Effect of Magnesium on the Hydrophobicity of Sphalerite

The use of untreated recycled water has negative effects in the flotation of zinc sulfide ores due to the presence of dissolved species, such as magnesium and calcium. Although it has been found that magnesium is a more potent depressant than calcium, it has not been investigated in this role or for the effect of adding sodium carbonate. The results of an investigation to evaluate the effect of magnesium on the hydrophobicity of Cu-activated sphalerite conditioned with Sodium Isopropyl Xanthate (SIPX) are presented. Zeta potential of natural and Cu-activated sphalerite as a function of the conditioning pH and Cu(II) concentration, respectively, was first evaluated. Later, the effect of pH and presence of magnesium on the contact angle of Cu-activated sphalerite conditioned with SIPX was studied; it was also evaluated the effect of sodium carbonate to counteract the effect of magnesium. Cu-activation enhances the zeta potential of sphalerite up to a concentration of 5 mg/L. Contact angle tests, thermodynamic simulation, and surface analysis showed that magnesium hydroxide precipitates on the sphalerite surface at pH 9.6, decreasing its hydrophobicity. Addition of sodium carbonate as alkalinizing agent precipitates the magnesium in the form of a species that remained dispersed in the bulk solution, favoring the contact angle of Cu-activated sphalerite and, consequently, its hydrophobicity. It is concluded that the use of sodium carbonate as alkalinizing agent favors the precipitation of magnesium as hydromagnesite (Mg5(OH)2(CO3)4∙4H2O) instead of hydroxide allowing the recovery of sphalerite.

Nanoplastic transport in aqueous environments: The role of chemo-electric properties and hydrodynamic forces for nanoplastic-mineral interaction.

The fate and transport characteristics of nanoplastic (NP) through different environmental systems is largely governed by physio-chemical processes and their specific interaction with environmental constituents (i.e., minerals, dissolved species, suspended particles). A hydrodynamic component present in almost all terrestrial and marine aqueous environments impact the physio-chemical processes micron-scale is largely overlooked in NP transport studies. Therefore, we tested the interaction behavior of nanosized plastic polystyrene particles of various coatings in the presence of minerals abundant in the Earth crust within a hydrodynamic continuum representing flow rates from groundwater to surface water systems. Our batch experiments show that particle-mineral adsorption is largely driven by the magnitude of opposite charge configurations, which is either produced by mineral type or specific nanoplastic surface coating. Zetapotential serves as a good predictor of adsorption between uncoated and carboxyl-coated polystyrene with minerals. It fails, however, to predict adsorption behavior between NH2 coated polystyrene and apatite or feldspars, due to the more complex and varying compositions of these minerals. Incorporating the hydrodynamic force component into the particle- mineral interaction scheme reproduces those adsorption trends at slow flowrates of 1e-04 m/d. However, increasing flow rates by a factor of 100 modifies charge-driven adsorption between minerals and plastics. This study highlights the unabating importance of hydrodynamic conditions when predicting nanoplastic transport in different subsurface environments, and has implications for nanoplastic behavior in both terrestrial and marine aqueous environments.

DFT Investigation of the Molecular Properties of the Dimethylglyoximato Complexes [M(Hdmg)2] (M = Ni, Pd, Pt)

Important applications of the NiII, PdII and PtII complexes [M(Hdmg)2] (H2dmg = dimethylglyoxime) stem from their metal...metal stacked virtually insoluble aggregates. Given the virtual insolubility of the materials, we postulated that the rare reports on dissolved species in solution do not represent monomolecular species but oligomers. We thus studied the structural and spectral properties of the monomolecular entities of these compounds using density functional theory (DFT) and time-dependent DFT computations in dimethyl sulfoxide (DMSO) as a solvent. The molecular geometries, IR and UV-vis spectra, and frontier orbitals properties were computed using LANL2DZ ecp and def2TZVP as basis sets and M06-2X as the functional. The results are compared with the available experimental and other calculated data. The optimised molecular geometries proved the asymmetric character of the two formed O–H…O bonds which connect the two Hdmg‒ ligands in the completely planar molecules. Calculated UV-vis spectra revealed the presence of three absorptions in the range 180 to 350 nm that are red-shifted along the series Ni–Pd–Pt. They were assigned to essentially ligand-centred π−π* transitions in part with metal(d) to ligand(π*) charge transfer (MLCT) contributions. The notorious d‒p transitions dominating the colour and electronics of the compounds in the solid-state and oligomeric stacks are negligible in our monomolecular models strongly supporting the idea that the previously reported spectroscopic observations or biological effects in solutions are not due to monomolecular complexes but rather to oligomeric dissolved species.

