Effects of Calcium and Chloride Ions in Iron Ore Reverse Cationic Flotation: Fundamental Studies

In this work, the simultaneous effects of Ca2+ and Cl− ions in an aqueous solution at pH 10.5 on the flotation of quartz (the main impurity in itabiritic iron ore) and hematite by starch and amine was investigated. A strong depression in the flotation of both quartz and hematite conditioned with CaCl2 was observed. This effect was higher for hematite than for quartz. Based on zeta potential measurements and the speciation diagram of calcium in aqueous solutions, the physical adsorption of Ca2+ on the surfaces of both minerals was inferred. The infrared spectrum of quartz conditioned with CaCl2 at pH 10.5 was similar to its reagent-free reference spectrum. However, a new band at the wavenumber of 1465 cm−1 was identified in the spectrum of hematite conditioned with CaCl2; this band did not exist in its reference spectrum. This new band may indicate the chemical adsorption of Cl− ions on the hematite surface. The complexation of Ca2+ by ethylenediaminetetraacetic acid enabled complete quartz recovery with amine. For hematite, recovery was partially restored, probably because of the positive chloro-complexes on the hydrated iron surfaces of hematite, which prevented the adsorption of aminium ions at these sites. Therefore, the selective inverse cationic flotation of itabiritic iron ore at pH 10.5 in water containing Ca2+ is possibly only after complexing them with EDTA.