Efficient selective flotation separation of fluorite from calcite using ferrous and ferric species as combined depressant

Abstract

It is known that the flotation separation of fluorite/calcite is extremely difficult because of their similar surface features. In this research, the combination of FeSO4·7H2O and Fe2 (SO4)3 (FF) as depressant for possible flotation separation of calcite/fluorite was systematically investigated, with sodium oleate (NaOL) as collector. Besides large gap between mono-mineral flotation results of fluorite and calcite, even for 1:1 mixed sample, CaF2 grade of 80.29 % and CaF2 recovery of 90.79 % of fluorite concentrate can be achieved with FeSO4·7H2O (300 mg/L) and Fe2 (SO4)3 (150 mg/L) used as combined depressant and NaOL (40 mg/L) as collector at pH = 6. In addition to the quantitative micro-flotation results on mono-mineral and artificially mixed sample, SEM-EDS, contact angle measurement, zeta potential measurement, FTIR and XPS analyses, as well as collector adsorption experiment, were carried out to clarify the selective inhibition mechanism. Characterizations confirmed that, under interaction with iron sulfates (FF), ferrous hydroxide, ferric hydroxide, hydroxyl iron oxide and green rust were in-suit generated on calcite surface due to the presence of the hydrolysis of OH− and CO32− on calcite surface, while such Fe-related components were barely discernible on fluorite surface. These different adsorption features for Fe (II) and Fe (III) species on mineral surfaces exactly hindered the complexation of NaOL on calcite surface, while maintained the adsorption of collector on fluorite surface, thereby to realize the selective separation of fluorite from calcite.