Bismuth speciation

SWV was used for the investigation of charge transfer kinetics of dissolved zinc(II) ions [215-218] and uranyl-acetylacetone [219], cadmium(II)-NTA [220] and mthenium(III)-EDTA complexes [221], and the mechanisms of electrode reactions of bismuth(III) [222], europium(III) [223,224] and indium(III) ions [225], 8-oxoguanine [226] and selenium(IV) ions [227,228]. It was also used for the speciation of zinc(II) [229,230], cadmium(II) and lead(II) ions in various matrices [231-235]. 

In the present work we conducted spectroscopic studies of anodic dissolution of metallic niobium, dissolution of niobium pentachloride and chlorination of various niobium oxides (NbO, Nb02, Nb205) by HCl in LiCl-KCl and NaCl-CsCl eutectics and NaCl-KCl equimolar melts at 450-750 °C. In a separate series of experiments the speciation of niobium was studied using spectroelectrochemistry and exchange reactions between niobium metal and bismuth, silver or nickel ions in NaCl-KCl-based melts. Oxidimetric titration [9] was employed to determine an average oxidation state of niobium in melt samples rapidly quenched under inert conditions. 

In a separate series of experiments the speciation of niobium was studied using exchange reactions of metallic niobium with bismuth, silver or nickel ions in NaCl-KCl melts. The starting NaCl-KCl-BiC melt was prepared by chlorinating bismuth metal (>98%, Reahim) by chlorine gas in the molten salt mixture. Nickel and silver chloride-containing melts were prepared by dissolving anhydrous nickel chloride (98%, Aldrich) and silver chloride (99%, Aldrich), respectively, in NaCl-KCl with HCl gas bubbled through the electrolyte for 2 h to eliminate traces of absorbed moisture. 

Feldmann, J., Koch, I., and Cullen, W. R. (1998) Complementary use of capillary gas chromatography-mass spectrometry (ion trap) and gas chromatography-inductively coupled plasma mass spectrometry for the speciation of volatile antimony, tin and bismuth compounds in landfill and fermentation gases. Analyst, 123, 815-20. 

The stability and solubility constants derived at 25 C for zero ionic strength have been used to create a predominance speciation diagram for bismuth(III). The diagram is illustrated in Figure 15.8. It shows that there is a predominance region for each of the monomeric species as well as for the hexameric species Bi5(OH)i2 -The solid phase considered was bismite, Bi203(s), and the minimum solubility calculated for bismuth(III) is just greater than 10 mol kg . ... 

Figure 15.8 Predominance diagram for the speciation of the bismuth(lll) ion at 25 °C. The behaviour in the region of 2 > -log [H+] >12 should be treated with caution due to changes in activity coefficients.

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