Coal ash is known to contain a noticeable amount of valuable elements, including transition metals and lanthanides. Therefore it is quite actual problem to extract them for metallurgy and other applications. This paper presents the results of high gradient magnetic and mechanical separation, microscopy, element analyses and optical spectroscopy of brown coal ash taken from the combustion camera and chimney-stalk of Angren thermal power station. The separated magnetic fraction was 3.4 wt.%, where the content of Fe in ferrospheres increased to 58 wt.%. The highest contents of Fe and rare earth elements were found in the fine fractions of 50-100 µm. Optical absorption spectroscopy of water solutions of the magnetic fractions revealed Fe 2+ and Fe 3+ions in the ratio of ~1:1. The separated coal ash could be used for cleaning of technological liquid waste by means of the high gradient magnetic field.

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The BCS-like pairing of polaronic carriers in underdoped and optimally doped high-Tc cuprates above the superconducting transition temperature Tc is considered. Such a BCS-like pairing correlation leads to the formation of bosonic Cooper pairs and the appearance of a pseudogap on the Fermi surface at a characteristic temperature T* > Tc. It is shown that the calculated doping dependence of the BCS-like pseudogap agrees quite well with the experimentally observed doping dependence of the pseudogap in La2–xSrxCuO4 (where x is the doping level). The mechanisms of the unusual metallic transports of different types of charge carriers above and below T* along the CuO2 layers (i.e., ab planes) in high-Tc cuprates are identified. The conductivity of the three types of charge carriers (large polarons, excited Fermi components of bosonic Cooper pairs, and bosonic Cooper pairs themselves) at their scattering by lattice vibrations is considered. It is established that the linear temperature dependence of the in-plane resistivity ρab (T) observed, as a rule, in underdoped and optimally doped cuprates above T* is associated with the scattering of polaronic carriers by acoustic and optical phonons. Theoretical results compared with the experimental data allow for confirming that the different (upward and downward) deviations from the linearity in ρab (T) below T* and the most interesting resistive transitions [i.e., a clear jump and a sharp drop in ρab (T)] at T = T* are caused by the pseudogap effect on the conductivity of the excited Fermi components of bosonic Cooper pairs and by the excessive conductivity of bosonic Cooper pairs in high-Tc cuprates above Tc.

The intrinsic mechanisms of the unusual metallic transports of three types of relevant charge carriers (large polarons, excited (dissociated) polaronic components of bosonic Cooper pairs and bosonic Cooper pairs themselves) along the CuO2 layers of high-Tc cuprates are identified and the new features of metallic conductivity in the CuO2 layers (i.e. ab -planes) of underdoped and optimally doped cuprates are explained. The in-plane conductivity of high-Tc cuprates is associated with the metallic transports of such charge carriers at their scattering by lattice vibrations in thin CuO2 layers. The proposed charge transport theory in high-Tc cuprates allows to explain consistently the distinctive features of metallic conductivity and the puzzling experimental data on the temperature dependences of their in-plane resistivity pab. In underdoped and optimally doped cuprates the linear temperature dependence of pab(T) above the pseudogap formation temperature T∗ is associated with the scattering of polaronic carriers at acoustic and optical phonons, while the different (upward and downward) deviations from the linearity in pab(T) below T∗ are caused by the pseudogap effect on the conductivity of the excited Fermi components of bosonic Cooper pairs and by the dominating conductivity of bosonic Cooper pairs themselves in the normal state of these high-Tc materials.