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During the period when zinc was mined, flourishing for the last time after 1870, the state management built a large enrichment plant at Maiern, at the head of the Ridnauntal, equipped with all the latest technological improvements. Initially, it was only used to enrich zinc ore.
Each building was constructed along a slope, so that ore could be carried inside the plant by exploiting the force of gravity or in trucks on rails.
Ths plant is described in detail in the ‘Österreichischen Zeitschrift für Berg- und Hüttenwesen’ of 1881. In 1893, the Imperial mining administrator and company manager at Maiern, Josef v. Billek, published a very detailed description of the plant and stressed the continual improvements to machinery and the progress made in facing the problem of dust and smoke.
In summer, unprocessed ore was taken to two large depots above the plant. The preparation of the coarse ore, that is, its crushing and the separation of ore-rich products, was carried out first in one crushing mill. Further reduction involved ‘roasting’ the ore and sending it through piston-operated crushers, soon replaced by cylindrical crushers. Vibrating sieves and screens further sorted the crushed product into pebbles up to 45 mm in diameter.
Grains more than 16 mm across finished on the sorting tables, where sorters carefully made a preselection and then a final selection. Medium-sized and fine ores were roasted, partly to remove some of the sulphur contained in the coarse ore and partly to make siderite, closely associated with blende, more friable and magnetic. Lastly, very careful sorting of all ferrous minerals (iron, magnetite, siderite) was made by means of electromagnetic drums.
The main separation phase was carried out in the lower washery through a large number of vibrating screens, sieves and sifters. The vibrating screens struck bumpers, whereas the sifters were subjected to alternating movement. The finely ground mineral, spread out in a thin layer on the sorting table, was washed with water. With the jolting and alternate movements of the screens and sifters, the larger and heavier grains slowly fell to the bottom, whereas the smaller, lighter ones accumulated at the top and were washed away.
Since they were magnetic, minerals of the same or similar size could not be separated in this enrichment plant. The same problem arose for the fine mixing of different minerals, since the machinery of the time could only reduce raw materials to a millimeter in diameter.
The amount of zinc in the final product was small, on average 42%, and high losses occurred during separation. About 50% of the blende was lost in the raw mineral.
All this only changed when the flotation process was introduced.
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history of mining on Schneeberg
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