Model for Investigating Relationships between Surfactant Micropollutant Properties and Their Separation from Liquid in a Bubble Column.

The removal of surfactant micropollutants, such as dyes, pharmaceuticals, and proteins, through foam is very important in biotechnology and wastewater treatment. The literature shows that previous models consider mass balances within the foam but not the adsorption dynamics of micropollutant surfactants on bubble surfaces in the liquid solution. Thus, the main objective of this work is to examine the removal of surfactant micropollutants in a bubble column considering both mass balance and adsorption dynamics to calculate surfactant transport from the liquid bulk to the bubble surface. This allows investigation of the relationships between surfactant hydrophobicity and surfactant separation efficiency from the liquid. It was found that the removal of the surfactant strongly depends on the dynamic adsorption behavior of surfactant on bubble surfaces, and the highest foam fractionation performance was achieved when the surfactant molecule was highly hydrophobic. This work demonstrates that the adsorption dynamics rather than adsorption thermodynamics on bubble surfaces is critical when modeling the removal of surfactant micropollutants from water solutions.

Influence of calcination temperatures on lithium deportment by screening hard rock lithium.

Calcination of spodumene is a pre-treatment stage in preparation for sulfation roasting and leaching in lithium recovery. During calcination, α-spodumene (less reactive, monoclinic crystal structure) is converted to ß-spodumene (more reactive, tetragonal crystal structure). A third, metastable γ-phase has been identified at lower temperatures than full conversion to the ß-phase. It has been previously observed that calcination greatly alters the physical properties of the various minerals in pegmatite ores, impacting comminution energy and liberation. Thus, this work investigates the relationships between calcination temperatures and the physical behaviour of hard rock lithium ores. The results showed that the increase in calcination temperature resulted in a higher lithium deportment in the finest size fraction (-0.6 mm) and thus a higher lithium grade and recovery. The samples calcined at 813.15 K and 1223.15 K did not show a significant increase in lithium grades in the finest size fraction. This work shows the incremental change in the physical properties of various minerals in the ore with increasing calcination temperature.

Lithium deportment by size of a calcined spodumene ore.

Calcination of spodumene is used to convert α-spodumene to more reactive ß-spodumene, has been shown to greatly impact the physical characteristics of some of the components in the ore. This work investigates the energy efficiency of different grinding circuits used for upgrading the lithium content in the finer fraction of the calcined spodumene ore. The results showed that closed-circuit grinding resulted in 89% lithium recovery of the finest size fractions (- 0.6 mm) while open-circuit grinding led to 65% lithium recovery for the same grinding time. Closed-circuit grinding consumed lower energy than open-circuit grinding. The grade of the finest size fraction in the case of the open-circuit grinding was 1.7 times more than that in the case of the closed-circuit grinding. This work shows the potential of using different grinding modes to maximize energy efficiency and lithium deportment by size. However, it is suggested that open circuit grinding should be used for beneficiations of spodumene ores.

Effect of calcination on coarse gangue rejection of hard rock lithium ores.

Processing of spodumene ores requires calcination as a compulsory pre-treatment to convert α-spodumene to a more reactive ß-spodumene phase. This transformation takes place at an elevated temperature of above 900 °C and results in a 30% volumetric expansion of the mineral and the product having highly altered physical properties. This work examines these induced properties and the effect of calcination on lithium grade deportment with particle size. XRD analysis showed a significant amount of ß-spodumene in the calcined finest fraction (i.e. the particles less than 0.6 mm). A marked reduction in the bond ball mill work index of the calcined lithium samples (i.e. 42.3%) was recorded supporting the observed fracturing and friable appearance of the sample following α to ß-spodumene conversion. The deportment of lithium to finer fractions was significantly increased when the sample was calcined, indicating selective breakage of the spodumene over gangue minerals.

The Stefan-Reynolds Model and the Modified Stefan-Reynolds Model for Studying Bubble-Particle Attachment Interactions in the Context of Flotation.

Bubble-particle attachment is the key step for successful flotation. Modeling of attachment interactions between air bubbles and particles after their collision can be analyzed using the Stefan-Reynolds model (immobile bubble surfaces) and the modified Stefan-Reynolds model (mobile bubble surfaces). However, these models have been rarely used, and the limitations of these models have not yet been reported. The objective of this paper is to address this matter under a wide range of experimental flotation conditions. It was found that the Stefan-Reynolds model can be used to determine the real bubble-particle hydrophobic constants at low surfactant concentrations. However, at high surfactant concentrations, the real bubble-particle hydrophobic constants cannot be determined, but the fictive bubble-particle hydrophobic constants can be obtained by using the linear extrapolation method. The same analysis was also performed using the modified Stefan-Reynolds model. The results showed that the attachment of quartz particles to air bubbles in the presence of dodecyl amine hydrochloride is accelerated due to the mobility of the air-water interface. This paper demonstrated that the limitations of the Stefan-Reynolds model and the modified Stefan-Reynolds model to analyze the bubble-particle attachment interactions can be addressed by introducing the fictive bubble-particle hydrophobic constants.

A review of induction and attachment times of wetting thin films between air bubbles and particles and its relevance in the separation of particles by flotation.

Bubble-particle attachment in water is critical to the separation of particles by flotation which is widely used in the recovery of valuable minerals, the deinking of wastepaper, the water treatment and the oil recovery from tar sands. It involves the thinning and rupture of wetting thin films, and the expansion and relaxation of the gas-liquid-solid contact lines. The time scale of the first two processes is referred to as the induction time, whereas the time scale of the attachment involving all the processes is called the attachment time. This paper reviews the experimental studies into the induction and attachment times between minerals and air bubbles, and between oil droplets and air bubbles. It also focuses on the experimental investigations and mathematical modelling of elementary processes of the wetting film thinning and rupture, and the three-phase contact line expansion relevant to flotation. It was confirmed that the time parameters, obtained by various authors, are sensitive enough to show changes in both flotation surface chemistry and physical properties of solid surfaces of pure minerals. These findings should be extended to other systems. It is proposed that measurements of the bubble-particle attachment can be used to interpret changes in flotation behaviour or, in conjunction with other factors, such as particle size and gas dispersion, to predict flotation performance.