A new understanding of the adsorption mechanism of oleate on cassiterite surfaces is presented by density functional theory (DFT) calculations. Various convergence tests were conducted to optimize the parameter settings for the rational simulation of cassiterite bulk unit cell and surface slabs. The calculated surface energies of four low-index cassiterite cleavage planes form an increasing sequence of (110) < (100) < (101) < (001), demonstrating (110) is the most thermodynamically stable surface of cassiterite. The interaction strengths of the oleate ion (OL⁻), OH⁻, and H₂O on the SnO₂ (110) face are in the order of H₂O < OH⁻ < OL⁻, which reveals that the OL⁻ is able to replace the adsorbed H₂O and OH⁻ on the mineral surfaces. Mulliken population calculations and electron density difference analysis show that electrons transfer from the Sn atoms on the cassiterite (110) surface to the O atoms offered by carboxyl groups of oleate during the interaction. The populations of newly formed O1–Sn1 and O2–Sn2 bonds are 0.30 and 0.29, respectively, indicating that these two bonds are of a very low covalency. Density of states analysis reveals that the formation of an O1–Sn1 bond mainly results from the 5s and 5p orbitals of the Sn1 atom and the 2p orbital of the O1 atom.

The flotation, adsorption and bonding mechanisms of styrene phosphonic acid (SPA) to cassiterite were studied using microflotation tests, zeta potential measurements, solution chemistry analysis and density functional theory (DFT) calculations in this paper. Flotation results demonstrated SPA was an excellent collector for cassiterite which could recover over 85% cassiterite particles with the pH range 4.3–6.06 and 40 mg/L SPA. Zeta potential measurements and solution chemistry analysis revealed the adsorption of SPA was mainly contributed by the chemisorption of the monoanions on cassiterite surfaces. Frontier molecular orbital theory analysis and adsorption energy calculation results proved the monoanion of SPA was able to replace the OH⁻ on cassiterite surfaces. The adsorption structure optimization results confirmed the binuclear complex was the most favorable adsorption configuration of SPA on cassiterite (110) surface. Mulliken population calculations and density of states analysis indicated during the bonding process the Sn3 atom lost electrons to O3 atom, and the bonding interaction between O3 and Sn3 atoms was mainly from the contribution of the 2p orbital of O3 atom and the 5s and 5p orbitals of Sn3 atom.

To reveal the growth behavior and size characterization of iron particles in coal-based reduction, we reduced oolitic hematite–coal composite briquettes at various temperatures, durations and ore size fractions. The degree of metallization and microstructure of the reduced briquettes and the characteristic of iron particle size were investigated through chemical composition analysis, scanning electron microscopy, energy dispersive spectroscopy, and Bgrimm process mineralogy analysis. Results showed that iron oxides in the oolitic hematite ore were reduced to metallic iron from outer to inner layers; these oxides gradually grew into quasi-spherical iron particles with random distribution in the gangue. As reduction continued, iron grains agglomerated occurred, and iron particle clusters were formed in the form of quasi-spherical, chained, blocky, and clavate when they were viewed in the cross section. The boundaries among the iron grains of the iron particle cluster continuously faded and disappeared, and an iron particle with increased size and homogeneity was finally produced. The reduction temperature, time, and ore size fraction influenced the reduction of composite briquettes and iron particle size. The degree of metallization increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased until the equilibrium of reaction was achieved. Moreover, the iron particle size gradually increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased.

The structure–property relationship and adsorption mechanism of a novel collector for cassiterite, 2-carboxyethylphenylphosphinic acid (CEPPA), were comprehensively investigated and compared with those of styrene phosphonic acid (SPA) by density functional theory (DFT) calculations and flotation tests. The net Mulliken charge and frontier molecular orbital (FMO) theory study results indicated that CEPPA exhibited stronger electron-donating ability and higher chemical reactivity than SPA. The flotation test results demonstrated that CEPPA had stronger collecting ability for cassiterite in a much wider effective pH range than SPA. The adsorption simulation results confirmed that the CEPPA molecule was adsorbed on cassiterite (110) surface by two hydrogen bonds. CEPPA monoanion and dianion were adsorbed on cassiterite (110) surface by a series of O-Sn bonds, and the interactions between the O atoms in CEPPA phosphinic group with the Sn atoms on cassiterite (110) surface were stronger than those between the O atoms in CEPPA carboxyl group with the Sn atoms on cassiterite (110) surface. The formation of the O-Sn bonds was mainly contributed from the 2p orbital of O atoms and 5s and 5p orbitals of Sn atoms. The various adsorption configurations of CEPPA on cassiterite accounted for the better collecting ability of CEPPA for cassiterite than that of SPA. The quantitative analysis results were in good agreement with the qualitative experimental test results in a previous paper.