In this study, the removal of nickel (Ni(II)) by adsorption from synthetically prepared solutions using natural bentonites (Lieskovec (L), Hliník nad Hronom (S), Jelšový Potok (JP), and Stará Kremnička (SK)) was investigated. All experiments were carried out under batch processing conditions, with the concentration of Ni(II), temperature, and time as the variables. The adsorption process was fast, approaching equilibrium within 30 min. The Langmuir maximum adsorption capacities of the four bentonite samples used were found to be 8.41, 12.24, 21.79, and 21.93 mg g^–1, respectively. The results best fitted the pseudo-second-order kinetic model, with constant rates in a range of 0.0948–0.3153 g mg^–1 min. The effect of temperature was investigated at temperatures of 20, 30, and 40 °C. Thermodynamic parameters, including standard enthalpy (ΔH⁰), Gibbs energy (ΔG⁰), and standard entropy (ΔS⁰), were calculated. The adsorption of Ni(II) by bentonite samples was an endothermic and spontaneous process. These results indicated that, of the bentonite samples used, the natural bentonites from JP and SK were most suitable for the removal of nickel from synthetically prepared solutions.

In the present research, the removal of zinc from concentrated galvanic wastewater (pH 3.1, conductivity 20.31 mS/cm, salinity, 10.16 g/L, Chemical Oxygen Demand (COD) 2900 mg O₂/L, Total Organic Carbon (TOC) 985 mg/L, zinc (Zn) 1534 mg/L and ethylenediaminetetraacetic acid (EDTA) 70 mg/L) by combination of lime (Ca(OH)₂) and sodium trithiocarbonate (Na₂CS₃) as precipitation agents is studied. Central Composite Design (CCD) and response surface methodology (RSM) were applied for modelling and optimizing the designed wastewater treatment process. Analysis of Variance (ANOVA) and the experimental verification of the model confirmed the consistency of the experimental and estimated data calculated from the model (R² = 0.9173, R²_adj. = 0.8622). The use of Ca(OH)₂ and Na₂CS₃ in the optimal condition calculated from the model (pH = 10.75 ± 0.10, V Na₂CS₃ dose 0.043 mL/L and time = 5 min) resulted in a decrease in the concentration of Zn in treated wastewater by 99.99%. Other physicochemical parameters of wastewater also improved. Simultaneously, the application of Ca(OH)₂ and Na₂CS₃ reduced the inhibition of activated sludge dehydrogenase from total inhibition (for raw wastewater) to −70% (for treated wastewater). Under the same conditions the phytotoxicity tests revealed that the seed germination index for the raw and treated wastewater increased from 10% to 50% and from 90% to 100% for white mustard (Sinapis alba) and garden cress (Lepidium sativum L.), respectively. The parameters of root and shoot growth showed a statistically significant improvement. Treated wastewater (1:10) showed a stimulating effect (shoot growth) compared to the control sample (GI = −116.7 and −57.9 for S. alba and L. sativum L., respectively). Thus, the use of Na₂CS₃ is a viable option for the treatment of concentrated galvanic wastewater containing zinc.

The study of Cu(II) from aqueous solutions using the adsorption process on synthetically modified geopolymers was performed under static conditions. Three geopolymers (based on metaphase of Serbian clay, metaphase of German clay and metaphase of German clay plus 10% of carbon cloth) were used. The geopolymers were made by condensing a mixture of metaphases and alkali activator solution at a fixed ratio at room temperature and then at a temperature of 60 °C in a dry oven. Then, the geopolymer samples were pre-crashed to a fixed-radius size. Their properties were characterized by X-ray diffractometry (XRD), Diffuse Reflectance Infrared Fourier Transform (DRIFT) analysis and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). Adsorption experiments were carried out under batch process as a function of the dose, concentration of metal, and contact time. The uptake of Cu(II) was rapid, and it increased with increasing metal concentration. The sorption percentage decreased with increasing concentration of Cu(II). The equilibrium adsorption capacity of geopolymers was measured and extrapolated using more isotherms. The data fit very well the linear Langmuir isotherm model. The pseudo-second-order kinetic model can well describe the adsorption behavior of Cu(II) ions with geopolymers samples. These results show that used geopolymers hold great potential to remove Cu(II) from industrial wastewater.

Repeated drought–rehydration episodes expose perennial fruit trees to alternating stress and recovery phases, while treatment-level averages can obscure genotype-specific response strategies. We evaluated seven biochemical markers in fourteen apple (Malusdomestica Borkh.) genotypes during two consecutive drought–rehydration cycles: proline, malondialdehyde (MDA), total phenolics, total flavonoids, and the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). Both drought cycles increased all measured markers, with the strongest overall response at the end of the second drought cycle (T6). Relative to the control, mean values at T6 increased by 272.4% for proline, 136.4% for MDA, 45.3% for total phenolics, 76.5% for total flavonoids, 109.1% for SOD, 89.0% for CAT, and 117.5% for POX. Genotype-specific log₂(Stress/Control) profiles at the first (T2) and second (T6) drought maxima revealed contrasting combinations of osmotic adjustment, oxidative damage, antioxidant-enzyme activity, and secondary-metabolite accumulation. B11 combined comparatively low MDA induction with strong antioxidant-enzyme responses, whereas HL1282 and HL1579 showed lower proline and MDA induction together with stronger phenolic, flavonoid, and selected enzyme responses. In contrast, ‘Idared’ showed strong proline and MDA induction. The first two principal components explained 75.1% of the total variance. Overall, the results identify distinct genotype-specific biochemical response strategies and show that coordinated marker profiles provide substantially more information than individual biomarkers or treatment averages alone.

Repeated drought–rehydration episodes expose perennial fruit trees to alternating stress and recovery phases, while treatment-level averages can obscure genotype-specific response strategies. We evaluated seven biochemical markers in fourteen apple (Malus domestica Borkh.) genotypes during two consecutive drought–rehydration cycles: proline, malondialdehyde (MDA), total phenolics, total flavonoids, and the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). Both drought cycles increased all measured markers, with the strongest overall response at the end of the second drought cycle (T6). Relative to the control, mean values at T6 increased by 272.4% for proline, 136.4% for MDA, 45.3% for total phenolics, 76.5% for total flavonoids, 109.1% for SOD, 89.0% for CAT, and 117.5% for POX. Genotype-specific log₂(Stress/Control) profiles at the first (T2) and second (T6) drought maxima revealed contrasting combinations of osmotic adjustment, oxidative damage, antioxidant-enzyme activity, and secondary-metabolite accumulation. B11 combined comparatively low MDA induction with strong antioxidant-enzyme responses, whereas HL1282 and HL1579 showed lower proline and MDA induction together with stronger phenolic, flavonoid, and selected enzyme responses. In contrast, ‘Idared’ showed strong proline and MDA induction. The first two principal components explained 75.1% of the total variance. Overall, the results identify distinct genotype-specific biochemical response strategies and show that coordinated marker profiles provide substantially more information than individual biomarkers or treatment averages alone.