Gold speciation in natural waters: II. The importance of organic complexing--Experiments with some simple model ligands

Details Gold speciation in natural waters: II. The importance of organic complexing--Experiments with some simple model ligands Gold speciation in natural waters: II. The importance of organic complexing--Experiments with some simple model ligands

Jun 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990gecoa..54.1575v&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 54, Issue 6, pp.1575-1586

Computer Science

4

Scientific paper

The solubility of Au has been measured at 25°C in aqueous solutions in the presence of various organic ligands (acetate, benzoate, oxalate, phthalate, salicylate, and thiosalicylate). These ligands were chosen as simple analogs of humic acid moieties in order to model the complexation of Au by humic and fulvic acids in natural waters. With the first five ligands ( L = 0.1 M ), solubilities were generally below 25 g/l, whereas in the thiosalicylate solutions ( L = 0.45 M ), a maximum Au concentration of 680 mg/1 was measured. Acetate and benzoate complexes are too weak to detect by the solubility method. Oxalate appears to have a reducing effect on Au in solution, and both oxalate and phthalate complexes of Au(I) may be coordinatively unfavorable. It was only possible to identify one salicylato complex ( log 2 = 17.5 ± 0.5) and two thiosalicylato species ( log 1 = 29.9 ± 0.3 and log 2 = 31.7 ± 0.3). In addition, stability constants for a number of O-, N-, and S-donor complexes of Au(I) were estimated from linear free energy relationships with Cu(I), Ag(I), and Hg(II). General trends in stability constants of Au-organic complexes with various donor atoms are S >> N O. Calculations based on a simple model of a fulvic acid suggest that Au is almost exclusively bound to S-donor sites under reducing conditions, but AuOH(H 2 O) 0 and complexing by organic O-donors are more important in oxidizing environments.

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