Marcela Achimovičová

Hallmarks of mechanochemistry: from nanoparticles to technology

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

Influence of mechanical activation on the alkaline leaching of enargite concentrate

Abstract In this study the alkaline leaching of enargite Cu3AsS4 (El Indio, Chile) in the medium of sodium sulphide was investigated. The rate of leaching can be influenced by the pre-treatment consisting of mechanical activation of the concentrate in a stirring ball mill (attritor). The XRD and XPS methods used to characterise the bulk and surface properties of the solid phase after leaching have shown that arsenic extraction from enargite leads to its transformation to covellite CuS. On the basis of the value of experimental activation energy (62 kJmol−1) we can conclude that a chemical reaction is the rate-determining process of the reaction between Cu3AsS4 and Na2S. The applied procedure represents a potentionality of de-arsenification of sulphidic concentrates and preparation of a charge convenient for further processing, e.g., by pyro-treatment.

Leaching of antimony and mercury from mechanically activated tetrahedrite Cu12Sb4S13

Abstract In this study the physico-chemical transformations and leachability of antimony and mercury from tetrahedrite concentrate mechanically activated by intensive grinding in a planetary mill were investigated. It has appeared that the leaching of antimony and mercury from tetrahedrite in alkaline solution of sulphide solution is a structure-sensitive reaction. The temperature dependence of both reactions investigated in the temperature interval 298–363 K has shown that these reactions do not involve any change in mechanism. The experimental activation energies found in this connection were E = 7 kJ mol −1 for the leaching of mercury and E = 33 kJ mol −1 for the leaching of antimony.

Leaching and dissolution of a pentlandite concentrate pretreated by mechanical activation

Abstract This paper describes the properties and leaching behaviour of a pentlandite concentrate mechanically activated by grinding in an attritor (stirring ball mill) in H2O for 15–60 min. It appears that mechanical activation brings about an increase in specific surface area and a decrease in the content of crystalline phase of the mineral components pentlandite (Fe,Ni)9S8, chalcopyrite CuFeS2 and pyrite FeS2. These transformations are accompanied by mechano-chemical surface oxidation of individual minerals and the formation of water-soluble Ni, Cu and Co compounds. The process of mechanical activation in water and subsequent leaching in an acid solution (Fe2(SO4)3) proceeds in two steps. In the first step (dissolution in H2O), 46% of Ni, 29% of Cu and 29% of Co dissolve; and the rest can be extracted in the second step (leaching in Fe2(SO4)3 solution). Mechanical activation affects the selectivity of extraction of individual minerals.

Properties of a new nanosized tin sulphide phase obtained by mechanochemical route

Abstract The paper deals with the properties of a new 4H-SnS2 phase (N-phase) synthesized together with berndtite 4H-SnS2 by a mechanochemical route from elemental tin and sulphur. The surface and bulk properties of SnS2 phases were verified by surface area measurements, particle size analysis, electron microscopy, XRD, Mossbauer spectroscopy and chemical dissolution methods. The particles of synthesized product are 12–18 nm in size and during milling, secondary particles (aggregates) are formed that are 20–60 μm in size. The particle size and a high developed surface area (7–21 m2 g−1) greatly influence the solid–liquid reaction and solid transformations of mechanosynthesized tin sulphide products.

Structural and morphological study of mechanochemically synthesized tin diselenide

Mechanochemical synthesis of tin diselenide, SnSe2, was performed by high-energy milling of tin and selenium powder in a planetary ball mill. The mechanosynthesized product was characterized by X-ray diffraction, 119Sn MAS NMR and 119Sn Mossbauer spectroscopy, which confirmed the presence of the hexagonal SnSe2 phase after 100 min of milling. The size and morphology of tin diselenide particles were studied by specific surface area measurements, and transmission electron microscopy. The specific surface area of powders was found to increase with increasing time of mechanochemical synthesis. Electron diffraction revealed reflections that correspond to hexagonal SnSe2 modification. TEM observations show that the mechanochemical preparation route results in the formation of nanosized thick barrel-shaped SnSe2 platelets. SnSe2 nanoparticles show good absorption in the visible region of the UV-Vis optical spectrum and they evidence direct and indirect types of transitions in the lattice.

Combined chemical and bacterial leaching of ultrafine ground chalcopyrite

Abstract The changes in surface properties and the leaching of chalcopyrite CuFeS 2 after ultrafine grinding are examined. Surface area measurement and photoelectron spectroscopy (XPS) were used for characterization of the ground samples. A gradual decrease in the particle size, from 32 μm, for as received CuFeS2, to 2 μm, for the sample ground for 60 min, as well as increasing the surface area from 0.23 m 2 g −1 to 2.68 m2 g −1 for equal samples was observed. Analysis of the XPS line of sulphur S2 p electrons has shown the existence of sulphur in three different chemical forms: S 2- , So and S 6+ . The ground samples exhibited a greater proportion of higher oxidation states. The samples were chemically preleached with an acid solution of Fe(III) sulphate to an equal conversion degree (ϵ cu = 25%), characterized and subsequently leached by the bacteria Thiobacillus thiooxidans . While the rate of chemical leaching is proportional to the increase in CuFeS 2 surface area, the rate of subsequent bacterial leaching is limited by 15 min grinding. The different behaviour of the samples ground for a long time may be explained by differences in the chemical composition of surface layers.

Characterization of mechanochemically synthesized lead selenide

Mechanochemical synthesis of lead selenide PbSe nanocrystals was performed by high-energy milling of lead and selenium powders in a planetary ball mill. The structure properties of synthesized lead selenide were characterized by XRD analysis that confirmed crystalline nature of PbSe nanocrystals. Calculated average size of PbSe crystallites was 37 nm. The methods of particle size distribution analysis, specific surface area measurement, SEM and TEM were used for the characterization of surface and morphology of PbSe nanocrystals. SEM analysis revealed agglomerates of PbSe particles. However, HRTEM analysis confirmed perfect stoichiometric PbSe cubes with NaCl structure as well. UV-VIS-NIR spectrophotometry was used to confirm the blue shift of the small particles occurring in the powder product obtained by the mechanochemical synthesis.

Chalcogenide mechanochemistry in materials science: insight into synthesis and applications (a review)

The aim of this paper on recent development in chalcogenide mechanochemistry is to provide a comprehensive review of advances achieved in the field of mechanochemical synthesis of nanocrystalline binary, ternary and quaternary chalcogenides and their nanocomposites. The synthetic approaches from elements and compounds are reviewed. The current focus of mechanochemical synthesis is on materials with potential utilization in future. In order to demonstrate the suitability of mechanochemically prepared chalcogenides for various applications, the concrete examples of the utilization of these materials in materials engineering, bioimaging and cancer treatment are provided. The possibility of scaling for industrial applications is also reviewed. The simplification of the synthesis processes with their reproducibility and easy way of operation, ecological safety and the product extraordinariness (nanoscale aspects) emphasizes the suitability of mechanochemistry application in chalcogenide synthesis.

Ultrafast mechanochemical synthesis of copper sulfides

Covellite, CuS and chalcocite, Cu2S were prepared within a few seconds by ball milling of the elemental precursors. The morphology of the used copper, related to its preparation method, was found to be the key factor for the ultrafast reaction. The explosive character of the reaction was monitored by the gas pressure changes in the milling vessel and the reaction progress was pursued by X-ray diffraction analysis and Soxhlets extraction. The local temperature at the contact site between the milling media and the milled mixture at the time of explosion was calculated as 950 °C for CuS and 700 °C for Cu2S. The mean crystallite size of the prepared products was 15 nm for CuS and 65 nm for Cu2S.