Uptake of Fe(II) and Mn(II) on chitin as a model organic phase

David J. Hawke, Sara Sotolongo, Frank J Millero

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Abstract

The sorption of Fe(II) and Mn(II) onto chitin has been measured in seawater as a function of pH (3-9), temperature (5-45°C), and salinity (0-35). The two metals showed markedly different pH effects. Uptake of Fe(II) was greatest at high pH, whereas Mn(II) showed negligible uptake above pH 6.3-7.3 and precipitated at high pH. The decrease in Mn(II) uptake above pH 6.3-7.3 could be related to the second acid dissociation site of chitin, which has p*Ka2 = 6.4. Fe(II) follows a Langmuir isotherm at pH 8.2 at intermediate concentrations, as did Mn(II) below pH 6.3. Uptake of both metals increased with temperature from 5 to 45°C, yielding a calculated sorption enthalpy of 14.2 ± 0.6 kJ mol-1 g-1 chitin for Fe(II) and 11 ± 3 kJ mol-1 g-1 for Mn(II) at pH 4. Increasing salinity from zero to 35 increased the uptake of Fe(II) by 50%; at pH 4 the Mn(II) uptake also increased substantially. Calculations indicate that uptake onto chitin-like material cannot account for the partitioning between dissolved and particulate forms of either Mn(II) or Fe(II) in two typical anoxic systems (the Black Sea and Framvaren fjord).

Original languageEnglish (US)
Pages (from-to)201-212
Number of pages12
JournalMarine Chemistry
Volume33
Issue number3
DOIs
StatePublished - 1991

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Chitin
chitin
Sorption
sorption
Metals
pH effects
salinity
metal
fjord
enthalpy
Seawater
Isotherms
Enthalpy
isotherm
partitioning
temperature
seawater
Temperature
Acids
acid

ASJC Scopus subject areas

  • Chemistry(all)
  • Oceanography

Cite this

Uptake of Fe(II) and Mn(II) on chitin as a model organic phase. / Hawke, David J.; Sotolongo, Sara; Millero, Frank J.

In: Marine Chemistry, Vol. 33, No. 3, 1991, p. 201-212.

Research output: Contribution to journalArticle

Hawke, David J. ; Sotolongo, Sara ; Millero, Frank J. / Uptake of Fe(II) and Mn(II) on chitin as a model organic phase. In: Marine Chemistry. 1991 ; Vol. 33, No. 3. pp. 201-212.
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AB - The sorption of Fe(II) and Mn(II) onto chitin has been measured in seawater as a function of pH (3-9), temperature (5-45°C), and salinity (0-35). The two metals showed markedly different pH effects. Uptake of Fe(II) was greatest at high pH, whereas Mn(II) showed negligible uptake above pH 6.3-7.3 and precipitated at high pH. The decrease in Mn(II) uptake above pH 6.3-7.3 could be related to the second acid dissociation site of chitin, which has p*Ka2 = 6.4. Fe(II) follows a Langmuir isotherm at pH 8.2 at intermediate concentrations, as did Mn(II) below pH 6.3. Uptake of both metals increased with temperature from 5 to 45°C, yielding a calculated sorption enthalpy of 14.2 ± 0.6 kJ mol-1 g-1 chitin for Fe(II) and 11 ± 3 kJ mol-1 g-1 for Mn(II) at pH 4. Increasing salinity from zero to 35 increased the uptake of Fe(II) by 50%; at pH 4 the Mn(II) uptake also increased substantially. Calculations indicate that uptake onto chitin-like material cannot account for the partitioning between dissolved and particulate forms of either Mn(II) or Fe(II) in two typical anoxic systems (the Black Sea and Framvaren fjord).

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