Coordinative and hydrophobic interaction of humic substances with hydrophilic Al[sub 2]O[sub 3] and hydrophobic mercury surfaces

Journal Article · Sat Jan 01 04:00:00 EST 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90494-4· OSTI ID:5177324

Ochs, M; Stumm, W ^[1]; Cosovic, B ^[2]

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1. Swiss Federal Institute for Environmental Science and Technology, Duebendorf (Switzerland)
2. Ruder Boskovic Institute, Zagreb (Croatia)

The extent and kinetics of adsorption of a peat-derived humic substance (HS) onto a hydrophobic surface (mercury electrode) and a polar mineral surface ([gamma]-Al[sub 2]O[sub 3] colloids) was studied. Adsorption on the Hg-electrode was assessed by directly measuring the change of the double layer capacitance caused by the adsorption of HS on the electrode surface through phase-selective a.c. polarography; the extent of adsorption of HS on the [gamma]-Al[sub 2]O[sub 3]-surface was monitored by determining the residual HS-concentration in solution. On both surfaces, HS is adsorbed strongly over a wide pH-range; hydrophobic interaction (i.e., expulsion from solution) prevails at the mercury surface while coordinative adsorption (ligand exchange), enhanced by hydrophobic effects, is the predominant mechanism at the oxide surface. Adsorption kinetics are characterized by an initial fast process, where even in dilute solutions (<1 mg HS L[sup [minus]1]), a high surface coverage is attained initially. True adsorption equilibrium, however, cannot be reached within hours. The slow approach to equilibrium is though to be caused mainly by the polydispersity of HS resulting in fractionation processes, where presumably fast-adsorbing low-molecular weight compounds are successively displaced from the surface by slow-adsorbing compounds of higher molecular weight. Slow molecular rearrangements of HS-molecules at the interface cannot be ruled out, however. These results suggest that adsorption of humic substances on mineral as well as hydrophobic aquatic surfaces may lead to a progressive and selective immobilization of certain fractions of humic substances. This may have significant effects on the qualitative composition and reactivity of dissolved vs. particulate organic carbon and on the residence time of different fractions of humic substances in natural systems.

• OSTI ID: 5177324
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:2; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540210* -- Environment
Terrestrial-- Basic Studies-- (1990-)
540310 -- Environment
Aquatic-- Basic Studies-- (1990-)
ADSORPTION
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMISTRY
ELEMENTS
FULVIC ACIDS
HUMIC ACIDS
MATTER
MERCURY
METALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC MATTER
OXIDES
OXYGEN COMPOUNDS
SOIL CHEMISTRY
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES