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The long-time accumulation of low-rank coal can induce many environmental problems and severe waste of carbon resources. Flotation technology based on gas/liquid/solid interfacial interaction remains an efficient way to recovery combustible matter and realize clean utilization of coal. The traditional collector, kerosene, has demonstrated its low flotation efficiency and environmental hazards for low-rank coal. In this work, the kerosene was highly dispersed through emulsification with the biocompatible surfactant alkyl polyglucosides (APG) and optimized based on HLB of emulsifiers and emulsion phase diagrams. The emulsion with the mixture of hydrophilic APG and hydrophobic Span65 as emulsifier exhibits the strongest dispersibility and stability due to the formation of a stable composite molecular adsorption film of the mixed emulsifiers at oil/water interface. Compared with kerosene, the prepared emulsion collectors exhibited much higher flotation efficiency with combustible matter recovery increasing by 31.4% and simultaneously consumption of kerosene decreasing by 57.8% under optimal operation conditions. The hydrophobicity of coal surface is obviously enhanced after treatment by emulsion with the contact angle increasing from 26.6° to 71.7°. High-speed camera observation showed that only 76.59 ms was taken for the impinging emulsion droplet to adhere to low-rank coal surface followed with a faster spreading, indicating stronger interfacial interaction between emulsion collector and low-rank coal surface. The proposed 'bridging action' of emulsifier molecule between oxygen-containing groups at coal surface and kerosene in emulsion could remarkably enhance the differences in surface hydrophilicity between combustible coal and other contents, resulting in high flotation efficiency. These results constitute a substantial step forward in technical development for resource recycling of low-rank coal. [Display omitted] [ABSTRACT FROM AUTHOR]

The surface properties and flotation response of coal samples of different rank correspond to results from similar experiments for coal samples with different degrees of oxidation. Three principal types of oxygen-containing functional groups (C = O, C-O, O = C-O), were detected at the surface of low rank coals and oxidized coals by XPS, complementing results of previous researchers reported in the literature. The hydroxylation of these polar oxygen groups to C-OH groups and O = C-OH groups seems to account for the observed decrease in hydrophobic character and reduced flotation recovery. Hydration of the coal surface is facilitated at these hydroxylated sites by hydrogen bonding with interfacial water molecules. [ABSTRACT FROM AUTHOR]

Flotation continues to be a major technique for the production of potash from low grade, complex systems containing a variety of ores and ions. The specific ion effects on the behavior of the flotation collector in the KCl flotation system becomes important to the interpretation of the flotation mechanism. In this work, specific ion effects on the turbidity, surface tension and aggregation behavior of the common collector in KCl flotation, octadecylamine hydrochloride (ODA), have been investigated. The results from turbidity and surface tension studies of ODA solutions show that both cations and anions can affect the colloidal properties of ODA. Molecular dynamics simulations show that the binding that energy barrier between ODA headgroups and anions is principally responsible for the specific anion effect of γ of ODA solutions. In addition, the ion effect on the ODA aggregation particle size was also studied by using transmission electron micrographs (TEM) and dynamic light scattering. The data reveal that the presence of salt ions can induce the formation of larger ODA colloidal particles, on which the cation effect is more significant. This work provides detailed information of specific ion effect on colloidal properties of ODA, which may promote a further understanding of the flotation mechanism and help to improve the flotation of KCl from brine sources. [ABSTRACT FROM AUTHOR]

Understanding the adsorption process of collectors and the interaction between bubbles and mineral particles during KCl froth flotation are still weaknesses in our interpretation of the mechanism of flotation. In this study, we investigated in detail the adsorption kinetics and adsorption isotherm of a commonly used collector, octadecylamine hydrochloride (ODA), at the surface of KCl crystals. The effects of bubbling and temperature are discussed systematically. Our results indicated that the adsorption of ODA onto the surface of KCl crystals can be facilitated by bubbles, and that the adsorption kinetics of this process can be interpreted according to a pseudo-second order model. Both the Langmuir and Freundlich isotherm models were found to fit the adsorption isotherm of ODA on KCl crystal surface inappropriately, implying that the adsorption of ODA upon KCl crystal surfaces is a more complex process than typical monolayer, or multilayer, adsorption. This might be because the adsorption of ODA on KCl crystal surfaces takes place through an aggregated intermediate, rather than through the direct interaction of dispersed molecules. We note that the quantity of ODA adsorbed at 0 °C increased markedly with increasing numbers of bubbles. Micro-flotation tests suggested that increasing the gas flow rate effectively improved flotation recovery at 0 °C, consistent with the adsorption behavior. These results provide complementary information on the adsorption behavior of ODA at the surface of KCl crystals and on the effect of bubbles during froth flotation, which could help to design new flotation process and improve flotation recovery of KCl at low temperatures. [ABSTRACT FROM AUTHOR]

