Adsorption geochemistry

G. A. Parks, Surface energy and adsorption at mineral/water interfaces an introduction, in M. F. Hochella and A. F. White, eds., Mineral-Water Interface Geochemistry, The Mineralogical Society of America, Washington, D. C (1990). 

Figure 4. Modeled U-series date profiles across a 10 ky bone according to the D-A model under constant conditions. The dates are calculated using the closed system assumption. The parameter D/R is the diffusion-adsorption parameter and is related to the water content of the soil, the state of preservation of the bone and aspects of the geochemistry of the burial environment. After Pike et al. (2002). [Used by permission of Elsevier Science, from Pike et al. (2002), Geochim Cosmochim Acta, Vol. 66, Fig. 2, p. 4275.]...

Leaching and desorption of As from its associated mineral surfaces such as iron, aluminum and manganese oxides under the influence of the aquifer complex geochemistry, largely take part in its transport from sediment to aquifer pore-water. Adsorption has widely been considered as the retardation of As transport (Smedley 2003). 

The fast reactions of ions between aqueous and mineral phases have been studied extensively in a variety of fields including colloidal chemistry, geochemistry, environmental engineering, soil science, and catalysis (1-6). Various experimental approaches and techniques have been utilized to address the questions of interest in any given field as this volume exemplifies. Recently, chemical relaxation techniques have been applied to study the kinetics of interaction of ions with minerals in aqueous suspension (2). These methods allow mechanistic information to be obtained for elementary processes which occur rapidly, e.g., for processes which occur within seconds to as fast as nanoseconds (j0. Many important phenomena can be studied including adsorption/desorption reactions of ions at electri fied interfaces and intercalation/deintercalation of ions with minerals having unique interlayer structure. 

G.L. Grandjean, E. (eds.) Mdssbauer spectroscopy applied to inorganic chemistry. Plenum Publ. Corp., 3 417-444 Webb, J. Macey, D.J. Mann, S. (1989) Biomineralization of iron in molluscan teeth. In Mann, S. Webb, J. Williams, R.J.P. (eds.) Biomineralization Chemical and biochemical perspectives. VCH Weinheim, 345-387 Webster, J.G. Swedlund, P.J. Webster, K.S. (1998) Trace metal adsorption onto an acid mine drainage iron(lll) oxy hydroxy sulfate. Environ. Sci.Techn. 32 1361-1368 Wedepohl, K.H. (1969) Composition and abundance of common igneous rocks. In Wedepohl, K.H. (ed.) Handbook of geochemistry. Springer, Berlin, 1 227-249 Wedepohl, K.H. (1969a) Composition and abundance of common sedimentary rocks. 

In Wedepohl, K.H. (ed.) Handbook of geochemistry. Springer, Berlin, 1 250-271 Weerasooriya, R. Tobschall, H.J. (2000) Mechanistic modelling of chromate adsorption onto goethite. Colloids Surfaces 162 167-175... 

Adsorption of anions at mineral surfaces is important in soils because of the limit this process imposes on the availability of plant nutrients such as P, S, and Mo which occur naturally as anions and are added in anionic form in fertilizers. Anion adsorption is also relevant in geochemistry, ore processing, and other fields where minerals with high surface areas are brought into contact with aqueous solutions of anions. Selenite and goethite were chosen for this study because in Western Australia a selenium deficiency in pastures has been shown to be related to the incidence of white muscle disease in sheep (3), and according to workers quoted by Rosenfeld and Beath (9) selenium in soils of higher... 

Simeoni, M.A., Batts, B.D. and McRae, C. (2003) Effect of groundwater fulvic acid on the adsorption of arsenate by ferrihydrite and gibbsite. Applied Geochemistry, 18(10), 1507-15. 

Goh, K.-H. and Lim, T.-T. (2004) Geochemistry of inorganic arsenic and selenium in a tropical soil effect of reaction time, pH, and competitive anions on arsenic and selenium adsorption. Chemosphere, 55(6), 849-59. 

The Henry constant J Cis a function of T but not P. (In some theoretical treatments, the Henry constant is the ratio of fugacity to quantity adsorbed, i.e., the inverse of the sense used here.) It is generally expected that adsorption will be governed by Henry s law at sufficiently low pressures. It is possible to construct theoretical models for adsorption in which an isotherm does not reduce to Henry s law, Equation (2.3), even in the limit P —> 0, but it is not clear that such situations obtain in practice and doubtful that they are important in noble gas geochemistry. 

The Langmuir model also provides a convenient basis for estimating when Henry s law or saturation effects can be expected. If an individual attachment site has an area a 2 x 10 15 cm2, the order of atomic cross-sectional area (cf. Table 2.1), then Ns 5 x 1014 atoms/cm2 = 2 x 10 5cm3STP/cm2. Surface concentrations approaching this order of magnitude can be expected to exhibit saturation behavior. Conversely, much lower concentrations indicate 9 1 and lead to the expectation of Henry s law behavior. Possible adsorption effects important in noble gas geochemistry always involve much lower concentration than this illustrative value, which is one reason why Henry s law violation is not expected. 

Adsorption is sometimes invoked not only as a factor in geochemistry but also as a laboratory nuisance. Analyzed samples are often found to have a superficial or loosely bound component ascribed to air contamination, which is frequently described as adsorbed on the sample. Without further qualification, this makes little sense. An air contamination effect certainly exists, as can be inferred clearly when an intrinsic sample gas is isotopically distinct (cf. Section 2.4), but whether adsorption is responsible or even involved is questionable. In all such noble gas analyses, a necessary step is storage in laboratory vacuum before gas extraction. By definition, adsorbed gas is desorbed under vacuum. The relevant factor is the timescale required... 

Davis J. A., Payne T. E., and Waite T. D. (2002) Simulation of the pH and pC02 dependence of Uranium(VI) adsorption by a weathered schist with surface complexation models. In Geochemistry of Soil Radionuclides (eds. P. Zhang and P. Brady). Soil Science Society of America, pp. 61-86. 

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