Metal ions are widely present in flotation pulp. Metal ions change solution chemistry and mineral surface properties, consequently affecting mineral flotation. In this work, the effect of strontium ions on bastnaesite flotation with salicylhydroxamic acid (SHA) was investigated by microflotation tests, contact angle measurements, zeta-potential measurements, and X-ray photoelectron spectroscopy (XPS) analysis. Microflotation tests confirmed that the addition of strontium ions decreased bastnaesite floatability, compared with that in the absence of strontium ions. Contact angle measurements suggested that the pretreatment of strontium ions decreased SHA adsorption. Zeta potential measurements confirmed that the bastnaesite was depressed by the adsorption of positively charged strontium species, and the lower adsorption capacity of SHA onto the bastnaesite surfaces was obtained after modifying with strontium ions. XPS analysis demonstrated that strontium ions adsorbed onto the bastnaesite surfaces through the interaction between strontium ions and oxygen atoms of surface $\equiv {\mathrm{CeOH}}^0$ groups. This occurrence hindered surface Ce sites which chelated with SHA and therefore, decreased bastnaesite floatability.

Ca²⁺, Mg²⁺, Sr²⁺ and Fe³⁺ were found to be commonly released into bastnaesite flotation pulp from minerals with relatively high concentrations. The influence and corresponding mechanism of Ca²⁺, Mg²⁺, Sr²⁺, Fe³⁺ and Al³⁺, on bastnaesite flotation, have been studied by micro flotation tests, induction time measurements, adsorption measurements and solution chemistry analysis. It was found that all aforementioned metal ions depressed bastnaesite flotation. The order of depression ability was Fe³⁺ > Al³⁺ > Mg²⁺ > Sr²⁺ > Ca²⁺ and the depression ability changed along with pH. The depression was mainly attributed to the adsorption of metals ions, which hindered collector adsorption. The species diagrams of metal ions changed along with pH, consequently changing the adsorption of metal ions on mineral surfaces, and therefore leading to different influences on flotation.

The article discusses the application of hydrophobic polystyrene nanoparticles as a collector for coal flotation, aiming to demonstrate the possibility of sorting coal fines with nanoparticles. The results of the flotation tests conducted in this study show that a clean concentrate was successfully obtained from floating high ash coal fines by using nanoparticles. The nanoparticles significantly increased the combustible recovery while kept the concentrate ash content at a low level. Contact angle measurements and electron probe microanalyzer micrographs indicate that the deposition of hydrophobic nanoparticle on coal surface increased the hydrophobicity and microscale roughness of coal particles, which was beneficial to flotation process. Although the current nanoparticles used were effective for coal flotation, the dosage consumption was relatively high due to the coagulation of nanoparticles. This suggests that it is important to increase nanoparticle colloidal stability and improve nanoparticle deposition selectivity for practical applications.

Low-rank coals are difficult to float using common hydrocarbon oily collectors, such as dodecane and diesel. In this investigation, a mixture of dodecane and n-valeric acid was used as a collector to enhance low-rank coal flotation. The changes in the induction time and surface functional groups of low-rank coal were measured before and after different collector’s adsorption to indicate its absorption mechanism. The surface free energy was calculated to identify the interaction mechanism quantitatively between coal and collectors. The results showed that the flotation performance using the mixture as a collector was much better than that using dodecane or n-valeric acid solely. The induction time of coal conditioned with the mixed collector was the shortest, which meant the better hydrophobicity and floatability. When used the mixture as collector, the polar group of the n-valeric acid interacting with the oxygenated functional group on the coal surface by hydrogen bond while dodecane primarily covers the hydrophobic sites on the coal surface. Additionally, the mixed collector can minimize the surface free energy of raw coal, the dodecane primarily reduces the nonpolar part of the coal surface free energy while the n-valeric acid reduces the polar part of the coal surface free energy.

The flotation performance and kinetics for a low-rank coal were investigated using air bubbles and oily bubbles. Five flotation kinetic models were applied to the test data to estimate the relationships between the flotation rate constant, the maximum recovery, and the collector dosage. The results showed that the oily-bubble flotation (OBF) obtained lower ash content and higher combustible recovery with less collector dosage than the air-bubble flotation (ABF). But this advantage of OBF gradually diminished with the collector dosage. It was found that the flotation of a low-rank coal in ABF and OBF can be best described with the second-order kinetic model and classical first-order model, respectively. The OBF had higher maximum combustible recovery values and lower maximum ash recovery values. The flotation rate constants of OBF were higher in all the models except the fully mixed reactor model. Furthermore, the effect of collector dosage on the low-rank coal flotation kinetics was evaluated. It was indicated that the maximum recovery values and modified rate constants increased with the collector dosage. The similar trend was observed in the flotation rate constants for all of the models except the fully mixed reactor model.