In this study, the effect of MnCl2 on scheelite flotation with sodium oleate (NaOL) as a collector and sodium silicate as a depressant was assessed by a combination of flotation experiments, Fouriertransform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and solution chemistry. The flotation experiments confirmed that the addition of MnCl2 before sodium silicate showed an adverse effect on flotation and the recovery of scheelite gradually decreased as the amount of MnCl2 was increased. When MnCl2 was added afte r sodium silicate, the recovery of scheelite gradually increased with an increase in the amount of MnCl2. The results of FTIR, XPS, and solution chemistry indicated that MnCl2 acted on the surface of scheelite in the form of manganese ions. When MnCl2 was added before sodium silicate, manganese ions adsorbed on the surface of scheelite reacted with sodium silicate to form a hydrophilic silicate, which covers the surface of scheelite and blocks the adsorption of NaOL. However, when MnCl2 was added after sodium silicate, manganese ions are continued to be adsorbed on the surface of scheelite, which increases the cations on the surface of scheelite, and hence the condition becomes conducive for the interaction between scheelite and NaOL.
The flotation separation (FS) of both scheelite and calcite minerals with similar physicochemical properties remains challenging, since the Ca active sites exist on their surfaces. The present work investigated the effects of different addition points of MnCl2 on the FS of scheelite and calcite by micro-flotation tests, zeta potential measurements, UV-Vis spectrophotometer measurements, infrared spectrum analysis, and X-ray photoelectron spectroscopy (XPS) tests, and the mechanism of separation is elucidated. Interestingly, the recovery of scheelite was 91.33% and that of calcite was 8.49% when MnCl2 was added after sodium silicate. Compared with the addition of MnCl2 before Na2SiO3, the recovery of scheelite was 64.94% and that of calcite was 6.64%. The sequence of adding MnCl2 followed by Na2SiO3 leads to the non-selective adsorption of Mn2+ on the surface of scheelite and calcite firstly, and later, sodium silicate will interact with it to produce hydrophilic silicate. This substantially enhances the hydrophilicity on the surface of both minerals, making separation impossible. In contrast, the addition of MnCl2 after sodium silicate can promote the formation of a metal silicate and enhance the selectivity and inhibition effect on calcite. Meanwhile, under this dosing sequence, the adsorption of Mn2+ on the scheelite surface offered more active sites for sodium oleate, which improved the scheelite surface hydrophobicity. This leads to a great improvement of the FS effect of scheelite and calcite.
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