Surface iso-transformation and floatability of calcite and fluorite.

[Display omitted] • Surface iso -transformation mechanisms between calcite and fluorite was revealed. • F− ions increased calcite recovery, but CO 3 2− ions decreased fluorite recovery. • F− bonded with Ca2+ on calcite surface, but CO 3 2− did not bond with Ca2+ on fluorite. • Adsorption heat and rate of NaOL on iso -transformed calcite increased, approaching to fluorite. Fluorite (CaF 2) and calcite (CaCO 3), both minerals containing calcium and owning similar surface properties, which is unfavorable to the selective separation. This study revealed the mechanisms of surface homogeneity transformation between them. Flotation results showed that F− ions increased the recovery of calcite, but CO 3 2− decreased the recovery of fluorite, due possibly to the surface homogenization of these two minerals. In addition, the surface evolution changed the adsorption of collector (i.e. , sodium oleate). SEM tests further showed the formation and adsorption of scattered cubic CaCO 3 crystals on the surface of fluorite. Differently, a significant quantity of spherical CaF 2 crystals uniformly coated the calcite surface. Moreover, apparent dissolution occurred on calcite surface. Furthermore, XPS tests showed that Ca-F bonds were formed on calcite surface while Ca-CO 3 bonds were formed on fluorite surface, but the content of former was higher than the latter. XRD tests further showed the formation of fluorite on calcite surface. The DFT calculation exhibited that the adsorption energy of F− and Ca2+ on calcite (1 0 4) surface was −20.78 kJ/mol, more negative than that of CO 3 2− and Ca2+ on fluorite (1 1 1) surface (−6.57 kJ/mol). Moreover, the higher affinity of sodium oleate towards the surface of fluorite-converted calcite was demonstrated by the increased reaction heat and rate, leading to difficult flotation separation of them. This study exhibits the iso -transformation mechanisms of calcite and fluorite, shedding lights on the surface evolution of these two minerals, thereby providing scientific evidence in promoting their flotation separation efficiency. [ABSTRACT FROM AUTHOR]