Flotation and adsorption of muscovite using mixed cationic–nonionic surfactants as collector

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., "circular" shaped in the talc group, "fine-grained" shaped in the chlorite group, and "donut" shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

Froth flotation is the most versatile process in mineral beneficiation, extensively used to concentrate a wide range of minerals. This process comprises mixtures of more or less liberated minerals, water, air, and various chemical reagents, involving a series of intermingled multiphase physical and chemical phenomena in the aqueous environment. Today's main challenge facing the froth flotation process is to gain atomic-level insights into the properties of its inherent phenomena governing the process performance. While it is often challenging to determine these phenomena via trial-and-error experimentations, molecular modeling approaches not only elicit a deeper understanding of froth flotation but can also assist experimental studies in saving time and budget. Thanks to the rapid development of computer science and advances in high-performance computing (HPC) infrastructures, theoretical/computational chemistry has now matured enough to successfully and gainfully apply to tackle the challenges of complex systems. In mineral processing, however, advanced applications of computational chemistry are increasingly gaining ground and demonstrating merit in addressing these challenges. Accordingly, this contribution aims to encourage mineral scientists, especially those interested in rational reagent design, to become familiarized with the necessary concepts of molecular modeling and to apply similar strategies when studying and tailoring properties at the molecular level. This review also strives to deliver the state-of-the-art integration and application of molecular modeling in froth flotation studies to assist either active researchers in this field to disclose new directions for future research or newcomers to the field to initiate innovative works.

Research on the wetting mechanism of coal dust by different surfactants: combination of experimental characterization and molecular dynamics simulation

Surfactants can reduce the surface tension of water and improve the efficiency of spray dust reduction, but the synergistic mechanism of composite surfactant solutions wetting coal dust remains unclear. In this study, sodium dodecyl sulfonate (SDDS)/sodium dodecylbenzene sulfonate (SDBS) solution and SDDS/primary alcohol ethoxylate (AEO-9) solution were prepared to wet three types of coal with different deterioration degrees. The surface tension, contact angle, and functional group composition were measured. The results show that SDDS/AEO-9 solution had lower surface tension and critical micelle concentration than SDDS/SDBS solution at the same mixing ratio. When the ratio of SDDS: SDBS was 2:1, it had the best wetting effect on coal dust. It is found that for SDDS/SDBS solutions, aliphatic hydrocarbons and surface tension have a positive correlation with the contact angle, and hydroxyl groups have a negative correlation with the contact angle. For SDDS/AEO-9 solution, only the surface tension and contact angle show a significant linear relationship. The main factors that affect the wetting change with the combination of surfactants. AEO-9 has an electrostatic shielding effect on SDDS, while SDBS increases the electrostatic repulsion between SDDS solution and electronegative functional groups of coal. The synergism among these surfactants plays an important role in the process of wetting coal.

Molecular Dynamics Simulation Study on the Interactions of Mixed Cationic/Anionic Collectors on Muscovite (001) Surface in Aqueous Solution

In this study, the adsorption mechanisms of dodecylamine hydrochloride(DDAHC), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate(SDBS), and their mixed anionic/cationic collectors at ten different molar ratios on a muscovite (Mcv) surface in neutral aqueous solution were assessed by molecular dynamics simulations (MDS). According to the snapshot, interaction energy, radial distribution function (RDF), and density profile between the Mcv surface and collector molecules, the individual DDAHC collector was an effective collector for the flotation of Mcv. The molar ratio of anionic/cationic collectors was determined to be an essential factor in the flotation recovery of Mcv. The DDAHC collector was involved in the adsorption of the mixed anionic/cationic collectors on the Mcv (001) surface, whereas SDS and SDBS collectors were co-adsorbed with DDAHC. The mixed cationic/anionic collector showed the best adsorption on the Mcv surface in a molar ratio of 2. Additionally, SDBS, which has one more benzene ring than SDS, was more likely to form spherical micelles with DDAHC, thus resulting in better adsorption on the Mcv surface. The results of micro-flotation experiments indicated that the DDAHC collector could improve the flotation recovery of Mcv in neutral aqueous solution, which was in agreement with MDS-derived findings. In conclusion, DDAHC alone is the optimum collector for Mcv flotation under the neutral aqueous conditions, while the mixture of DDAHC and SDBS collectors (molar ratio = 2:1) exhibits the similar flotation performance.

