engleski

Preliminary studies of vanadium and sulfide/polysulfide system

The facile formation of thiometalate ions [MOxS4-x n- ; x=0-4 ; M=Mo(VI), As(V), W(VI), Sb(V), Re(VII)] containing the metal in its highest oxidation state has been demonstrated repeatedly within aqueous solutions involving the corresponding oxyanion and hydrogen sulphide. Such transformations are well-known to affect the solubility and mobility of thiometalate-forming metals [e.g. 1-2]. The formation of MoOxS4-x 2- (x=0-4) seems to control Mo solubility in anoxic environments [3]. Increased As concentration in groundwater appears to result from formation of AsOxS4-x 3- (x=0-4) and/or AsOxS3-x 3- (x=0-3) [2]. Although V also has the potential to form of thiovanadate (VOxS4-x 3- ; x=0-4) and thiovanadite (VOxS3-x 3- ; x=0-3) soluble complexes, available literature on V oxoanions and their behaviour in aqueous hydrogen sulphide solutions is sporadic. An early spectrophotometric study of vanadate (VO4 3- ) and hydrogen sulphide solutions indicated the formation of VOxS4-x 3- only at pH ˃10 [4]. Wanty and Goldhaber (1992) offered evidence of vanadyl ion (VO2+) reduction at near neutral pH [5]. Here, novel chromatographic data is presented for neutral to mildly alkaline solutions initially containing VO4 3- and aqueous sulphide. Data indicate VO4 3-reduction with polysulfides as the main oxidized product in test solutions. Chromatograms suggest VOxS3-x 3- formation, while in accordance with previous studies, no evidence of VOxS4-x 3- formation is found. We also note the formation of unidentified colloidal solids in these same V + S solutions. Precipitates obtained from pH 6.5 solutions are brown ; those formed in pH 8.5 solutions are white. Preliminary XAFS data suggest mildly alkaline precipitates contain V(III).

vanadium ; sulfide ; polysulfide

nije evidentirano