The effect of pressure on transition metals in seawater

Frank J. Millero, Fen Huang

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

The effect of pressure (P) on the activity coefficients (γiPi0) of ions (i) in seawater can be estimated from the partial molal volumes and compressibilities of the ions in water (V-0 and κ-0) and seawater (V-* and κ-*) ln(γP0)=(V-*-V-0)P/RT-0.5(κ-*-0)P2/RT where R and T have their normal meaning. One can also use the partial molal volumes and compressibilities of ions to estimate the effect of pressure (KP/K0) on ionic equilibria constants M2++X2-=MX, K = [MX]/[M2+][X2-]from the changes in the volume for the chemical reaction in seawater. δV*=V-*(MX)-V-*(M2+)-V-*(X2-), ΔV* = V-*(MX)-V-*(M2+)- V-*(X2-) using ln (K*P/K*0)=(ΔV*/RT)P-0.5 (Δκ*/RT)P2 The densities and sound speeds of a number of transition metal chlorides have been determined in 0.725m NaCl solutions (the ionic strength of average seawater, S~35) at 25°C. These results have been used to determine the partial molal volumes and compressibilities of transition metal ions (Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+). These results and our earlier measurements (Mg2+, Ca2+, Sr2+ and Ba2+) were used to develop correlations between the values in water and NaCl. These correlations were used to predict the values of other divalent ions in water and NaCl (Be2+, Pb2+, Hg2+ and Fe2+) that were difficult to directly measure. These studies allow one to make estimates of the effect of pressure on the activity coefficients of these ions in seawater and ionic equilibria in the deep oceans. The lower stability constants will result in increased concentrations of free transition metals in the deep ocean.

Original languageEnglish (US)
Pages (from-to)298-305
Number of pages8
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Volume58
Issue number3
DOIs
StatePublished - Mar 1 2011

Keywords

  • Complex formations
  • Compressibility
  • Pressure
  • Seawater
  • Transition metals
  • Volume

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science

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