The increasing pollution from the textile industry, particularly organic azo dyes, presents a significant environmental challenge, necessitating the development of effective and sustainable treatment methods. This study investigates the adsorption potential of hazelnut shells (raw—RHSs; modified—MHSs) for the removal of organic azo dyes from aqueous solutions. As biomass, hazelnut shells are biodegradable and represent a sustainable alternative to synthetic adsorbents, thereby reducing the ecological footprint. Through a series of batch adsorption experiments, the influence of various parameters, including pH, contact time, concentration, and temperature, on adsorption capacity was examined. Characterization of the hazelnut shells was conducted using optical microscopy and ATR-FTIR, XRF, and XRD spectroscopy, confirming its suitability as a biosorbent. The analyzed isotherms showed that adsorption onto RHSs was best fitted by the Freundlich model, while adsorption onto MHSs was best fitted by the Temkin model. Kinetic studies demonstrated that the adsorption process is well described by the pseudo-second-order model, suggesting that chemical adsorption plays a significant role. The maximal adsorption capacity was 62.11 mg/g for RHSs and 80.65 mg/g for MHSs, highlighting the potential of hazelnut shells as an abundant, low-cost, and eco-friendly adsorbent. Furthermore, recycling studies indicated the feasibility of the adsorbent, underscoring its practical applicability in real scenarios.

This study focuses on Pb²⁺ and As(V) adsorption on mineral heterostructures based on a mixture of Si, Fe, and Ti oxides (MOHs). Various techniques were performed to analyze the morphological and structural properties of the synthesized metal oxide samples. In addition to the experimental optimization of the parameters determined by the response surface method (RSM), the effects of pH, adsorbent dosage, temperature, and contact duration on the batch and column system adsorption efficiency of single-component and simultaneous lead and arsenate removal were tested. The pseudo-second-order kinetic model and Weber–Morris model were more relevant to the adsorption on the metal(loid)s. The adsorption of Pb²⁺ was related to the Langmuir isotherm model, while the adsorption of As(V) was fitted to the Freundlich isotherm model. The thermodynamic parameters indicate the spontaneity of the adsorption process with a low endothermic character. The MOHs were more effective in removing Pb²⁺ and As(V) in the multi-component system (87.7 and 46.1%, respectively) than in the single-component system (56.3 and 23.4%, respectively). This study demonstrates that mineral heterostructures can be effectively used to remove cations and anions from water systems, and due to their fast kinetics, they can be applied to the needs of rapid interventions after pollution.

The Republic of Serbia generates the majority of its electricity at the thermal power plants (TE) Nikola Tesla, Kolubara, and Kostolac. Coal is extracted from the Kolubara basin, which produces approximately 70% of lignite (an average of 30 million tons per year), and the Kostolac basin, which produces 30% of lignite. Ash, fly ash, and slag are examples of coal combustion residues. Because of the high content of potentially hazardous elements such as As, Pb, Cd, and Cr, environmental pollution with ash and fly ash has been extensively researched. Stable isotopes of lead can be used to trace lead sources. It is possible to monitor the presence, transformation pathways, and environmental impact of Pb by determining its isotopic composition in coal and fly ash. For the first time, the isotopic composition of selected coal samples from the Kolubara and Kostolac mines, as well as fly ash from the Kolubara (A and B), Kostolac (A and B), and Nikola Tesla (TENT A3, A2, B2) thermal power plants, was investigated in this study. The obtained data for 206Pb/207Pb in coal serve as the foundation for ranking domestic coals, whereas the isotopic ratios 206Pb/207Pb and 208Pb/207Pb in fly ash can be used to monitor and control lead pollution from investigated sources.

The modification of agricultural wastes for improved phosphate removal from wastewater is an innovative approach aimed to address the growing environmental challenges posed by nutrient pollution. As agricultural runoff contributes significantly to the eutrophication of water bodies, the effective removal of phosphorus from wastewater has become a critical necessity for environmental sustainability. This field of study not only explores the repurposing of agricultural residues but also emphasizes their potential as low-cost bio-based sorbents for phosphate remediation, thereby offering a dual benefit of waste reduction and environmental protection. Research has shown that various types of agricultural wastes, when modified through physical and chemical processes, can enhance their ability to capture and retain phosphorus from wastewater. Techniques such as metal loading and biochar production have proven effective, leading to notable advancements in the efficacy of these materials as phosphate adsorbents. Studies have indicated that chemically and thermically modified agricultural wastes can achieve phosphorus removal efficiencies comparable to traditional methods, making them a promising alternative in wastewater treatment applications. Despite the potential benefits, the implementation of modified agricultural wastes also faces several challenges. Issues such as: the economic feasibility of large-scale application, the complexity of modification processes, and concerns about the long-term sustainability of these technologies present significant hurdles. Overall, the modification of agricultural wastes represents a vital intersection of waste management and environmental conservation, promoting a circular bioeconomy while providing practical solutions to the pressing problem of nutrient pollution in aquatic systems.

Sustainable development and the circular economy are becoming the new imperative of industrial growth, as the world faces the depletion of natural resources and consequences of climate change. The utilization of waste streams through the concept of ‘new added value’ gives life to the production of materials and their environmental application. Therefore, the development of novel, eco-friendly, nature-based adsorbents that possess high degradable and recyclable potential is on the forefront of research. The modifications of wood derivates, such as cellulose and lignin, are widely applied as natural polymers due to their economic feasibility, ecological similarity and adsorption capabilities.The subject of this study is the adsorption of nickel(II) and cadmium(II) ions from aqueous solutions using 5.0 mass % of alginate lignin microspheres (A-LMS). Due to their toxicity, persistence, high solubility and mobility, such heavy metals are widely dispersed throughout environmental media (chiefly, aquatic bodies), leading to ecological and public health problems. The raw lignin used as a source material in the study originates from the waste stream of the lumber industry. The porous microspheres are of a radius of 50 to 950 microns and a surface area of 36.9 m2 g-1 were synthesized via inverse suspension copolymerization of the kraft lignin with a poly(ethylene imine) grafting-agent and an epichlorohydrin cross-linker. The structural and surface characteristics were confirmed via Fourier transform-infrared (FTIR) spectroscopy, x-ray diffraction (XRD) and scanning electron microscopy (SEM). The textural properties of the synthesized A-LMS were determined according to the Brunauer, Emmett and Teller (BET) method of analyzing nitrogen adsorption. The adsorption batch and column testing were carried out by varying the reaction time, temperature, adsorbent mass, at predefined pH values of the initial solutions. The maximum adsorption capacity of the A-LMS for nickel (II) ions was 89.286 mg g-1 at a temperature of 318 K, while for the adsorption of cadmium(II) ions it was 96.154 mg g-1 at a temperature of 308 K. The kinetic data followed the pseudo-second-order kinetic model, while the Weber-Morris model indicated intra-particle diffusion as a rate limiting step. The thermodynamic parameters for the A-LMS further confirm that the adsorption process was spontaneous and endothermic.The study indicates the high potential of by-products or waste products from heavy industry to be repurposed for environmental engineering applications by which they may serve a benefit as opposed to being a detrimental risk. Such is the case here with lignin-natural polymers taken from the lumber industry, which themselves may be reutilized for the removal of heavy metals from wastewater.AcknowledgmentsThis work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (project no. 172007). The authors would like to acknowledge the financial support provided by COST-European Cooperation in Science and Technology, to the Cost Action CA17133: Circular City.