Speciation of Lead

The common compounds of lead derive from the +2 oxidation state. As a number of the periodic group IV-A, lead also forms tetravalent compounds, which are covalent. The most important are the tetraalkylleads, which are used as gasoline additives. The Pb - C bond is very non-polar, and the organolead species tend to be kinetically inert, like organomercurials. 

The speciation of lead(II) in aqueous solution involves several polymeric hydroxo-complexes. Below pH 5.5, Pb +(aq) predominates. However, with increasing pH, Pb4(OH)g, and Pb3(OH)4 form consequently with following deposition of Pb(OH)2(s). 

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Baena et al. [949] studied the speciation of lead in environmental waters. 

Prause et al. 1985). At pH 6.5 and water alkalinity of 25 mg CaC03/L, elemental Pb+2 is soluble to 330 pg/L however, Pb+2 under the same conditions is soluble to 1000 pg/L (Demayo et al. 1982). In acidic waters, the common forms of dissolved lead are salts of PbS04 and PbCl4, ionic lead, cationic forms of lead hydroxide, and (to a lesser extent) the ordinary hydroxide Pb(OH)2. In alkaline waters, common species include the anionic forms of lead carbonate and hydroxide, and the hydroxide species present in acidic waters (NRCC 1973). Unfortunately, the little direct information available about the speciation of lead in natural aqueous solutions has seriously limited our understanding of lead transport and removal mechanisms (Nriagu 1978a). 

Benes, P., M. Cejchanova, and B. Havlik. 1985. Migration and speciation of lead in a river system heavily polluted from a smelter. Water Res. 19 1-6. 

Uncorrected and corrected results for the trace metal speciation of lead are presented in Table V. It can be seen that the competition between true complexes and coulombic ion-pairs modifies considerably the speciation of lead. The fractions do not add up to 100% because species such as PbCl2° Pbc ", etc., were not entered into the table. 

The fate of lead during energetics hydrolysis in the presence of picrate is not understood. Until more information becomes available on the speciation of lead and the solubility of lead picrate under the conditions of hydrolysis, the possibility of solid lead picrate formation cannot be dismissed. As a precautionary measure, lead-based propellants should be processed separately from tetryl and tetrytol, eliminating the possibility of lead picrate formation. 

OSTERGREN, J. D., BROWN, G. E. JR., PaRKS, G. A. Tingle, T. N. 1999. Quantitative speciation of lead in selected mine tailings from Leadville, CO. Environmental Science Technology, 33, 1627-1636. 

Harrison, R.M. and Laxen, D.P.H., 1980. Physicochemical speciation of lead in drinking water. Nature, 286 791-793. 

Whitfield, M. and Turner, D.R., 1980. The theorerical studies of the chemical speciation of lead in seawater. In M. Branica and Z. Konrad (eds), Lead in the Marine Environment. Pergamon, Oxford, pp. 109-148. 

Tills and Alloway [113] investigated the speciation of lead in soil solution using a fractionation scheme, ion exchange chromatography and graphite furnace atomic absorption spectrophotometry. Soils from four sites were selected (Snertingdal in Norway, Pen Craig-ddu in Dyfed, Wales, Velvet Bottom... 

Erten-Unal, M., Wixson, B.G., Gale, N. and Pitt, J.L. (1998) Evaluation of toxicity, bioavailability and speciation of lead, zinc and cadmium in mine/mill wastewaters, Chemical Speciation and... 

Figure 4.2 Resolution of Me2Bu2Pb and Et3BuPb peaks for rain water taken from Sensitive speciation of lead in environmental waters by capillary gas-chromatography microwave induced plasma atomic emission spectrometry (Lobinski and Adams, 1992).

Biggins, P.D.E. and Harrison, R.M. (1980) Chemical speciation of lead compounds in street dusts. Environ. Sci. TechnoL, 14, 336-339. 

Baxter, D.C. and Freeh, W. (1995) Speciation of lead in environmental and biological samples. PureAppl. Chem., 67, 615-648. 

Lam, M.T., Chakrabarti, C.L., Cheng, J. and Pavski, V. (1997) Rotating disk electrode voltammetry/anodic stripping voltammetry for chemical speciation of lead and cadmium in freshwaters containing dissolved organic matter. Electroanalysis, 9, 1018-1029. 

Cordos, E.A., Frentiu, T., Rusu, A.-M. and Vatca, G. (1995) Elemental speciation of lead, zinc and copper in sedimented dust and soil using a capacitively coupled plasma atomic emission spectrometer as detector. Analyst, 120, 725-731. 

Sauve, S., McBride, W.B. and Henderskol, W.H. (1997) Speciation of lead in contaminated soils. Environ. Poll., 98,149-155. 

Spear, T.M., Svee, W., Vincent, J.H. and Stanisich, N. (1998) Chemical speciation of lead dust associated with primary lead smelting. Environ. Health Perspectives, 106, 565-571. 

Figure 5.15 Direct potentiometic speciation of lead ion in Zurich tapwater as a function of pH. Dotted lines expected from the known anions in the water sample and their complex equilibria with lead ion for two different carbonate concentrations. (Reproduced with permission from Ref. 42.)...

Kozelka, P.B., Sanudo-Wilhelmy, S., Flegal, A.R., and Bruland, K.W. (1997) Physicochemical speciation of lead in south San Francisco Bay. Estuar. Coastal Shelf Sci. 44, 649-658. 

Speciation of lead in air and atmospheric particulates is still a topic of great environmental relevance. Sodium tetrahydroborate may be used to hydrogenate inorganic lead ions and alkyl-lead species.60 As in the study by Balls outlined above, cryogenic trapping may again be used to trap temporarily the plumbane and alkyl- and tetraalkyl-lead compounds, which are then released sequentially by heating for detection by flame AAS. 

S. Rapsomanikis, O. X. F. Donard, J. H. Weber, Speciation of lead and methyllead ions in water by chromatography/atomic absorption spectrometry after ethylation with sodium tetraethyl borate, Anal. Chem., 58 (1986), 35-37. 

Speciation of lead compounds may be performed using gas chromatography with microwave-induced plasma and atomic-emission detection (GC-MIP-AED Pereiro and Diaz 2002). 

Speciation of lead in mining wastes and contaminated soils and sediments. Lead is the most common heavy metal pollutant at the earth s surface and is associated with a... 

Figure 26. Speciation of lead in a soil affected by alkyllead compounds used as antiknock additives in gasoline. The soil EXAFS spectrum (solid) is compared to model spectra from a library of lead compounds. This comparison identifies salicylate and catechol functional groups as the predominant complexing chelates for divalent Pb. Adapted from Manceau et al. (1996). Figure continued on facing page.)...

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