Cassiterite deposits

Additional sources of the elements are tin slag and scrap. For instance, cassiterite deposits, in Australia, Brazil, Thailand and some other countries, contain a significant amount of tantalum. The bulk of this tantalum is collected in the slag and processed separately. Recycling of various tantalum-bearing scrap is also a veiy important source for tantalum production. These scrap materials include powder surplus from sintering operations, scrap from mill products, rejected and used capacitors, scrapped cutting tools and furnace hardware. 

Because cassiterite is a stable mineral and does not tend to decompose, it forms sand deposits by decomposition of pegmatitic and quartz-cassiterite deposits. Such deposits are common in Asia. 

The common ore of tin is tinstone or cassiterite. Sn02, found in Cornwall and in Germany and other countries. The price of tin has risen so sharply in recent years that previously disregarded deposits in Cornwall are now being re-examined. Tin is obtained from the tin dioxide, Sn02, by reducing it with coal in a reverbatory furnace ... 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

The most important tin deposits are hydrothermal deposits (hypothermal and mesothermal). The magmatic deposits do not often contain tin mineralization. Tin may also be present in pegmatitic ore bodies. However, tin found in pegmatitic deposits can be classified into two basic types (a) quartz-cassiterite lenses in granite, when cassiterite is associated with topaz, beryl and, to a lesser degree, sulphides (b) sulphide deposits, where tin is mainly cassiterite associated with arsenopyrite, pyrite, chalcopyrite and pyrrhotite. Such deposits are common in South America (Peru, Bolivia). 

Disseminated deposits. In these deposits, the cassiterite grains range from 0.2 to 0.001mm. Cassiterite is mostly dispersed in gangue matrix of alumosilicates, tourmaline and quartz. Recovery of cassiterite from these deposits is quite difficult. 

The cassiterite ore from underground, hard rock veins is finer grained than alluvial deposits. From this ore, good concentrate grade is produced but at relatively low tin recoveries. Fines from the gravity tailing assay between 0.4% and 0.8% Sn. 

Research work has shown that cassiterite from various deposits and often even from parts of the same deposit differ in chemical composition, colour, flotation properties, chemical activity and electrophysical characteristics. Therefore, the mineralogical composition of tin ores and the physiological properties of the minerals, in particular cassiterite, determine to a great extent the quantity of tin lost during gravity processing and especially during flotation. 

Moderately difficult floating ores - cassiterite sulphide deposits with small quantities of chloritic tourmaline and Fe-oxides are considered to be moderately difficult. 

Pneumatalitic-hydrothermal deposits contain Ta/Nb as isomorph impurities in cassiterite and wolframite. Ta/Nb from these ores is recovered in a tin and wolframite concentrate. 

Xenotime, like monazite, is a rare-earth phosphate. Up to 60% of its rare-earth content is yttria [1314-36-9], Y203. Xenotime has a higher proportion of heavy rare earths than does monazite. Xenotime occurs with monazite in beach sand deposits. A second source of xenotime is that of cassiterite (tin ore) deposits. 

Germanium, tin, and lead have relatively low abundances in the earth s crust (Table 19.4, page 823), but tin and lead are concentrated in workable deposits and are readily extracted from their ores. Tin is obtained from the mineral cassiterite (Sn02) by reducing the purified oxide with carbon ... 

Tin The principal ore of tin is cassiterite or tin stone Sn02 The miners speak of tinstone as tin or black tin to distinguish it from White tin, the name given to the metal. Minor deposits as sulphides are also known for tin. Chief suppliers of tin are Malaysia, Indonesia, Thailand (Siam), Bolivia (South America), Nigeria (Africa) and Burma. In India, small quantities of tinstone are available in Hazaribagh (Bihar) and Orissa. More than 80 per cent of the world s total requirement of tin is met by South Asia. 

Tin-mining methods depend on the character of the deposit. Primary deposits are embedded in undeiground granitic rock and recovery methods are complex. The more important secondary deposits are in the form of an alluvial mud in the stream beds and placers and the recovery is simpler than lode mining. Cassiterite is recovered from alluvial deposits by dredging, hydraulicking where a head of water permits it, jets and gravel pumps on level... 

Tin bronze is another matter because, apart from rare copper ore deposits also containing tin (e.g., some of those in Cornwall), tin from a quite different source than the copper has almost always been added to copper to produce bronze. The only tin mineral that is likely to contain lead is stannite, which is not common except as a mineralogical curiosity. Tin has always been obtained in very large quantities from cassiterite, which almost never contains even a trace of lead. The tin ingots found underwater off the coast of Israel contain no lead. Our work on Cypriot Late Bronze Age bronzes indicates no perturbation away from the characteristic Cypriot lead isotope composition, even for bronzes containing 18% tin. 

Table IV. Trace Element Concentrations in Cassiterite (Sn02) Smelts from Cornwall, England, Deposits and Mean Values Obtained in Residues from Tel Dan, Israel...

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