The use of paper sludge as a waste stream from industrial facilities represents a significant environmental challenge due to its quantity and heterogeneous composition. The aim of the study was to evaluate the adsorption characteristics of paper sludge in neutral mine effluents and aquatic solutions of metal ions: Cu(II), Zn(II), Cd(II), and Mn(II). The main novelty of the research is a comparison of the adsorption process in synthetically prepared aquatic solutions and neutral mine drainage from field sampling. The adsorption process of the monitored metals was evaluated in terms of adsorption capacity, parameters of the Freundlich and Langmuir adsorption isotherm, and the separation factor. The adsorption capacity of paper sludge of all metals is significantly lower in neutral mine drainage (NMD) compared to adsorption in aquatic solution. The adsorption capacity of Zn(II) in aqueous solution reaches equilibrium over time, similarly to Cu(II), with values ranging from 0.2 to 1.6 mg/g. For Cd(II), a slight increasing trend in the adsorption capacity of paper sludge is observed at higher initial concentrations (3–5 mg/L) over a contact time of 90–120 min. In general, aqueous solutions of metal ions exhibited higher adsorption capacities compared to NMD, with the highest value recorded for Cu(II) at 4.742 mg/g. As the concentration values in the original solution increased, a decline in K_R (from 268% to 137% at a C0 range of 4–20 mg/L) was observed. In the mine drainage with the addition of Zn(II), K_R values were also lower compared to those in aquatic solutions. The reduction in K_R became more pronounced with increasing initial concentration, showing a decrease of 29.9% to 38.9% at C0 levels ranging from 2 to 10 mg/L. The separation factors for Cu(II), Zn(II), and Cd(II) were lower in NMD, indicating better metal separation from real mine waters. The results confirm the potential of paper sludge as a low-cost adsorbent for the treatment of heavy metal contaminated waters.

In this paper, we compared the sorption of copper and zinc on three adsorbents - bentonite, zeolite, and dewatered digested sludge from a wastewater treatment plant. Sorption was carried out at 27ºC and subsequently at a reduced temperature of 10ºC and the results were compared. The reduced temperature positively affected the sorption efficiency and increased the adsorption capacity of the monolayer of each sorbent. Regardless of the temperature, the sorption progression was not linear. In the initial phase, the sorption proceeded rapidly, but after about 90 min the system reached equilibrium and the concentrations of metals in solution did not change significantly. The size of the specific surface area of the sorbents did not directly correlate with the removal efficiency of Cu2+ and Zn2+. Copper sorption by bentonite reached a level of almost 100% at reduced temperature and 80% at room temperature. The efficiency of zinc removal by bentonite was found to be 40% at reduced temperature. The efficiency of copper removal using zeolite was approximately 90% at both laboratory and reduced temperature. For bentonite and zeolite, we confirmed their good sorption properties. The sludge showed low Cu2+ sorption efficiency, but Zn2+ removal efficiency was higher than bentonite and zeolite. In both cases, the reduced temperature had a positive effect on the sorption capacity of the sludge. Sludge as a waste material could be used for heavy metal removal by modifying the sorption conditions or its modifying, which should be further investigated.

Brake wear particles (BWPs) represent a major source of non-exhaust particulate matter from road traffic, contributing substantially to human exposure, particularly in urban environments. While traditionally associated with coarse and fine fractions, mounting evidence shows that brake systems emit large quantities of ultrafine particles (UFPs; <100 nm), which dominate number concentrations despite contributing little to mass. This paper synthesizes current knowledge on BWP formation mechanisms, physicochemical characteristics, environmental behavior, and toxicological effects, with a specific emphasis on UFPs. Mechanical friction and high-temperature degradation of pad and disc materials generate nanoscale primary particles that rapidly agglomerate yet retain ultrafine structural features. Reported real-world and laboratory number concentrations commonly range from 10³ to over 10⁶ particles/cm³, with diameters between 10 and 100 nm, rising sharply during intensive braking. Toxicological studies consistently demonstrate that UFP-rich and metal-laden BWPs, particularly those containing Fe, Cu, Mn, Cd, and Sb compounds, induce oxidative stress, inflammation, mitochondrial dysfunction, genotoxicity, and epithelial barrier disruption in human lung and immune cells. Ecotoxicological studies further reveal adverse impacts across aquatic organisms, plants, soil invertebrates, and mammals, with evidence of environmental persistence and food-chain transfer. Despite these findings, current regulatory frameworks address only the mass of particulate matter from brakes and omit UFP number-based limits, leaving a major gap in emission control.