Self-Assembly of NaOL-DDA Mixtures in Aqueous Solution: A Molecular Dynamics Simulation Study

The self-assembly behaviors of sodium oleate (NaOL), dodecylamine (DDA), and their mixtures in aqueous solution were systematically investigated by large-scale molecular dynamics simulations, respectively. The interaction mechanisms between the surfactants, as well as the surfactants and solvent, were revealed via the radial distribution function (RDF), cluster size, solvent-accessible surface area (SASA), hydrogen bond, and non-bond interaction energy. Results showed that the molecules more easily formed aggregates in mixed systems compared to pure systems, indicating higher surface activity. The SASA values of DDA and NaOL decreased significantly after mixing, indicating a tighter aggregation of the mixed surfactants. The RDF results indicated that DDA and NaOL strongly interacted with each other, especially in the mixed system with a 1:1 molar ratio. Compared to van der Waals interactions, electrostatic interactions between the surfactant molecules were the main contributors to the improved aggregation in the mixed systems. Besides, hydrogen bonds were found between NaOL and DDA in the mixed systems. Therefore, the aggregates in the mixed systems were much more compact in comparison with pure systems, which contributed to the reduction of the repulsive force between same molecules. These findings indicated that the mixed NaOL/DDA surfactants had a great potential in application of mineral flotation.

Wettability Alteration and Adsorption of Mixed Nonionic and Anionic Surfactants on Carbonates

Mixed-surfactant systems consisting of secondary alcohol ethoxylates and anionic sulfonates are evaluated as wettability alteration agents for enhanced oil recovery. The cloud points of the nonionic surfactants are raised by the addition of the sulfonates. The oil/water interfacial tension and contact angles of oil on initially oil-wet calcite are reported at different temperatures and surfactant compositions. Adsorption experiments are performed for select mixed systems at high temperatures. The extent of the increase in the cloud point, changes in the contact angle, and adsorption are influenced by co-surfactants, surfactant concentrations, and temperatures. Mixed surfactant systems were identified which modified the oil-wet surface to a water-wet surface with final contact angles as low as 70°. Mixed surfactants exhibit a linear trend in adsorption and wettability alteration with the thermodynamic descriptor of cloud point temperature difference, which has been used previously for single surfactants. These findings enable the design of surfactant formulations for wettability alteration in high temperature, high salinity reservoirs.

Adsorption Behavior of Surfactant on Lignite Surface: A Comparative Experimental and Molecular Dynamics Simulation Study

Experimental and computational simulation methods are used to investigate the adsorption behavior of the surfactant nonylphenol ethoxylate (NPEO10), which contains 10 ethylene oxide groups, on the lignite surface. The adsorption of NPEO10 on lignite follow a Langmuir-type isotherm. The thermodynamic parameters of the adsorption process show that the whole process is spontaneous. X-ray photoelectron spectroscopic (XPS) analysis indicates that a significant fraction of the oxygen-containing functional groups on the lignitic surface were covered by NPEO10. Molecular dynamics (MD) simulations show that the NPEO10 molecules were found to adsorb at the water-coal interface. Moreover, polar interactions are the main effect in the adsorption process. The density distributions of coal, NPEO10, and water molecules along the Z axis show that the remaining hydrophobic portions of the surfactant extend into the solution, creating a more hydrophobic coal surface that repels water molecules. The negative interaction energy calculated from the density profiles of the head and tail groups along the three spatial directions between the surfactant and the lignitic surface suggest that the adsorption process is spontaneous. The self-diffusion coefficients show that the presence of NPEO10 causes higher water mobility by improving the hydrophobicity of lignite.

