Co-precipitation of Sr2+ and Ba2+ with aragonite by membrane diffusion of CO2 between 10 and 50 °C

Aragonite is precipitated by a new CO2-diffusion technique from a Ca2+-Mg2+-Cl- Solution between 10 and 50 degreesC. Crystallisation of aragonite instead of calcite occurs by maintaining a [Mg2+]/[Ca2+] ratio of 2 in the fluid. The dissolved inorganic carbon (DIC) is received by diffusion Of CO2 through a polyethylene membrane (diffusion coefficient: D-CO2 = 10(-6.4) cm(2) s(-1) at 19 degreesC). It is suggested that significant amounts of DIC may be transferred by diffusion Of CO2 in natural systems if the CO2 gradient is high. The CO2-diffusion technique is used as a kind of simple mixed flow reactor for the co-precipitation of barium and strontium with aragonite. The distribution coefficients of Ba2+ and Sr2+ decrease from 10 to 50 degreesC according to D-Ba,D-a* = 2.42 - 0.03595T (degreesC) and D-Sr,D-a* = 1.32 - 0.005091 T (degreesC). At 25 degreesC, the distribution coefficients are D-Ba,D-a* = 1.5 +/- 0.1 and D-Sr,D-a* = 1.19 +/- 0.03. The effect of temperature on D-Ba,D-a* is about one order of magnitude higher versus that on D-Sr,D-a*. Thus, Ba2+ may be a potential paleotemperature indicator if the composition of the solution is known. (C) 2003 Elsevier B.V. All rights reserved.