Comparative Geochemistries of Pd^II and Pt^II:: Formation of Mixed Hydroxychloro and Chlorocarbonato-complexes in Seawater

Authors

Jeanette M. Cosden, University of South Florida
Robert H. Byrne, University of South FloridaFollow

Document Type

Article

Publication Date

2003

Digital Object Identifier (DOI)

https://doi.org/10.1016/S0016-7037(02)01271-1

Abstract

Comparative observations of Pd^II and Pt^II hydrolysis in chloride solutions indicate that [PdCl₃OH²⁻]/[PdCl42−] and [PtCl₃OH²⁻]/[PtCl42−] concentration ratios in salinity 35 seawater (S = 35) are smaller than one at a typical surface ocean pH (∼8.2), and are larger than one at pH = 8.2 when S < 10. The hydrolysis behaviors of PdCl42− and PtCl42− are very similar. In 0.5 M NaCl at 25°C the hydrolysis constant for both elements, written in the form β₁ = [MCl₃OH²⁻][Cl⁻][H⁺][MCl42−]⁻¹, is logβ1*=−8.97. Between ionic strengths 0.3 M and 1.0 M for Pd^II and between 0.1 M and 1.0 M for Pt^II, log β₁ is within approximately 0.1 units of the value appropriate to 0.5 M NaCl. This small dependence of PdCl42− and PtCl42− hydrolysis constants on ionic strength is consistent with predictions based on expected activity coefficient behavior.

Carbonate is observed to complex PdCl42− significantly, but to a smaller extent than OH⁻ under conditions appropriate to seawater. Complexation of PtCl42− by CO32− was observed in this work but the rate of complexation was too slow to allow equilibrium observations. The principal dissimilarity between the chemistries of Pd^II and Pt^II in our investigation was the sharp contrast in observed Pd^II and Pt^II reaction rates. Differences in reaction kinetics may cause fractionation of Pd^II and Pt^II in the environment. The speciation of Pt^II, unlike Pd^II, is likely to be based on chemical environments experienced by Pt^II over a period of days, and perhaps weeks.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Geochimica et Cosmochimica Acta, v. 67, issue 7, p. 1331-1338

Scholar Commons Citation

Cosden, Jeanette M. and Byrne, Robert H., "Comparative Geochemistries of Pd^II and Pt^II:: Formation of Mixed Hydroxychloro and Chlorocarbonato-complexes in Seawater" (2003). Marine Science Faculty Publications. 1738.
https://digitalcommons.usf.edu/msc_facpub/1738