Stannites

A sodium stannite solution was prepared by addition of aqueous sodium hydroxide (2.5 mol, lOOg) to aqueous stannous chloride (0.25 mol, 56g). The initially formed precipitate redissolved to form a clear solution. This solution was gradually added to a solution of 16.3g (0.1 mol) phenyl-2-nitropropene in THF at room temperature. A slightly exothermic reaction ensued, and the reaction mixture was stirred for 30 min, a saturated sodium chloride solution was added, and the solution was extracted with ether and the pooled extracts were evaporated under vacuum to give essentially pure P2P oxime in 80% yield. 

Tin, having valence of +2 and +4, forms staimous (tin(II)) compounds and stannic (tin(IV)) compounds. Tin compounds include inorganic tin(II) and tin(IV) compounds complex stannites, MSnX., and staimates, M2SnX, and coordination complexes, organic tin salts where the tin is not bonded through carbon, and organotin compounds, which contain one-to-four carbon atoms bonded direcdy to tin. 

If tin and sulfur are heated, a vigorous reaction takes place with the formation of tin sulfides. At 100—400°C, hydrogen sulfide reacts with tin, forming stannous sulfide however, at ordinary temperatures no reaction occurs. Stannous sulfide also forms from the reaction of tin with an aqueous solution of sulfur dioxide. Molten tin reacts with phosphoms, forming a phosphide. Aqueous solutions of the hydroxides and carbonates of sodium and potassium, especially when warm, attack tin. Stannates are produced by the action of strong sodium hydroxide and potassium hydroxide solutions on tin. Oxidizing agents, eg, sodium or potassium nitrate or nitrite, are used to prevent the formation of stannites and to promote the reactions. 

Solutions of anhydrous stannous chloride are strongly reducing and thus are widely used as reducing agents. Dilute aqueous solutions tend to hydrolyze and oxidize in air, but addition of dilute hydrochloric acid prevents this hydrolysis concentrated solutions resist both hydrolysis and oxidation. Neutralization of tin(II) chloride solutions with caustic causes the precipitation of stannous oxide or its metastable hydrate. Excess addition of caustic causes the formation of stannites. Numerous complex salts of stannous chloride, known as chlorostannites, have been reported (3). They are generally prepared by the evaporation of a solution containing the complexing salts. 

Stannous Oxide Hydrate. Stannous oxide hydrate [12026-24-3] SnO H2O (sometimes erroneously called stannous hydroxide or stannous acid), mol wt 152.7, is obtained as a white amorphous crystalline product on treatment of stannous chloride solutions with alkaH. It dissolves in alkaH solutions, forming stannites. The stannite solutions, which decompose readily to alkaH-metal stannates and tin, have been used industrially for immersion tinning. 

Toluene from Toluidine.—It is often desirable to obtain tbe hydiocarbon from the base. The process of diazotisntion offers the only convenient method. The diazonium salt may be reduced by alcohol (Reaction 1, p. 162) or, as in the piesent instance, by sodium stannite. Less direct methods are the con-veision of the diazonium compound into (i) the hydrazine (see p. 174), (2) the acid and distillation with lime (p. 200), (3) the halogen derivative and reduction with sodium amalgam, 01, finally (4) the phenol and distillation with zinc dust. 

Zinnozydul, n. stannous oxide, tin(II) oxide, -chlorid, n. stannous chloride, tin(II) chloride. -hydrat, n. stannous hydroxide, tin(II) hydroxide, -natron, n. sodium stannite. -reserve, /. stannous oxide resist, -salz, n. stannous salt, tin(II) salt, -verbindimg, /. stannous compound, tin(II) compound. 

Tin when made anodic shows passive behaviour as surface films are built up but slow dissolution of tin may persist in some solutions and transpassive dissolution may occur in strongly alkaline solutions. Some details have been published for phosphoric acid with readily obtained passivity, and sulphuric acid " for which activity is more persistent, but most interest has been shown in the effects in alkaline solutions. For galvanostatic polarisation in sodium borate and in sodium carbonate solutions at 1 x 10" -50 X 10" A/cm, simultaneous dissolution of tin as stannite ions and formation of a layer of SnO occurs until a critical potential is reached, at which a different oxide or hydroxide (possibly SnOj) is formed and dissolution ceases. Finally oxygen is evolved from the passive metal. The nature of the surface films formed in KOH solutions up to 7 m and other alkaline solutions has also been examined. 

If the applied current density is reduced when a tin anode has been made passive in alkaline solution with the formation of a brown him and evolution of oxygen, the surface him changes to one of yellow colour and dissolution of tin as stannite ions proceeds freely . This effect is exploited in the electrodeposition of tin from sodium or potassium stannate solutions. 

Tin anodes dissolve by etching corrosion in acid baths based on stannous salts, but in the alkaline stannate bath they undergo transpassive dissolution via an oxide film. In the latter the OH" ion is responsible for both film dissolution and for complexing the tin. Anodes must not be left idle because the film dissolves and thereafter corrosion produces the detrimental divalent stannite oxyanion. Anodes are introduced live at the start of deposition, and transpassive corrosion is established by observing the colour of the film... 

