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This study aimed to develop a niosome-encapsulated clindamycin phosphate (CMP) formulation for topical delivery. The possibility of encapsulation of this antibiotic in niosomes, its stability, cytotoxicity, and antibacterial capability were evaluated. Diverse combinations of sorbitan esters and their ethoxylated derivatives with cholesterol were used to prepare the lipid vesicles. This series of niosomes had high physical stability depicted as unchanged size distribution curves during 6-month storage. Formulations composed of Span 60 and Tween 60 in combination with 30 mol% of cholesterol exhibited the highest encapsulation efficiency (47.14%). Minimal inhibitory concentration of the niosomal CMP against Staphylococcus aureus was higher than free CMP. Slow and biphasic release profile of CMP was also shown. These results indicate that niosomes can be used as stable carriers for topical delivery of CMP in acne.

Reprocessing and valorization of secondary resources is a possible solution to alleviate the supply-demand disparity for critical materials. The current study investigated the recovery of P and enrichment of REEs from Florida waste clay (WC). Clays, dolomite, and quartz are the main associated gangue minerals, while apatite is the predominant P-bearing mineral, and monazite and xenotime are the rare earth minerals in this WC. A 1.5-in. diam. hydro-cyclone unit was initially employed for the removal of clays. Froth flotation was then examined for the separation of values from the cyclone underflow. Various depressants and surface modifying agents were assessed for both direct and reverse flotation separations. Results showed that the direct flotation does not offer a solution for the selective recovery of P from WC. Despite their documented affinity for apatite and rare earths, hydroxamic acid collectors do not produce a selective separation. A single-stage reverse cationic process provides a more economically viable route due to its capability to avoid the loss of REEs. Test results of the single-stage reverse cationic process indicated that the P2O5 grade was increased to 21 wt.% from an initial grade of ∼8 wt.% with a corresponding recovery of approximately 80%. The REE content was elevated from an initial value of 307.1 ppm to 800 ppm, with an 80% recovery resulting from the same process. The removal of clays, silicates, and carbonates up to a point to meet the medium-grade phosphate ore specifications also facilitates the subsequent recovery of REEs using chemical separation.

Fluorapatite flotation is influenced by the dissolved lattice metal ions. Al3+ and Mg2+ from the associating gangue minerals influence the adsorption of collector molecules onto the fluorapatite surface during flotation. Hence, unveiling new insights on such interactions in the context of froth flotation at an atomic level paves the way for improving flotation selectivity. An original multiscale approach has been developed involving flotation experiments, electro-kinetic and adsorption density measurements, X-ray photoelectron spectroscopy studies, and density functional theory simulations. Fatty acid establishes an enhanced interaction with the bare apatite surface compared to the hydroxamates. Na+ counter-ion contributes to the adsorption of fatty acid on bare apatite. Both Al3+ and Mg2+ ions are beneficial for the adsorption of fatty acid, thereby the fluorapatite flotation. For octanohydroxamic acid, the presence of Al3+ results in a stronger collector-apatite interaction, and therefore an enhanced flotation. For fatty acid and hydroxamates, adsorption of Mg2+ leads to an improved collector-apatite interaction. Benzohydroxamic acid is more vigorously adsorbed than octanohydroxamic acid in the presence of Mg2+. Fatty acid establishes a stronger interaction with bare and Al3+/Mg2+-treated fluorapatite, as opposed to hydroxamates. Mg2+ is more favorable than Al3+ in fluorapatite flotation using both fatty acid and hydroxamates.

In flotation, among the key parameters that dictate the hydrodynamic characteristics are bubble rising velocity and trajectory. This study aims to investigate the trajectory and rise velocity of lo...

In this study, a theoretical evaluation of the effect of inertial forces in particle-bubble interactions during the flotation process is presented and supported by the experimental data. The effects of positive and negative inertial forces were analyzed by comparing the differences between the models, which either consider or neglect the inertial forces. The Sutherland collision model and the Nguyen attachment model that completely ignore the effect of particle’s inertial forces (inertialess models) were implemented into the general flotation kinetic model. The modified model was then compared with one of the most accurate inertial models, which considers the Generalized Sutherland Equation (GSE) for collision efficiency along with the Dobby-Finch model for attachment efficiency. The flotation kinetics of chalcopyrite and galena particles were estimated using the general flotation kinetic model in order to demonstrate the effect of particle density on the model, which emphasizes the effect of inertial forces. The influence of positive and negative inertial forces on flotation kinetics was evaluated for various explicit parameters such as particle density, turbulence (energy dissipation), and bubble size and velocity. Obtained theoretical results clearly showed the potential of the particle density to counterbalance the negative effects of the inertial forces. The capability of the positive inertial forces for galena particles (high density) to overcome its negative effect was shown when the general flotation kinetic model was used. Theoretical calculations were further confirmed by experimental bubble loading measurements. It was shown that the inertial forces should not be omitted in any flotation model amidst concerns over the complexity.

