The flotation behavior of beryl and spodumene (typical silicate minerals) was studied at wet-grinding conditions with different grinding mediums, with dodecylamine or sodium oleate as the collector. The mechanism of potential influence of the grinding medium to the flotation behavior was investigated through measuring zeta potential of pure minerals, micro scanning by X-ray photoelectron spectroscopy (XPS), surface interaction simulation and etc. The test data suggested that, with dodecylamine as the collector and relatively lower pH, the recoveries of beryl and spodumene are higher with zircon balls as wet-grinding media than those with iron balls, while in the higher pH, the recovery difference became smaller. With sodium oleate as a collector, within the same pH environment, the recovery of beryl and spodumene under zircon ball wet-grinding is lower than those under iron wet-grinding. We observed formation of iron-hydroxyl complexes on the mineral surface after iron ball grinding, which are significant influence on the flotation behavior of silicate minerals. Furthermore, for iron wet-grinding, the iron adsorbed on the mineral surface increased the adsorption energy between laurylamine (cationic collector) and silicate minerals, which inhibited the interaction between collectors and minerals. On the other hand, the interaction energy between sodium oleate (anion collector) and silicate minerals was decreased, which promoted the interaction between collectors and minerals.

The pulp rheology is an important factor affecting flotation performance. Gangue minerals have a significant impact on the rheological property of smithsonite (ZnCO₃). The complex pulp rheology (high viscosity, poor dispersion) will adversely affect the grade and recovery of concentrate. To address this problem, the effect of gangue minerals (kaolinite, calcite, and quartz) on the rheological property and flotation behavior of smithsonite was investigated with the pulp rheology measurement and a flotation test. The results showed that the flotation recovery is closely associated with the pulp rheology and high apparent viscosity and that yield stress resulted in a low recovery. The detrimental influence of gangue minerals on the rheology and yield of smithsonite was kaolinite > calcite > quartz. The coarse mineral particles (150–74 μm, 74–38 μm) could reduce the apparent viscosity and yield stress and present good floatability, while fine particles (38–23 μm, −23 μm) could greatly increase the values and show poor floatability. Therefore, to control the pulp rheology of smithsonite, it is necessary to remove fine gangue minerals (−38 μm) before flotation, especially the fine kaolinite.

Direct reduction is an emerging utilization technology of ferric bauxite. However, it requires much more sodium carbonate than ordinary bauxite does. The volatilization is one of the most significant parts of sodium carbonate consumption, as reported in previous studies. Based on the new direct reduction method for utilization of ferric bauxite, this paper has systematically investigated factors including heating temperature, heating time, and sodium carbonate dosage influencing sodium volatilization. For the purpose of reducing sodium volatilization, the Box–Benhken design was employed, and the possibility of separating iron and sodium after direct reduction was also investigated.

Scheelite associated with calcium-containing minerals such as calcite and fluorite is difficult to separate by flotation because of the Ca ions contained in the mineral lattices, which cause scheelite to have similar surface properties and floatability to gangue minerals. Traditional collectors such as oleic acid need to add a large amount of sodium silicate as gangue inhibitors, which causes difficulties for the settlement of tailings. In addition, the use of benzohydroxamic acid (BHA), which needs the addition of Pb(NO₃)₂ as the scheelite activator, can also cause environmental pollution. In this paper, Fe-BHA, a new collector containing the iron complex, was studied to investigate its flotation ability of scheelite, as well as its BHA/FeCl₃ ratio on scheelite flotations. In the single mineral flotations, the Fe-BHA showed a significant difference in the flotation recoveries of scheelite and calcite, with a scheelite recovery of 77.03% at pH 8.0 and calcite recovery of 16.69% at the same pH. The results of the roughing tests of Xianglushan actual ore showed that the scheelite with Fe-BHA (500 g/t BHA and 200 g/t FeCl₃) and 40 g/t oleic acid as collectors obtained satisfactory flotation results with a WO₃ grade of 1.56% and WO₃ recovery of 65.52%, which were much higher than those of scheelite with BHA or oleic acid as the collector, but there was still a gap with those of scheelite using Pb(NO₃)₂ as activation and BHA as the collector. The UV-Vis curves of the Fe-BHA with different BHA/FeCl₃ ratios indicated that the Fe-BHA chelates might have several different structural forms, and the single mineral tests of the BHA/FeCl₃ ratios showed that when the molar ratio of benzohydroxamic acid to FeCl₃ was about 1.2:1, the best scheelite flotation result was obtained in this test. In addition, the XPS analyses proved that the adsorption of the Fe-BHA on the scheelite surface occurred, and by fitting the peaks of Ca 2p and O 1s of scheelite, it was found that the mechanism of the Fe-BHA acting on the Ca sites of the scheelite surface was through the removal of H₂O from the Ca-OH of scheelite and Fe-OH from Fe-BHA to form Fe-O-H.

Ferric ions produced during grinding influence the flotation separation between kyanite and quartz adversely. In this study, citric acid was used as a regulator to eliminate the effect of ferric ions on the separation of kyanite from quartz with sodium oleate (NaOL) as a collector. The microflotation test results indicated that the quartz was selectively activated by FeCl₃ and maintained significant quartz recovery. However, the citric acid could selectively eliminate the effect of ferric ions on the quartz and minimally influenced the kyanite. Contact angle tests demonstrated that FeCl₃ significantly increased the interaction between NaOL and quartz, resulting in the high hydrophobicity of quartz, and the addition of citric acid made the quartz surface hydrophilic again but slightly influenced the kyanite. Fourier-transform infrared spectroscopy showed that FeCl₃ facilitated NaOL adsorption onto the quartz surface, and the addition of citric acid eliminated the activation of FeCl₃ on the quartz, resulting in the nonadsorption of NaOL onto the quartz surface. However, the FeCl₃ and citric acid exhibited a negligible effect on NaOL adsorption onto the kyanite surface. X-ray photoelectron spectroscopy analysis indicated that the citric acid eliminated FeCl₃ activation on the quartz.

The sodium leaching ratio (η_N) of ferric bauxite direct reduction process is much lower than that of ordinary bauxite; thus, the former consumes more sodium than the latter. η_N can be promoted by increasing the dosage of sodium or restricted by increasing the heating temperature and time. However, the restriction effect of heating temperature is 16.67 times larger than that of heating time, and the restriction effect decreases 47.03 times faster when heating temperature increases than that process of heating time. These imply that η_N improves with the increasing sodium carbonate dosage and the decreasing heating temperature.