Carbonatite ores

Carbonatite ores are mainly composed of calcite, dolomite and phosphates as the main gangue minerals. The beneficiation process for pegmatites containing pyrochlore mostly includes gravity preconcentration. Such deposits are common in Africa (Kongo, Madagascar). 

The major minerals contained in pyrochlore-containing ores are pyrochlore, columbite and sometimes ilmenorutile to a lesser extent. Table 22.1 shows pyrochlore minerals present in pegmatite and carbonatite ores. 

The gangue composition of the various carbonatite ores varies considerably. Calcite-dolomite content in some ores ranges from 30% (Niobec, Canada) up to 70% (Panda Hills, Africa). From a mineralogical point of view, pyrochlore usually occurs in crystallized form, as well as octahedron form. Pyrochlore occurs in considerable range of colours, varying from translucent white to opaque black appearance with glassy surfaces. The Nb205... 

Pyrochlore minerals contained in pegmatite and carbonatite ores... 

The treatment process and flotation properties of pyrochlore are very much dependent on the gangue composition of the ore. The selective flotation of pyrochlore from carbonatite ore is not possible since calcite and dolomite have similar flotation properties as pyrochlore. In addition, in the presence of carbonates, the stable pH required for flotation of pyrochlore (i.e. 5.0-5.5) cannot be maintained. 

In the case of carbonatite ores, a beneficiation process involves preflotation followed by reactivation and flotation of pyrochlore. In the case of pegmatitic ores that contain silicates, biotite, albite and limonite, as the gangue minerals, direct flotation of pyrochlore can be achieved with a variety of different collectors. 

The successful flotation of pyrochlore from carbonatite ores depends on a number of factors ... 

Figure 22.1 Effect of pH on calcite-dolomite recovery from carbonatite ores.

Extensive studies have been carried out using orthodihydroxybenzene, known as catechol (commercial name). This reagent has improved the rate of fine pyrochlore flotation and also has a beneficial effect on selectivity. Research work with this reagent was conducted on carbonatite ore from Canada. 

In the majority of cases, amines are used as pyrochlore collectors during treatment of carbonatite ores. Aliphatic mono amines, aliphatic diamines, condesates of capritic acid and partially neutralized diamines are the principal collectors for pyrochlore. Tallow diamine acetate (Duomac T, Akzo Nobel, USA and Canada) is also used as a pyrochlore collector. 

There are several operating plants treating pyrochlore-containing ores from carbonatite and pegmatite ores. Operating plants that treat carbonatite ores described in this chapter include St. Honore Niobec, Canada, and OKa, Quebec, Canada. The operating plant that treats pegmatite ore is Araxa (Brazil). 

Flotation properties of bastnaesite depend largely on the gangue composition of the ore and the impurities present in the mineral itself. Bastnaesite found in a carbonatite ore is recovered using fatty acid collector after heat pretreatment of the flotation feed. The effect of heat temperature on bastnaesite grade-recovery is illustrated in Figure 24.3. 

Floatability of bastnaesite found in barite-fluorite ores is extremely poor using either fatty acid flotation or sodium oleate. Research work conducted on an ore from Central Asia showed that the floatability of bastnaesite improved significantly after barite preflotation [5]. The flotation of bastnaesite from a carbonatite ore improved with the use of oleic acid modified with phosphate ester. The flotation of bastnaesite from deposits ofpegmatitic origin can be successfully accomplished with several types of collectors, including tall oil modified with secondary amine, and tall oil modified with petroleum sulphonate-encompassing group. 

L. V. Katashin, Flotation ofPyrochlorefrom Slimes Left After Gravitational Concentration of Rare Metal Carbonatite Ores, Nauch. Tr, Irktsk, Gos. Nauch Issled. Inst. Redk. Isvet. Metal, No. 19 (1968). 

Indirectly, the carbonates play a central role in the rare earth industry, as carbonatite ores are among the most important sources of rare earths. The immense bastnaesite deposit in Mountain Pass, California, for instance, has accounted for more than 80% of world rare earth production during recent years (Moore, 1980 Griffiths, 1984). 

The types of igneous deposits in which commercially important concentrations of apatite have been found are nepheline-seyenite and carbonatites. The world s largest apatite deposit, located in Russia s Kola Peninsula, is associated with nepheline-seyenite. Carbon-atite deposits that are mined for their phosphate content include Siilinjarvi in Finland, Araxa and Jacupiranga in Brazil, and Phalaborwa in South Africa. By-product recovery from carbonatite ores is common. At Siilinjarvi, by-product calcite is recovered for use as agricultural lime, whereas copper concentrate and baddeleyite (zirconium oxide) are byproducts at Phalaborwa. 

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