Equilibrium, kinetic and thermodynamic studies of uranium biosorption by calcium alginate beads

Elucidating uranium interactions with synthetic Na-P1 zeolite/Ca2+-substituted alginate composite granules through batch and spectroscopic studies: Emphasizing the significance of ion exchange and complexation

Uranium, a key member of the actinides series, is radioactive and may cause severe environmental hazards once discharged into the water due to high toxicity. Removal of uranium via adsorption by applying tailored, functional adsorbents is at the forefront of tackling such pollution. Here, we report the optimized functionalization of the powder coal fly-ash (CFA) derived Na-P1 synthetic zeolite to the form of granules by employing the biodegradable polymer-calcium alginate (CA) and their application to remove aqueous U. The optimized synthesis showed that granules are formed at the CA concentration equals to 0.5 % wt., and that application of 1% wt. solution renders the most effective U scavengers. The maximum U adsorption capacity (qmax) increases significantly after CA modification from 44.48 mgU/g for native, powder Na-P1 zeolite to 62.53 mg U/g and 76.70 mg U/g for 0.5 % wt. and 1 % wt. CA respectively. The U adsorption follows the Radlich-Peterson isotherm model, being the highest at acidic pH (pHeq∼4). The U adsorption kinetics reveals swift U uptake, reaching equilibrium after 2h for 1 % ZACB and 3 h for 0.5 % wt. ZACB following the pseudo-second-order (PSO) kinetic model. SEM-EDXS investigation elucidates that adsorbed U occurs onto materials as an inhomogenous, well-dispersed, and micrometer-scale aggregate. Further, XPS and μ-XRF spectroscopies complementarily confirmed the hexavalent oxidation state of adsorbed U and its altered distribution on ZACBs with varying CA concentrations. U distribution was probed "in-situ" onto materials while correlations between the major elements (Al, Si, Ca, U) contributing to U scavenging were calculated and compared. Finally, a real-life coal mine wastewater (CMW) polluted by 238U and 228,226Ra was successfully purified, satisfying WHO guidelines after treatment using ZACBs. These findings offer new insights on successful yet optimized Na-P1 zeolite modification using biodegradable polymer (Ca2+-exchanged alginate) aimed at efficient U removal, displaying a near-zero environmental impact.

3D printing calcium alginate adsorbents for highly efficient recovery of U(VI) in acidic conditions

In this study, a three-dimensional (3D) porous calcium alginate (3D CA) scaffold was successfully constructed using a direct-ink-writing-based 3D printing method combined with an in-situ calcium ion cross-linking procedure. The 3D CA contained orderly aligned microstructures with excellent structural robustness and an abundant number of active binding sites. The adsorption experiments verified that 3D CA had a considerably wide pH value (3-10) serving range, but also delivered a significantly higher adsorption capacity for U(VI) (117.3 mg/g at pH = 2.5) under acidic conditions, compared to other previously reported alginate-based porous adsorbents. The adsorption mechanisms originated from the synergistic effect of electrostatic interactions and ion exchange. The 3D CA eluted the adsorbed U(VI) in a strong acid solution through protonation mechanism, facilitating the continued enrichment and recycling of U(VI). In addition, the 3D CA demonstrated good microstructure stability and absorption capacity stability when it was immersed in hydrochloric acid solutions at different concentrations (3.6 × 10^-3 to 2 mol/L) for 24 h. Therefore, the 3D CA could be used for the removal and recycling of U(VI) from acidic solutions beyond its wide pH working range, due to its stronger acid stability and higher U(VI) adsorption capacity.

Polyethyleneimine incorporated chitosan/α-MnO2 nanorod honeycomb-like composite foams with remarkable elasticity and ultralight property for the effective removal of U(VI) from aqueous solution

The development of new adsorbents is needed to address the environmental challenges of radioactive wastewater treatment. Herein we reported a novel polyethyleneimine incorporated chitosan/α-MnO₂ nanorod honeycomb-like composite (PCM) foam with remarkable elasticity and ultralight property for U(VI) removal. Among different PCM sorbents, PCM-40 possessed the highest sorption capacity for U(VI) due to its highly developed macroporous structure and high content of amine/imine groups. The kinetics were well-simulated by the pseudo-second-order model, indicating chemisorption as the rate-controlling step. The isotherms could be described by the Langmuir model, suggesting mono-layer homogeneous sorption of U(VI). The maximum sorption U(VI) capacity for PCM-40 reaches up to 301.9 mg/g at pH 4.5 and 298 K. The thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. The main sorption mechanism is related to the complexation of uranyl ions with the amine/imine and hydroxyl groups. The high sorption capacity, fast kinetic rate and relatively good selectivity of PCM-40 highlights its promising application in radioactive pollution cleanup.

