TY - JOUR
T1 - Inorganic Speciation of Dissolved Elements in Seawater: the Influence of pH on Concentration Ratios
AU - Byrne, Robert H.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - 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 p K n = −log K n or p K n * = −log K n * respectively, where K n and K n * are equilibrium constants. For equilibria involving carbonate complexation, the constant C is written as p Q = −log( K 2 / K n [HCO 3 − ]) where K 2 / is the HCO 3 − dissociation constant, K n is a cation complexation constant and [HCO 3 − ] 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.
AB - 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 p K n = −log K n or p K n * = −log K n * respectively, where K n and K n * are equilibrium constants. For equilibria involving carbonate complexation, the constant C is written as p Q = −log( K 2 / K n [HCO 3 − ]) where K 2 / is the HCO 3 − dissociation constant, K n is a cation complexation constant and [HCO 3 − ] 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.
UR - https://digitalcommons.usf.edu/msc_facpub/1629
UR - https://doi.org/10.1039/B109732F
U2 - 10.1039/B109732F
DO - 10.1039/B109732F
M3 - Article
VL - 3
JO - Geochemical Transactions
JF - Geochemical Transactions
ER -