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.

Insight into the Binding Mechanisms of Quartz-Selective Peptides: Toward Greener Flotation Processes.

Mining practices, chiefly froth flotation, are being critically reassessed to replace their use of biohazardous chemical reagents in favor of biofriendly alternatives as a path toward green processes. In this regard, this study aimed at evaluating the interactions of peptides, as potential floatation collectors, with quartz using phage display and molecular dynamics (MD) simulations. Quartz-selective peptide sequences were initially identified by phage display at pH = 9 and further modeled by a robust simulation scheme combining classical MD, replica exchange MD, and steered MD calculations. Our residue-specific analyses of the peptides revealed that positively charged arginine and lysine residues were favorably attracted by the quartz surface at basic pH. The negatively charged residues at pH 9 (i.e., aspartic acid and glutamic acid) further showed affinity toward the quartz surface through electrostatic interactions with the positively charged surface-bound Na+ ions. The best-binding heptapeptide combinations, however, contained both positively and negatively charged residues in their composition. The flexibility of peptide chains was also shown to directly affect the adsorption behavior of the peptide. While attractive intrapeptide interactions were dominated by a weak peptide-quartz binding, the repulsive self-interactions in the peptides improved the binding propensity to the quartz surface. Our results showed that MD simulations are fully capable of revealing mechanistic details of peptide adsorption to inorganic surfaces and are an invaluable tool to accelerate the rational design of peptide sequences for mineral processing applications.

Insights into interphase thickness characterization for graphene/epoxy nanocomposites: a molecular dynamics simulation.

This work presents a molecular dynamics simulation study on the interfacial characterization of graphene/epoxy nanocomposites. In polymeric nanocomposites, the thermo-mechanical properties of a system strongly depend on the characteristics of the interphase region between the matrix and the inclusions. The first step in the characterization of this interphase is to distinguish its border limit (i.e., the interphase thickness). Here, we present a methodology to systematically quantify the interphase thickness based on analyzing the variation of the local mass density profile. To this end, three functions (average accumulated mass density, accumulated standard deviation (ASD) and its first derivative) are successively applied on the local mass density profile. Using this procedure, the interphase limit can be easily detected regardless of the oscillatory nature of the local mass density. The effect of the epoxy crosslinking density and number of graphene layers on the interphase thickness is then investigated, and the results are analyzed by studying the interaction energies, polymer dynamics and distribution quality of reacted and unreacted components, as well as conformational changes of the polymer chains in the interphase region. The results reveal that the crosslinking density is the most influential parameter on the interphase thickness: the higher the crosslinking degree, the thicker the interphase region. To a lower extent, the interaction energy has also an effect on the interphase thickness since there is an inverse relationship between the interaction energy and the crosslinking density in our case study. Overall, the reported findings highlight useful insights into the detection and properties of the interphase region in thermoset composites.

Effect of untreated zirconium oxide nanofiller on the flexural strength and surface hardness of autopolymerized interim fixed restoration resins.

OBJECTIVE: Autopolymerized poly methyl methacrylate (PMMA) resin is commonly used for the construction of interim restorations; however, it has less than optimal mechanical properties. In this article, we evaluated the reinforcing effect of adding untreated zirconia nanoparticles on the flexural strength and surface hardness of this resin. METHODS: A total of 80 specimens were fabricated. Forty each were used for the flexural strength test and for the surface hardness test. The specimens were categorized into four groups of 10 specimens each as follows: pure PMMA, PMMA with 1%, PMMA with 2.5%, and PMMA with 5% weight of untreated zirconia nanofillers. The flexural strength of the specimens was evaluated by the three-point bending test, and the surface hardness was assessed by micro Vickers hardness test. The data obtained from these tests were statistically analyzed using one-way ANOVA and Tukey tests. In addition, the fracture surface characteristics were assessed using scanning electron microscopy. RESULTS: Flexural strength testing showed a significant increase in the group with 2.5% zirconia nanofillers, but not in the groups with 1% and 5% nanofillers. Surface hardness was also significantly increased in the groups with 2.5% and 5% nanofillers, but not in the 1% group. The SEM images showed a highly brittle fracture in the pure PMMA group and noticeably less brittle fracture in the group with PMMA with 2.5% weight of zirconia nanofillers. Several cracks and void were also observed in the group with 5% weight of nanofillers. CONCLUSION: Reinforcement of the autopolymerized acrylic resin with 2.5% weight of untreated zirconia nanofillers significantly increased its flexural strength and surface hardness. CLINICAL SIGNIFICANCE: The interim restorations play an important role in protection of hard and soft oral tissue and providing the critical function and esthetics before the final restoration replacing. Temporary restorations must have sufficient flexural strength to resist deformation during mastication force. Moreover, sufficient surface hardness is also necessary to resist abrasion. The color stability of materials is considered as an important clinical criterion, specifically in esthetics zone. Several materials have been applied to improve the flexural strength and surface hardness for representing clinical success. Zirconia nanoparticles show desirable features, such as high hardness, biocompatibility, and favorable color because of its white color. It seems that the addition of the nano zirconia to acrylic resins can be the appropriate method for improving interim restoration.