The industrial sectors involved with the extraction from the earth of mineral resources include:
• the extraction, including mining and quarrying, of fuel materials, and their subsequent processing to usable fuels;
• the mining and quarrying of non-energy resources, both metal ores and non-metallic minerals, and their conversion to metals and non-metallic products.
The two components of the extractive industries – energy and non-energy – differ also in the nature of the extraction process. The energy materials are produced from the ground in a reasonably concentrated state, and subsequent processing involves refining with relatively little waste (except perhaps for coal and oil shales – and, as reserves become exhausted, the processing will become more difficult). By contrast, many metallic ores occur naturally mixed with large quantities of unwanted material – gangue – from which they have to be separated: the mineral dressing process.
The proportion of waste tends to increase the more valuable the product metal is because high-value products (such as gold or platinum) can justify the cost of extracting and processing low-grade ores. In many cases, the nature of the materials in a natural deposit, metal ore on the one hand and gangue on the other, maybe so different – in density or surface properties – as to make their separation relatively easy.
At this stage of the production process, filtration is largely used in the form of dry screens, stationary or vibrated, supplemented by devices such as shaking tables, jigs (using fluidized beds), and spiral separators. Filtration has a much more significant part to play in the process operations for the treatment of metallic ores and non-metallic minerals, once they have been classified in the dressing stages, where much of the processing and recovery take place in suspension in water. The equipment used here, such as vacuum belt filters or band presses, can be very large.
In addition, dewatering filters help meet metal recovery targets in the Mining Practical filtration process.