Metalliferous Ores

The overall extraction process is sometimes subdivided into two general categories according to the main mechanisms responsible for the dissolution stage (/) those operations that occur because of the solubiHty of the solute in or its miscibility with the solvent, eg, oilseed extraction, and (2) extractions where the solvent must react with a constituent of the soHd material in order to produce a compound soluble in the solvent, eg, the extraction of metals from metalliferous ores. In the former case the rate of extraction is most likely to be controUed by diffusion phenomena, but in the latter the kinetics of the reaction producing the solute may play a dominant role. 

Sudo, T. (1954) Types of clay minerals closely a.s.sociated with metalliferous ores of the epithermal type. Sci. Repts. Tokyo Kyoiku Daigaku, Sen C, 3, 173-197. 

FIGURE 33 Smelting flowchart. The chart shows, in diagrammatic form, the sequence of metallurgical processes required for extracting metals from their ores from the initial mining of metalliferous ores to the final refining of the smelt metals. 

The first alloys made by humans were probably those of copper, namely, bronze and brass, which were already being made during the Chalcolithic period (see Table 33). The most important, however, later became the alloys of iron, known as the ferrous alloys (from the Latin word ferrum, for iron). Since iron ores are one of the most abundant metalliferous ores on the crust of the earth, and its alloys are relatively easy to produce, ferrous alloys have been the most widely used alloys for the last three millennia (see Table 34). 

Corrosion is the process of gradual waste and degradation undergone by most metals and alloys exposed to weathering agents in the environment. The products of the process are chemical compounds in which the corroded metals are combined mainly with oxygen but also with other elements or ions, such as sulfur, carbonate, and sulfate. The composition of the corrosion products is often almost identical to that of the metalliferous ores from which the metals are extracted. 

Many metalliferous ore deposits and most coalfields are characterized by the presence of sulphide minerals, such as pyrite (FeS2), galena (PbS), or sphalerite (ZnS). When exposed to water and oxygen, these sulphides have a tendency to oxidize, releasing dissolved metals, sulphate and, in the case of pyrite, acid (equations I and 2). 

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