Adsorption of heavy metals on natural zeolites: A review.

In recent decades, environmental pollution has become a significant problem for human health and environmental impact. The high accumulation of heavy metals in waters and soils from different sources was conducted in finding efficient and environmentally friendly treatment methods and materials for their removal, respectively. Natural zeolites have found wide-ranging applications in environmental remediation and protection, considering various treatment and modification methods designed to enhance the natural zeolites' adsorptive or ion-exchange capabilities for increased efficiency. This paper briefly consolidates the recent scientific literature related to the main characteristics of natural and modified zeolites, the advantages and limitations of their applying for environmental remediation, and summarizes the methodologies applied to natural zeolites in order to improve their properties. Their application for removing heavy metals from water systems and soils is also comprehensively discussed. This review highlights the excellent potential of natural zeolites to be used after specific treatment or modification as a sustainable and green material to solve numerous environmental pollution issues. 

Modification of natural zeolites and their applications for heavy metal removal from polluted environments: Challenges, recent advances, and perspectives

The radionuclides of cesium (Cs) and strontium (Sr) are dangerous products of nuclear fission that can be accidentally released into wastewater. In the present work, the capacity of thermally treated natural zeolite (NZ) from Macicasu (Romania) to remove Cs+ and Sr2+ ions from aqueous solutions in batch mode was investigated by contacting different zeolite quantities (0.5, 1, and 2 g) of 0.5–1.25 mm (NZ1) and 0.1–0.5 mm (NZ2) particle size fractions with 50 mL working solutions of Cs+ and Sr2+ (10, 50, and 100 mg L−1 initial concentrations) for 180 min. The concentration of Cs in the aqueous solutions was determined by inductively coupled plasma mass spectrometry (ICP-MS), whereas the Sr concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The removal efficiency of Cs+ varied between 62.8 and 99.3%, whereas Sr2+ ranged between 51.3 and 94.5%, depending on the initial concentrations, the contact time, the amount, and particle size of the adsorbent material. The sorption of Cs+ and Sr2+ was analyzed using the nonlinear form of Langmuir and Freundlich isotherm models and pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The results indicated that the sorption kinetics of Cs+ and Sr2+ on thermally treated natural zeolite was described by the PSO kinetic model. Chemisorption dominates the retention of both Cs+ and Sr2+ by strong coordinate bonds with an aluminosilicate zeolite skeleton.

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Removal of Cesium and Strontium Ions from Aqueous Solutions by Thermally Treated Natural Zeolite

In the first stage of this study, zinc oxide nanoparticles (ZnO-NPs) were synthesized. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area diffraction (SAED), and X-ray diffraction analyses (XRD). Subsequently, a composite material was obtained by coating ZnO-NPs with zeolite from Rátka, Hungary. The photocatalytic degradation of ZnO-NPs using Hungarian zeolite in the ZnO-Zeolite composite was investigated. The objective was to evaluate the efficacy of the ZnO-Zeolite composite in degrading methylene blue (MB) under ultraviolet-visible spectroscopy (UV). It was observed that the composite materials were influenced by the light source. The degradation rates showed that the ZnO-Zeolite composite with 100 mg L-1 MB achieved the highest photodegradation rate of 96.70% when exposed to sunlight for 210 min. These findings indicate that the ZnO-Zeolite composite with a 1:5 ratio has the potential to significantly increase the photocatalytic activity, achieving a high yield of 96.70% compared to raw zeolite. In the last stage of the study, equilibrium, kinetic, and thermodynamic studies were carried out. The photocatalytic maximum adsorption capacity of MB for the ZnO-Zeolite composite was calculated as qm=41.32 mg g-1. In the adsorption and kinetic studies of the obtained composite, the best results were obtained with the Langmuir adsorption isotherm and pseudo-second-order kinetics. A desorption study has been conducted, and it has been determined that the composite can be reused for up to 7 cycles. 

Zeolite supported zinc oxide nanoparticles composite: Synthesis, characterization, and photocatalytic activity for methylene blue dye degradation.

In this paper, we describe the characterization and application of adsorbent derived from the pyrolysis of cocoa shells, which is a natural source of adsorbent materials. The adsorbent that was used in this experiment is an environmentally friendly adsorbent that was prepared by the pyrolysis of cocoa shells. For 1.5 hours, the pyrolysis process was carried out at temperatures ranging from 300 to 380 °C. The adsorbent was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and analysis with an X-ray diffraction (XRD) analyzer. Water-ash content and iodine absorption capacity were also determined in accordance with SNI 06-3730-1995. At a contact time of 90 minutes, the adsorption capacity of mercury ions was found to be 0.106 mg/gram. In this study, the adsorption of mercury ions with the adsorbent followed pseudo-second-order models with an R2 value of 0.9929.

Adsorbent Characterization from Cocoa Shell Pyrolysis (Theobroma cacao L) and Its Application in Mercury Ion Reduction

Efficient mercury removal from water by using modified natural zeolites and comparison to commercial adsorbents

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Efficient mercury removal from water by using modified natural zeolites and comparison to commercial adsorbents