Partitioning of impurity element

At the third level, the most detailed partition of luminescence minerals is carried out on the basis of metals in the mineral formulae, hi rare cases we have minerals with host luminescence, such as uranyl minerals, Mn minerals, scheelite, powellite, cassiterite and chlorargyrite. Much more often luminescent elements are present as impurities substituting intrinsic cations if their radii and charges are close enough. Thus, for example, Mn + substitutes for Ca and Mg in many calcium and magnesium minerals, REE + and REE substitutes for Ca, Cr substitutes for AP+ in oxygen octahedra, Ee substitutes for Si in tetrahedra and so on. Luminescence centers presently known in solid-state spectroscopy are summarized in Table 4.2 and their potential substitutions in positions of intrinsic cations in minerals in Table 4.3. 

If we consider NaOH, KOH, and NaF, which act as mineralizers, to be the solvent components, and other minor amounts of elements such as Fe +and Al " to be impurity elements, then the partitioning of these impurity elements is controlled principally by kinetics. The impurity partitioning is related to color, or radiation-induced color, and crystal morphology. 

Contaminants of Concern - All phosphate ore contains traces of radioactive elements, and some contain a number of metals. These impurities are studied in relation to their impact on health and the environment. During the processing of the phosphate rock they are partitioned between ore beneficiation process waste, add process waste, and final product. 

Amongst the disadvantages of this purification technique is the occurrence of some secondary processes such as volatilization or oxidation of particular impurities, which may influence the course of the concentration process. Also, the fact that values of partition coefficient between the solid and liquid phases for various elements and compounds will differ, detracts from facility with which purification can be effected by zone refining. 

In ionic crystals, trace element partition coeflBcients are inversely proportional to the ionic radius of the impurity ion. Nagasawa (118) obtained good agreement between experimentally determined coeflBcients and values calculated from the energy required for introducing the impurity ion into the host lattice, if the substituting ion was larger than the host ion. No such calculations have been made for ice. 

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