Mobility, geochemical

The behavior of technetium in soils is important from an ecological viewpoint, but is quite complicated and depends on many factors. Stalmans et al. [27] stated that it is ruled by a combination of chemical, physicochemical and biological factors and understanding of it is needed on two main accounts bioavailability and geochemical mobility . They also noticed that organic matter in soils and sediments play a significant role as a geochemical sink for technetium. 

Helium, like Rn (see Chapter 11), should be an ideal pathfinder for U mineralisation. Both are daughter products of U and hence must be present and being gases, they have different geochemical mobilities to U. Calculations show that 1 g of U and its decay products in equilibrium produce 1.17 x 10 ml (STP) He. In a U deposit having a grade of 1%, a porosity of 20% and a bulk density of 2.2, the He concentration of the pore space... 

Explain the processes of geochemical mobility of boron. Compare the migration of this trace element in acid and alkaline soils. 

In this section mantle evolution curves are presented for neodymium (Nd), hafnium (Hf), lead (Pb) and osmium (Os) isotopes. A summary of these isotopic systems is given in Text Box 3.2. Earlier studies based upon the study of Sr isotopes in the mantle (e.g. Bell et al., 1982) are now known to be unreliable because of its high geochemical mobility (Goldstein, 1988). The significance of the mantle evolution curves described here is that they demonstrate that the mantle does not operate as an isolated system but that it has evolved in its composition over time, in response to core formation, crust extraction, and the recycling of crustal material. 

Estimation on the remobilization of metals under changing environmental conditions and on the potential uptake by biota are two major objectives of species differentiation on particle-bound trace metals. However, many authors have shown that with respect to bioavailability, as distinct from geochemical mobility, the present state of knowledge on solid matter speciation of metals is still somewhat unsatisfactory. The... 

The Cd content in the absence of obvious pollution and geochemical mobility in hydrosphere and geosphere is detailed in Table 6.2 (Baudo and Muntau 1990). 

Technetium, one of the key elements in the treatment of radioactive liquid waste, because of its long half-life and geochemical mobility, was separated from concentrated alkaline solutions by SLMs containing 2-nitrophenyloc-tyl ether (NPOE) [180]. The hollow-fiber SLM, containing bis(2-ethylhexyl)phosphonic acid, was tested for carrier-free separation of from °Sr [181]. 

It is only approximate since sediments are not just one solid phase. In reality molecules are bound in different solid phases in a sufficiently similar way that m/y approaches some sort of solubility, aptly referred to a defined class of solid. To avoid confusion the expression geochemical mobility has been used with reference to the distribution between solid or immobile and liquid or mobile phases. 

The ratio mM/y Ycan also be termed geochemical mobility . Inasmuch as M and Y are constant for all substances there is neither inconsistency nor ambiguity in the use of either definition. 

With -V, y in the range of a few ppm U and X and Y some 150kg/cm, m = 0.001 mg/kg, A/= 280kg/cm and, in terms of flow, fT=0.02kg/year cm with w = 0.0005 mg/kg. The geochemical mobility of uranium can be expressed by assuming that about one-thousandth of its total mass in sediments, or of its total removed mass from crystalline lithosphere, is dissolved in ocean water and, hence, is available for transport and precipitation anywhere on earth. 

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