The paper presents an assessment of flotation efficiency in the separation of plastics from metals derived from printed circuit boards (PCBs). The PCBs were ground in a knife mill prior to flotation. The contact angles of various materials corresponding to the grains from ground PCBs were measured, and a series of flotation tests was carried out to obtain the best product. The impact of the following parameters were investigated: the reagent and its dose, the airflow rate through the flotation tank and the feed concentration. The highest efficiency of metal recovery from PCBs was achieved for Dimethoxy dipropyleneglycol at a concentration of 157 mg/dm3 and with an airflow of 200 dm3/h and a feed concentration of <50 g/dm3. In the hydrophilic product (concentrate), it was mainly Cu (40%) and Sn (7.8%) that were identified by means of XRF, but there were also trace amounts of precious metals such as Au (0.024%), Ag (0.5797%) and Pd (149 ppm). Impurities in the form of Si (5%), Ca (3.2) and Br (2.1) were also identified in this product. Small amounts of metals in their metallic form were identified in the hydrophobic product (waste), mainly Cu (2.3), Al (1.7) and Sn (1.1). As a result of the research, high recovery ratios were obtained for Cu (93%), Sn (84), Ag (83) and Au (69). The purity of obtained metal concentrate with this method was lower in comparison with the other methods of the recovery of metals from ground PCBs for the same feed, i.e. electrostatic or gravity separation. Also considering other factors such as the environmental impact of the flotation process, the number of facilities and their energy consumption, this process should not be used in the developed metal recovery technology. Using electrostatic separation for the same feed obtained much better results.

When discussing the perception of international events in the Polish pre-war press, it should be noted that these were frequently the subject matter in times of loss of independence such as partitioning of Poland and subsequent world wars. Some of the events happening in the history of the United States were of interest to local and national press. It applied even to one of the most violent and racist of American organizations — the infamous Ku Klux Klan. The purpose of this article is to acquaint readers with the image of the most powerful Klan of 1920’s in the Polish press. It is intriguing that the subject of Klan remains relatively unknown to Polish scientific literature. As of April 2020 there have been published only four monographies about the Invisible Empire written by Polish authors. This is puzzling because, as stated above, the subject matter of the Klan already existed in the Polish press at the time of its greatest power. Moreover, Polish-language readers during the partitions of Poland could familiarize themselves with current social and ethnic issues in the United States*. One example would be a series of articles in Galician press on the William Cody’s Wild West Show which toured Polish lands in 1906**.

This study reveals significant and emergent research topics in the field ‘engineering, mechanical’ through bibliometric analysis of articles indexed in Web of Science (WoS) from 1997 to 2016. Publications under consideration (219,191 articles) were examined using quantitative and qualitative methods to evaluate general information about publications; evolution of research topics by keyword analysis; performance of countries, research centers and journals; and international collaborations. There was a threefold increase in number of articles throughout the period. The publications were related to 35 WoS categories; and mechanics and thermodynamics were dominating ones. International Journal of Heat and Mass Transfer was the leading journal in the field. The USA and China were outstanding countries of the field. Collaboration between these countries corresponded to 6.57% of all collaborative publications. Industrialized and developing countries dominated research activities in the field. Indian Institute of Technology was the leading research center due to number of publications. The results showed that heat transfer, finite element method, friction, wear, simulation, and fatigue are important topics of the field. There is an upward trend in research related to nanofluids, microchannel, phase change materials, and carbon nanotubes.