Intensifying the separation efficiency of rhodochrosite from calcite in NaClO-oxidation flotation system with a dithiocarbamate-hydroxamate collector

The dissolution characteristics of rhodochrosite and calcite results in their similar surface properties, which makes the separation of rhodochrosite from calcite more difficult. Therefore, surface modification was adopted to oxidize the Mn(II) species on rhodochrosite to higher valence states, reducing the solubility of Mn²⁺ and differentiating the surface properties from calcite. Sodium hypochlorite (NaClO) was a suitable oxidant to enhance the floatability of rhodochrosite. Meanwhile, N-[(3-hydroxyamino)-propoxy]-N-hexyl dithiocarbamate (HAHD) was a versatile collector, which can be oxidized into a Gemini molecule of (HAHD)₂ and featured a selective performance in the NaClO-oxidized flotation system of rhodochrosite-calcite artificially mixed minerals. The selectivity index I_Mn of HAHD in the oxidized flotation of mixed minerals reached 32.2, much higher than that of sodium oleate (9.9). Interestingly, UV spectra and XPS analyses indicated that HAHD was oxidized to a Gemini structure (HAHD)₂ in the oxidized flotation system. In HAHD-NaClO-rhodochrosite flotation system, REDOX reaction occurred, that was, the surface Mn(II) of rhodochrosite was first oxidized to Mn(IV) which oxidized HAHD to (HAHD)₂, then some of Mn(IV) species were reduced to Mn(II). A potential mechanism was proposed finally to reveal the essence of the selective flotation of rhodochrosite from the mixture with calcite.