The effects of particle characteristics and hydrodynamic conditions on the flotation rate constant (k) and bubble–particle collision efficiency (Ec) of pyrite and chalcopyrite particles were investigated. Experimental results showed that k increases with increase of bubble surface area flux (Sb) and Ec. Artificial neural network (ANN) and multivariable linear regression procedures were used to predict both k and Ec based on the particle characteristics and hydrodynamic conditions. Multivariable linear regression resulted in R2 of 0.6 and 0.93 for k and Ec, respectively. Using an ANN model, R2 as high as 0.98 was achieved in modeling the Ec with regard to the available parameters. The proposed ANN model can be reliably used to determine both k and Ec parameters in froth flotation.

The daily growing demand for critical materials has further highlighted the importance of secondary sources such as industrial waste streams. Waste clay, a phosphate ore process tailing, contains a remarkable amount of critical materials such as P and REEs so that comparing to different phosphate ore process streams, waste clay presents the highest concentration of REEs after phosphate rock. Due to the enormous volume of this waste accumulated in Florida to date, this reserve can satisfy a great portion of U.S. domestic demand for REEs, as an example. However, due to its troublesome nature, this reserve poses severe environmental problems along with economic loss. Two required attempts are the removal of extremely fine-sized clays, followed by the recovery of phosphate content, which can pave the path for the recovery of REE-bearing phases. Different possible remedies or combination of them have been considered by various research/ industrial trials, including froth flotation, selective-flocculation, floc-flotation, cycloning, gravity separation, magnetic separation, leaching, etc., most of which have shown no promising solution because of failing to address economic and of course environmental concerns. Moving from mostly chemical separation processes to the primarily physical/ physicochemical processes with low operational costs and environmental impacts could be a general solution. This requires detailed mineralogical and elemental characterization, physicochemical, rheological, electrochemistry, surface chemistry, crystal chemistry, solution chemistry, and quantum chemistry investigations on each single and then mixed-phase systems composing waste clay. Such insights can help develop the fundamental knowledge, upon which more versatile and efficient solutions can be established.

This study aimed to introduce a new approach to determine the mass transfer rate constant in a laboratory column flotation through an analogy to a mass transfer process. The RTD of the column at two separate bubble sizes were modeled using both conventional N-mixer and N-mixer with back-mixing flow models. The number of perfect mixers (N) and the corresponding backflow coefficients (λ) were optimized using MINLP solver in MATLAB environment where N = 5 with λ = 0.567 at the bubble size of 1.8 mm and N = 8 with λ = 0.643 at the bubble size of 0.8 mm were obtained. The bubble active surface coefficient was introduced as a new parameter to study the flotation kinetics. Thus, the mass transfer rate constant was determined for various operational conditions based on the bubble active surface coefficient and bubble loading measurements. Results showed that the mass transfer rate depends on the physical and surface properties such as particle size, particle surface hydrophobicity, and the carrying capacity. At the fine particle size, the mass transfer continues such that a long bubble retention time is required. However, for the coarse particles, bubbles reach their maximum loading capacity prior to the pulp-froth interface so that any additional retention time does not contribute to the flotation. Besides, at the coarse particle size, due to the poor stability of the aggregates, especially for particles with low surface hydrophobicity, the mass transfer rate and thereupon the bubble loading decreases remarkably. Moreover, the fine particles show lower flotation kinetics in the presence of the large bubbles.

Loading of particles on a bubble is the result of a successful collision, attachment, and balancing of the forces between particles and the bubble. In this study, a mathematical model to estimate the bubble loading was developed based on the force balance on the lowest particle attached to the bubble. Gravity, buoyancy, hydrostatic pressure, viscous drag, capillary, and capillary pressure induced forces were taken into account in the model. The resultant force of the tangential components of the normal force applied by particles on top of the lowest particle and the viscous drag exerted on the attached particles by the surrounding fluid is balanced with other forces to predict whether detachment of the lowest particle occurs or not. The model estimation results were further compared with the experimental measurements using monodisperse silica beads and two minerals with different densities in a steady state column flotation to validate the model. Comparison results indicate a close agreement with a very minor discrepancy that could be attributed to the shape and morphological features of solid particles used for the flotation experiments.