The wolframite structure

The wolframite structure is another which can be described as having a fluorite-related cation sub-lattice about which the anions adopt some convenient arrangement. The unit cell is monoclinic, space group Pile, and has a = 4.68 A,... 

Fig. 28.68(a) and 28.68(b). Two projections of the wolframite structure showing the corner sharing of planes of edge-shared octahedra. The relationship to fluorite is evident in (a) where cation heights in units of y/100 are shown. (Figure 28.68(b) after Keeling, 1957). 

Fven though the literature on this topic has been mainly focussed on the structural and chemical-physical properties of Bi molybdates, and on the reachvity of its various polymorphs (the a, P and y structures), the industrial catalyst consists of several divalent and trivalent metal molybdates. Indeed, Bi is present in minor amounts in catalyst formulahons. The two classes of molybdate contribute differently to catalyhc performance (1) trivalent Bi/Fe/Cr molybdates, having the Schee-lite-type shucture, contain the catalytically active elements while (2) divalent Ni/Go/Fe/Mg molybdates, having the Wolframite-type structure, mainly enhance the catalyst re-oxidahon rate. 

Li4Np(W04)4 and pointed out their similarity to the wolframite (FeW04) structure type which in turn can be considered as a distorted scheelite structure. 

Kihlborg and Gebert 1970). As with wolframite, the sanmartinite structure belongs to space group P2/c, but that for cuproscheelite is 1. Nevertheless, these minerals exhibit complete solid solution across the binary join (Schofield and Redfem 1992). Explorations of the transition behavior in this system are motivated by their technological potential. Cuproscheelite is an -type semiconductor with possible uses as a photoanode, and sanmartinite may serve as a high Z-number scintillator (Doumerc et al. 

Metals at the border line may show polymorphism or other structural complexity (for example, under high pressure, CaW04 exhibits wolframite structure). 

The molecular structures of several new collectors have been designed as shown in Table 5.37 [21]. The carbon numbers of non-polar group required for given collector-mineral systems are also calculated and given in Table 5.37. The results in Table 5.38 show that the collector synthesized according to the calculated carbon numbers of non-polar group is the best one for given collector-mineral systems. These new collectors can be used as selective collectors for flotation separation of chalcopyrite from sphalerite, cassiterite or wolframite from calcite, malachite from smithsonite and calcite. 

These tungstate.s show broad band emissions originating from the tungstate octahedron (in contradistinction with the scbeelite CaW04, they have the wolframite crystal structure). This type of luminescence was treated in Sect. 3.3.5. 

ATa04 In Crystallizes in the monoclinic wolframite-type structure, like the FeNb04 compound (see text). 464... 

Organic depressants for Fe " -activated wolframite and quartz Depression of wolframite-quartz flotation with various flotation agents is shown in Figs. 5.16a and 5.16b. Experimental results for the concentration of the reagents for good depression of the above two minerals are listed in Table 5.22. The structural characteristics of the depressant molecules can be summarized as follows ... 

Fig. 28.67. Projection of the structure of M -fergusonite along [010] showing its relationship to wolframite. Different cation types are indicated by filled and open circles and different heights of these by shading of the polyhedra. Two rows of MOe octahedra and one row of MO4 tetrahedra are shown.

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