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.