ELECTROMAGNETIC DETECTION OF IRON TRACERS FOR MONITORING PARTICLES DISPLACEMENT IN GRAVITY SETTLERS

Knowledge of the residence time distributions of solid particles through gravity settlers of the Bayer’s process is essential to verify that they are operated at an adequate level of effectiveness. For instance, residence times may be calculated using various mathematical simulations, but their actual measurement is difficult. The settling behaviour through the settlers could be analysed using these distributions, if they were available, and different physical parameters, such as residence times, could be measured. A novel electromagnetic inductance measurement method using iron particles as ferromagnetic tracers is presented here. In this method iron particles of a known size distribution are injected with the slurry in the feed well and are monitored in the carrying red mud as their presence modifies the magnetic permeability detected inside an inductive coil located in the underflow pipe. The inductive coil must be uniformly wound with great care and a frequency stabilized generator is required. The apparatus was tested in an industrial settler of an Alcan alumina refinery.