Among alternative anode materials for high-temperature fuel cells, the complex ceramic oxide La0,75Sr0,25Mn0,5Cr0,5O3 (LSCM) has recently shown good catalytic activity regarding fuel oxidation and sufficient stability in reductive environments at relatively low steam-to-carbon ratios. However, the electrical and ionic conductivities of LSCM are lower compared to some other perovskite materials. One of the possibilities to improve the conductivity of LSCM is in its composition variations, i.e., altering the Sr-content, doping on the A-site of the perovskite with other ions (Ba, Ca and Mg), and varying the Mn-to-Cr ratio on the B-site of the perovskite. In this paper, systems with the general formula La0.75SrxA0.25-xCr0.5Mn0.5O3 (A = Ba, Ca, Mg, x varies between 0 and 0.25) are described. Within the investigated system, prepared materials after synthesis contain the perovskite structure as a main crystallographic phase with relatively low additions of secondary phases. Any secondary phases are undesired, because they may substantially influence the electrical properties of the final materials. In samples with relatively high Sr-additions, a secondary Sr-rich phase Sr2CrO4 is also identified. Ca-doping may result in traces of CaCr2O4 phase in as-synthesized samples, while Ba-doping may lead to BaCrO4 or BaCO3 phases with higher Ba-additions. The quantity of the secondary phases may be controlled by calcination program or sintering conditions. Secondary phases, which may form additional grains or liquid phase, also influence the development of microstructures during sintering. Within the investigated compositions, the most promising materials are La0.75SrxCa0.25-xCr0.5Mn0.5O3 (x = 0.05–0.15), because they exhibit single-phase microstructure with fine grains after sintering at 1200 °C. Materials with Ba- or Mg-additions form precipitates of secondary phases at 1200 °C, which also remain present after sintering at higher temperatures.
Nowadays challenges in industries abroad are environmental oriented. As landfilling is getting more restricted, new, innovative options are addressed. Also, the aluminium industry is not immune to this problem as it generates tons of hazardous wastes. One of them is especially critical as no proposed treatment technology is economically justified. Spent Pot lining (SPL) is a hazardous waste material which originates from the primary aluminium production – the electrolysis cathode pot. Suggestions from the professional and scientific sources on how to approach the problem with state-of-the-art solutions were taken into account. A robust model to economically treat SPL was presented. Results showed a carbon content of 82 % after 2 step alkali reactive extraction and 90 % after acid reactive step. The acid step can, therefore, be omitted as the difference is not essential. The benefits of using just alkali instead of the additional acidic step are much greater. This prevents the occurrence of complex filtrates, while at the same time, with the absence of an acidic reagent, we avoid high operating costs and an investment in additional equipment. In addition, the CaF2 reduction is not a significant factor for purification effectivity, as the metallurgical industry to some extent needs this additive. The carbon product with a carbon content between 85 and 90 % can be used in ironworks while the silicate part is useful in brickwork. The by-products of the process are also useful. They appear in form of fluorspar which is used as a flux to lower the melting point of raw materials in steel production to aid the removal of impurities. The other by-product is NaOH which is mostly used in the process itself.
Bitumen, which is the most important component of asphalt and has the biggest impact on its behavior, is ageing during the use of asphalt layers. Ageing of bitumen is most frequent cause for degradation of asphalt layers and this finally leads to the removal of asphalt layers. But asphalt granulate prepared from the removed asphalt layer, can be added to freshly produced asphalt mixtures. Using special additives, i.e. rejuvenators, bitumen can regain its basic properties, and in this way we can increase the proportion of asphalt granulate added to the asphalt mixture. Final standard tests showed that when the rejuvenator is added, the properties of asphalt mixtures are improved with the addition of recycled aspWe developed alternative rejuvenator from the process of pyrolysis of waste tires. First, we tested the efficiency of the various pyrolytic products that were produced by varying the time and temperature of the pyrolysis. Various concentrations (3%, 5%, 10% and 20%) of the most suitable pyrolysis product were mixed into bitumen. We examined its effect on the viscoelastic properties of fresh and laboratory aged bitumen. With standard mechanical tests, rheological investigations and rheological modeling, we have proven that with addition of the alternative rejuvenator to aged bitumen some basic properties of bitumen are regained. We determined the most appropriate bitumen content that should be added to mixture of fresh asphalt and recycled asphalt. Final standard tests showed that when the rejuvenator is added, the properties of asphalt mixtures are improved with the addition of recycled asphalt, and the rate of recycling can be increased. Reuse of recycled asphalt means reducing waste material and so preserving the environment.
The production of aluminium achieved significant step regarding energy efficiency while the main waste stream remains untreated. Namely, this waste, also known as Spent Pot lining “SPL”, derives from each individual electrolytic cell, or more precisely from the material of the cathode electrode. The SPL stream contributes to about million tons per year of hazardous waste in the world’s smelters production. The carbonaceous content represents 60 wt% of the whole SPL mass and consists of a great part of graphite. This part of waste represents a great opportunity to harvest its usable material flows. Laboratory tests confirmed inefficiency of one-step treatment separation of different impurities as needed. The challenge is to separate Cryolite as the almost insoluble matter out of the carbon matrix. There are some chemical techniques present that address this problem in a feasible way, but the economics and circular mass flow are not proven to be successfully closed. With the help of laboratory investigations, the possibilities of material utilization of SPL have been studied. Comprehensive aspects from preliminary inquiry allows realising products that satisfy customer’s needs. This approach improve process economics and effectively close the circular loop of mass flow.