Polysaccharides as Support for Microbial Biomass-Based Adsorbents with Applications in Removal of Heavy Metals and Dyes

The use of biosorbents for the decontamination of industrial effluent (e.g., wastewater treatment) by retaining non-biodegradable pollutants (antibiotics, dyes, and heavy metals) has been investigated in order to develop inexpensive and effective techniques. The exacerbated water pollution crisis is a huge threat to the global economy, especially in association with the rapid development of industry; thus, the sustainable reuse of different treated water resources has become a worldwide necessity. This review investigates the use of different natural (living and non-living) microbial biomass types containing polysaccharides, proteins, and lipids (natural polymers) as biosorbents in free and immobilized forms. Microbial biomass immobilization performed by using polymeric support (i.e., polysaccharides) would ensure the production of efficient biosorbents, with good mechanical resistance and easy separation ability, utilized in different effluents' depollution. Biomass-based biosorbents, due to their outstanding biosorption abilities and good efficiency for effluent treatment (concentrated or diluted solutions of residuals/contaminants), need to be used in industrial environmental applications, to improve environmental sustainability of the economic activities. This review presents the most recent advances related the main polymers such as polysaccharides and microbial cells used for biosorbents production; a detailed analysis of the biosorption capability of algal, bacterial and fungal biomass; as well as a series of specific applications for retaining metal ions and organic dyes. Even if biosorption offers many advantages, the complexity of operation increased by the presence of multiple pollutants in real wastewater combined with insufficient knowledge on desorption and regeneration capacity of biosorbents (mostly used in laboratory scale) requires more large-scale biosorption experiments in order to adequately choose a type of biomass but also a polymeric support for an efficient treatment process.

The Removal of Benzothiophene from Model Diesel on NaY and NiY Zeolites: Equilibrium and Kinetic Studies

This work investigates the adsorption of sulfur compounds in model fuel (benzothiophene dissolved in n-octane) on NaY and NiY zeolites from the points of adsorption equilibrium and kinetics. The crystal structures, textural properties and chemical compositions of zeolites were characterized by XRD, N2 physisorption and ICP-AES, respectively. The adsorption of sulfur from model diesel was processed in a batch experiment on NaY and NiY zeolites, and the effects of adsorption temperature and adsorption time on adsorption capacity were investigated. The experimental isotherm data were fitted using Langmuir, Freundlich and Toth models. The pseudo-first order, pseudo-second order, pseudo-n order and intra-particle diffusion models were applied to fit the kinetic data and determine the adsorption mechanism. It is observed from the correlation coefficient (R2) that Toth model is more appropriate to depict the isotherm equilibrium adsorption process and the sulfur uptake process follows the pseudo-n order rate expression on NaY and NiY zeolites. The diffusion study indicated that the adsorption of benzothiophene is controlled by two steps. Moreover, the results of the relative error (RE) analysis further confirm the conclusion of the kinetic study. Thermodynamic studies demonstrated that the adsorption process is exothermal and spontaneous. The equilibrium adsorption sulfur capacities are 20.66 and 28.21 mgS˙g−1 on NaY and NiY zeolites at 50 °C, respectively.

Isotherms, thermodynamic and mechanism studies of removal of low concentration uranium (VI) by Aspergillus niger

In order to develop an effective and economical method for removing low concentration radioactive wastewater of uranium, the biomass of 'CMCC(F)-98003' Aspergillus niger was investigated in a batch system. The maximum uranium adsorption capacity of 12.5 mg g^-1 was obtained at the initial uranium concentration of 0.75 mg L^-1. The biosorption data on a biomass concentration of 0.029 g L^-1 fitted well to the Freundlich isotherm with a correlation coefficient (R²) of 0.987. The calculated thermodynamic parameters showed that the biosorption of uranium ions was endothermic (ΔH° < 0). The results of scanning electron microscope and Fourier transform infrared spectrometry analysis revealed that nano-particles of uranium precipitation were formed on the cell surfaces after biosorption, and the functional groups of -CH, N-H, -COOH, P = O and the carbohydrates and alcohols were involved in the biosorption process between A. niger and uranium ions.