Mine effluents represent a serious environmental problem on a global scale. Therefore, the effective treatment of this water is a serious issue in the scientific field. The adsorption process seems to be one of the attractive methods, especially due to the simplicity of design, affordability or high efficiency. The latest scientific knowledge has shown that the use of waste and natural adsorbents is economical and effective. This study aimed to evaluate the efficiency of the adsorption process of natural and waste materials—zeolite, bentonite and fly ash—under the influence of temperature and modification of these adsorbents. The novelty of this study resides in an adjustment of the modification method of adsorbents compared to previous research: thermal–alkaline treatment versus hydrothermal one. Another novelty is the use of modified fly ash from biomass combustion as an adsorbent in comparison with the previously used fly ash from coal combustion. The modification of the adsorbents made the adsorption process more effective at all experimental concentrations. The characterisation of adsorbent samples was performed using X-ray diffraction (XRD). The parameters of the adsorption isotherms, Langmuir, Freundlich and Temkin, were estimated by nonlinear regression analysis. The adsorption capacity of Cu(II) of fly ash was comparable to natural adsorbents. Adsorption processes were better described by pseudo-second-order kinetics. At the end of this study, the suitability of using the adsorbents to reduce the concentration of Cu(II) in neutral mine effluents was observed in the following order at 30 °C: unmodified fly ash > modified bentonite > unmodified zeolite. At the temperatures of 20 °C and 10 °C, the same trend of the suitability of adsorbents use was confirmed: modified bentonite > modified zeolite > modified fly ash. The practical applicability of this study lies in the expansion of knowledge in the field of adsorption processes and in the improvement of waste management efficiency of heating plants not only in Slovakia, but also globally.

Pollution of surface water by heavy metals is a major environmental problem worldwide. The aim of the study was to evaluate the effectiveness of natural adsorbents (bentonites from the Kopernica deposit) with commercial types (zeolites of different quality) in removing selected heavy metals from the polluted surface stream in the monitored area. The adsorption process of the monitored metals was evaluated in terms of adsorption capacity and percentage of metal ion removal efficiency. The surface flow in the monitored area is significantly polluted and does not achieve the necessary water quality. The results of the research point to the high adsorption capacity of bentonites for Hg, while zeolites showed this ability less and were suitable only for some of the monitored heavy metals. The adsorption of zeolite of the type ZeoCem Eco Micro 200 (type C) is suitable for metals in the direction from the most adsorbed heavy metal to the least adsorbed as follows: Sb > Hg > Cr > Cd > Cu > Zn. As showed no affinity for adsorption onto zeolite C. The research confirmed the suitability of low-cost adsorbents for the remediation of polluted water in the monitored area.

Neutral mine drainage may contain potentially toxic metals even under circum-neutral pH conditions. This study investigated the competitive effect of Cu(II) on the removal of Cd(II), Mn(II), and Zn(II) from real neutral mine drainage using unmodified bentonite, natural zeolite, and biomass-derived fly ash. Batch experiments were conducted for 120 min using 0.5 g of adsorbent per 100 cm³ of mine water, with Cu(II) additionally introduced at 20 mg·dm⁻³. Biomass fly ash increased the solution pH to 9.4 and achieved the highest removal efficiencies in the presence of Cu, reaching 98.8% for Cu(II), 99.3% for Mn(II), and 100.0% for Zn(II). In contrast, Cd(II) removal by fly ash decreased from 57.3% without Cu to 0.0% with Cu, whereas Cd(II) removal increased from −199.8% to 100.0% with bentonite and from −224.6% to 38.4% with zeolite. Cu addition also increased Mn(II) removal from −5.1% to 85.6% for bentonite, from −20.7% to 71.4% for zeolite, and from −40.0% to 99.3% for fly ash, while Zn(II) removal increased to 100.0%, 96.8%, and 100.0%, respectively. Two-way analysis of variance confirmed highly significant Cu × adsorbent interactions for Cd(II) (p < 0.001), Mn(II) (p < 0.001), and Zn(II) (p < 0.001). Langmuir analysis gave the highest calculated q_m for Mn(II) with Cu addition: 0.864 mg·g⁻¹ for zeolite, 0.754 mg·g⁻¹ for fly ash, and 0.720 mg·g⁻¹ for bentonite; for fly ash, these values should be interpreted considering simultaneous adsorption and precipitation. No desorption of Cu(II), Mn(II), or Zn(II) was observed after adsorption. Overall, biomass fly ash showed strong potential for Cu(II), Mn(II), and Zn(II) removal from real neutral mine drainage, while the competitive suppression of Cd(II) highlights the importance of multicomponent interactions in practical treatment systems.