Przeróbka odpadów mineralnych ma ogromne znaczenie w gospodarce narodowej przede wszystkim ze względu na duże ilości masowe tych odpadów, jak też ich różnorodność. Odpady mineralne występują w wielu gałęziach przemysłu w szczególności w górnictwie węgla i surowców skalnych oraz w energetyce. Wiele z tych odpadów ma zresztą dużą wartość a możliwości ich wykorzystania są bardzo szerokie. Stąd też często zamiast pojęcia "odpady" mówi się o surowcach towarzyszących wydobyciu głównego surowca kopalnego
Screening of grained waste is divided into several stages, the first one is separation of large grains, that is those that should be subjected to deep milling, in different grinding machines. The second stage of waste processing is a multiple (depending on needs) classification of waste on sieves, so screening in different screening machines. Basing on many years of experience, authors of the paper recognize that sifters with flat screens are the most appropriate machines for screening of waste. They are definitely more recommend than sieving drums. The use of flat screen sifters consists in selection of machine among manufactured sifters. It is best to use free-standing screen with all of its equipment The present study demonstrates the results of the research programme carried out at the Department of Process Equipment, Technical University of Lodz, and concerns double-frequency screens. On the basis of the research results the design assumptions of the industrial machine aimed at fine-grained screening have been elaborated. It is widely known that the shape of trajectory in the oscillating motion of the screen has a relevant meaning for obtaining the best processing properties of the machine. Therefore, the trajectories of oscillating motion, which will lead to the intensive segregation of the grain layer moving on the sieve, have been searched for a long time. Seemingly, it is possible to obtain a double-frequency screen. Two rotational vibrators of the same or different static moments are applied for the drive of such a screen. As the name indicates, it is a screen which is characterised by two different rotational speeds of those drive vibrators. The construction of the screen enables to regulate (for research objectives) all the basic operation parameters of the machine, such as:the inclination of the sieve against the level, setting of the engines against the middle part of the sieve, exciting forces generated by the engines, the engine rotational speeds. Basing on results of the research on a double-frequency screen in a laboratory scale, the concept of building an industrial screen (Fig. 13) was developed, which will be installed in one of the mining companies exploiting mineral aggregates. Supporting structure will be welded-bolt together structure made of typical steel rolled profiles. It must be composed of such elements, in order to it was possible to transport the entire screen (dismantled) by road transport. Supporting structure is a free-standing element, placed on a paved surface. It should contain catwalks for operation stuff and control box where all elements of machine drives control will be placed. Supporting structure should also allow to change screens angle = 0-20°, by tilting the entire sieve of screen.