Tratamento do rejeito de mineração

Abstract

The mine in study have mineral resources of 5,6 billion tons of iron ore. Produces 26 million tons of concentrate per year and the final concentrate presents iron grades higher than 66% Fe. On the other hand, 45 million tons of tailings are discarded every year with no additional treatment. Despite this, it is possible to observe a small quantity of iron oxides inside the material, which may have some potential to be recovered. Thinking in that, a study started with the objective of recover the iron oxides from final tailings. From the study, it was possible to observe that material <106μm presents a good potential to be concentrated once this size fraction shows a considerable Fe grade (23.55%), not so high SiO2 (65.00%) and a high liberation degree. To assess material behavior within a concentration process, flotation and magnetic separation circuits were performed with <106 μm material. The objective was o achieve concentrates with more than 66% Fe and less than 4% SiO2. Some circuits of magnetic separation were evaluated. In a first moment, a circuit with two stages of concentration (rougher and cleaner) was evaluated, but the amount of magnetite present in the material disturbed the circuit, leading to the inclusion of a MIMS stage in the process. Another point observed during the project was the necessity to increase liberation degree in rougher concentrate to achieve the desired quality in concentrate, which was solved including a grinding stage in the circuit. Finally, 3 different circuits of magnetic separation produced concentrates with more than 66%Fe. Among the three circuits, the one that presented the best results was composed by MIMS stage (2000 G), WHIMS rougher stage (30% of solids, 1.5 mm matrix, 10000 G and 1000mL of water for washing) and a screening stage (to cut the fraction >75μm of WHIMS rougher concentrate) followed by a grinding stage (to grind this material to a P80 of 75μm and refeed it into WHIMS). Using this circuit was possible to produce a concentrate with 67.3% Fe and 3.87% SiO2, with a mass recovery of 30.2% and Fe recovery of 87.8%. Some flotation tests were also performed but due to mass restrictions was not possible to perform a detailed study. EDA was used as collector and Starch as depressant. The circuit evaluated was composed by rougher (200g/t of collector, 300 g/t of depressant, pH 10.5 and 35% of solids in pulp) and cleaner stages (100g/t of collector, 400 g/t of depressant, pH 10.5 and 35% of solids in pulp) and produced a concentrate with 65.63% Fe and 5.57% SiO2, with a mass recovery of 30.8% and Fe recovery of 91.4%.