Probing the Interaction Mechanism between Benzohydroxamic Acid and Mineral Surface in the Presence of Pb2+ Ions by AFM Force Measurements and First-Principles Calculations

Probing the Interaction Mechanism of Sodium Oleate and Dodecyl Amine with Quartz Surfaces in the Presence of Ca2+ Ions by AFM Force Measurement

Quartz is a key raw material in high-tech fields (such as photovoltaics and semiconductor microelectronics), and the most efficient extraction method of quartz is mineral flotation. Quartz activation plays a crucial role in mineral flotation. However, the mechanism underlying the process remains unclear, and the role of additional metal ions is controversial. In this study, the interaction forces between the quartz surface, the dodecylamine (DDA) cation/sodium oleate (NaOL) anion mixed collectors, and Ca2+ were analyzed using atomic force microscopy in order to systematically explore the activation process of quartz flotation. The results confirmed that the activation process was initialized from NaOL, which was adsorbed on the surface of a calcium-covered quartz surface. The existence of DDA inhibited the binding of Ca2+ to NaOL so that more Ca2+ was adsorbed on the quartz surface to provide the adsorption site for NaOL. Moreover, the best adsorption condition of Ca2+ + NaOL + DDA mixed solution was analyzed by quartz crystal microbalance with dissipation, and it demonstrated that the most stable chemisorption environment on the quartz surface was at pH 11.0. In these circumstances, Ca2+ could first adsorb in a point-like manner on the quartz surface, which was then adsorbed with a mixture of NaOL and DDA. This result showed that, at a specific pH, Ca2+ could encourage the coadsorption of cationic/anionic mixed collectors on quartz. This work provides an important new understanding of the intermolecular interactions that take place during complex mineral flotation processes between chemical additives and mineral surfaces. The methodology used in this study can be easily adapted to different interfacial processes, including water treatment, membrane technology, bioengineering, and oil production.

Flotation Performance and Adsorption Mechanism of a Novel Chelating Collector for Azurite

Thiophosphate compounds have attracted much attention in coordination chemistry, but their deep adsorption mechanism remains underexplored as flotation collectors. The flotation performance and adsorption mechanism of a novel (dibutoxy-thiophosphorylsulfanyl)-acetic acid (CDDP) chelating collector on azurite surfaces were studied by micro-flotation tests, zeta potential measurements, and Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM) analysis. The micro-flotation results indicated that CDDP exhibited superior collecting performances to direct flotation recovery of azurite and floated over 91.44% of azurite at pH 7. For sodium isopentyl xanthate (NaIX) and Benzohydroxamic acid (BHA) collectors, the addition of Na2S still did not show good collection performance. The results of zeta potential, FTIR, XPS and FE-SEM measurements, all confirmed that CDDP showed a better affinity to azurite surfaces than NaIX and BHA. Furthermore, XPS and FE-SEM provided obvious evidence that CDDP could easily react with Cu2+ sites on azurite surfaces. Using the density functional theory (DFT) method, the collection capacity of azurite was CDDP > BHA > NaIX, which exactly matched the micro-flotation results. In addition, this study provided an atomic-scale understanding of the structure–property relationship of CDDP as chelating agents for copper mineral flotation.

Interface Interaction of Benzohydroxamic Acid with Lead Ions on Oxide Mineral Surfaces: A Coordination Mechanism Study

Surface coordination chemistry is important in areas such as adsorption, separation, and catalysts. In this work, surface coordination interactions of benzohydroxamic acid (BHA) with the lead ion [Pb(II)] adsorbed on the cassiterite surface have been investigated by first-principles calculations due to its great significance in froth flotation. Cluster calculations show that BHA possesses the weakest chelation with Pb(II) due to the electron withdrawal ability of the benzyl ring in comparison with other hydroxamic acids. Pb(II) thermodynamically prefers to react with the cassiterite surface rather than BHA. On the other hand, the partial density of states and the atomic overlap populations have consistently verified that the adsorption of BHA results in a better symmetry in electron densities than the hydrated Pb(II). The electron density maps and the electronic localization functions have further visualized the rearrangement of the 6s² lone pair around the lead atom. It can be concluded that the surface coordination mechanisms of Pb(II) on oxide minerals can be attributed to the coordination ability of BHA and the unique electronic structure of Pb(II), which accounts for the reported better flotation performance of the pre-assemble strategy than the pre-activating approach. This work sheds some new light on the unique coordination activation mechanism of metal ions on oxide mineral surfaces. It should be instructive to design and screen new environment-friendly flotation reagents and flotation flowsheets.

Effects of Hydration on the Adsorption of Benzohydroxamic Acid on the Lead-Ion-Activated Cassiterite Surface: A DFT Study

The strategy of enhancing the surface activity by preadsorption of metal ions (surface activation) is an effective way to promote the adsorption of surfactant on surfaces, which is very important in surface process engineering. However, the adsorption mechanism of surfactant (collector) on the surface preadsorbed by metal ions in the explicit solution phase is still poorly understood. Herein, the effects of hydration on the adsorption of benzohydroxamic acid (BHA) onto the oxide mineral surface before and after lead-ion activation are investigated by first-principles calculations, owing to its importance in the field of flotation. The results show that the direct adsorption of BHA on the hydrated surface is not thermodynamically allowed in the absence of metal ions. However, the adsorption of BHA onto the lead-ion-activated surface possesses a very low barrier and a very negative reaction energy difference, indicating that the adsorption of BHA on hydrated Pb²⁺ at cassiterite surface is very favorable in both thermodynamics and kinetics. In addition, the adsorption of BHA results in the dehydration of hydrated Pb²⁺. More interestingly, the surface hydroxyl groups could participate in and may promote the coordination adsorption through proton transfer. This work sheds some new lights on understanding the roles of interfacial water and the mechanisms of metal-ion surface activation.

Determination and modulation of the typical interactions among dispersed phases relevant to flotation applications: A review

Flotation is a process involving multi-components, multi-scales, and gas-liquid-solid three phases, where the material separation is achieved based on the difference in surface hydrophobicity of various constituents. In a flotation system, fluids are usually regarded as the continuous phase, while the dispersed phases refer to scattered particles, bubbles, and droplets with low solubility as a dispersion that is surrounded by the aqueous environment. Fundamentally, the interactions among dispersed phases exist throughout the flotation process, and play distinct roles during different periods. For example, the liquid collector-solid, solid-solid, bubble-bubble and gas bubble-solid interactions are closely associated with the particle surface modification, particle behavior, bubble size evolution and separation in flotation, respectively. Therefore, the influences of each stage are all worthy of concern, and should be spared sufficient attention, which requires to formulate a horizontal writing structure. In this review, instead of summarizing all available characterization techniques or measurements, certain typical examples or methods were consciously chosen to perform analysis or comparison, aiming to summarize recent studies on the determination and modulation of dispersed phase interactions. The determination on the interactions among dispersed phases is helpful for fundamentally understanding the microcosmic process connotations, and their modulation contributes to firmly providing macroscopic optimization schemes for practical applications. By integrating some typically available theoretical calculations and experimental measurements related to the dispersed phase interactions, the present article is devoted to revealing the influential factors, finding out the current challenges or knowledge gaps, and affording certain references or suggestions for future investigations.