Speciation of metals in natural waters

Frank J Millero

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The form or speciation of a metal in natural waters can change its kinetic and thermodynamic properties. For example, Cu(II) in the free ionic form is toxic to phytoplankton, while copper complexed to organic ligands is not toxic. The form of a metal in solution can also change its solubility. For example, Fe(II) is soluble in aqueous solutions while Fe(III) is nearly insoluble. Natural organic ligands interactions with Fe(III) can increase the solubility by 20-fold in seawater. Ionic interaction models that can be used to determine the activity and speciation of divalent and trivalent metals in seawater and other natural elements will be discussed. The model is able to consider the interactions of metals with the major (Cl-, SO 4 2-, HCO 3 -, CO 3 2-, Br -, F -) and minor (OH -, H 2PO 4-, HPO 4 2-, PO 4 3-, HS -) anions as a function of temperature (0 to 50 °C), ionic strength [0 to 6 m (m=mol kg -1)] and pH (1 to 13). Recently, it has been shown that many divalent metals are complexed with organic ligands. Although the composition of these ligands is not known, a number of workers have used voltammetry to determine the concentration of the ligand [L n] and the stability constant (K ML) for the formation of the complex M 2+ + L n → ML n+2 K ML =[ML n+2]/[M 2+][L n] We have added the experimental values of K ML for the formation of complexes of natural organics in seawater of known concentration ([L n]) with Cu 2+, Zn 2+, Cd 2+, Co 2+, and Fe 3+. The model can be used to examine the competition of inorganic and organic ligands for divalent metals as a function of ionic strength. The importance of organic ligands in controlling the solubility of Fe(III) in seawater will be discussed. New experimental studies are needed to extend the model to higher temperatures and ionic strength.

Original languageEnglish (US)
Pages (from-to)56-64
Number of pages9
JournalGeochemical Transactions
Volume2
DOIs
StatePublished - Sep 12 2001

Fingerprint

ligand
Metals
Ligands
Water
metal
Seawater
water
Ionic strength
seawater
solubility
Solubility
Poisons
Phytoplankton
thermodynamic property
Carbon Monoxide
Voltammetry
Anions
anion
Copper
Thermodynamic properties

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

Cite this

Speciation of metals in natural waters. / Millero, Frank J.

In: Geochemical Transactions, Vol. 2, 12.09.2001, p. 56-64.

Research output: Contribution to journalArticle

Millero, Frank J. / Speciation of metals in natural waters. In: Geochemical Transactions. 2001 ; Vol. 2. pp. 56-64.
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