Solubility of Hydrous Ferric Oxide and Iron Speciation in Seawater

Robert H. Byrne, Dana R. Kester

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Abstract

Iron solubility equilibria were investigated in seawater at 36.22‰ salinity and 25°C using several filtration and dialysis techniques. In simple filtration experiments with 0.05 μm filters and Millipore ultra-filters, ferric chlorides fluorides, sulfates, and FeOH 2+ species were found to be insignificant relative to Fe(OH) 2 + at p[H + ] = −log [H + ] greater than 6.0. Hydrous ferric oxide freshly precipitated from seawater yielded a solubility product of ∗Kso=[Fe3+][H+]−3= 4.7 · 105">∗Kso=[Fe3+][H+]−3= 4.7 · 105 . Solubility studies based on the rates of dialysis of various seawater solutions and on the filtration of acidified seawater solutions indicated the existence of the Fe(OH) 3 0 species. The formation constant for this species can be calculated as ∗β3=[Fe(OH)30] [H+]3/[Fe3+] = 2.4 · 10−14">∗β3=[Fe(OH)30] [H+]3/[Fe3+] = 2.4 · 10−14 . The Fe(OH) 4 species is present at concentrations which are negligible compared to Fe(OH) 2 + and Fe(OH) 3 0 in the normal pH range of seawater. However, there is at least one other significant ferric complex in seawater above p[H + ] = 8.0 (possibly with bicarbonate, carbonate, or borate ions) in addition to the Fe(OH) 2 + and Fe(OH) 3 0 species.

Original languageAmerican English
JournalMarine Chemistry
Volume4
DOIs
StatePublished - Jan 1 1976
Externally publishedYes

Disciplines

  • Life Sciences

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