Main opaque minerals are chalcopyrite, cassiterite, stannite, arsenopyrite, bismuth-inite, pyrrhotite and sphalerite. The FeS content of sphalerite is high (about 18 mol% FeS). 

Temperature and sulfur fugacity estimated from iron and zinc partitioning between coexisting stannite and sphalerite and coexisting stannoidite and sphalerite... 

Stannite is the most common tin sulfide mineral in the ore deposits associated with tin mineralization. This mineral sometimes contains appreciable amounts of zinc, together with iron. Several workers have suggested that the zinc and iron contents of stannite are related to temperature. With respect to the study of the phase relationships in the pseudobinary stannite-kesterite system. Springer (1972) proposed zincic stannite as a possible geothermometer mainly based on the chemical compositions of the two exsolved phases (stannite and kesterite). Nekrasov et al. (1979) and Nakamura and Shima (1982) experimentally determined the temperature dependency of iron and zinc partitioning between stannite and sphalerite. 

Because natural stannite contains a considerable amount of zinc, sphalerite contains a considerable amount of iron, and these contents can be easily analyzed using an electron microprobe, a stannite-sphalerite pair is expected to be a useful indicator of formation temperature and sulfur fugacity. 

Iron and zinc partitioning between stannite and sphalerite is represented by the exchange reaction. 

Figure 1.177. Comparison between the stannite-sphalerite geothermometer after Nekrasov et al. (1979) and one after Nakamura and Shima (1982). Crossbars indicate experimental uncertainties (Shimizu and Shikazono, 1985).

Figure 1.178 represents a comparison between the stannite-sphalerite temperatures and homogenization temperatures of fluid inclusions or sulfur isotope temperatures. It can be seen in Fig. 1.178 that Nakamura and Shima s geothermometer would be rather consistent with the temperature estimated based on the fluid inclusions or sulfur isotope studies. It is notable that almost all stannite-sphalerite temperatures are within 30°C of average homogenization temperatures and sulfur isotope temperatures. 

The relationship between the iron content of stannite in equilibrium with sphalerite and pyrite or with sphalerite and pyrrhotite was derived based on thermochemical data by Scott and Barnes (1971), Barton and Skinner (1979) and Nakamura and Shima (1982). These types of deposits are skam-type polymetallic (Sn, W, Cu, Zn, Pb, Au, Ag) vein-type and Sn-W vein-type deposits. As shown in Fig. 1.181, the /s -temperature range for each type of deposits is different at a given temperature, /sj increases from Sn-W vein-type through skam-type to polymetallic vein-type deposits. It is interesting to note... 

Figure 1.179. Iog(XFes/A znS)sphaleri.e - log(A cujFeSnSa/- Cu2Zt,SnS4 )s.annitc diagram showing that sphalerite and stannite are associated with pyrrhotite (Po) and/or pyrite (Py). Temperature lines are based on data by Nakamura and Shima (1982). Solid curves show log/s, based on data by Scott and Barnes (1971) in the pyrrhotite field. Abbreviations are the same as in Fig. 1.178 (Shimizu and Shikazono, 1985).

Shimizu and Shikazono (1987) studied the compositional relations of coexisting stannoidite, sphalerite and tennantite-tetrahedrite (Fig. 1.182). Based on these data they estimated the sulfur fugacity of stannoidite-bearing tin ore. Considering the complementary work on stannite-bearing tin ores from Japanese ore deposits (Shimizu and Shikazono, 1985), a comparison between environmental conditions of these two types of tin sulfides was made. Their study is described below. 

As mentioned already, Shimizu and Shikazono (1985) have estimated the /s2 temperature range for stannite-bearing assemblages from Japanese vein-type and skam-type tin deposits. This estimated /sj-temperature region is also shown in Fig. 1.183. The /s2-temperature range for the formation of these two types of tin sulfides is different. 

Microscopic observation suggests that stannite formed earlier than stannoidite on the scale of one polished section, although in general coexistence of stannoidite and stannite cannot be observed in the same polished section. If stannite formed at an earlier stage than stannoidite, it could be inferred that /sj increased or that temperature decreased (or both) with evolution of tin mineralization. 

Figure 1.183 shows /sj and temperature region for stannoidite-bearing tin deposits is different from that for stannite-bearing tin deposits. 

Lee, M.S., Takenouchi, S. and Imai, H. (1974) Occurrence and paragenesis of the Cu-Fe-Sn-S minerals, with reference to stannite, stannoidite and mawsonite. J. Mineral. Soc. Japan, 11, Spec. Issue 2, 155-164 (in Japanese). 

Nakamura, Y. and Shima, H. (1982) Fe and Zn partitioning between sphalerite and stannite (abst.). Joint Meeting of Soc. Mining Geol. Japan. Assoc. Miner. Petr. Econ Geol., Mineral. Soc. Japan, A-8 (in Japanese). 

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