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Solvent extraction scheme to isolate Zn, Cu, and Ni from glutamate media as hypothetical product of electric arc furnace dust alkaline leaching was developed, with concentrations being 17.6, 0.35, and 0.14 g/L, respectively. Three extractants were investigated: Cyanex 272, DEHPA, and Acorga M5640 selectively separated Zn, Ni, and Cu from each other. Aside from pH, parameters investigated included O/A ratio, extractant concentration in kerosene as diluent, and sulfuric acid concentration as stripping agent. pH was the most critical factor in determining the separation factor among three metals since pH controlled metal speciation in pregnant leach solution and regulated the interaction between metal ions and extractant. Based on previous studies, a flowsheet for Zn, Cu, and Ni isolation is proposed, which obeys the following sequence: Zn separated from Cu and Ni by Cyanex 272 (in pregnant leach solution at pH 8, log separation factor Zn–Cu 4.78, Zn–Ni 2.51), followed by Ni separation from Cu by DEHPA (in raffinate at pH 7, log separation factor Ni–Cu 3.92), and finally Cu extraction (in raffinate at pH 4, log distribution coefficient 3.19). Sulfuric acid was proved to be a suitable stripping agent with optimum concentrations of Zn, Ni, and Cu being 0.5, 0.25, and 2 M, respectively.

Global demand and consumption of rare earth elements and compounds have led to increasing research to further our understanding of their beneficiation and recovery. Monazite is the second-most important rare earth-bearing mineral that can be exploited. In this study, the surface chemistry of monazite in terms of zeta potential, adsorption density, and flotation responses using octanohydroxamic acid is determined. Apatite, ilmenite, quartz, rutile, and zircon are the minerals that frequently occur with monazite, and hence they were chosen as gangue minerals in this study. The isoelectric points of monazite, apatite, ilmenite, quartz, rutile, and zircon are 5.3, 8.7, 3.8, 3.4, 6.3, and 5.1, respectively. Thermodynamic parameters of adsorption were evaluated. Ilmenite has the highest driving force for adsorption. Adsorption density value shows that octanohydroxamic acid adsorbs onto monazite and its gangue minerals. This observation was further confirmed by microflotation experiments. Increasing the temperature to 80 °C raises the adsorption and floatability of monazite and gangue minerals, which does not allow for separation. Monazite is best recovered at a pH range of 7.5–10. Appropriate use of depressant is recommended in order to enhance the separation of monazite from its gangue.

The fundamentals of the surface chemistry of ancylite, strontianite, and calcite in the presence of hydroxamic acid (HXY) were investigated based on their zeta potential, adsorption, infrared measurement, and microflotation. Zeta potential studies indicate that the isoelectric points of ancylite, strontianite, and calcite are around 5.46, 4.50, and 5.50, respectively. HXY is chemically adsorbed onto the surface of ancylite, which was confirmed by both zeta potential and infrared measurements. At room temperature, the monolayer coverage of HXY on ancylite is shown as 20 µmol/m2, which is much higher than the monolayer coverages for strontianite and calcite. In the comparison of adsorption densities of strontianite, calcite, and ancylite at both room temperature and 50 °C, the results show that strontianite and calcite appear more sensitive to temperature than ancylite. Microflotation studies of pure minerals show that theoretically, calcite could be separated from strontianite and ancylite at pH 7.5 in the presence of 5 × 10−4 M HXY, and ancylite can be separated from strontianite in the presence of 2 × 10−4 M HXY when pH is around 9. However, as indicated from the zeta potential results, the dissolved species from minerals significantly change the flotation behavior of minerals’ mixture. Thus, a successful flotation separation could not be achieved without any modifiers.

This research study was designed to investigate the principles of surface chemistry and microflotation of xenotime and selected gangue minerals, and to achieve a better understanding of the factors affecting flotation performance and separation of xenotime from associated gangue minerals in an efficient way. A preconcentrated xenotime sample and four selected gangue minerals such as ilmenite, zircon, schorl, and staurolite were used in this study. Using octanohydroxamic acid as a collector, surface chemistry was investigated through surface area measurements, zeta potential tests, and adsorption density determinations. The zeta potential of xenotime was measured as 3.90 in this study. The results of adsorption studies showed a mechanism of chemisorption and correlated well with the results of microflotation tests conducted at room temperature in a Partridge–Smith cell. In this paper, the surface chemistry and microflotation behaviors are discussed based on both the lab observations and literature review, in the hope to shed light on further research and industrial flotation operation.