Selective and effective adsorption of cesium ions by metal hexacyanoferrates (MHCF, M = Cu, Co, Ni) modified chitosan fibrous biosorbent

Selective removal of cesium ions from aqueous solution by different metal (Zn2+/Ni2+) hexacyanocobaltate

Radioactive 137Cs removal and treatment have attracted widespread attention since the Chernobyl disaster and the Fukushima Daiichi nuclear plant accident. So far, Prussian blue analogs (PBAs) are recognized as the most effective Cs+ adsorbents possessing excellent sorption ability and radiation resistance. Here, two types of PBA-based Cs+ adsorbents, potassium zinc hexacyanocobaltate (Zn-Co PBA) and potassium nickel hexacyanocobaltate (Ni-Co PBA), were prepared by chemical precipitation method. Consequently, Zn-Co PBA and Ni-Co PBA had fast adsorption kinetics, and could remove 86.12% and 91.49% of Cs+ within 5 min, respectively. Zn-Co PBA and Ni-Co PBA were stable in a wide pH range, with Qmax of 96.53 and 77.52 mg/g for Cs+, respectively, both removing 98.5% of Cs+. In addition, Zn-Co PBA can eliminate 93.79% of Cs+ even in Cs+ spiked seawater containing high concentration of competitive cations. The adsorption mechanism indicates that the primary process involves ion exchange between K+ in the adsorbent and Cs+.

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Amino modified nanofibers anchored to Prussian blue nanoparticles selectively remove Cs+ from water

To improve the selective separation performance of silica nanofibers (SiO2 NFs) for cesium ions (Cs+) and overcome the defects of Prussian blue nanoparticles (PB NPs), PB/SiO2-NH2 NFs were prepared to remove Cs+ from water. Among them, 3-aminopropyltriethoxysilane (APTES) underwent an alkylation reaction with SiO2, resulting in the formation of a dense Si-O-Si network structure that decorated the surface of SiO2 NFs. Meanwhile, the amino functional groups in APTES combined with Fe3+ and then reacted with Fe2+ to form PB NPs, which anchored firmly on the aminoated SiO2 NFs surface. In our experiment, the maximum adsorption capacity of PB/SiO2-NH2 NFs was 111.38 mg/g, which was 31.5 mg/g higher than that of SiO2 NFs. At the same time, after the fifth cycle, the removal rate of Cs+ by PB/SiO2-NH2 NFs adsorbent was 75.36% ± 3.69%. In addition, the adsorption isotherms and adsorption kinetics of PB/SiO2-NH2 NFs were combined with the Freundlich model and the quasi-two-stage fitting model, respectively. Further mechanism analysis showed that the bond between PB/SiO2-NH2 NFs and Cs+ was mainly a synergistic action of ion exchange, electrostatic adsorption and membrane separation.

Cesium adsorption from an aqueous medium for environmental remediation: A comprehensive analysis of adsorbents, sources, factors, models, challenges, and opportunities

Considering the widespread and indispensable nature of nuclear energy for future power generation, there is a concurrent increase in the discharge of radioactive Cs into water streams. Recent studies have demonstrated that adsorption is crucial in removing Cs from wastewater for environmental remediation. However, the existing literature lacks comprehensive studies on various adsorption methods, the capacities or efficiencies of adsorbents, influencing factors, isotherm and kinetic models of the Cs adsorption process. A bibliometric and comprehensive analysis was conducted using 1179 publications from the Web of Science Core Collection spanning from 2014 to 2023. It reviews and summarizes current publication trends, active countries, adsorption methods, adsorption capacities or efficiencies of adsorbents, tested water sources, influencing factors, isotherm, and kinetic models of Cs adsorption. The selection of suitable adsorbents and operating parameters is identified as a crucial factor. Over the past decade, due to their notable capacity for Cs adsorption, considerable research has focused on novel adsorbents, such as Prussian blue, graphene oxide, hydrogel, and nanoadsorbents (NA). However, there remains a need for further development of application-oriented laboratory-scale experiments. Future research directions should encompass exploring adsorption mechanisms, developing new adsorbents or their combinations, practical applications of lab-scale studies, and recycling radioactive Cs from wastewater. Drawing upon this literature review, we present the most recent research patterns concerning adsorbents to remove Cs, outline potential avenues for future research, and delineate the obstacles hindering effective adsorption. This comprehensive bibliometric review provides valuable insights into prevalent research focal points and emerging trends, serving as a helpful resource for researchers and policymakers seeking to understand the dynamics of adsorbents for Cs removal from water.

