Search

for Extractive Metallurgy, Materials Science and Medicine P. Balao*, M. Balao, M. Achimovi£ova, Z. Buj¬akova and E. Dutkova Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, Ko2ice, Slovakia In this review paper recent advances in chalcogene mechanochemistry are described. Three selected areas are being covered, i.e. metallurgy, materials science, and medicine. In extractive metallurgy, the processing of copper arsenic mineral enargite (Cu3AsS4) with the aim of its dearseni cation and subsequent preparation of a new anticancer drug (Na3AsS4) and of copper in nanocrystalline state (≈ 20 nm) illustrate the non-traditional prospect of ore treatment. In material science, the new nanocrystalline semiconductors were synthesized mechanochemically, e.g. selenides of zinc and lead (ZnSe, PbSe) and bismuth sulphide (Bi2S3). Metal and chalcogene were applied as reaction precursors. In some cases, the amino acids (cystine, cysteine) were applied as sulphur precursor, in order to provide reactive sites on synthesized solid (PbS) for bioconjugation and to prevent agglomeration. The concept of nanomilling is described as a way to prepare e ective substances for cancer treatment in medicine. In vitro activity of realgar (As4S4) as an example is described. In all three areas the focus is aimed also on industrial applications where suitable large-scale mills are described. The described examples represent the contemporary aim of mechanochemists to prepare substances with the desired properties in a reproducible way under easyoperating, environmentally friendly and essentially waste-free conditions.

Within this work, the dechlorination of polyvinylchloride (PVC) chemical as a model by co-milling with eggshell was performed in a planetary ball mill in order to show that mechanochemistry can be utilized for the simultaneous treatment of two wastes, while the products of the treatment can be used in further applications. The products of the reaction are water-soluble calcium chloride (CaCl2), which can be used e.g. for de-icing of roads in winter and organic residue on the basis of ethylene, which can be recovered as energy source. The highest dechlorination yield (almost 97%) was achieved under following milling conditions: molar ratio between Ca and Cl: 2.34, ball-to-powder ratio: 65, rotation speed of the planet carrier: 550 rpm, milling time: 4 h and material of milling media: tungsten carbide. The optimum conditions were then applied for the removal of chlorine from industrial waste the abandoned PVC window parapet. In this case, 95% dechlorination was evidenced.

CdSe@ZnS nanocrystals have been prepared by a two-step solid state mechanochemical synthesis. CdSe prepared from elements in the first step is mixed with ZnS synthesized from zinc acetate and sodium sulfide in the second step. The crystallite size of the new type CdSe@ZnS nanocrystals determined by X-ray diffraction Rietveld refined method was 35 nm and 10 nm for CdSe and ZnS, respectively. Energy dispersive/transmission electron microscopy/energy dispersive spectroscopy methods show good crystallinity of the nanoparticles and scanning electron microscopy elemental mapping illustrate consistent distribution of Cd, Se, Zn and S elements in the bulk of samples. UV-VIS spectra show an onset at 320 nm with calculated bandgap 3.85 eV. This absorption arises from the vibration modes of Zn-S bonds. The nanocrystals show the blue shift from the bandgap of bulk ZnS (3.66 eV). The synthesized CdSe@ZnS nanocrystals have been tested for dissolution, cytotoxicity and L-cysteine conjugation. The dissolution of Cd was less than 0.05 μg mL -1 (in comparison with 0.8 μg mL -1 which was evidenced for CdSe alone). The very low cytotoxic activity for selected cancer cell lines has been evidenced. CdSe@ZnS nanocrystals coated with L-cysteine are water-soluble and have a great potential in biomedical engineering as fluorescent labels.