Abstract
UV spectrophotometry was used to directly observe the partitioning of lead(II) between PbCO 3 0 and the forms of lead in natural seawater ( S = 35.4) that are dominant at low pH (Pb 2+ and complexes with Cl − and SO 4 2− ). Lead carbonate formation constants were determined in the form, β 1 = M PbCO 3 ( M Pb M CO 3 ) − 1 , where M PbCO 3 represents the concentration (mol/kg) of PbCO 3 0 , M Pb represents the sum concentrations of free lead (Pb 2+ ) and its complexes with chloride and sulfate, and M CO 3 represents the sum concentration of free and ion paired carbonate in seawater. Over a range of temperature between 15 and 35 °C, the reaction enthalpy appropriate to β 1 was calculated as Δ H = − 1.4 ± 0.6 kJ/mol. This is sufficiently small that, in the context of the uncertainties in β 1 measurements at each temperature, the PbCO 3 0 formation constant over the 20 °C range in temperature is effectively constant ( β 1 = (1.27 ± 0.02) × 10 4 (mol/kg) − 1 ). For total dissolved inorganic carbon concentrations in the order of 2 mm (millimolal), PbCO 3 0 is the dominant inorganic form of lead(II) when pH is greater than 7.6.
Original language | American English |
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Journal | Marine Chemistry |
Volume | 110 |
DOIs | |
State | Published - Jan 1 2008 |
Keywords
- Carbonate
- Chemical speciation
- Complexation
- Lead
- Seawater
- Spectrophotometry
Disciplines
- Life Sciences