Iron Ore Slimes Flotation Tests Using Column and Amidoamine Collector without Depressant

This work describes the concentration of iron ore slimes on a pilot scale by using a 500-mm diameter flotation column and a novel collector, which renders the use of a depressant unnecessary. The pilot column was operated in series with the industrial plant Vargem Grande 2 (Iron Quadrangle, Brazil) receiving, as feed, part of the underflow from the desliming thickener. These pilot tests represented only the rougher stage of a flotation circuit. The novel collector used was an amidoamine (average collector dosage of 160 g/t), and the tests were carried out in the absence of starch, at pH 10.5 and with bubbles/microbubbles generated by cavitation tube. It was possible to achieve a concentrate, by reverse flotation, with an average iron content of 53% and an average metallurgical recovery of 91.5% The recovery of the silica in the froth was 53.1% in average for one stage of flotation. The high variability of the slime characteristics rendered difficult the stabilization of the SiO2 recovery; however, the applicability of the amidoamine collector was proven. In an industrial scale circuit, the use of online analyzers for Fe and SiO2 content and the adoption of control logics based on the adjustment of parameters such as reagents dosage and washing water flow rate adjustment should contribute to the optimization of the results obtained in the pilot scale tests. Further studies adding a cleaner concentration stage should be performed.

The Characteristics of Iron Ore Slimes and Their Influence on The Flotation Process

The flotation has been successfully applied to process the iron ore for the particle size (Ps) from 10 µm up to 150 µm. The presence of the slimes (Ps < 10 µm) is harmful on the reverse flotation of quartz, so they are usually prior removed by hydrocyclones. The main effects of the presence of slimes on the flotation are related to the increase on reagents consumption, the froth stability, and decrease on the selectivity. The lower floatability of coarse quartz particles (+74 µm) combined with the presence of slimes, even in small quantities, drastically affect the flotation response. This paper shows a study of characterization of a typical iron ore slime, aiming to create a better understanding of its role on the concentration by flotation. The main characteristics of typical slimes from the Iron Ore Quadrangle in Brazil are the presence of almost 70% of hematite, 25% of quartz, and 5% of kaolinite, as the main silicates gangue minerals. Furthermore, the particle size distribution revealed that 80% of the hematite and the kaolinite are below 20 µm. The affinity between the ultrafine kaolinite of the slimes with the corn starch is harmful to the reverse flotation of quartz, as the starch has an important depressing action over the hematite. The presence of 20% of hematite −20 µm decreased the recovery to the froth of quartz + 74 µm from 97% to 62%, where the slimes coating seems to be the main responsible.