Metal-humate interactions. 1. Discrete ligand and continuous distribution models

Journal Article · Tue Jul 01 00:00:00 EDT 1986 · Environ. Sci. Technol.; (United States)

DOI:https://doi.org/10.1021/es00149a004· OSTI ID:5022754

Dzombak, D A; Fish, W; Morel, F M.M.

In this paper the authors examine critically the theory underlying discrete and continuous multiligand models for metal-humate binding. The concepts and equations that unify the various models are presented, and a general solution to the fundamental integral equation for ion binding in a multiligand system is given. Particular attention is paid to the continuous distribution models (normal distribution, affinity spectrum, and continuous stability function) which are relatively new tools in the field of metal-humate complexation. It is shown that the lower half and extreme right of the Gaussian ligand distribution assumed in the normal distribution model never affect metal speciation measurably and hence are not knowable. It is also shown that an affinity spectrum does not correspond to an actual distribution of ligands; rather, each peak in the spectrum indicates the most probable stability constant controlling metal binding in a particular region of the experimental formation function. Application of the affinity spectrum model leads to a set of discrete ligands. A close examination of the continuous stability function model shows that it contains implicitly the same assumption as the affinity spectrum approach and thus leads also to discrete ligands.

• Research Organization: Massachusetts Institute of Technology, Cambridge (USA)
• OSTI ID: 5022754
• Journal Information: Environ. Sci. Technol.; (United States), Journal Name: Environ. Sci. Technol.; (United States) Vol. 20:7; ISSN ESTHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
520200 -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
AFFINITY
CHEMICAL BONDS
CHEMICAL REACTIONS
ELEMENTS
HUMIC ACIDS
LIGANDS
MATHEMATICAL MODELS
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS