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 closure of coal mines does not terminate their impact on the environment. Gas emissions into the atmosphere are the one of the problems. The closed ''Gliwice II'' shaft has been selected for a series of measurements to assess greenhouse gas emissions from the closed mine; however, only CO 2 emission has been detected. The article compromises obtained knowledge about the rate of emissions and the influence of meteorological parameters on this phenomenon-baric tendency, difference in dry-bulb temperature between flowing gas and the atmosphere (buoyancy effect) and wind speed. In the course of the conducted research, it was detected that the highest amount of carbon dioxide emission was V CO 2 = 0.023 m 3 /s (which is 82.8 m 3 /h) when baric tendency of pressure drop was 0.57 hPa/h, and the difference between dry-bulb temperatures gas and atmosphere was ?4.4°C (the highest difference in the obtained results). The rate of CO 2 emissions varied from 12.7 to 162.3 kg CO 2 =h. Carbon dioxide was detected up to 43 m from the shaft. The results can be considered as a general conclusion about gas behavior when it flows from the underground sites to the surface in natural conditions and about gas concentrations near a point of emission, especially in the case of former mines. However, it may also be useful for other applications, e.g., the leakages from installations of underground coal gasification, or gas drainage.

Without the use of appropriate recycling technologies, the growing amount of electronic waste in the world can be a threat to the development of new technologies, and in the case of improper waste management, may have a negative impact on the environment. This is due to the fact that this waste contains large amounts of valuable metals and toxic polymers. Therefore, it should be recycled in accordance with the assumptions of the circular economy. The methods of mechanical recovery of metals from electronic waste, including printed circuits, may be widely used in the future by waste management companies as well as metal production and processing companies. That is why, a well-known and easily applicable electrostatic separation (ES) method was used to recover metals from printed circuit boards. The grain class of 0.32 - 0.10 mm, obtained after grinding the boards, was fed to a separator. Feed and separation products were analyzed by means of ICP-AES, SEM/EDS and XRD. The concentrate yield obtained after electrostatic separation amounted to 32.3% of the feed. Its density was 11.1 g/cc. Out of the 91.44% elements identified in the concentrate, over 90% were metals. XRD, SEM observations and EDS analysis confirmed the presence of non-metallic materials in the concentrate. This relatively high content of impurities indicates the need to grind printed circuit board into grain classes smaller than 0.32-0.10 mm.

Zero-valent iron has received considerable attention for its potential application in the removal of heavy metals from water. This paper considers the possibility of removal of zinc ions from water by causing precipitates to form on the surface of iron. The chemical states and the atomic concentrations of solids which have formed on the surface of zero-valent iron as well as the type of the deposited polycrystalline substances have been analyzed with the use of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The BET surface area, the pH at point of zero charge (pHPZC), the ORP of the solutions, and the pH and chemical concentrations in the solutions have also been measured. Furthermore, the paper also considers the possibility of release of zinc from the precipitates to demineralised water in changing physicochemical and chemical conditions. In a wide range of pH values, ZnxFe3 − xO4 (where x ≤ 1) was the main compound resulting from the removal of zinc in ionic form from water. In neutral and alkaline conditions, the adsorption occurred as an additional process.

The purpose of the work was to recover metals from e-scrap, in particular from mainboards of desktop computers, using gravity, electrostatic and magnetic separation. The article describes the method of comminution as well as the yield of size fraction after this process. In addition, the separation of the fraction of 0.32 - 0.56 mm with the use of two systems: I) electrostatic and magnetic separation, and II); gravity and magnetic separation, was presented. The feed to the magnetic separator for both systems was metals (high density products). The yield of fraction 0.32 - 0.56 mm obtained after comminution was 40.7% while the yields of the products obtained from the first system were as follows: in the case of electrostatic separation, 24.9% metals and 75.1% plastics and glass; and for magnetic separation 0.7% of ferromagnetics, 19.0% of diamagnetics and 5.3% of paramagnetics. The yields of the products in the second system were: in the case of gravity separation, fraction with a density ρ > 2.96 g/cc = 33.0% and fraction with a density ρ<2.96 g/cc = 67.0%; and for magnetic separation 0.8% of ferromagnetics, 25.3% of diamagnetics and 6.9% of paramagnetics.

This paper evaluates the efficiency of metal recovery from printed circuit boards (PCBs) using two gravity separation devices: a shaking table and a cyclofluid separator. The test results were compared with the results obtained from previous research, where an electrostatic separation process was used for an identically prepared feed. The feed for the separators consisted of PCBs shredded in a knife mill at cryogenic temperatures. The separation efficiency and purity of the products were evaluated based on microscopic analysis, ICP-AES, SEM-EDS, XRD, and specific density. The yield of concentrates (valuable metals) obtained from the shaking table and the cyclofluid separator amounted to 25.7% and 18.9%, respectively. However, the concentrate obtained from the cyclofluid separator was characterised by much higher purity, amounting to ~88% of valuable metals, compared to ~72% for the shaking table. In both cases, middlings formed a significant share, their yield amounting to ~25%, with the share of valuable metals of ~15%. The yield of waste obtained from the shaking table and the cyclofluid separator were 42.6% and 52.5%, respectively. In both cases, as a result of the applied process, the waste was divided into two homogeneous groups differing in grain size and shape. The recovery of metals through gravity separation is possible, in particular, by using a shaking table. These processes can also be applied to separate waste (plastics) into two groups to be selectively processed to produce new materials in line with a circular economy.

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The coal mine waste dumps located in the southern provinces of Poland pollute groundwater with metals. As a result of batch experiments presented in the paper, it can be said that it is possible to remove chromium and copper from the groundwater (which is affected by acid mine drainage, thus characterized by low pH) with the use of zero-valent iron in permeable reactive barrier technology. The contaminants are removed from the aquifer by the flow of groundwater through a reactive barrier filled with a special reactive material. Rapid metal removal likely occurred due to the reduction and the precipitation/co-precipitation and/or due to the adsorption onto the iron metal surface or/and onto the iron corrosion products. In accordance with the research it has also been found that in more alkaline environment, the oxidation of Fe(0) proceeds slower. A rapid decrease of the redox potential as well as the increases of pH have also been observed in the batch tests when the dose of Fe(0) in solutions increased.