Inorganic Speciation of Dissolved Elements in Seawater: the Influence of pH on Concentration Ratios

Authors

Robert H. Byrne, University of South FloridaFollow

Document Type

Article

Publication Date

2014

Digital Object Identifier (DOI)

https://doi.org/10.1039/B109732F

Abstract

Assessments of inorganic elemental speciation in seawater span the past four decades. Experimentation, compilation and critical review of equilibrium data over the past forty years have, in particular, considerably improved our understanding of cationhydrolysisand the complexation of cationsby carbonateions in solution. Through experimental investigations and critical evaluation it is now known that more than forty elements have seawater speciation schemes that are strongly influenced by pH. In the present work, the speciation of the elements in seawater is summarized in a manner that highlights the significance of pH variations. For elements that have pH-dependent species concentration ratios, this work summarizes equilibrium data (S = 35, t = 25 °C) that can be used to assess regions of dominance and relative species concentrations. Concentration ratios of complex species are expressed in the form log[A]/[B] = pH − C where brackets denote species concentrations in solution, A and B are species important at higher (A) and lower (B) solution pH, and C is a constant dependent on salinity, temperature and pressure. In the case of equilibria involving complex oxy-anions (MO_x(OH)_y) or hydroxy complexes (M(OH)_n), C is written as pK_n = −logK_n or pK_n* = −logK_n* respectively, where K_n and K_n* are equilibrium constants. For equilibria involving carbonate complexation, the constant C is written as pQ = −log(K₂^/K_n[HCO₃⁻]) where K₂^/ is the HCO₃⁻ dissociation constant, K_n is a cation complexation constant and [HCO₃⁻] is approximated as 1.9 × 10⁻³ molar. Equilibrium data expressed in this manner clearly show dominant species transitions, ranges of dominance, and relative concentrations at any pH.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Geochemical Transactions, v. 3, issue 2, p. 11-16

Scholar Commons Citation

Byrne, Robert H., "Inorganic Speciation of Dissolved Elements in Seawater: the Influence of pH on Concentration Ratios" (2014). Marine Science Faculty Publications. 1629.
https://digitalcommons.usf.edu/msc_facpub/1629