SEPARATION PROCESSES
SOLUTIONS
STRONTIUM