Constructing porous ZnFC-PA/PSF composite spheres for highly efficient Cs+ removal

Radioisotope leaking from nuclear waste has become an intractable problem due to its gamma radiation and strong water solubility. In this work, a novel porous ZnFC-PA/PSF composite sphere was fabricated by immobilization of ferrocyanides modified zinc phytate into polysulfone (PSF) substrate for the treatment of Cs-contaminated water. The maximum adsorption capacity of ZnFC-PA/PSF was 305.38 mg/g, and the removal efficiency of Cs+ was reached 94.27% within 2 hr. The ZnFC-PA/PSF presented favorable stability with negligible dissolution loss of Zn2+ and Fe2+ (< 2%). The ZnFC-PA/PSF achieved high-selectivity towards Cs+ (Kd = 2.24×104 mL/g) even in actual geothermal water. The adsorption mechanism was inferred to be the ion-exchange between Cs+ and K+. What's more, ZnFC-PA/PSF worked well in the fixed-bed adsorption (E = 91.92%), indicating the application potential for the hazardous Cs+ removal from wastewater.

A Unified Adsorption Kinetic Model Inspired by Epidemiological Model: Based on Adsorbates "Infect" Adsorbents

Adsorption is a unit operation used in various fields, including the environmental, chemical, and pharmaceutical industries. Understanding the adsorption kinetics is crucial to designing efficient adsorption systems. However, existing empirical adsorption models are limited in providing insights into the mass transfer mechanisms. Additionally, the absence of a unified adsorption kinetic model hampers the effective comparison of different adsorption systems. Here, we viewed the adsorption as an "infectious process of adsorbates by adsorbents" akin to epidemiology. In epidemiology, individuals can be divided into susceptible, infected, and recovered compartments, ignoring the complexities of movement among individuals. Analogously, we have categorized the adsorbates as adsorbable, adsorbed, and removed compartments. Thus, we proposed a unified adsorption kinetic model (the monolayer-multilayer-adsorbable-adsorbed-removed model) that accommodates monolayer/multilayer adsorption. The model was designed to encompass diverse adsorption setups, including continuous and batch processes with fixed/dispersed adsorbents. The versatility and applicability of the model were demonstrated through validation using a diverse set of experimental data. This validation underscored its effectiveness in water/wastewater treatment, salt reduction, metal recovery, and drug purification. A MATLAB-based program for solving this model was made available to researchers for their utilization and further investigations. Overall, this study developed a versatile adsorption kinetic model that offers a comprehensive and unified understanding of adsorption kinetics across various applications.

A novel monolayer adsorption kinetic model based on adsorbates "infect" adsorbents inspired by epidemiological model

Adsorption is a unit operation process with broad applications in environmental, pharmaceutical, and chemical fields, with its most significance in environmental fields for water and wastewater treatment. Adsorption involves continuous/batch modes with fixed/dispersed adsorbents, leading to diverse systems. The adsorption kinetic models provide essential insights for effectively designing these systems. However, many adsorption models are semi-empirical/empirical, making it challenging to identify the adsorption mechanisms. Additionally, a consistent method for modelling the adsorption kinetics of different processes would be helpful for the comparison and analysis of various adsorption systems, but no such unified model is available. In epidemiological modeling, populations are often categorized into susceptible, infected, and removed individuals, simplifying disease transmission dynamics without considering individual-level movement intricacies. Likewise, we have employed a similar approach within adsorption systems, classifying adsorbates into absorbable, adsorbed, and removed (to the effluent) segments, thus developing the Monolayer-Absorbable-Adsorbed-Removed (MPQR) kinetics model. This model is applicable to continuous/batch adsorption systems, regardless of whether fixed or dispersed adsorbents are employed. The model was validated using experimental data across water/wastewater treatment, drug separation/purification, metal recovery, and desalination. The results showed that our model successfully fitted the kinetic data from various adsorption systems. It outperformed commonly used models for continuous/batch adsorption. The model allowed us to directly compare the parameters among various adsorption processes. The solving method based on Excel was provided and can be used by the researchers. Our model offers a versatile and unified approach to model adsorption kinetics, enabling the analysis and design of various adsorption systems.