The flotation and adsorption of mixed collectors on oxide and silicate minerals

The analysis of flotation and adsorption of mixed collectors on oxide and silicate minerals is of great importance for both industrial applications and theoretical research. Over the past years, significant progress has been achieved in understanding the adsorption of single collectors in micelles as well as at interfaces. By contrast, the self-assembly of mixed collectors at liquid/air and solid/liquid interfaces remains a developing area as a result of the complexity of the mixed systems involved and the limited availability of suitable analytical techniques. In this work, we systematically review the processes involved in the adsorption of mixed collectors onto micelles and at interface by examining four specific points, namely, theoretical background, factors that affect adsorption, analytical techniques, and self-assembly of mixed surfactants at the mineral/liquid interface. In the first part, the theoretical background of collector mixtures is introduced, together with several core solution theories, which are classified according to their application in the analysis of physicochemical properties of mixed collector systems. In the second part, we discuss the factors that can influence adsorption, including factors related to the structure of collectors and environmental conditions. We summarize their influence on the adsorption of mixed systems, with the objective to provide guidance on the progress achieved in this field to date. Advances in measurement techniques can greatly promote our understanding of adsorption processes. In the third part, therefore, modern techniques such as optical reflectometry, neutron scattering, neutron reflectometry, thermogravimetric analysis, fluorescence spectroscopy, ultrafiltration, atomic force microscopy, analytical ultracentrifugation, X-ray photoelectron spectroscopy, Vibrational Sum Frequency Generation Spectroscopy and molecular dynamics simulations are introduced in virtue of their application. Finally, focusing on oxide and silicate minerals, we review and summarize the flotation and adsorption of three most widely used mixed surfactant systems (anionic-cationic, anionic-nonionic, and cationic-nonionic) at the liquid/mineral interface in order to fully understand the self-assembly progress. In the end, the paper gives a brief future outlook of the possible development in the mixed surfactants.

Synergistic Adsorption and Flotation of New Mixed Cationic/Nonionic Collectors on Muscovite

The mixed cationic collector cetyltrimethylammonium chloride (CTAC) and nonionic collector octanol (OCT) was found to exhibit a synergistic effect on the flotation and adsorption of muscovite. To understand the underlying synergistic mechanism, flotation, contact angle, surface tension, and adsorption measurements were carried out. The results obtained from flotation measurements indicated that the mixed CTAC/OCT exhibits a better collecting ability than CTAC or OCT. The recovery of muscovite with CTAC only rapidly decreased from 97.25% at pH 2.64 to 75.26% at pH 5.82, followed by a flat horizontal at a pH is higher than 6. In contrast, a high recovery of greater than 85% muscovite was observed using mixed CTAC/OCT at α CTAC = 0.67 (the mole ratio of CTAC:OCT = 2:1) over the investigated pH range. From the surface activity parameters (CMC, γ CMC, Γmax, Amin) estimated from surface measurements and interaction parameters (βm, βσ), in addition to the micellar and interfacial compositions ( x 1 m , x 1 σ ) obtained from the theory of regular solutions, a synergistic effect is evident in the mixed micelle and at the water/air interface. Moreover, the mixed CTAC/OCT at α CTAC = 0.67 exhibited the maximum synergistic interaction. The results obtained from surface tension measurements indicated that the mixed CTAC/OCT exhibits considerably higher surface activities compared to single CTAC or OCT. The contact angle results confirmed that the mixed CTAC/OCT is a better collector than the individual CTAC or OCT for the flotation of muscovite. According to the results obtained from adsorption experiments, compared with that of individual CTAC or OCT, the amounts of CTAC and OCT adsorbed on the muscovite surface are considerably increase in the mixed systems because of co-adsorption. Based on these results, the mixed CTAC/OCT exhibits a remarkable synergistic effect during the flotation and adsorption of muscovite.

Some physicochemical aspects of water-soluble mineral flotation

Some physicochemical aspects of water-soluble mineral flotation including hydration phenomena, associations and interactions between collectors, air bubbles, and water-soluble mineral particles are presented. Flotation carried out in saturated salt solutions, and a wide range of collector concentrations for effective flotation of different salts are two basic aspects of water-soluble mineral flotation. Hydration of salt ions, mineral particle surfaces, collector molecules or ions, and collector aggregates play an important role in water-soluble mineral flotation. The adsorption of collectors onto bubble surfaces is suggested to be the precondition for the association of mineral particles with bubbles. The association of collectors with water-soluble minerals is a complicated process, which may include the adsorption of collector molecules or ions onto such surfaces, and/or the attachment of collector precipitates or crystals onto the mineral surfaces. The interactions between the collectors and the minerals include electrostatic and hydrophobic interactions, hydrogen bonding, and specific interactions, with electrostatic and hydrophobic interactions being the common mechanisms. For the association of ionic collectors with minerals with an opposite charge, electrostatic and hydrophobic interactions could have a synergistic effect, with the hydrophobic interactions between the hydrophobic groups of the previously associated collectors and the hydrophobic groups of oncoming collectors being an important attractive force. Association between solid particles and air bubbles is the key to froth flotation, which is affected by hydrophobicity of the mineral particle surfaces, surface charges of mineral particles and bubbles, mineral particle size and shape, temperature, bubble size, etc. The use of a collector together with a frother and the use of mixed surfactants as collectors are suggested to improve flotation.