Statistics – Applications
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58..625w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 2, pp.625-637
Statistics
Applications
2
Scientific paper
The interaction of Pd with some O-donor organic acid anions has been investigated using solubility measurements and a variety of spectroscopic techniques (UV-visible, Raman, FTIR, 13 C NMR). Some of the ligands investigated (acetate, oxalate and fulvic acid) occur naturally in relatively high concentrations, whereas others (phthalate and salicylate) serve as models of potential binding sites on humic and fulvic acids. Solubility measurements show that the presence of acetate, phthalate, salicylate and fulvic acid (oxalate was not studied via solubility methods) can increase the mobility of Pd over various pH ranges, depending on the organic ligand. In the case of acetate, UV-visible and Raman spectroscopy ( 13 C NMR results were inconclusive) provide strong evidence for the formation of electrostatically bound, possibly outer-sphere palladium acetate complexes. Oxalate was confirmed by UV-visible and FTIR spectroscopy to compete favorably with chloride (0.56 M NaCl) for Pd even at oxalate concentrations as low as 1 mM at pH = 6-7. Available data from the literature suggest that oxalate may have an influence on Pd mobility at free oxalate concentrations as low as 10 -8 -10 -9 M. UV-visible spectroscopy provides evidence of an initially rapid, followed by a slower, reaction between PdCl 4 2- and o -phthalate ion. Our findings lend support to the idea that similar binding sites on fulvic acid may be capable of complexing and solubilizing Pd in the natural environment. Although thermodynamic data are required to fully quantify the extent, it is concluded that simple carboxylic acid anions and/or fulvic and humic acids should be capable of significantly enhancing Pd transport in the surficial environment by forming truly dissolved complexes. On the other hand, flocculation of fulvic/humic acids, owing to changing ionic strengths or pH, or adsorption of these acids onto mineral surfaces, may also provide effective means of immobilizing Pd. These results have applications in exploration geochemistry and disposal of radioactive waste containing 107 Pd.
Janecky David R.
Tait Drew C.
Vlassopoulos Dimitri
Wood Scott A.
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