Influences of electronic spin structures on magnetic properties of Fe, Co and Ni ions and adsorption of collectors

Flotation method, in mineral processing, is used to separate and concentrate ores by altering their surfaces to a hydrophobic or hydrophilic condition. It has been suggested that the flotation methods for oxide minerals are greatly different from those of sulfide minerals. Specifically, O-containing collectors, such as oleic acid, alkyl sulfonic acid and cupferron, are used for oxide mineral flotation, and S-containing collectors, such as alkyl (C₂-C₄) dithiocarbonate, dialkyldithiocarbamate and dialkyldithiophosphate, are often used for sulfide mineral flotation. Ideally, metals coordinated by S ligand have been seen to have different properties from those coordinated by O ligand. Minerals which contain 3d transition metals, such as Mn, Fe, Co and Ni, may have magnetic properties due to the special d-electron configurations; however, the spin state of metal in oxide and sulfide minerals may be different. As such, the presence of unpaired electrons in the orbitals can cause a spin magnetic moment for the metal compound, and the numbers of unpaired electrons decide the spin magnitude. At present, the crystal field theory (CFT) has been shown to be one of the most successful method in explaining many of the spin properties of transition metal complexes.

Noteworthy research has also shown that different electronic properties of metals in the mineral crystal can affect the interaction between metal and flotation reagents. In general, there is still need for further development of this technique so as to overcome the mentioned ambiguity in results. On this account, researchers at the Guangxi University in China: Professor Jianhua Chen, Dr. Xi Yang, Dr. Yuqiong Li and Dr. Yingchao Liu employed  the density functional theory (DFT) to study the electronic spin states and structural properties of Fe, Co and Ni ions in the octahedral field formed by O and S ligands. Their work is currently published in the research journal, Minerals Engineering.

In their approach, the rationality of M-O and M-S mineral models was tested. In addition, the interactions of O- and S-containing collectors with metal ions in O and S ligand filed were studied. To be precise, the researchers constructed M-O and M-S mineral models by coordinated O and S ligands to simulate oxide and sulfide minerals, following which the rationality and correctness of these mineral models were tested and verified by coordination field theory (CFT). In the end, the adsorption of O- and S-containing collector molecules on the minerals was simulated.

The authors found that in M-O octahedral field, the metal exhibited a high spin nature, whereas in M-S octahedral field, the metal exhibited a low spin nature. This suggested that O atom was a weak-field ligand and S atom was a strong-field ligand. Additionally, it was also found that M-O atoms were mainly ionicly bonded, whereas M-S atoms were mainly covalently bonded. This result was noted to be consistent with the M-O and M-S bonds in the real metal oxide and sulfide minerals.

In summary, density functional theory calculations were performed on M-O and M-S mineral models (M = Fe, Co, Ni) by coordinating O and S ligands to simulate the oxide and sulfide minerals and to prove that they could represent the real metal oxide and sulfide minerals and then could be used to simulate the real mineral crystal structures to some extent. Overall, the researchers established that the simulation results were consistent with coordination field theory, also consistent with flotation practices. In a statement to Advances in Engineering, Dr. Yuqiong Li mentioned that their work presented a pivotal stepping stone towards the assessment of the adsorption of flotation reagents on the real mineral surfaces with the aim of providing a detailed result of the effect of crystal and electronic structures on the adsorption of flotation reagents on mineral surfaces.