Large amounts of coal combustion products (as solid products of thermal power plants) with different chemical and physical properties cause serious environmental problems. Even though coal fly ash is a coal combustion product, it has a wide range of applications (e.g., in construction, metallurgy, chemical production, reclamation etc.). One of its potential uses is in zeolitization to obtain a higher added value of the product. The aim of this paper is to produce a material with sufficient textural properties used, for example, for environmental purposes (an adsorbent) and/or storage material. In practice, the coal fly ash (No. 1 and No. 2) from Czech power plants was firstly characterized in detail (X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), particle size measurement, and textural analysis), and then it was hydrothermally treated to synthetize zeolites. Different concentrations of NaOH, LiCl, Al₂O₃, and aqueous glass; different temperature effects (90–120 °C); and different process lengths (6–48 h) were studied. Furthermore, most of the experiments were supplemented with a crystallization phase that was run for 16 h at 50 °C. After qualitative product analysis (SEM-EDX, XRD, and textural analytics), quantitative XRD evaluation with an internal standard was used for zeolitization process evaluation. Sodalite (SOD), phillipsite (PHI), chabazite (CHA), faujasite-Na (FAU-Na), and faujasite-Ca (FAU-Ca) were obtained as the zeolite phases. The content of these zeolite phases ranged from 2.09 to 43.79%. The best conditions for the zeolite phase formation were as follows: 4 M NaOH, 4 mL 10% LiCl, liquid/solid ratio of 30:1, silica/alumina ratio change from 2:1 to 1:1, temperature of 120 °C, process time of 24 h, and a crystallization phase for 16 h at 50 °C.

The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char were prepared by high-energy ball co-milling from either raw Slovak lignite or coal-based char together with a ferrofluid. The products were characterised by X-ray diffraction, electron microscopy, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), volumetric magnetic susceptibility, and low-temperature nitrogen adsorption, and both magnetic carbons were comparatively tested as potential sorbents of As(V) oxyanions and Cd(II) cations in aqueous solutions. The magnetic char was an excellent sorbent of As(V) oxyanions (Q_m = 19.9 mg/g at pH 3.9), whereas the magnetic lignite was less effective. The different sorption properties towards arsenic anions may have been due to different oxidation states of iron on the surfaces of the two magnetic composites (determined by XPS), although the overall state of iron monitored by Mössbauer spectroscopy was similar for both samples. Both magnetic composites were effective sorbents for removing Cd(II) cations (Q_m (magnetic lignite) = 70.4 mg/g at pH 6.5; Q_m (magnetic char) = 58.8 mg/g at pH 6.8).

This study describes the bioleaching of a flotation concentrate by acidophilic iron- and sulfur-oxidizing bacteria at ambient temperature in shake flasks. The concentrate was prepared from polymetallic Ag–Cu–Sb–siderite ores from Rožňava (Slovakia) and consisted of tetrahedrite and siderite, with small amounts of chalcopyrite, pyrite, and quartz. Biologically driven Cu and S extraction was significantly greater than the extraction in the abiotic control. The oxidation of 1 mol of tetrahedrite (nominally Cu ₁₀ ⁺ Cu ₂ ²⁺ Sb ₄ ³⁺ S ₁₃ ²⁻ ) to produce sulfate involved the transfer of 122 mol of electrons. The stoichiometry of the reaction was confirmed by gas analyses and the concentration profiles of the oxidation products and can be described by the equation Cu ₁₂ Sb ₄ S ₁₃ + 122Fe ³⁺ + 52H ₂ O → 12Cu ²⁺ + 4Sb ⁵⁺ + 13SO ₄ ²⁻ + 122Fe ²⁺ + 104H ⁺ . The rate of bacterial ferrous iron oxidation highly exceeded that of the chemical reduction of Fe ³⁺ at the tetrahedrite surface, as indicated by the high Fe ³⁺ -to-Fe ²⁺ ratio in the leaching liquors. The sulfur entity (S ²⁻ ) of tetrahedrite was oxidized ultimately to sulfate. After 120 days of tetrahedrite bioleaching, the concentration of Cu in the leaching liquor exceeded 4 g L ⁻¹ , which is equivalent to > 80% metal yield. While the recovery of Cu and S increased proportionally with time, the Sb concentration approached 40 mg L ⁻¹ , and subsequently decreased, which indicates the formation of secondary antimony minerals. Electron microprobe analyses of the solid residues showed that the alteration products are distinctly depleted in Cu and S and enriched with Sb and Fe when compared to the primary tetrahedrite. Graphical Abstract

