ABSTRACT
Coal gangue (CG), an industrial solid waste with high contents of Li and Ga, has attracted the attention of researchers. However, the utilization of CG remains an economic challenge. Pre-enrichment of Li and Ga by flotation was carried out with a view to improving the comprehensive utilization of CG. Mineral composition, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and elemental composition were used to investigate the embeddedness of each mineral and the mode of elemental occurrence in the CG. The results showed that the main mineral compositions of the CG were kaolinite, quartz, and pyrite. Li and Ga were mainly associated with kaolinite and other clay minerals. Li and Ga had a high correlation with Al2O3 and SiO2, while Li and Ga were highly correlated with SiO2/Al2O3, indicating that Li and Ga may be associated with one or more high-alumina minerals. In addition, flotation tests proved that synergistic sorting of ash impurities and valuable components from the CG was a cost-effective method. The ash content of the final product was increased by 3% under the process of prediscarding concentrate-dissociation-secondary flotation, and the contents of Li and Ga in the final product were also slightly enriched, and the recovery rate of the carrier minerals of Li and Ga can reach 66.1%.
ABSTRACT
Fatty acids, which are enriched in vegetable oil, have attracted much attention in low-rank coal flotation because of their unique chemical structure. In this study, density functional theory calculations, molecular dynamics simulations, and atomic force microscopy were employed to investigate the adsorption structure and forces between collectors and hydrophilic surfaces. The results show that fatty acids can be easily adsorbed onto surfaces through hydrogen bonds, and can cover the oxygen sites. The existence of hydration film on hydrophilic surfaces prevented nonpolar molecules from being able to adsorb, while polar fatty acids could adsorb and expel water molecules. The adhesion force between the RCOOH-terminated probe and the surface appeared in the retraction process, which differed significantly from that of the RCH3-terminated probe, indicating that polar fatty acids are more suitable as flotation collectors for low-rank coal than nonpolar hydrocarbon oil. The simulation and AFM test revealed the mechanisms of polar fatty acids, and can provide guidance for low-rank coal flotation applications.
Subject(s)
Coal , Fatty Acids , Adsorption , Hydrophobic and Hydrophilic Interactions , Water/chemistryABSTRACT
Dextrin is a derivative of starch produced by partial thermal degradation under acidic conditions, which is usually used as a depressant in the mineral processing industry. Dextrin can also effectively depress coal particles in the reverse flotation process. To study the effect of dextrin on the flotation behavior of both coal and gangue mineral in coal reverse flotation, this research compared the adsorption behavior difference between sub-bituminous coal and silica as well as the surface property change of both sub-bituminous coal and silica after being treated by dextrin. The result illustrates that the adsorbing capacity of sub-bituminous coal on dextrin is much higher than that of silica under different initial concentrations and different interaction times. The isoelectric points of both sub-bituminous coal and silica increase after being treated by dextrin. But the increasing ζ-potential value of silica is larger than that of sub-bituminous coal. Dextrin could enhance the hydrophilicity of sub-bituminous coal and weaken the hydrophilicity of silica slightly according to the result of surface wetting rate tests. Reverse flotation using dextrin as a depressant indicates that good performance could be obtained with the addition of dextrin. Larger dextrin dosage might deteriorate silica flotation slightly.
ABSTRACT
Ammonium salt is a common collector in coal reverse flotation. This study compared the difference of adsorption behavior on ammonium salt Lilaflot D817M between sub-bituminous coal and silica as well as the surface characteristic change after being processed by ammonium salt. The results indicate that the adsorption capacity of sub-bituminous coal is always higher than that of silica under different experimental conditions, such as different initial concentrations of ammonium salt, different adsorption times, different concentrations of the depressant dextrin, and different pH values. Ammonium salt could increase the isoelectric point of both silica and sub-bituminous coal greatly. However, the hydrophobicity of silica enhances much more significantly than that of sub-bituminous coal after being treated by Lilaflot D817M. This indicates that the surface wettability change degrees of sub-bituminous coal and silica after being treated by ammonium salt are not proportional to the adsorption capacity because of their different surface structures. The reverse flotation test result shows that 2 kg/t Lilaflot D817M dosage could help obtain relatively good flotation indexes.
