Molecular self-assembly, a promising strategy for modifying surfaces on the nanometer scale, is essential for developing functional materials in electronics, catalysis, or twodimensional (2D) crystal engineering. In this work, we are shifting attention to the physical chemistry of the process at a molecular level through a study of the effect of concentration on the overall process of self-assembled molecular network formation using scanning tunneling microscopy. The overarching idea is to correlate experimental results with analytical thermodynamic models to improve the understanding of supramolecular chemistry in two dimensions by obtaining quantitative data. For this purpose, a series of isophthalic acids have been chosen as a model system. The effect of the concentration on the adsorption behavior, focusing on the surface coverage, has been evaluated at the nanoscale. Our results confirm the existence of a critical concentration above which self-assembly occurs and that a change in the molecular structure (the length of the alkyl chain) has a remarkable impact on the value of this critical threshold. Finally, we report highly cooperative behavior in studied systems, which presents one of the rare examples of quantitative measurement of cooperative phenomena at the liquid/solid interface.
Sulfidic copper−lead−zinc tailings can pose a significant environmental threat, ranging from generation of acid mine drainage (AMD) to dam failures. On the other hand, they can also be considered as low-grade ore resources for zinc and copper provided that novel economically feasible metal extraction and metal recovery techniques are developed. Due to the low metal concentrations in these resources, the leaching will generate dilute leachates from which metal recovery is a challenge. Ion flotation is a foam separation technique capable of recovering metal ions from dilute aqueous leachates. In this paper, ion flotation was applied to separate copper from ammoniacal leachates of microwave-roasted sulfidic tailings samples. The sulfidic tailings were first roasted at 550 °C for 60 min, for the oxidation of sulfide minerals to more easily soluble sulfates using microwave assisted irradiation as heating source. The microwave-roasted material was then leached with a mixture of ammonia and ammonium carbonate solutions. The optimum leaching efficiencies of zinc (86%) and copper (75%) were obtained under the following conditions: liquid-to-solid ratio = 10 mL g -1 , T = 90 °C, [NH3+NH4 + ] = 4 mol L -1 , NH3:NH4 + = 2:1, t = 5 h. From the generated pregnant leach solution, it was possible to selectively separate 85% of copper to the foam phase by ion flotation, with sodium dodecyl sulfate (SDS) surfactant, as colloidal tetraammine copper(II) dodecyl sulfate under the optimized conditions: [SDS]total = 5.85 mmol L -1 , [EtOH] = 0.5 % (v/v), ttotal = 5 h, flotation stages = 3. The zinc that remained in the solution after ion flotation was recovered by precipitation (95%) as basic zinc carbonate.
The modified Debus–Radziszewski reaction was used as a one-pot on-water reaction to allow a greener synthesis of long-chain 1,3-dialkylimidazolium acetate ionic liquids in high yield from long-chain linear amines.
Due to an ever-increasing demand for commodity and technology metals, secondary resources can complement the primary resource supply. Sulfidic mining waste from the Neves-Corvo mine (Portugal) is a pyrite-rich tailing that still contains valuable metals (Cu, Zn) and minor amounts of technology metals (Co, Mn) in the form of sulfides. In this work, by fine-tuning a fast microwave (MW)-assisted oxidative roasting process (5 min, 550 °C), the sulfide minerals containing the desired metals converted to water-soluble sulfate phases, whereas pyrite converted to waterinsoluble magnetite and hematite. The desired metals Cu (76%) and Zn (46%), as well as Co (66%) and Mn (53%), could thus be selectively leached over Fe (2.9%) in water (25 °C, 30 min). The obtained leachates were further purified by selectively precipitating Fe (95%) and As (100%) by a MW-assisted hydrothermal treatment (150 °C, 1 h), leaving Cu, Zn, Mn, and Co in solution for further recovery. In the proposed three-step method, no chemicals other than water were used, and the environmental risks of the final residues were significantly decreased, compared to those of the original sulfidic mining waste.
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