Mineral phases

Other Interaction Processes. The selectivity of flotation reagents in a pulp and their functions depend on their interactions with the mineral phases to be separated, but other physicochemical and hydrodynamic processes also play roles. AH adsorption—desorption phenomena occur at the sohd—hquid interfacial region. Surface processes that influence such adsorptions include activation and depression. Activators and depressants are auxiUary reagents. 

In addition, uranium and lead transport mechanisms ia radioactive minerals have been studied ia order to evaluate the suitabiUty of mineral phases as hosts for radioactive wastes. Zircon is one of the most commonly used geochronometers, as well as a proposed nuclear waste matrix material, and there are many mechanisms by which uranium and lead can migrate through its stmcture (19). 

The extent of substitution of magnesium and siUcon by other cations in the chrysotile stmcture is limited by the stmctural strain that would result from replacement with ions having inappropriate radii. In the octahedral layer (bmcite), magnesium can be substituted by several divalent ions, Fe ", Mn, or Ni ". In the tetrahedral layer, siUcon may be replaced by Fe " or Al ", leaving an anionic vacancy. Most of the other elements which are found in vein fiber samples, or in industrial asbestos fibers, are associated with interstitial mineral phases. Typical compositions of bulk chrysotile fibers from different locations are given in Table 3. 

The Ca(Il) coaceatratioa ia blood is closely coatroUed aormal values He betweea 2.1 and 2.6 mmol/L (8.5—10.4 mg/dL) of semm (21). The free calcium ion concentration is near 1.2 mmol/L the rest is chelated with blood proteias or, to a lesser extent, with citrate. It is the free Ca(Il) ia the semm that determines the calcium balance with the tissues. The mineral phase of bone is essentially ia chemical equiUbrium with calcium and phosphate ions present ia blood semm, and bone cells can easily promote either the deposition or dissolution of the mineral phase by localized changes ia pH or chelating... 

Spanos, N. and Koutsoukos, P.G., 1998. The transformation of vaterite to calcite effect of the conditions of the solutions in contact with the mineral phase. Journal of Crystal Growth, 191, 783-790. 

Most feldspars can be cla.ssified chemically as members of the ternary system NaAlSi30s-KAlSi30s-CaAl2Si20 . This is illustrated in Fig. 9.14, which also indicates the names of the mineral phases. Particularly notable... 

In the presence of mineral phases containing anions that would form sparingly soluble compounds (e.g. POt - and F for the lower oxidation states) an enhanced plutonium uptake due to chemisorption can be expected (57). For plutonium in the higher oxidation states the formation of anionic carbonate complexes would drastically reduce the sorption on e.g oxide and silicate surfaces. 

Phosphorus is the tenth most abundant element on Earth with an average crustal abundance of 0.1% and may be found in a wide variety of mineral phases. There are approximately 300 naturally occurring minerals in which PO4 is a required structural component. Phosphate may also be present as a trace component in many minerals either by the substitution of small quantities of POt into the crystal structure or by the adsorption of P04 onto the mineral surface (Nriagu and Moore, 1984 Slansky, 1986). 

Rey, C., Renugopalakrishnan, V., Shimizu, M., Collins, B. and Glimcher, M.J. 1991 A resolution-enhanced Fourier transform spectroscopic study of the environment of the COj ion in the mineral phase of enamel during its formation and maturation. Calcified Tissue International 49 259-268. 

Mossbauer Spectral Analysis and Analog Measurements. Mossbauer spectra were obtained in the temperature range between 200 and 270 K and in two different energy windows (14.4 and 6.4 keV), which provide depth selective information about a sample [346]. To compensate for low counting statistics due to limited integration time, all available spectra were summed for the integrations on the undisturbed and brushed surface, respectively. In addition to kamacite (a-(Fe,Ni)) ( 85%) and small amounts of ferric oxide (see Fig. 8.38), all spectra exhibit features indicative for an additional mineral phase. Based on analog measurements... 

Schaeffer et al. (1993) analyzed mineral phases extracted from the 1985 dacitic pumice erupted by Nevado del Ruiz (Colombia) pyroxene, plagioclase, magnetite, glass and whole rock define an U-Th isochron with a near-zero age (7 6 ka, 2g Fig. 10b). 

The Th within the mineral phases produces Ra that is ejected by... 

The study of separate mineral phases or of granulometric fractions is another approach which can be used to recover temporal information from radioactive disequilibria in weathering profiles. Such approaches rely on the assumption that the fractions only contain or concentrate minerals phases specific of a single or of few stages of formation and evolution of weathering profiles, and hence can help to characterise the time constants of the corresponding stages. 

Lovley D, Philhps EJP, Gorby YA, Landa ER (1991) Microbial reduction of itraniitm. Nature 350 413-416 Lowson RT, Short SA, Davey BG, Gray DJ (1986) " U/ U and °Th/ " U activity ratios in mineral phases of a lateritic weathered zone. Geochim Cosmochim Acta 50 1697-1702 Ludwig KR (2003) Mathematical-statistical treatment of data and errors for h/U geochronology. Rev Mineral Geochem 52 631-636... 

Vigier N, Bourdon B, Turner S, Allegre CJ (2001) Erosion timescales derived from U-decay series measurements in rivers. Earth Planet Sci Lett 193 549-563 von Gunten HR, Roessler E, Lowson RT, Reid PD, Short SA (1999) Distribution of uranium- and thorium series radionuclides in mineral phases of a weathered lateritic transect of a uranium ore body. Chem Geol 160 225-240... 

---