Cassiterite structure

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

The naturally occurring form of Sn02 (cassiterite) has the rutile structure (see Chapter 7), and it is an amphoteric oxide as illustrated by the following equations ... 

The reason for such a behaviour of arsenic acid is that arsenic is a member of the group 5A elements in the periodic table. Phosphorus and antimony are also group 5 elements and are known to be chemically similar to arsenic. On this basis [8,9], the antimonic acids were found to be poor cassiterite collectors. The alkyl phosphonic acids were not selective collectors. The ethylphenylene phosphonic acid was found to produce similar or better results compared to /7-tolyl arsonic acid. The structural formula for phosphonic acid (Figure 21.5) is similar to that of /7-tolyl arsonic acid but arsenic was replaced with phosphoms. The styrene phosphonic acid radicals are C6H5-CH-CH and p-ethylphenylene CH3-CH2-C6H4. 

In 1980, in search for new collectors for cassiterite, a new collector [11] was synthesized at Freiberg Mining Academy. The investigations were carried out with alkane carboxylic acids with the general structure as shown in Figure 21.7, which was altered by controlled substitution with -COOH and other groups. 

The X-ray diffraction pattern of the solid phase obtained by complete neutralization of an acidic solution of SnCl4-5H20 is presented in Fig. 13.18. Cassiterite Sn02 (rutile-type structure) was identified and Laue-Scherrer s law gives an average particle size of 2 0.2 nm in good agreement with transmission electron microscopy observations. 

Fig. 3. Mineralization linked to the ring structures I - Urkuveem (Mo with Ag and Bi, greisen type), II -Keyukveem (polymetallic), III - Kitivelgin (Au, arsenic-antimony association), IV - Belaya Sopka (Sn, cassiterite-sulfide association), V - Shestakovka (Sn with Ag and Bi, cassiterite-silicate association). Total productivities Pj, m %) for more promising catchment areas (outlined) and/or linear and ring structures are numbered.

High productivity of dispersion fiows P ) for the major associated elements (Sn, Pb, Zn, Cu) that are typical for cassiterite-sulfide mineralization have been established for the Belaya Sopka Volcano-Plutonic Structure that made the like-named mountain range a high, first-priority target (Ananchenko 1982). 

It crystallizes in the tetragonal rutile structure (see Fig. 5.27) with cell dimensions a = 474 pm and c = 319 pm in the single-crystal form it is known by its mineralogical name, cassiterite. It is a wide band gap semiconductor, with the full valence band derived from the 02p level and the empty conduction band from the Sn 5s level. The band gap at OK is approximately 3.7eY, and therefore pure stoichiometric Sn02 is a good insulator at room temperature when its resistivity is probably of the order of 106Qm. 

This tetragonal structure (Fig. 6.5(a)) is named after one of the polymorphs of Ti02 it is also referred to as the cassiterite (Sn02) structure. The coordinates of the atoms are ... 

Figure 6.19 Powder diffraction patterns of materials with the rutile structure (a) tin dioxide, cassiterite, Sn02l (b) lead dioxide, Pb02...

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. 

The rutile structure type is adopted by Sn02 (cassiterite, the most important tin-bearing mineral), P-Mn02 (pyrolu-site) and Pb02. 

Na, metal Cdl2, layered structure octahedral site, 6-coordinate Ga-doped Si, extrinsic semiconductor Na2S, antifluorite structure perovskite, double oxide CaF2, fluorite structure GaAs, intrinsic semiconductor wurtzite and zinc blende, polymorphs Sn02, cassiterite. 

Structurally, both Fe-Sb-0 and Sn-Sb-0 catalysts contain the rutile crystalline phase as the majority solid-state component. For the former, the majority phase is FeSb04 (44), whereas in the case of the latter, the dominate phase is cassiterite Sn02 containing Sb +, and possibly Sb + cations in solid solution with the rutile tin oxide phase (33,34). 

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