In Slovakia, there are a number of contaminated sites that have occurred due to intensive mining, mineral processing, metallurgical activities, chemical industry, fossil fuel combustion, and industrial agriculture in the past. This paper summarizes the occurrence, chemistry, toxicity, and mineralogy of arsenic species related to soil and water contamination in Slovakia. Four main localities with arsenic exposure were identified. Additionally, magnetically modified carbon biochar (MWchar-Mag) was tested for arsenic removal from a model solution alongside real mine water discharged from the abandoned Hauser adit. For the model aqueous solution, the maximum adsorption capacity was established at 6.2 mg of As per g of MWchar-Mag at natural pH. In the case of mine water with a concentration of arsenic at around 0.2 mg/L, adsorbent dosage, pH influence experiments, and kinetic tests were realized. The results confirmed 100% arsenic removal efficiency at pH~3–7 and extremely fast kinetics.

This paper analyses Saharan dust (SD) from settled precipitation from the episode of its record occurrence in eastern Slovakia at the end of March and early April 2024.The aim is to assess the impact of SD on atmospheric deposition (AD) and particulate matter immissions in the Košice area with the metallurgical industry present. The particles' size and distribution, chemical, and phase composition were analyzed. The methods of laser granulometry, electron microscopy (SEM and EDX), ICP MS, CHNS, and X - ray powder diffraction analysis were used. Saharan dust is polydisperse, with a mean geometric grain diameter of 15.1 μm; the proportion of particles with sizes below 10 and 2.5 μm is 37 and 10.9 %, respectively. The proportion of particles larger than 20 μm is 45 %. The SD sample is polymineralic, with quartz as the dominant component, accompanied by calcite and dolomite to a lesser extent. Additionally, feldspars, micas, kaolinite, and other common phyllosilicates and rock - forming minerals were confirmed. The main components of the analyzed EDX spectra, apart from oxygen and silicon, also included elements such as Al, Ca, K, Fe, Mg, and Na. The SD sample contained a relatively high carbon content (9.6%). Based on their occurrence in the spectra, the elements were present in the following order: O, Si, Al, Fe, Ca, Mg, K, C, Ti, Na, Cu, P, Mn, Nb, Ba, Br, Cr, and Pt. The chemical composition of SD is very similar to the average composition of the Earth's crust. Compared to the concentrations of the monitored elements in AD, the SD sample exhibited higher levels of aluminum and, to some extent, calcium and magnesium. In the case of other elements, their concentrations in AD from an area in the metallurgical industry were significantly higher than in Saharan dust. The estimated contribution of Saharan dust to the atmospheric deposition of the solid fraction in the study area ranges from 4.6% to 22%, depending on the emission loading rate.

The presented article focuses on the possibilities of using microwave energy in the treatment of flue dust originating from the production of steel in EAF, as well as flue dust arising in the hot-dip galvanizing process of steel. The mentioned types of waste in the form of flue dust contain significant amounts of zinc (22-43%) and iron (0.6-30%), which could be reused after heat treatment in the sense of a circular economy. Since zinc is also found in the mentioned wastes in the form of a stable spinel structure of franklinite (ZnFe2O4), its treatment through microwave roasting in the presence of suitable susceptors of electromagnetic radiation is a prospective method of obtaining pure metals. The advantage of microwave processing is the volumetric nature of the heating, the faster course of carbothermic reactions and the sufficiently lower temperature of the waste treatment compared to conventional heating.