Chitosan-minerals-based composites for adsorption of caesium, cobalt and europium

Currently, there is a growing interest in the use of natural materials in various fields of science, technology and environmental protection due to their availability, low-cost, non-toxicity and biodegradability. Chitosan, natural clay of local origin, montmorillonite, zeolite, cross-linking agents (epichlorohydrin, sodium tripolyphosphate, glutaraldehyde) and plasticisers (glycerol) were used to synthesise composites. The composites were characterised by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction analysis (XRD) and scanning electron microscope (SEM), tested for their antibacterial activity and used in batch experiments to study the adsorption of caesium, cobalt and europium ions. The maximum capacities for adsorption of caesium, cobalt and europium on the composites were 1400 mg/g, 900 mg/g and 18 mg/g, respectively. The experimental data fit better the Langmuir isotherm model and indicate favourable monolayer adsorption of Cs+, Co2+ and Eu3+ at homogeneous sites of the composites. The experimental data were in better agreement with the pseudo-second-order non-linear kinetic model for most elements and adsorbents. Adaptive neuro-fuzzy inference system proved to be a practical tool with good performance and generalisation capability for predicting the adsorption capacity of composites for caesium, cobalt, and europium ions. It was found that the predicted data were very close to the experimental data.

Application of apatite particles for remediation of contaminated soil and groundwater: A review and perspectives

With rapid industrial development and population growth, the pollution of soil and groundwater has become a critical concern all over the world. Yet, remediation of contaminated soil and water remains a major challenge. In recent years, apatite has gained a surging interest in environmental remediation because of its high treatment efficiency, low cost, and environmental benignity. This review summarizes recent advances in: (1) natural apatite of phosphate ores and biological source; (2) synthesis of engineered apatite particles (including stabilized or surface-modified apatite nanoparticles); (3) treatment effectiveness of apatite towards various environmental pollutants in soil and groundwater, including heavy metals (e.g., Pb, Zn, Cu, Cd, and Ni), inorganic anions (e.g., As oxyanions and F-), radionuclides (e.g., thorium (Th), strontium (Sr), and uranium (U)), and organic pollutants (e.g., antibiotics, dyes, and pesticides); and (4) the removal and/or interaction mechanisms of apatite towards the different contaminants. Lastly, the knowledge or technology gaps are identified and future research needs are proposed.

Efficient removal of cesium ions using Prussian blue loaded on magnetic porous biochar synthesized by one-step calcination

Prussian blue (PB) is widely used for the selective removal of radioactive cesium ions (Cs+) from aqueous solutions. Due to its small size and easy dispersion in water, PB requires a carrier that is both inexpensive and easily separable. Magnetic porous biochar (MPBC) was formed by activating starch with FeCl3 through a one-step calcination method. MPBC can be used as a carrier for Prussian blue, which is easily separated from the solution. This composite material (PB/MPBC) has a rich pore structure and maintains effective surface area, which can facilitate the penetration of Cs+ into the adsorbent. Besides, PB/MPBC exhibits high selectivity and good adsorption capacity achieving a large removal capacity of 101.43 mg/g. Thus, this study provides a novel approach for preparing composites with efficient removal of Cs+.

Efficient adsorptive removal of Co2+ from aqueous solution using graphene oxide

This study aimed to utilize synthesized graphene oxide (GO) for adsorptive removal of cobalt ions and investigate the adsorption mechanism using advanced techniques such as X-ray absorption spectra (XAFS). The GO was synthesized via an improved Hummers method, resulting in high surface area (93.7 m2/g) and abundant oxygen-containing functional groups. Various characterizations, including SEM, TEM, Raman, FT-IR, TG, potentiometric titrations, and N2 sorption-desorption measurements, were employed to characterize the GO. The adsorption behavior of GO towards Co2+ was investigated, and the results showed that the adsorption process followed a pseudo-second-order kinetic model and the Langmuir model, with a maximum sorption capacity of 93.7 mg/g. The adsorption process was chemisorption and endothermic, with GO showing adsorption selectivity order of Co2+ > Sr2+ > Cs+. Based on various characterizations such as X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), FT-IR, and XPS, the sorption mechanism of Co2+ onto GO was discussed, with the results indicating that coordination and electrostatic interaction were the primary adsorption mechanisms, with oxygen-containing functional groups playing a vital role. The first coordinating atom for Co2+ was O, and the coordination environment was similar to that of cobalt acetate and CoO. Overall, this study provides comprehensive understanding of the adsorption behavior and mechanism of Co2+ onto GO, highlighting its potential as an effective adsorbent for removing nuclides from aqueous solution.