Cassiterite flotation

The chemistry of cassiterite flotation has been a subject of considerable research for many years. The findings that sulphosuccinamates, phosphonic acid and arsonic acid were selective collectors for cassiterite flotation lead to the introduction of flotation as a complementary recovery process to gravity concentration at most primary tin mill concentrators in the early 1970s. In spite of continued research, subsequent progress in development has been rather limited. Cassiterite flotation still remains a secondary tin recovery process in most plants, for beneficiation of cassiterite below 40 pm size. 

The lack of progress in cassiterite flotation can be attributed to a number of factors, some... 

This collector has the formula shown in Figure 21.3. The identification of /7-tolyl arsonic acid as a selective collector for cassiterite flotation led to the introduction of this collector into many industrial plants. The first recorded industrial use of /7-tolyl arsonic acid was at the Alterberg mine in Germany. By the early 1970s, this collector was introduced into a number of operations, including Rooiberg and Union Tin (South Africa), the Renison and Cleveland tin mines (Australia). 

Most recently, interest has been renewed in the use of methyl benzyl and a mixture of p-and o-tolyl arsonic acid as a cassiterite collector [6,7]. The reagent under the trade name MTAA, which consists of approximately 50 50 of p- and o-tolyl arsonic acid, is now exclusively used in cassiterite flotation in the Peoples Republic of China. 

From the point of view of cassiterite flotation, the adsorption of phosphonic acid on cassiterite increases with decreasing pH and reaches a maximum at pH 2.0 and sharply decreases at a pH below 2.0. 

Using phosphonic acid as a collector if cations are present in the flotation pulps affects the cassiterite flotation negatively. High iron levels in particular have a strong depressing effect on flotation using phosphonic acid. 

A phenomenon observed in both laboratory and pilot plant testing of ores with phosphonic acid collectors is complete cassiterite flotation at a pH below 4.0. In fundamental practice, it indicates that a pH region below 4 is the region of maximum flotation. However, in plant practice, at a low pH (below 4), loss of flotation occurred. The loss of flotation at a low pH has not been established. It is, however, postulated that loss of flotation is believed to be associated with complex solution chemical interaction between phosphonic acid collectors and cationic species, in particular, those of iron, which is always present in industrial flotation pulp. 

The depressant of choice for cassiterite flotation depends very much on the type of gangue minerals present in the ore. Extensive research work has been carried out in which a number of depressants have been examined on tin ores containing different gangue minerals [12-14], A number of these depressants have been introduced into various operating plants around the world. 

Figure 21.7 General formula of alkane carboxylic acid used for cassiterite flotation studies.

The quality of the water in which the cassiterite flotation takes place is also highly important. Both ions found in process water supply and those generated by the minerals present in the pulp may affect the performance of the collectors as well as the surfaces of either cassiterite or gangue minerals by either depressing or activating them. 

Because there are no similarities in the ore or cassiterite flotation pulp in the world, it is the requirement that the flowsheet and reagent scheme usually be custom-made for each particular case. Great care should be exercised in order that laboratory testing duplicate the commercial plant conditions, which is quite a difficult task. 

Development work and operation of cassiterite flotation plants... 

Kirchherg, H., and Wottgen, L., The Effect of Phosphorus and Antimony Surfactants on Cassiterite Flotation, Chemistry, Physics and Application of Surface Active Substances, London, pp. 693-704, 1976. 

Baldauf, H., Scoen.Herr, J., and Schubert, H., Alkane Dicarboxilic Acids and Amino Naphthol-Sulphonic Acids - a New Reagent Regime for Cassiterite Flotation, International Journal of Mineral Processing, Vol. 15, pp. 117-133, 1985. 

Daomin, S., Cassiterite flotation vs. the electtical nature of its surface. Fizykochemiczne problemy mineralurgii, 20, 157, 1988. 

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 mineral is cassiterite (Sn02). Theoretically, the tin content of cassiterite is 78%. However, in the majority of cases, cassiterite contains impurities and the tin content may vary from 65% to 78%. The major impurities of cassiterite include tantalum, niobium, titanium and other elements, usually in the form of solid solutions. The impurities in the cassiterite often have a pronounced effect on flotation properties of cassiterite. 

The type of gangue minerals present, i.e. the selective flotation of cassiterite depends on the proper selection of depressant for certain gangue minerals. 

An unusual feature of arsonic acid flotation of cassiterite is the immobility to recover cassiterite coarser than 40 pm in size. The results obtained at the Renison Mine (Australia) indicated that cassiterite recovery in fractions above 20 pm drops sharply (Table 21.2). 

The phosphonic acid flotation of cassiterite is similar in many ways to that of arsonic acid. Optimum plant flotation for both collectors is generally considered to be in the pH region 4.5-5.5. The phosphonic acid, like arsonic acid, also has the inability to effectively recover cassiterite coarser than 20 pm. The reason for this is not known, because no research data is available on the flotation properties of plus 20 micron cassiterite particles. 

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. 

Zhu, J., and Zhu, Y., The Effect of Ions in Water on the Benzyl Arsonic Acid Flotation of Cassiterite Slimes, Journal of Central-South Institute of Mining and Metallurgy, Vol. 1, No. 1, pp. 29-37, 1985. 

Arbiter, N., Beneficiation of Cassiterite Ore by Froth Flotation, British Patent 1,110,643, 1968. 

Strebzyn, V.G., Selective Flotation of Cassiterite in the Presence of Iron-Bearing Minerals, Obogasthenie Rud, No. 13, pp. 3-6, 1968. 

Topfer, G., Gruner, U., and Menzer, D., The behaviour of gangue minerals in the flotation of cassiterite, Symposium for Tin Beneficiation, Pudi, Praha, pp. 277-280, 1971. 

Andrews, P.R.A., Flotation Characteristics of Cassiterite, Tourmaline and Topaz, MSC Thesis, University of Melbourne, Australia, 1971. 

Tin(IV) oxide is mined from naturally-occurring cassiterite. Various techniques are employed in mining (See Tin). The ore is crushed, ground, and separated hy gravity concentration and froth flotation. Sulfide impurities are removed hy roasting the ore concentrates at high temperatures. 

Chelating agents that can form insoluble, hydrophobic chelates on the surface of minerals are potential collectors for the selective flotation of minerals.3 4 As early as 1927, Vivian5 reported the use of cupferron, a well-known analytical reagent, as a collector for the flotation of cassiterite (Sn02). Since then, there have been a number of reports on the use of chelating agents in flotation. 

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