The processing of iron ore to recover the valuable iron oxide minerals is\ncommonly carried out using spiral concentrators that separate valuable\nminerals from non-valuable ones on the basis of the specific gravity of\nminerals. This paper shows that the analysis of the operation of spirals\nshould not only focus on the minerals (as it is usually the case), but should\nalso consider the particle size of these minerals. Indeed, the sampling of\ntwo industrial iron ore circuits and the data processing of the resulting\nmeasurements show that unexpectedly about 10% of the coarse heavy iron\noxide minerals are not recovered by the spirals of the two circuits. Tests\nconducted by an independent research center confirm this plant observation.\nThe pilot plant tests also show that the wash water flowrate addition\nmay adversely affect the recovery of coarse heavy mineral particles. A mathematical\nmodel for the spiral was implemented into a simulator for an\niron ore gravity concentration circuit. The simulator shows a potential\n0.7% increase of iron recovery by simply changing the strategy used to distribute\nthe wash water between the rougher and the cleaner/recleaner spirals\nof the circuit. The simulator also shows that the introduction of a hydraulic\nclassifier into the gravity concentration circuit yields a marginal\nimprovement to the performances of the circuit.
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