Abstract
The processing of iron ore to recover the valuable iron oxide minerals is commonly carried out using spiral concentrators that separate valuable minerals from non-valuable ones on the basis of the specific gravity of minerals. This paper shows that the analysis of the operation of spirals should not only focus on the minerals (as it is usually the case), but should also consider the particle size of these minerals. Indeed, the sampling of two industrial iron ore circuits and the data processing of the resulting measurements show that unexpectedly about 10% of the coarse heavy iron oxide minerals are not recovered by the spirals of the two circuits. Tests conducted by an independent research center confirm this plant observation. The pilot plant tests also show that the wash water flowrate addition may adversely affect the recovery of coarse heavy mineral particles. A mathematical model for the spiral was implemented into a simulator for an iron ore gravity concentration circuit. The simulator shows a potential 0.7% increase of iron recovery by simply changing the strategy used to distribute the wash water between the rougher and the cleaner/recleaner spirals of the circuit. The simulator also shows that the introduction of a hydraulic classifier into the gravity concentration circuit yields a marginal improvement to the performances of the circuit.
Highlights
The valorization of iron ores is commonly carried out by gravity and/or magnetic separation depending upon the nature of the valuable iron oxide minerals
Since most of the plant rejects for the two studied iron ore concentration circuits come from the rougher spirals, iron losses mainly originate from these spirals as fine and coarse iron oxide minerals
A decrease in the wash water addition will reduce the iron content of the rougher concentrate which may eventually cause the iron content of the final concentrate to fall below the target 66% Fe. This can be compensated by increasing the addition of wash water into the cleaner and recleaner spirals. This action will increase the final concentrate grade but may induce losses of coarse hematite to the middling streams that are returned to the rougher spirals for which the reduced wash water addition is favorable to the recovery of coarse iron minerals
Summary
The valorization of iron ores is commonly carried out by gravity and/or magnetic separation depending upon the nature of the valuable iron oxide minerals. This paper deals with the gravity concentration of iron ores. Iron ore plants usually process on a daily basis more than 100,000 t [1] of ore through spirals For such throughput, a 0.5% improvement in the recovery of iron minerals can yield additional revenues of several hundred thousand dollars per year. It should be indicated that none of these papers reported the introduction of such fundamental model into a simulator for a gravity separation circuit. The other class of papers dealing with spirals considers the spiral as a black box [4] and relates the recovery of iron rather than that of the minerals that carry iron to the spiral input variables (namely, the openings of the concentrate cutters, the spiral slurry feed rate and density...). The main weakness of these approaches is related to the fact that the effect of particle size is seldom incorporated into the model
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