Hydrophobic agglomeration of rhodochrosite fines in aqueous suspensions with sodium oleate

Encapsulation on rhodochrosite stabilizes toxic CdS nanoparticles in aqueous oxidation systems

Manganese (Mn) redox cycling and phase variation reactions play a crucial role in natural water settings. Rhodochrosite (MnCO3), a mineral commonly found in oxygen-deprived environments, develops a surface oxide film upon exposure to oxygen. This Mn oxide film significantly influences the fate of nanoparticles within its proximity. Employing atomic force microscopy (AFM), this study examined the growth of the Mn oxide film on MnCO3 and the encapsulation of cadmium sulfide nanoparticles (CdS-NPs). Results revealed the gradual development of a nanometer-thick oxide film on MnCO3 over time in aerobic conditions, with the rate of film formation correlated to the solution's ionic strength. The oxide film on MnCO3 encapsulated pre-adsorbed CdS-NPs, either through embedding or covering. Intriguingly, CdS-NPs were found to enhance the growth of the Mn oxide film, contributing to the fixation of CdS-NPs. Furthermore, an ultrasonic desorption protocol verified the stability of CdS-NPs encapsulated by the Mn oxide film on MnCO3. This study elucidates a novel mechanism for immobilizing CdS-NPs in aqueous oxidizing conditions, providing valuable insights into the behavior and distribution of toxic nanoparticles in environmental contexts. ENVIRONMENTAL IMPLICATION: This study classifies cadmium sulfide nanoparticles (CdS-NPs) as "hazardous material" due to the inherent toxicity of cadmium, posing risks to both ecological and human health. The research addresses environmental concerns by exploring the interaction between CdS-NPs and manganese (Mn) redox cycling. The formation of a Mn oxide film, encapsulating CdS-NPs, suggests a mechanism for limiting the dispersion of these hazardous nanoparticles in oxidizing water. This provides valuable insights for managing the environmental impact of CdS-NPs, offering a proactive strategy to mitigate their adverse effects in natural systems.

Monitoring effects of hydrodynamic cavitation pretreatment of sodium oleate on the aggregation of fine diaspore particles through small-angle laser scattering

Hydrodynamic cavitation (HC) enhanced fine particle aggregation could be largely due to the generation of tiny bubbles and their role in bridging particles. However, the lack of adequate characterizations of aggregates severally limits our further understanding of the associated aggregation behaviors. In this study, the aggregation of fine diaspore particles was comparatively investigated in sodium oleate (NaOl) solutions with and without HC pretreatment through the small-angle laser scattering (SALS) technique in a shear-induced aggregation (SIA) system. Results showed that HC pretreatment caused the formation of bulk nanobubbles (BNBs), which significantly modified the particle interactions and thereby modified the size and mass fractal dimension (Df) of aggregates under different SIA conditions. Although HC pretreatment did not noticeably alter the gradual change trend of aggregate size and structure characteristics under specific variables, BNBs bridging facilitated the aggregation process towards the diffusion-limited cluster aggregation model, resulting in the formation of larger but looser aggregates. This effect was more pronounced under relatively high NaOl concentrations. Apart from BNBs, the aggregation was also affected by cavitation bubbles formed during shear cavitation, which was more significant under high stirring intensity conditions (i.e., 1800 rpm) than the low stirring intensity conditions (i.e., 600 rpm).

Interaction Behavior between Coarse and Fine Particles in the Reverse Flotation of Fluorapatite and Dolomite

The precondition for efficient flotation of middle- to low-grade phosphate ore is the dissociation of apatite from gangue minerals through fine grinding. However, fine gangue minerals, such as dolomite, have a lower hardness and are thus easily overground and converted into slime during the grinding stage. The effect of -10 μm dolomite fines (Dol-10μm) on the flotation of -75 + 25 μm dolomite (Dol-75+25μm) and -75 + 25 μm fluorapatite (FAp-75+25μm) from a detailed mechanism was investigated by microflotation tests, cryo-electron microscopy analysis, contact angle measurements, bubble-particle attachment test, and EDLVO theory. It was found that Dol-10μm significantly reduced the recovery of Dol-75+25μm and FAp-75+25μm. The Dol-10μm particles could decrease the flotation recovery of Dol-75+25μm particles by masking on their surfaces, thus reducing the hydrophobicity of mineral surfaces and preventing them from floating. Furthermore, Dol-10μm particles were easily adsorbed on the FAp-75+25μm surface and could not be effectively floated, which results in fine dolomite being mixed into the concentrate at the bottom of the tank, thereby reducing the selectivity of reverse flotation for phosphate ore. The interaction energy calculation showed that the presence of NaOL led to an attractive interaction force between Dol-10μm and Dol-75+25μm, as well as between Dol-10μm and FAp-75+25μm. As a result, Dol-10μm particles presented a nonselective aggregation with Dol-75+25μm and FAp-75+25μm particles, explaining the phenomenon of "slime coating" and the depressing effect of dolomite fines on phosphate reverse flotation.

Extraction of Manganese and Iron from a Refractory Coarse Manganese Concentrate

In this research, the coarse manganese concentrate was collected from a manganese ore concentrator in Tongren of China, and the contents of manganese and iron in coarse manganese concentrate were 28.63% and 18.65%, respectively. The majority of the minerals in coarse manganese concentrate occur in rhodochrosite, limonite, quartz, olivine, etc. Calcium chloride, calcium hypochlorite, coke, and coarse manganese concentrate were placed in a roasting furnace to conduct segregation roasting, which resulted in a partial chlorination reaction of iron to produce FeCl3, ferric chloride reduced to metallic iron and adsorbed onto the coke, and rhodochrosite broken down into manganese oxide. Iron was extracted from the roasted ore using low-intensity magnetic separation, and manganese was further extracted from the low-intensity magnetic separation tailings by high-intensity magnetic separation. The test results showed that iron concentrate with an iron grade of 78.63% and iron recovery of 83.60%, and manganese concentrate with a manganese grade of 54.04% and manganese recovery of 94.82% were obtained under the following optimal conditions: roasting temperature of 1273 K, roasting time of 60 min, calcium chloride dosage of 10%, calcium hypochlorite dosage of 5%, coke dosage of 10%, coke size of −1 mm, grinding fineness of −0.06 mm occupying 90%, low-intensity magnetic field intensity of 0.14 T, and high-intensity magnetic field intensity of 0.65 T. Most minerals in the iron concentrate were Fe, Fe3O4, and a small amount of SiO2 and CaSiO3; the main minerals in the manganese were MnO, and a small amount of Fe3O4, SiO2, and CaSiO3. The thermodynamic calculation results are in good agreement with the test results.