Natural zeolites (NatZ) are widely available, porous, crystalline aluminosilicate minerals that are commonly used as cost-effective adsorbents in water treatment processes. Despite their efficiency in removing various heavy metal ions from wastewater, NatZ show relatively low affinity toward Ni²⁺ and Cr³⁺ ions. This study aimed to develop composite adsorbents based on NatZ and hydroxyapatite using two methods, hydrothermal and mechanochemical, and their adsorption properties for the removal of Ni²⁺ and Cr³⁺ ions from aqueous solutions were investigated. X-ray powder diffraction and scanning electron microscopy analyses confirmed that under hydrothermal conditions, needle-like hydroxyapatite crystals were formed on the surface of NatZ, while the zeolite structure remained unchanged. Compared to the mechanochemically prepared sample, this adsorbent showed higher efficiency, binding 6.91 mg Ni²⁺/g and 16.95 mg Cr³⁺/g. Adsorption kinetics of the tested cations in both cases can be described by a pseudo-second-order model (R² is higher than 0.95 for all adsorbents). It is concluded that the presence of hydroxyapatite on the zeolite surface significantly improves the adsorption performance of NatZ, demonstrating its potential for the removal of heavy metal ions in wastewater treatment.

The impact of milling process parameters on the physicochemical properties of waste plum stones was investigated to enable their further utilization as a functional material. The experiments were conducted using a planetary ball mill, with variations in milling duration (1–3 h), the ball-to-powder ratio (bpr) (10:1 and 20:1), and the rotation speed (250 and 500 rpm). Transformations of material in a function of process parameters were assessed by XRD, FTIR, and SEM analysis, revealing differences in particle size distribution, functional group composition, and surface morphology. Optimization of milling process parameters was focused on promoting fine particle formation and surface activation without causing significant material degradation. The best result was achieved with the PS-M10 sample, processed at a speed of 500 rpm and a bpr of 20:1 during a short milling time of 1 h. The milled sample demonstrated promising potential for further applications, particularly for heavy metal ion (Pb²⁺ and Cu²⁺) removal from aqueous solutions through adsorption.

In this study, porous ceramics, based on available and cost-effective raw materials natural zeolite and kaolin clay, were synthesized and examined as an adsorbent for removing ammonium (NH4+) ions from aqueous solutions. The synthesis was carried out using the foaming method with the addition of sodium dodecyl sulfate as the foaming agent, polyvinyl alcohol as an organic binder, and hydrogen peroxide as the blowing agent. The obtained green and sintered samples were characterized by thermogravimetric analysis, scanning electron microscopy, X-Ray diffraction, and Fourier transform infrared spectroscopy. After sintering, the porosity was 79.49%. The NH4+ adsorption kinetics and isotherms fit the pseudo-second-order and Langmuir models, confirming chemisorption. The maximum adsorption capacity obtained using the Langmuir model was approximately 7.66 mg g-1. The thermodynamic parameters showed that adsorption is a spontaneous and exothermic process. Based on the obtained results, it was demonstrated that the synthesis of porous ceramics based on natural zeolite and kaolin clay is a practical way to increase the adsorption performance of natural zeolite for NH4+ removal from water solutions.

In the last decade, access to clean water has become a challenge, because of the rapid population growth and enormous agricultural and industrial activities. There are numerous processes for removing dissolved heavy metals, including ion exchange, coagulation, precipitation and adsorption. Adsorption could be the most effective for this purpose because of the low cost, easy operation, and short duration time. Nowadays, porous ceramic materials are promising adsorbents for different heavy metal ions. Eco-friendly porous ceramics based on natural zeolite and bentonite clay were synthesized and adsorption capacity toward Zn2+ ions was investigated. The synthesis was performed using the foaming method without an organic binder. Hydrogen peroxide was used as the blowing agent, while sodium dodecyl sulfate was used as the foaming agent. The obtained green and sintered samples of porous ceramics were characterized in detail by different methods (TG/DTG, SEM, XRD, FTIR, XRF). Results showed that the foamed samples could be synthesized at room temperature and fully crystallized after being sintered at 800 °C. Total porosity of porous ceramic sample reached maximum value of 74.7%. The second-order model and Langmuir model best described the adsorption kinetic and isotherm data. The maximum adsorption capacity obtained using the Langmuir model was approximately 5.01 mg Zn2+/g. The thermodynamic parameters showed that adsorption is a spontaneous and endothermic process favored at higher temperatures. Overall, this study highlights the potential of porous ceramics based on natural zeolite and bentonite for the removal of heavy metals and provides insight into the mechanisms of the adsorption process.

Excessive mineral extraction and boric acid production can lead to elevated boron concentrations in wastewater. While boron is an essential micronutrient for humans, excessive exposure and intake can result in adverse health effects. Existing treatment processes for boron contaminated wastewater have various limitations related to effectiveness, production of additional solid waste and high operational costs. This study investigates the use of natural zeolite as a cost-effective, sustainable and environmentally friendly adsorbent for boron removal. Natural zeolites are alumosilicate porous minerals widely used in wastewater treatment applications. To enhance its adsorption properties, natural zeolite was modified using a nickel sulphate solution. In this work, four adsorbents were analyzed: raw natural zeolite, nickel-modified natural zeolite, zeolite/hydroxyapatite and nickel-modified zeolite/hydroxyapatite composite. The zeolite/hydroxyapatite composite was synthesized under hydrothermal conditions at 160 °C for 4 hours at autogenous pressure. Characterization of the adsorbents was performed using X-ray powder diffraction (XRPD), scanning electron microscopy and thermogravimetric analysis. XRPD analysis confirmed clinoptilolite as the dominant mineral phase in the zeolitic tuff and showed that hydrothermal treatment did not affect its crystallinity. The adsorption properties were tested using a synthetic boron solution at pH 9, where boron exists in both B(OH)3 and B(OH)4– forms. The results showed that the presence of nickel primarily on the surface of the adsorbent leads to an increase in boron adsorption, which is a consequence of its ability to form complexes with B(OH)4–. This research confirmed that adsorbents based on metal-saturated natural zeolite are promising adsorbents of boron compounds from wastewater.