This paper analyses the impact of the method of grinding printed circuit boards (PCBs) in a knife mill on the efficiency and purity of products obtained during electrostatic separation. The separated metals and plastics and ceramics can be used as secondary raw materials. This is in line with the principle of circular economy. Three different screen perforations were used in the mill to obtain different sizes of ground grains. Moreover, the effect of cooling the feed to cryogenic temperature on the final products of separation was investigated. The level of contamination of the concentrate, intermediate, and waste obtained as a result of the application of fixed, determined electrostatic separation parameters was assessed using ICP-AES, SEM–EDS, XRD, and microscopic analysis as well as specific density. The yields of grain classes obtained from grinding in a knife mill were tested through sieve analysis and by using a particle size analyser. The test results indicate that using a knife mill with a 1 mm screen perforation along with cooling the feed to cryogenic temperature significantly improves the efficiency of the process. The grinding products were characterised by the highest release level of the useful substance—metals in the free state. The purity of the concentrate and waste obtained from electrostatic separation was satisfactory, and the content of the intermediate, in which conglomerates of solid metal–plastic connections were present, was very low. The yield of concentrate and waste amounted to 26.2% and 71.0%, respectively. Their purity, reflected in the content of the identified metals (valuable metals), was at the level of 93.3% and 0.5%, respectively. In order to achieve effective recovery of metals from PCBs by means of electrostatic separation, one should strive to obtain a feed composed of grains <1000 μm and, optimally, <800 μm.

The transformation of the energy sector towards an increased share of renewable energy sources in the energy mix requires attention in the area of electricity storage. Renewable energy sources (photovoltaics or wind energy) are marked by the intermittency of electricity production and require the construction of energy storage to adapt the energy supply to the demand, providing greater stability. The authors focused on verifying the solution of gravitational energy storage in existing shafts of hard coal mines in Poland. The issue is significant for Poland, as a country with an extensive mining infrastructure, which is searching for new scientific and practical solutions to utilize disused mining shafts for new purposes. In the analysis, the focus was on one shaft located within the Upper Silesian Coal Basin (Górnośląskie Zagłębie Węglowe), maintained for the drainage of the neighboring deposit. The article presents the calculation of energy that can be stored and an analysis of the effectiveness of energy storage in the shaft. The basic assumption of the analysis was 1 cycle of work per day (charging and discharging) in order to use the effect of low prices at night and high prices during peak hours (according to Towarowa Giełda Energii (TGE) quotations). Although energy storage already functions around the world, the studied case is new, because it refers to the usage of existing shafts which makes it a non-investment case. The results of the study showed that the obtained economic effects of the analyzed solution are low, therefore there is no economic justification of activities related to its implementation, taking into account the current price conditions.

The objective of the European Green Deal is to change Europe into the world's first climate--neutral continent by 2050. Therefore, European countries are developing technological solutions to increase the production of energy from renewable sources of energy. In order to universally implement energy production from renewable energy sources, it is necessary to solve the problem of energy storage. The authors discussed the issue of energy storage and renewable energy sources, reviewing applied thermal and mechanical energy storage solutions. They referred to the energy sector in Poland which is based mainly on mining activities. The method that was used in this paper is a review of thermal and mechanical energy storage solutions. In industrial practice, various solutions on energy storage are developed around the world. The authors reviewed those solutions and described the ones which currently function in practice. Hence, the authors presented the good practices of energy storage technology. Additionally, the authors conducted an analysis of statistical data on the energy sector in Poland. The authors presented data on prime energy production in Poland in 2004-2019. They described how the data has changed over time. Subsequently, they presented and interpreted data on renewable energy sources in Poland. They also showed the situation of Poland compared to other European countries in the context of the share of renewables in the final gross energy consumption.

Hard coal run-of-mine contains a significant amount of waste rock, which must be removed to improve the quality of the extracted raw material. Coal processing is an integral and extremely important part of the production of commercial assortments. Water pulsating jig is one of the basic devices in which the material is separated. The article presents some possibilities of improving the qualitative and quantitative parameters of the beneficiation products due to design changes and control of the jig beneficiation node.

The article describes the design solutions of KOMAG drum crushers. In the case of significant differences in hardness of coal and gangue, these devices are the most appropriate and the cheapest means of preliminary beneficiation of run-of-mine. The results of laboratory tests of susceptibility to selective crushing of selected hard coal types by the drop method are presented. The possibilities of using a drum crusher for deshaling the analyzed materials are determined.