The surface chemical properties of spodumene, a pyroxene mineral typically found in lithium-rich pegmatites, are key to improve its recovery by means of flotation. Without this information, it is ...very difficult to find a collector that prefers the spodumene surface over that of associated aluminosilicates. The crystal structure of spodumene includes chains of Si-centered tetrahedra and Al-centered octahedra, with Li occupying cavities between the polyhedra. In this work, density functional theory (DFT) calculations are used for a small group of atoms of the mineral crystal to determine the termination of the (110) surface, the weakest plane, and then to determine the most energy-favorable deprotonation reaction. The excess charge generated by the removal of one hydrogen in the deprotonation reaction is distributed over the surface atoms of the spodumene cluster. Then, molecular dynamics simulations are used to study the adsorption of water and alkali and alkaline-earth metal cations from concentrated solutions on the surface (110) of a large slab of spodumene, both neutral and negatively charged. Results include density profiles of adsorbed cations, orientation profiles of water molecules close to the mineral surface for different cations, and the distance at which the mineral surface becomes neutral or reverses the charge. The new results on the surface chemistry of spodumene should allow reinterpretation of available data from spodumene flotation.
This work comprises a comparison between
Eucalyptus and
Pinus radiata pulp fibres, as raw materials for producing nanofibrils. The cellulose nanofibrils were produced mechanically and ...chemi-mechanically. Series of the fibres were subjected to a TEMPO mediated oxidation to facilitate the homogenization. The contents of carboxyl acids after the pre-treatment indicated a favourable situation for producing nanofibrils using
Eucalyptus pulp fibres as raw material. However, films made of
P. radiata-based nanofibrils evidenced less shrinkage and higher transparency levels, which were related to a higher fibrillation of the pulp fibres. The energy consumption during homogenization was quantified. The results demonstrated that for a given number of passes through the homogenizator, TEMPO pre-treatment will facilitate the homogeneous fibrillation of a given fibre. This implies that less energy is required for producing nanofibrils with homogeneous sizes.
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•Adsorption on silica follows Cs+>K+>Na+>Li+ and Ca2+>Mg2+.•Cation adsorption on anionic flocculant chains follows inverse series than silica.•Adsorption leads to 3D networks which ...resistance depends on the cation.•Silica and anionic flocculant lead to suspensions with high viscosity.•Silica and cationic flocculant lead to low viscosity suspensions.
The effect of various seawater electrolytes on the zeta potential and viscosity of silica suspensions has been studied as a function of electrolyte concentration, pH, flocculant and shear rate. Salts were alkali and alkaline-earth metal chlorides. The magnitude of the negative zeta potential of silica as a function of pH for monovalent cations follows Li+>Na+>K+>Cs+ implying that adsorption follows Cs+>K+>Na+>Li+. In the presence of divalent cations, the magnitude of the negative zeta potential as a function of pH decreases greatly following Mg2+>Ca2+, implying that adsorption follows Ca2+>Mg2+. Regarding the flocculant in solution, molecular simulations indicate that repulsion between anionic acrylate units causes the polymer to adopt expanded tertiary conformations, however with cations this repulsion is shielded causing the polymer to fold into balled-up conformations. The adsorption of cations on anionic flocculant chains follows inverse series than silica, i.e., Li+>Na+>K+>Cs+ and Mg2+<Ca2+. The different ability of silica and flocculant to adsorb cations leads to force fields that create three-dimensional networks of particles with resistance depending on the cation. The viscosity of silica suspensions formulated at 0.5M salt and pH 7 in anionic flocculant follows KI>KCl>NaCl>MgCl2> water, and in cationic flocculant follows KI<KCl<NaCl<MgCl2< water. In anionic flocculant, the counterion is the same for silica and flocculant leading to strong particle-flocculant interaction and suspensions with high viscosity. The resistance of the particle networks formed are weakened only slightly as the shear stress increases In cationic flocculant, the cation is the counterion of silica while the anion is the counterion of flocculant, their ionic atmospheres are different giving rise to weak particle-flocculant interaction and low viscosity suspensions. The resistance of such networks is increasingly weakened as the shear rate increases. The higher the pH, the higher the repulsion, and the lower the viscosities of the suspensions formulated with either flocculant.
•Crop diversity, directly and indirectly, promoted pest control in cotton fields.•Higher areas of forest promoted whitefly predation in cotton fields.•Larger average patch size in the landscape ...contributed to pest problems in cotton fields.•Presence of whiteflies reduced aphid predation likely due to predator–prey switching behavior.•Optimizing crop diversity and reducing field size is a promising habitat management strategy for pest control in cotton.
