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.

Rhamnolipids as Effective Green Agents in the Destabilisation of Dolomite Suspension.

In this paper, we describe an application of mono- and dirhamnolipid homologue mixtures of a biosurfactant as a green agent for destabilisation of a dolomite suspension. Properties of the biosurfactant solution were characterised using surface tension and aggregate measurements to prove aggregation of rhamnolipids at concentrations much lower than the critical micelle concentration. Based on this information, the adsorption process of biosurfactant molecules on the surface of the carbonate mineral dolomite was investigated, and the adsorption mechanism was proposed. The stability of the dolomite suspension after rhamnolipid adsorption was investigated by turbidimetry. The critical concentration of rhamnolipid at which destabilisation of the suspension occurred most effectively was found to be 50 mg·dm-3. By analysing backscattering profiles, solid-phase migration velocities were calculated. With different amounts of biomolecules, this parameter can be modified from 6.66 to 20.29 mm·h-1. Our study indicates that the dolomite suspension is destabilised by hydrophobic coagulation, which was proved by examining the wetting angle of the mineral surface using the captive bubble technique. The relatively low amount of biosurfactant used to destabilise the system indicates the potential application of this technology for water treatment or modification of the hydrophobicity of mineral surfaces in mineral engineering.

Effect of a lipopeptide biosurfactant on the precipitation of calcium carbonate.

Observing flora and fauna, it can be said that nature is a great architect. Nature can create amazing structures with unique properties that may find potential applications in industry. This phenomenon is why the biomimetic synthesis of calcium carbonate with various polymorphs, sizes and morphologies using natural biomolecules, such as proteins and polysaccharides, has become an interesting topic in recent years. This novel work uses natural surfactants produced by Bacillus species (surfactins) in the formation of calcium carbonate particles. Calcium carbonate was synthesized by the reaction of Na2CO3 and CaCl2. The effects of surfactin concentration and pH on calcium carbonate crystal growth were investigated. Precipitated calcium carbonate was characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The pore size and specific surface area were measured via the BET isotherm method. Surfactin molecules were observed to prevent the transformation of vaterite into calcite in the reaction system, especially at pH 8. Surfactin possesses two negatively charged groups (COO-), which have strong affinity towards metal ions at pH 8. When the surfactin concentration was 20 ppm, the surfaces of calcite crystals were punctuated by spherical and oval depressions. Surface roughness may substantially improve the properties of the obtained structures, for example, as inorganic templates for polymeric capsules.