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(1) Bauhaus-University Weimar, Faculty of Civil Engineering, Chair of Processing of Building Materials and Reuse, Germany Abstract ID Number: 247
Contact person for the paper: Prof. Dr.-Ing. habil. Anette Müller Presenter of the paper during the Conference: Dipl.-Ing. Lars Wienke Total number of pages of the paper (this one excluded): 8 MEASUREMENTS AND MODELS FOR THE GRAVITY CONCENTRATION OF C&D WASTE THROUGH JIGGINGProf. Dr.-Ing. habil. Anette Müller (1) and Dipl.-Ing. Lars Wienke (1)(1) Bauhaus-University Weimar, Faculty of Civil Engineering, Chair of Processing of Building Materials and Reuse, Germany AbstractThe process of gravity concentration through jigging is known since centuries and is used mainly in the mining and gravel industry. In the last few years a fresh impetus was given to this method by the (forced) recycling of building materials and other wastes. With these new fields of application of the jigging process open up. The insufficient state of knowledge about the wet gravity concentration and the application of the process for changed problems were the reason for this research work. The aim was to capture the current state of knowledge in the field of gravity concentration, to generate experimental data and to develop a mathematical model for the prediction of jigging results and for the design of jigs. During the current research work the jigging was realized in order to investigate the influence of the waveform of the pulsation on the stratification. The experiments were carried out on a test track especially made for this research work. Mainly symmetrical and asymmetrical vibrations with a fast acceleration phase and a slow phase of consolidation were used. The generated data form the basis of the model, which will be represented in the lecture. It can be shown how the stratification can be modelled and how therefore jigging processes can be predicted and optimized. Key words: Recycling, Jig, Modell 1. INTRODUCTIONThe process of gravity concentration by jigging is known at least since Agricola [1]. In jigs minerals are separated due to their differences in density, if the material consists of two components with different densities but nearly the same particle sizes. The main elements of a jig are the open tank filled with water, the horizontal jig screen and the device which generates the pulsation of the water. The input material forms a bed on the jig screen. The pulsating current of water flows upwards through the bed. During one period of oscillation the following processes take place in the material bed: On the pulsation stroke the bed is lifted and loosened. In this state the stratification occurs. The heavy particles move to the bottom of the bed, the light particles appear at the surface. On the suction stroke the consolidation of the layered material bed takes place. Originally jigs were used for the processing of coal, ore and gravel. Nowadays they become more and more important in the field of waste processing [2]. Because of these applications on other materials it is obviously that the existing methods in design and set-up are not applicable or not sufficient. Therefore different groups are developing Discreet Element Models about the basic operations of jigging [3];[4]. These models aim at the prediction of the movement and the stratification of the material in the jig. Although some promising approaches are described in the literature, there is no sufficient knowledge to design a jig for the new applications. The producers of jigs are confronted with the problem that they must guarantee certain parameters like the throughput and the partition ratio. They need tools which make the dimensioning of the machine and the prediction of these parameters for every specific problem possible. Experience and reports on findings about the influences of the particle size, the particle shape, the density etc. on the obtained separation are often used as such tools. Sometimes the statements in such documents are not sufficiently quantified or even only qualitative results are available. Nevertheless an expert can predict the dimensions and the set-up of the machine on the basis of his experience and well-founded knowledge about the process. If a mathematical model is not available, it is possible that the predictions of different experts result in different designs. Besides without such a model new findings can be only hardly integrated. From this follows that the potentials of existing machines cannot be completely used. New developments cannot be carried out so strictly like it would be possible on the basis of an useful mathematical description. 2. AIM (OBJECT) OF THE PROJECTThe insufficient
knowledge about the wet gravity concentration and the increasing importance of
this technique with regard to the waste treatment were the starting points of
the project. The main target was to optimize the process of jigging by
modification of the waveform of the oscillations which generate the pulsating
water current. To obtain this target on the one hand a laboratory jig machine
was designed, built and tested. On the other hand a mathematical model shall be
generated on the basis of empirical and theoretical approaches. The model is the
prerequisite to adjust the process parameters to materials with a broad range of
properties which must be expected in the field of waste processing. |