Module D for ‘clean sand’ production
Module D from the PST line has processed its first material. Module D is designed to ensure that the mineral fraction genuinely consists as much as possible of sand (mineral material). Carbon provides an indication of the non-mineral content of the material. This quantity must be less than eight per cent in the end product of the module (and hence of the factory). The clean end product is suitable for several specific applications, such as backfilling in worked out mines.. In this way, part of the car material is re-used.
Only part of the material that is fed into module D consists of sand. The other part consists of e.g. synthetics and fibres which escaped separation in module A. These can now be separated in module D thanks to the specific materials flow in that module. The mineral fraction is also stripped of magnetic materials in this module. This is necessary because the extremely high iron-oxide content of this flow is detrimental to the quality of the mineral fraction.
Materials can best be separated from each other if the particles in the flow being separated do not differ too much in size. The separation efficiency rule is: the smaller the physical differences between the materials, the more effective the separation processes are. For this reason, the incoming mineral material is first separated into three different sizes. The ingoing flow, 0 to 8 mm large, is separated in a sifter with two sieves (sifter decks) placed one above the other. The upper deck sifts down to 4 mm, the lower deck down to 1 mm. The result is three material fractions: 0 to 1 mm, 1 to 4 mm and 4 to 8 mm.
Because fine-particle material has a large surface area, the material in module D contains the largest proportion of the fluid of all the initial material. If this fluid content becomes too high, the effectiveness of the separation process can be impaired. To permit efficient processing, the mineral fraction is therefore classified using a double-deck flip-flop sifter instead of a sifter with a fixed sifter deck. A flip-flop sifter ‘shakes’ the material loose and can cope better with sticky material than a sifter with a fixed deck.
The 4 to 8 mm and 1 to 4 mm fractions
These fractions go through the same processes in a series of parallel machines. First, the material is led over a magnetic belt. Next, it goes through a zigzag windshifter; the light components, i.e. fibres, are extracted and transported to module C. The heavy components (sand, glass, copper and synthetics) drop down to a separation table, where small stones, glass and copper are separated and caught in a container. Depending on its copper content, this flow goes to customers for further metal separation or for use as a construction material. The synthetics go to module B.
The 0 to 1 mm fraction
This is basically the sand fraction. The material is led over a magnetic belt which separates the magnetic material. This consists of sand particles which have become magnetic because they contain steel dust, but also iron-oxide. Next, the material is led through a zigzag windshifter performing a final, extremely fine separation process. Dust is blown out of the materials flow, thus reducing the organic content of the sand and making it more suitable as a construction material.
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