Froth flotation is still an efficient technique for KCl production from low grade and complex systems containing various ions. In this work, the colloidal properties of one common collector, octadecylamine hydrochloride (ODA), in different saturated salt solutions at different temperature are investigated systematically. The results show that the turbidity of salt solutions increased substantially with the concentration of ODA increasing and the ODA colloidal particles aggregate seriously in the presence of MgCl 2 . Compared with ODA aqueous solutions, the surface activity and the critical aggregate concentration (CAC) of ODA became lower in saturated salt solutions. With the increase of MgCl 2 percentage, the CAC values of ODA solution decreased gradually, while the CAC value of KCl-MgCl 2 saturated solution was the lowest. The temperature has a great influence on the turbidity and surface activity of ODA aqueous solution, however, the effect is slight in saturated salt solutions. In addition, the salt solutions with MgCl 2 result in lower contact angle on KCl crystal surface indicating that the adsorption of ODA molecules can be inhibited in the salt solutions with MgCl 2 . [ABSTRACT FROM AUTHOR]

The low flotation recovery of sylvite from salt lakes at low temperatures has dogged the cryogenic producer for many years. Interfacial water structure at sylvite crystal surfaces has been considered as one noticeable aspect on interpreting the selected KCl collection during flotation, and so the microscopic structure of the water membrane over KCl crystal surfaces at low temperatures was modeled through the use of molecular dynamics methods. In our simulation, the properties of the water membrane adjacent to KCl crystal surface, such as molecular mobility, water structure and preferred molecular orientation, were compared to the results for an otherwise identical system at higher temperatures or in saturated KCl solutions in the absence of a KCl crystal. In our simulation, hydrogen atoms approached the KCl crystal surface more closely, and the mobility of water molecules was more restricted compared to results for saturated KCl solutions. When the temperature decreased, the mobility of water molecules decreased, the number of hydrogen bonds made by the water molecules in the membranes was reduced and the molecules exhibited greater order than in other systems we studied. It was proposed that the property of KCl salt may change from water ‘structure breaker’ to ‘structure maker’ when temperature decreases. These results may provide complementary information which cannot be obtained from experiments on the research of flotation at low temperature directly. [ABSTRACT FROM AUTHOR]

• HIP W/O emulsion enhances the flotation of fine oxidized coal at low dosage. • Stable W 1 /O/W 2 double emulsion is formed when HIP emulsion is dispersed in water. • Emulsion droplets dispersed in water attach and spread at the oxidized coal surface. • H-bonds between Span 80 and coal surface expected to facilitate droplet attachment. Flotation recovery of fine oxidized coal is frequently inefficient when using conventional oily collectors. A large amount of fine coal is discharged as tailings, leading to resource waste and environmental pollution. To solve the problem of high oil consumption and low efficiency associated with traditional flotation, research efforts have been focused on the use of oil-in-water emulsion to reduce oil consumption. Few studies concerning water-in-oil emulsion, especially the high internal phase water-in-oil (HIP W/O) emulsion, have been conducted. Our microflotation results showed a significant oil dosage reduction when a HIP W/O emulsion was used as a collector for coal flotation. The state of the HIP W/O emulsion dispersion in water and the emulsion droplets attachment at the coal surface are vital issues associated with achieving efficient flotation. In this study, optical microscopy and high speed video microscopy were employed to study the dispersion behavior and microstructure of the HIP W/O emulsion in water. This study found that the HIP emulsion tends to be dispersed as a W 1 /O/W 2 double emulsion during mixing in water because of the migration of the surplus Span 80 in the oil phase to the O-W 2 interface. The presence of NaCl in W 1 is also essential for a stable W 1 /O/W 2 double emulsion, which is formed when equilibrium of the Laplace and osmotic pressures between the W 1 phase and W 2 phase is obtained. In addition, the W 1 /O/W 2 emulsion droplets are negatively charged, and the emulsion aggregation appears to be inhibited by electrostatic repulsion. More importantly, the Span 80 emulsifier at the O-W 2 interface seems to facilitate hydrogen bond formation between the hydrophilic moieties of Span 80 and the oxygen containing functional groups at the coal surface, which is verified by the results from molecular dynamics simulation (MDS). The hydrogen bond formation plays a leading role in the attachment and/or spreading of the emulsion droplets at the oxidized coal surface. The HIP W/O emulsion could be a potential economical and efficient replacement for the traditional oily collectors as a promising collector for the flotation of fine oxidized coal. [ABSTRACT FROM AUTHOR]