Advances in Science and Technology Vol. 135

Abstract: The extraction and processing of silver minerals produce significant amounts of waste, which poses environmental challenges due to their low metal content and the potential release of toxic elements. The study investigates the application of Acidithiobacillus ferrooxidans (AF) bacteria to the bioleaching of these waste materials, with the aim of maximizing the recovery of iron, copper and arsenic. The objectives of the study include characterizing waste materials, optimizing the bioleaching process parameters and evaluating metal extraction efficiency. The samples were leached with additives (CuSO₄ 5H₂O and AgNO₃) to accelerate the kinetics of metal dissolution in solution and reduce the bacterial leaching time. The results showed that samples 1-2 and 2-2 containing additives had higher values of dissolved iron and copper in the leachate compared to samples 1-1 and 2-1 without additive application.

Abstract: The aim of this work was to evaluate the possibility to solidify radioactive expanded clay balls or radioactive sludge originating from the decommissioning of NPP V1 in Jaslovské Bohunice (Slovak Republic) into the geopolymer matrices. The radioactive wastes (RAW) in the proportion of 0 wt.%, 20 wt.%, 25 wt.%, and 30 wt.% were solidified using a geopolymer mixture GEOCEM (producer GEOFIX Ltd., Slovak Republic). The value of compressive strength linearly decreased with increasing addition of RAW from the value of 16.1 MPa to 12.4 MPa for radioactive expanded clay balls solidified and from the value of 16.1 MPa to 10.6 MPa in the case of radioactive sludge. Leaching test carried out according to ANSI/ANS 16.1.1986 showed that the calculated value of leachability index L_i at the highest proportion (30 wt.%) of radioactive expanded clay balls or radioactive sludge reached the value L_i = 10.3 or L_i = 9.7, respectively.

Abstract: Following the growing interest in monitoring the status, behavior and impact of micropollutants in the environment, a significant area of concern revolves around the degradation of plastics, which is closely associated with a range of environmental risks. The long-term goal is to investigate the degradation process of plastics in an aqueous environment within controlled laboratory settings and analyze the status of degraded particles over a specific period. The proposed methodology, which is the subject of this paper, aims to achieve this objective. Over the period of one year, both conventional and biodegradable plastics are subjected to the combined effects of UV radiation and water motion. This paper presents the design of laboratory setting and experimental setup for conducting the degradation process. Based on its implementation, the degradation process is evaluated including weight loss and conducting microscopic and FTIR analysis of microplastic particles (MP). By gaining a better comprehension of these processes, we expect to be able to effectively mitigate the adverse environmental consequences caused by plastics.

Abstract: The paper presents and discusses the durability parameters of concrete (total water absorption, capillary absorption, and compressive strength), which have been monitored over a long-term period of 3 years. The concretes were prepared with recycled brick aggregate of fraction 4/8, the latter being surface treated by different procedures before mixing the concrete. Surface treatments allow the RBA to achieve a lower water absorption capacity (45-82% decrease), thus gaining a potential to optimize the amount of mixing water, and thus improve the quality of the concrete. After 3 years of curing, all samples still show better property values than the initial values at 28 days, indicating good durability over this period.

Abstract: The article summarizes the development of the strength characteristics of concrete over 5 years of curing, prepared on the basis of 40% replacement of the binder with sediments from the Ruzin water reservoir. The results showed, that the use of the original fine-grained sediment as a binder indicates a continuous increase in the strengths of the composites during 5 years of curing. The addition of fly ash to the mixture confirm its slower effect on increasing compressive strengths at the beginning of hardening. An increase in the compressive strengths of the composites by 35% was observed after one year of curing. The compressive strengths of the composites prepared with 40% cement replacement by sediments after 5 years of hardening were at the level of 30 MPa and more. The decrease in strength in the initial stages of hardening, after 28 days, was at the level of 50% compared to the comparative sample while the decrease in strength compared to the comparative sample was only 35% after 5 years of hardening.

Abstract: This article presents the results of a research dealing with the use of construction and demolition waste - recycled concrete in the production of fresh concrete, as a partial substitute for natural aggregate. It describes the properties of concrete recyclate that is used for the proposed recipe of fresh concrete. The properties include the results of grain size analysis, bulk density and water absorption capacity. 2 recipes of fresh concrete were prepared for the research. Recipe 1 based on recycled concrete combined with natural aggregate fraction (fr.) 8/16 mm. Recipe 2 based on natural aggregate, which also served as the comparison recipe to demonstrate the effect of recycled concrete fr. 0/16 mm on the physical-mechanical and deformation properties of concrete. The presented results show that the substitution of natural aggregate fr. 0/16 mm with recycled concrete has caused: a reduction of cubic strength by about 12%, crushing strength of cylinders by about 7%, and static and dynamic modulus of elasticity values by about 22% and 25%.

Abstract: This work focuses on the issue of corrosion and durability of mortar mixtures in aggressive environment. The intention was to find out and compare the impact of replacements on the durability of cement mortar exposed to an aggressive environment by comparison of various substitutes for cement, which are currently not widely used for this purpose with the commonly used ones.

Abstract: The circular economy is currently a highly discussed topic in many areas of production, due to the potential scarcity of natural resources. In the construction sector, it is often associated in the first place with the high shortages of natural aggregates for the production of concrete. To produce concretes up to strength classes C 30/37, the partial or complete replacement of natural aggregates by concrete or brick crushed recyclates in the 4/22 mm fraction can be used very efficiently and safely. This paper will show the current legislative limitations for the use of recyclates as aggregates for concrete production, the possibilities of their use when limiting the degrees of environmental influence or physico-mechanical parameters. In both cases of strength classes C 16/10 and C 30/37, a decrease in compressive strength of 16% was observed with replacement of coarse natural aggregate. The results of physico-mechanical properties of different formulations experimentally and practically verified will be shown and the areas of their safe use will be discussed.

Abstract: In the Czech Republic, natural stone reserves at mining sites are decreasing. Mining companies face the problem of handling waste materials, especially when processing stone. The article describes research that proposes using stone dust in producing ecological building materials, the transition from a linear economy model to a circular one, and an investigation into the use of construction and demolition waste and basalt fibres. The results show that using stone dust in construction products, in terms of the consumption of binders and water, and its use through larger particles or manufactured aggregates, reducing the risk of deformations, is more effective work.