Insect herbivore abundances in agricultural fields partly depend on surrounding landscape compositional heterogeneity (e.g., landscape complexity). Landscape complexity can directly (e.g., dilution of host crops) and indirectly (promoting herbivore biocontrol) regulate herbivores in agricultural fields. While much is known about direct (e.g., resource concentration) and indirect effects (i.e., promoting biocontrol) of landscape complexity on herbivore populations, more work is needed to study whether landscape complexity can regulate herbivore populations by mediating within field multi-species interactions among herbivores and their shared natural enemies. During 2019 and 2020, we estimated Bemisia tabaci and Aphis gossypii abundances, their dominant predators (coccinellids, spiders, Orius spp., and Geocoris spp.), and their interaction (using molecular analysis) in 38 cotton fields along a gradient of landscape diversity across Georgia, USA. Within cotton fields, we assessed the effect of predator abundances, their frequency of feeding on herbivores, and the correlation between herbivore abundances (B. tabaci and A. gossypii) on the B. tabaci and A. gossypii abundance. At the landscape scale, crop diversity and different cover types influenced the abundance of B. tabaci and A. gossypii within cotton fields. We found a complex interaction among pests at the field scale, with higher aphid abundance correlated with decreased whitefly abundance. Our results support crop diversification for improving suppression of generalist pests in cotton landscapes through promoting biocontrol and diluting host crop area. Our result further suggests that the landscape complexity effect on whiteflies can indirectly mediate aphid abundance in cotton fields, indicating the importance of within field species interactions.
Molecular dynamics simulations are used to study adsorption of cations on the (010) kaolinite edge surface at and above the pH of zero charge. The cation solutions are highly concentrated and include ...alkali and alkaline-earth metals. It is known that the pH-dependent edge surface of kaolinite is more reactive than the basal surfaces and more eager to adsorb metal ions; however, knowledge of the atomic scale is scarce regarding the structure of the surface edge, charge distribution, solvation, and structure of layers of adsorbed cations. First, ab initio calculations are used to determine the energetically most favorable surface terminations and the distribution of partial atomic charges on both neutral (protonated) and negatively charged (deprotonated) edge surfaces of kaolinite. Then, molecular dynamics simulations are used to study the solvation of kaolinite and the adsorption of cations. Results include density profiles of adsorbed cations, orientation profiles of water molecules close to the mineral surface for different cations, and the distance at which such surfaces become neutral or reverse their charges. Results compare well with available experimental and simulation data. Findings are expected to contribute to the selection or design of organic compounds that effectively adhere to kaolinite in aqueous electrolyte solutions in water recovery processes.
Quartz and corundum surfaces in water are capable of adsorbing and releasing protons, a behavior attributed to the amphoteric character of their silanol and ab initio calculations are used to obtain ...different charge densities on crystalline (101) quartz and (001) corundum surfaces and the corresponding charge delocalization after deprotonation of the silanol and aluminol groups, respectively. Then, classical molecular dynamics simulations are used to study the interaction of water with the charged quartz and corundum surfaces in the presence of aqueous solutions of monovalent alkali and alkaline-earth metal chlorides. Results include density profiles of adsorbed cations, and the effect of cations on the orientation profiles of water molecules close to the mineral surfaces and the distance at which such surfaces become neutral or reverse their charges. In all cases where there are experimental or simulation data, the results here compare very well. The adsorption density of cations on quartz increases with the size of the cations, either monovalent or divalent. The density of adsorbed monovalent cations on corundum decreases for larger cation sizes, while this behavior on quartz is the opposite. In both cases the adsorption of cations is enhanced by the increase of the surface charge. Adsorption on corundum is much more extensive compared to that on quartz for all surface charges and cations. The sequence of simulations of cation adsorption on silica and alumina provide support to the idea that high isoelectric point materials preferentially adsorb well-hydrated cations and low isoelectric point materials preferentially adsorb poorly hydrated cations. The results of this work are expected to contribute to improving current knowledge on the interaction of mineral oxides with macromolecules, such as polyelectrolytes in solid–liquid separation processes and biomolecules in lung inflammatory processes.
Stingless bees such as Partamona helleri Friese play important roles in pollination of native plants and agricultural crops in the Neotropics. Global concerns about declining bee populations due to ...agrochemical pollutants have, however, been biased towards the honey bee, Apis mellifera Linnaeus. Here, we analysed the unintended effects of commercial formulations of a neonicotinoid insecticide, imidacloprid, and a fungicide mixture of thiophanate-methyl and chlorothalonil on color preference, respiration rates and group locomotory activities of both P. helleri and A. mellifera. Our results revealed that P. helleri foragers that were not exposed to pesticides changed their color preference during the course of a year. By contrast, we found that pesticide exposure altered the color preference of stingless bees in a concentration-dependent manner. In addition, imidacloprid decreased the overall locomotion of both bee species, whereas the fungicide mixture increased locomotion of only stingless bees. The fungicide mixture also reduced respiration rates of forager bees of both species. Forager bees of both species altered their color preference, but not their locomotory and respiration rates, when exposed to commercial formulations of each fungicidal mixture component (i.e., chlorothalonil and thiophanate-methyl). Our findings emphasize the importance of P. helleri as a model for Neotropical wild pollinator species in pesticide risk assessments, and also the critical importance of including groups of agrochemicals that are often considered to have minimal impact on pollinators, such as fungicides.
