Subject surface precipitation

The removal of Ra by adsorption has been attributed to ion exchange reactions, electrostatic interactions with potential-determining ions at mineral surfaces, and surface- precipitation with BaSO 4. The adsorptive behavior of Ra2+ is similar to that of other divalent cationic metals in that it decreases with an increase in pH and is subject to competitive interactions with other ions in solution for adsorption sites. In the latter case, Ra is more mobile in groundwater that has a high total dissolved solids (TDS) content. It also appears that the adsorption of Ra + by soils and rocks may not be a completely reversible reaction (Benes et al. 1984, 1985 Landa and Reid 1982). 

Internal oxidation is the process in which oxygen diffuses into an alloy and causes sub-surface precipitation of the oxides of one or more alloying elements. It has been the subject of reviews by Rapp, Swisher, Meijering, and Douglass. 

The first class, discussed in detail in Chapter 6, was reaction between a fluid and the minerals it contacts. The kinetics of the reactions by which minerals dissolve and precipitate was the subject of the preceding chapter (Chapter 16). The second class of reactions commonly observed to be in disequilibrium in natural waters, as discussed in Chapter 7, is redox reactions. The subject of this chapter is modeling the rates at which redox reactions proceed within the aqueous solution, or when catalyzed on a mineral surface or by the action of an enzyme. In the following chapter (Chapter 18), we consider the related question of how rapidly redox reactions proceed when catalyzed in the geosphere by the action of microbial life. 

Precipitation is generally much slower than adsorption. Table 3.14 compares rates of precipitation with rates of adsorption and other surface phenomena in soil systems. Rates vary greatly between precipitating compounds. They are also often subject to inhibition and catalysis by other solutes and solid phases present. 

In the previous sections of this book, we focused on the nature of contaminants and the geochemical reactions that can occur in the subsurface environment. Chemical compounds introduced into infiltrating water or in contact with soil or rock surfaces are subject to chemically and biologically induced transformations. Other compounds are retained by the soil constituents as sorbed or bound residues. Thus, in terms of geochemical interactions and reactions among dissolved chemical species, interphase transfer occurs in the form of dissolution, precipitation, volatilization, and various forms of physicochemical retention on the solid surfaces. 

A tremendous amount of research has been devoted to quantifying and modeling transport processes in the vadose zone, with readily available scientific literature (journals and textbooks) extending over the last half century. Modeling is used to quantify the dynamic redistribution of chemicals along the near surface and deeper subsurface profile, which often also is subject to reactive chemical processes including sorption, dissolution or precipitation, and volatilization. 

In order to investigate the active sites of these proteins, laccases I and III were subjected to ESR (electron spin resonance) spectroscopic analysis. The ESR spectra shown in Figure 5 indicate clear differences in peaks 2 and 6 which support the concept that the copper atoms in laccases I and III have different conformations in each molecule. Furthermore, immunological similarity between laccases I and III was also investigated. Antibody specific for laccase III was prepared from rabbit serum by conventional methods. When applied to Ouchterlony diffusion plates containing laccase I, no precipitation lines developed (Figure 6). This result showed that there were no conserved epitopes on the surfaces laccases I and III. 

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