Computer Science
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984gecoa..48.1493z&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 48, Issue 7, pp.1493-1503
Computer Science
4
Scientific paper
The dissolution of aluminium oxide was studied with an oxide film covered rotating disc aluminium electrode. This allows us to make measurements under conditions of well defined mass transport under conditions representative of those found in natural waters (conc. of Al, organic acids and fluoride), and permits us to distinguish between surface-controlled and transport-controlled rates. Under steady-state conditions, the dissolution current is a direct measure of the flux of dissolving Al ions at the aqueous interface of the amorphous hydrous oxide film. At pH 3-6 and in presence of organic ligands, dissolution is controlled by a surface process, i.e. the rate of detachment of surface complexes. Fluoride ions in concentrations 10 -6 M increase dramatically the dissolution rate: at pH = 4 the process is controlled by convertive diffusion of F - from the solution to the surface ( k F - = (3.6 ± 0.5) × 10 -2 cm s -1 ). Competitive and reversible adsorption of organic ligands (10 -6 - 10 -2 M ) displacing fluoride slows down the rate of detachment of the surface complex which becomes the rate-limiting step. The affinity of ligands for the Al 2 O 3 surface sites increases in the sequence: formate ~ chloride ~ carbonate < acetate < sulphate < salicylate < fumarate < maleate < malonate << oxalate fluoride citrate . The results are compared with simulated weathering experiments and interpreted in terms of the surface complexation model.
Stumm Werner
Žutić Vera
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