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•Apis mellifera and Partamona helleri exhibited different color preference patterns.•Partamona helleri color preference was altered by insecticides and fungicides.•Fungicide mixture-exposed P. helleri showed altered locomotion and respiration rate.•Honeybees may not always be a proxy for pesticide risks imposed on stingless bees.
A population balance model based on a detailed literature review is used to describe coagulation and flocculation kinetics as well as the time evolution of aggregate size distribution in a turbulent ...shear flow simultaneously with the breakage and restructuring of aggregates. The fractal nature and permeability of the aggregates and their evolution with time are also part of the model. Restructuring is absent in coagulation with soluble salts, but is present in flocculation caused by large polyelectrolyte molecules; in the latter, aggregates never reach a steady-state size, but a size that decreases gradually through particle and polymer rearrangement. The model is tested against available experimental data for monodisperse polystyrene particles coagulated with hydrated aluminium sulphate at different shear rates, and precipitated calcium carbonate flocculated with a cationic polyelectrolyte of very high molecular weight at different flocculant dosages. The numerical solution of the model requires adjusting three parameters, i.e, maximum collision efficiency (αmax), critical force needed for the breakage of the aggregates (B) and rate of aggregate restructuring (γ), which are obtained from minimising the difference between experimental data and model predictions. The model studied for the two very different systems shows excellent agreement with experimental flocculation kinetics and a reasonably good fit for aggregate size distributions. The model is most sensitive to the fragmentation rate through parameter B, somewhat less to the collision efficiency through parameter αmax and little to γ. When the aggregates undergo restructuring, properties such as permeability, breakage rate and collision rate change considerably over time. When the aggregates are permeable, the collision frequency is significantly smaller than when they are impervious.
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•A population balance model is used to describe flocculation kinetics.•Fractal nature and permeability of aggregates and its evolution with time are considered.•The model shows excellent agreement with data available in the literature.•The model is most sensitive to fragmentation.•Permeability, breakage and collision rates change considerably with restructuring.
The plant-based biopesticides have been proposed as insect pest control tools that seem to be safer for the environment and human health when compared to synthetic conventional molecules. However, ...such assumptions are generally made without considering the absence of detrimental effects on sublethally-exposed non-target organisms or showing the physiological basis of the selective action of such botanical products. Thus, by using in silico-based and in vivo toxicological approaches, the present investigation aimed to disentangle the ecotoxicological selectivity of clove, Syzygium aromaticum, essential oil against the aphid Rhopalosiphum maidis and the non-target ladybeetle, Coleomegilla maculata. We also investigated whether the sublethal exposure to clove essential oil would affect the locomotory and predatory abilities of C. maculata. We found that the clove essential oil concentration estimated to kill 95% (LC95: 0.17 μL/cm2) of the aphids was lethal to <18% of C. maculata. Indeed, our in silico results reinforced such differential susceptibility, as it predicted that eugenol and β-caryophyllene (i.e., the clove essential oil major components) bound to three potential molecular targets (i.e., transient receptor potential (TRP) channels, octopamine, and gamma-aminobutyric acid (GABA) receptors) of the aphids but only to the octopamine receptors of the ladybeetles. Additionally, the ladybeetles that were exposure to the clove essential oil exhibited unaffected abilities to locomote and to prey upon R. maidis aphids when compared to unexposed ladybeetles. Thus, by displaying lower toxicity against the ladybeetles, the clove essential oil represents a safer alternative tool to be integrated into programs aiming to manage aphid infestations.
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•Clove essential oil showed high selectivity against predatory ladybeetles.•Eugenol and β-caryophyllene were the major components of clove essential oil.•Oil major components bound to aphid's transient receptor potential (TRP) channels.•Eugenol and β-caryophyllene bound to aphids' γ-aminobutyric acid (GABA) receptors.•Octopamine receptors of both species were targeted by eugenol and β-caryophyllene.
The mining industry has resorted to using seawater while trying to find a solution to the water shortage, which is severe in some regions. Today, the industry looks to tailings dams to recover more ...water and, thus, increase recirculation. The migration of interstitial water due to the consolidation of particle networks can give rise to large water mirrors in different dam areas. These pools can contain enough water to be recovered and recirculated if the external stress caused by the weight of the pulp exceeds the compressive yield stress. The density and rheological properties of the discarded pulps determine the feasibility of water expulsion during tailings consolidation. As these conditions are largely established in the thickening stage, it is necessary to revisit operations, looking at the dam as a water source. Thus, a thorough understanding of the compressive properties that determine the level of consolidation of typical pulps and their relationships to aggregate properties, such as size and fractal dimension, is crucial. Here, the effect of two types of water, industrial water and synthetic seawater, on kaolin flocculation, sedimentation rate, yield stress, and compressive yield stress were studied. In addition, the relationship of these properties with the flocculant dose and the resulting aggregate size and fractal dimension was examined. One promising finding to practitioners was that salt and small doses of high molecular weight flocculant improved the consolidation of kaolin slurries under compression. These conditions generated low compressive yield stress compared to fresh water and water with low salt content, favoring the consolidation of the pulps and the release of water.
