A realistic description of the process of high-gradient magnetic separation

An experimentally well-supported model, which realistically describes parti cle behaviour in HGMS, was developed more than a decade ago. The model assu med that HGMS is essentially a deep bed filter onto which an external magne tic field is imposed. In this present contribution, the model is revisited. It is shown that under suitable conditions the collision efficiency of par ticles with the matrix approaches unity, even in the absence of the magneti c traction force. It is further shown that the efficiency of capture is det ermined by the interplay of the static dipolar magnetic interaction and hyd rodynamic shear stress. The threshold magnetic induction required for parti cles to be retained by the matrix is derived. Experimental data are used to demonstrate that there is a limited incentive to operate HGMS at a field h igher than 2 T Moreover, it is shown that undue emphasis on the magnetic fi eld strength usually results in poor metallurgical performance. Excessively high capital and operating costs are an additional consequence of such an approach. (C) 2001 Elsevier Science Ltd. All rights reserved.