Effect of ultrasound pre-treatment on carbonaceous copper-bearing shale flotation.

Although numerous studies have been implemented on identifying the impact of acoustic waves on mineral beneficiation, its fundamental aspects remain unclear in the literature. The present work, for the first time, systematically investigates the role of ultrasound pre-treatment (UPT) in the carbonaceous copper-bearing shale flotation. To this end, conditioning was carried out at different powers of applied ultrasound. Non-treated and UPT shale flotation tests were performed in the presence of frother (MIBC) and collector (KEX). To analyse particle surface charge variation and collector adsorption properties after application of UPT, zeta potential and ultraviolet-visible spectroscopy measurements were implemented, respectively. The generation of sub-micron bubbles due to the acoustic cavitation was characterised by laser-based particle size measurements. Shale hydrophobicity was determined using the sessile drop and captive bubble techniques. The micro-flotation results showed that the mass recovery increased by 40% at 20 W of applied ultrasonic power. The positive effect of UPT on the copper-bearing shale flotation was related to: i) generation of ultrafine bubbles due to the acoustic cavitation phenomenon and ii) the cleaning effect through transient bubble collapse. However, rigorous ultra-sonication diminished the recoverability of the sample owing to the less intensified number of ultrafine bubbles on the particle surfaces and formation of free H and OH radicals, which led to the oxidation of particle surfaces. These statements were correlated well with the observations of the zeta potential, particle size analysis and quantified ultrafine bubbles. Finally, we briefly highlighted fundamental knowledge gaps in flotation and ultrasound-related issues for future work.

Synergistic Effect of Binary Surfactant Mixtures in Two-Phase and Three-Phase Systems.

Cationic alkyltrimethylammonium bromides (CnTAB, with n = 8, 12, 16, 18) and their mixtures with n-octanol as a nonionic surfactant were chosen as a model system to study the synergistic effect on foamability (two-phase system) and floatability (three-phase system) of quartz in the presence of binary mixtures of ionic/nonionic surfactants. The foam height of one-component solutions and binary mixtures and floatability of quartz particles were characterized as a function of the surfactant concentration and the number of carbons (n) in the alkyl chain of CnTAB. The experimental results of foamability and floatability measurements in one-component and mixed solutions revealed the synergistic effect, causing a significant enhancement in the foam height and recovery of quartz. In the presence of n-octanol, the height of foam increased remarkably for all CnTAB solutions studied, and this effect, whose magnitude depended on the CnTAB hydrophobic tail length, could not be justified by a simple increase in total surfactant concentration. A similar picture was obtained in the case of flotation response. The mechanism of synergistic effect observed in mixed CnTAB/n-octanol solutions was proposed. The discussion was supported by molecular dynamics simulations, and the probable mechanism responsible for synergism was discussed. In addition, an analysis allowing accurate determination of the concentration regimes, where the synergistic effect can be expected, was given. It was shown that for the two-phase system, the n-octanol molecule preadsorption at the liquid/gas interface causes an increase in CnTAB adsorption coverage over the level expected from its equilibrium value in the one-component solution. In the case of the three-phase system, the synergistic effect was related to the ionic surfactants serving as an anchor layer for n-octanol, which, in water/n-octanol solution (one-component system), do not adsorb on the surface of quartz.

Froth flotation of fluorite: A review.

Fluorite, as a scarce nonrenewable strategic non-metallic mineral resource, is the primary raw material for fluorine products used in diverse fields such as metallurgy, national defense, chemical and optical industries. With the increasing expansion of the related fields, the demand for high-quality fluorite continues to grow. Hence, the surge of interest in effectively utilizing fluorite resources has led to vast attention worldwide. So far, significant endeavors have been done to enhance the beneficiation of fluorite from relatively low-grade ores. It has been well appreciated that the froth flotation is of the most importance. However, to the best of the authors' knowledge, it lacks a thorough and critical review on the recent developments in fluorite flotation. This article begins with introducing the deposits and unique physical and chemical properties of fluorite from the perspective of the crystal structure. It is followed by a systematic review of common reagents involved in fluorite flotation, including collectors, depressants, regulators, modifiers, and frothers. Specifically, the synergistic effect of collectors and depressants on the recovery of fluorite is elaborated for the first time. Finally, the most widely seen fluorite-flotation cases, including separation of fluorite from quartz, calcite, barite, and sulfide, are summarized individually. The present review sheds new light on the deep understanding of fluorite flotation, the future synthesis of reagents, as well as their schemes in practical use. Meanwhile, such a novel rain of thought provided in this work has the potential to guide the flotation of other similar minerals extensively.

On importance of external conditions and properties of the interacting phases in formation and stability of symmetrical and unsymmetrical liquid films.

Importance of external conditions and properties of phases creating liquid films, in outcome of the air bubble collisions with liquid/air and liquid/solids interfaces in clean water and in liquid solutions, is critically reviewed. The review is focussed on initial stages of the liquid films formation by bubbles colliding with interfaces, as well as, on analysis of the most important factors responsible for the collision's outcome, that is, either the rapid bubble bouncing or formation of the symmetrical or unsymmetrical liquid films and their thinning to the critical rupture thicknesses. Data on formation of liquid films under dynamic conditions, both in pure liquids and solutions of electrolytes and various surface-active substances, are reviewed and importance of hydrodynamic boundary conditions at interacting interfaces for energy balance in the system is discussed. It is shown that the liquid films stability, which in stagnant systems are directly determined by properties of the liquid/gas and liquid/solid interfaces, can be quite different in dynamic environment. A mechanism of the bubble bouncing from various interfaces in terms of interplay between energy exchange and kinetics of liquid film drainage is analyzed. It is shown that this mechanism is universal and irrelevant on the nature of interacting phases. Moreover, mechanisms responsible for wetting (unsymmetrical) film stability under dynamic conditions are discussed in light of the most recent studies, showing a crucial role of electrolyte, kind and concentration of surface-active substances, electrical surface charge, hydrophilic/hydrophobic properties of solids and presence of air entrapped (nano- and/or micro-bubbles) at surfaces of highly hydrophobic solids in the liquid films rupture.