Uranium removal by novel graphene oxide-immobilized Saccharomyces cerevisiae gel beads

To evaluate its ability to absorb dissolved uranium (VI), the waste biomass of Saccharomyces cerevisiae was immobilized using different agents, including Ca-alginate (Ca-SA), Ca-alginate with graphene oxide (GO), polyvinyl alcohol (PVA, 5% or 10%, w/v)-SA-GO in CaCl₂-boric acid solution. The experimental results showed that graphene oxide at 0.01% (w/v) could enhance the performance of the immobilized cells. The yeast gel beads prepared with 5% PVA-1% SA-2% yeast-0.01% GO-2% CaCl₂-saturated boric acid (4#) generally showed the better physical-chemical properties such as higher tolerance to the unfavorable environmental conditions. Moreover, the 4# gel beads exhibited more stable capacity for U(VI) sorption and desorption at various conditions, such as pH in the range of 3-9. A pseudo second-order kinetic model could describe the kinetics of U(VI) sorption onto the 4# gel beads (R² = 0.96). The Langmuir, Freundlich, Tempkin and Sips models could be used to describe U(VI) sorption by the 4# gel beads, with the R² being 0.90, 0.83, 0.96, 0.97, respectively. The Sips maximum capacity of 4# gel beads was 24.4 mg U/g dry weight. The desorption efficiency of U(VI) adsorbed onto the 4# gel beads was 91%, 73% and 40% by 0.1 M HNO₃, 0.1 M HCl and 0.1 M NaOH, respectively. However, the 4# gel beads exhibited lower U(VI) sorption capacity than the raw yeast cell (Sips maximum capacity of 35.6 mg U/g). The immobilized Saccharomyces cerevisiae using SA, PVA and/or GO showed obvious changes in the molecular vibration of functional groups such as carboxyl, amide and hydroxyl groups compared with the raw yeast cells, according to FTIR analysis. The SEM-EDX analysis showed that U(VI) was adsorbed unevenly on the cellular surface. Carboxyl and hydroxyl groups may be involved in U(VI) binding by yeast cells.

Study of polyethyleneimine- and amidoxime-functionalized hybrid biomass of Spirulina (Arthrospira) platensis for adsorption of uranium (VI) ion

This study investigates the potential application of the polyethyleneimine- (PEI) and amidoxime-modified Spirulina (Arthrospira) platensis biomasses for the removal of uranium ion in batch mode using the native biomass as a control system. The uranium ion adsorption was also characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra, zeta potential analysis, and surface area measurement studies. The effects of pH, biomass amount, contact time, initial uranium ion concentration, and ionic strength were evaluated by using native and modified algal biomass preparations. The uranium ion removal was rapid, with more than 70% of total adsorption taking place in 40 min, and equilibrium was established within 60 min. From the experimental data, it was found that the amount of adsorption uranium ion on the algal preparations decreased in the following series: amidoxime-modified algal biomass > PEI-modified algal biomass > native algal biomass. Maximum adsorption capacities of amidoxime- and PEI-modified, and native algal biomasses were found to be 366.8, 279.5, and 194.6 mg/g, respectively, in batchwise studies. The adsorption rate of U(VI) ion by amidoxime-modified algal biomass was higher than those of the native and PEI-modified counterparts. The adsorption processes on all the algal biomass preparations followed by the Dubinin-Radushkevitch (D-R) and Temkin isotherms and pseudo-second-order kinetic models. The thermodynamic parameters were determined at four different temperatures (i.e., 15, 25, 35, and 45 °C) using the thermodynamics constant of the Temkin isotherm model. The ΔH° and ΔG° values of U(VI) ion adsorption on algal preparations show endothermic heat of adsorption; higher temperatures favor the process. The native and modified algal biomass preparations were regenerated using 10 mM HNO3. These results show that amidoxime-modified algal biomass can be a potential candidate for effective removal of U(VI) ion from aqueous solution.