Geochemical partitioning fractional

Rule, J.H. and Alden, R.W. (1992) Partitioning of Cd in geochemical fractions of anaerobic estuarine sediments. Estuar. Coastal Shelf Sci., 34, 487. 

For geochemical purposes, the dependence of isotope fractionation factors on temperature is the most important property. In principle, fractionation factors for isotope exchange reactions are also slightly pressure-dependent, but experimental studies have shown the pressure dependence to be of no importance within the outer earth environments (Hoefs 2004). Occasionally, the fractionation factors can be calculated by means of partition functions derivable from statistical mechanics. However, the interpretation of observed variations of the isotope distribution in nature is largely empirical and relies on observations in natural environments or experimental results obtained in laboratory studies. A brief summary of the theory of isotope exchange reactions is given by Hoefs (2004). 

Sequential chemical extraction involves treatment of a sample of soil or sediment with a series of reagents in order to partition the trace element content. The principal advantage claimed for sequential extraction over the use of single extractants is that the phase specificity is improved. This technique has been used to determine the chemical forms of trace elements in soils, sediments, and suspended solids in natural waters, and is based theoretically and experimentally on more than 100 years of research (Jackson, 1985). A basic requirement of any extraction procedure should be the ability of the extractant to dissolve a specific component of a soil or sediment (Chao, 1984). Many different methods have been employed to fractionate trace elements, and these have proved useful for metal speciafion (Jones and Hao, 1993). Reviews of the fractionation methods used to determine the chemical forms of trace elements in soils and sediments (e.g. Pickering, 1981, 1986 Ross, 1994 Sheppard and Stevenson, 1997), in geochemical exploration (Chao, 1984), and in natural waters (Florence and Batley, 1977) are available. A few commonly used fractionation schemes for delineating different forms of trace elements are given in Table 6. 

Kawabe, L, Ohta, A., Ishii, S., Tokumura, M., and Miyauchi, K. (1999) REE partitioning between Fe-Mn oxyhydroxide precipitates and weakly acid NaCl solutions convex tetrad effect and fractionation of Y and Sc from heavy lanthanides. Geochem. /, 33, 167-179. 

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