Modelling the rheological behaviour of dense media and design of medium circuits in dynamic D.M.S. process

The most recent efforts in developing the Dense Medium Separation (DMS) technology have been particularly directed towards the treatment of the fines (in the range 0.5 to 0.1/0.3 mm), the separation at high density, the high sharpness separation and the use of multistage dynamic separation system. To this end, the control of the rheological properties of the suspensions used in dense medium separation is of primary importance. This means that: (a) a knowledge of the influence of the operating media composition on the rheological properties is necessary; (b) the medium cleaning circuits have to be properly designed in order to obtain the required composition of the medium. This implies the need of a model for describing the rheological behaviour of dense media. The model has been developed after test programmes conducted on suspensions of magnetite, ferrosilicon and various non-magnetic contaminants, under different conditions of volume concentration, proportion of components of the solid phase and shear rate. Basic data for using the model are the rheological properties of media made up of pure components or corresponding to selected compositions. In this paper the model has been checked for suspensions of ferrosilicon containing different types of contaminants. The principles underlying the design of medium regeneration circuits in modern dynamic DMS plants are highlighted. Some workable enhancements of the complex plant circuitry aimed at obtaining and controlling the required composition of the medium and, hence, modulating the viscosity of operating media are described.