Wormhole dynamics, competition for the flow and changes in transport behavior: an intermediate-scale experiment

<p>Salt flats (Salares) are complex evaporitic systems of economic interest and environmental value. On the one hand, these aquifers are usually exploited for variety of minerals, including dissolved species (e.g. Lithium and Potassium) extracted from the brines. On the other hand, the genesys of salares favors that they are surrounded by uncommon ecosystems, which must be protected. In this context, it is fear that brine pumping might favor the development of dissolution channels (Wormholes) that could connect the Salar nucleus with the environmental sensitive surroundings. Thus, a full understanding of the conditions and processes involved in wormhole formation and evolution has to be achieved. The hydraulic and geochemical conditions for conduits growth have been widely discussed in carbonate environments, while little has been done in halitic and gypsum environments. But we unknowledge experimental works aimed at understanding wormhole dynamics and the mechanism of competition for the flow that influence dissolution pattern evolution.</p><p>In this study, we want to improve the understanding of multiple wormholes growth in the context of wormhole competition and consequent changes in transport behaviors. For that purpose, we designed and performed a laboratory intermediate-scale tank experiment under controlled conditions. Halite in the form of granular medium is used to reproduce the aquifer. Hydrodynamics and geochemical conditions are set as to reproduce a dominant wormhole dissolution regime. Several coloured tracer tests are carried out to characterize the medium before, during and after the dissolution experiment.  Tracer concentration, hydrogeochemical and flow parameters, as well as tank images are continuously recorded. In particular, the use of fluorescent tracer jointly with image processing analysis highlights wormholes growth, shape and propagation through the medium at different times. Experimental results allow visualizing and analyzing several features related to wormhole competition, e.g. wormhole growth rate and density evolution, as well the redistribution of the flow towards areas where dominant wormholes are developing. Results are compared to available numerical and analytical solutions. Lastly, the interpretation of BTCs allows to understand changes in flow and trasport behavior and related processes, given the developing dissolution pattern.</p>

Realizing the potential of metallic iron for environmental remediation: Flee or adapt?

The evidence that metallic iron (Fe0) is not an environmental reducing agent has been declared to be a claim. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argumentation has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to graduate chemists, as it is a century old electrochemistry knowledge. Nevertheless, the peer review literature on "remediation using Fe0" seems to be aggressively controlled by self-appointed experts (e.g., journal editors) who are not tolerating any alternative thinking. This communication demonstrates the fallacy of the view that Fe0 donates any electron to a dissolved species. The sole goal is to reconcile a proven efficient technology with his scientific roots, and enable the design of better Fe0 remediation systems.

Welcome to Raman Spectroscopy: Successes, Challenges, and Pitfalls

Geoscientists quickly recognized the broad applicability of Raman micro-probe spectroscopy to the Earth and planetary sciences, especially after commercially built microprobe instruments became available in the early 1980s. Raman spectra are sensitive to even minor (chemical or structural) perturbations within chemical bonds in (even amorphous) solids, liquids, and gases and can, thus, help identify, characterize, and differentiate between individual minerals, fluid inclusions, glasses, carbonaceous materials, solid solution phases, strain in minerals, and dissolved species in multi-component solutions. The articles in this issue explore how Raman spectroscopy has deepened and broadened our understanding of geological and extraterrestrial materials and processes.

Mirsid volcanic tuff, alkaline activation, dissolved species, optimum activation time, optimum activating concentration

The purpose of this article is to study the activation of the Mir�id volcanic tuff with NaOH solutions at various concentrations. To be more specific, the work investigated the evolution of the concentrations of species that passed from the tuff into the activating solutions and the quantities of dissolved species from 100 g tuff. The species found in the activating solution were: potassium, magnesium, aluminium and silicon. The shape of the curves - a sudden increase followed by a plateau or a second stage of slower increase - allowed for setting up the optimal activation time at a half-hour. Another finding was the optimal concentration of 1 N for the activating solution. X-ray diffractograms showed the increase of clinoptilolite content in the tuff, thus improving the adsorbent as well as ion exchange properties by activation with NaOH solutions.