Cassiterite with gravity concentration

In general, the run-of-mine ore is composed of quartz and silicates, 40-50%, and sulphides (pyrite, marcasite, pyrrhotite and arsenopyrite). The principal tin mineral is cassiterite, with minor amounts of stannite. Based on liberation studies, a large portion of the tin is liberated at 300-400 pm size. A portion of the tin is liberated at-12 pm size. The generalized gravity concentration flowsheet is shown in Figure 21.9. 

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 cassiterite ore is obtained by dredging, open-cast mining, or gravel-washing, in which the ore is washed out of the deposit with high-pressure jets of water. The cassiterite has a density 2.5 times that of sand, and the ore is concentrated by gravity. It is roasted to remove arsenic and sulfur, and to convert metal sulfides into oxides, then it is reduced by smelting with coal or fuel oil in a reverberatory, rotary, or electric furnace (Equation 1.1.1). 

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