Batch and continuous fixed-bed column adsorption of Cs+ and Sr2+ onto montmorillonite–iron oxide composite: Comparative and competitive study

Nanosorbent based on coprecipitation of ZnO in goethite for competitive sorption of Cd(II)-Pb(II) and Cd(II)-Pb(II)-Ni(II) systems

Amongst the various water pollutants, heavy metal ions require special attention because of their toxic nature and effects on humans and the environment. Preserving natural resources will have positive impacts on living conditions by reducing diseases and water treatment by nanotechnology is effective in solving this problem owing to the properties of nanomaterials. In this study, a goethite nanoparticle was prepared by hydrothermal method, while ZnO/goethite nanocomposite by co-precipitation was developed. The nanoparticles were characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transform Electron Microscopy (TEM), Thermogravimetric Differential Thermal Analysis (TGA-DTA), Dynamic Light Scattering (DLS), and Breunner-Emmet-Teller (BET) surface area analysis. The adsorption of Cd(II)-Pb(II) and Cd(II)-Pb(II)-Ni(II) ions systems on ZnO/goethite nanocomposite was investigated in a batch mode. The findings of the study showed that nanoparticles ZnO/goethite composite were mixed of spherical and rod-like shapes. The BET results revealed average particle sizes of 41.11 nm for nanoparticles for ZnO/goethite while TGA/DTA confirmed the stability of the adsorbents. The optimum adsorption capacities of the nanocomposite for Pb(II), Cd(II), and Ni(II) ions from the Pb-Cd-Ni ternary system were 415.5, 195.3, and 87.13 mg g-1, respectively. The adsorption isotherm data fitted well with the Langmuir isotherm model. The study concluded that the nanoparticle adsorbents are efficient for the remediation of toxic pollutants and are, therefore, recommended for wastewater treatment.

Adsorption behavior of molybdenum onto K-doped γ-Al2O3 and iron clay nanocomposite

Adsorption of molybdenum was carried out on two materials; potassium doped γ-Al2O3 (KA) and bentonite iron oxide composite (BIOC) with purpose of using in production of chromatographic 99mTc generators, for KA absorbent, different ranges of potassium loadings have been considered, for BIOC solid the used weight ratio was (Bentonite/Fe = 2/1). Samples were characterized by XRD and WDXRF. Adsorption of MoxOy z− species was carried out at pH 2.5 and 25 °C, effects of contact time and pH were studied. The Mo adsorption data onto used materials were well fitted using Freundlich and Langmuir models. Doped alumina samples showed higher adsorption capacities (∼90 mg g−1) than the usual alumina used in generator technology (∼60 mg g−1), whereas adsorption capacities of BIOC solid were in the range of (∼75 mg g−1).

Biomass as source for hydrochar and biochar production to recover phosphates from wastewater: A review on challenges, commercialization, and future perspectives

Excessive phosphate run-off with total phosphorus concentration greater than 20 μg P L^-1 triggers the growth of harmful algal species in waterbodies and potentially leads to eutrophication. This has severe negative implications on aquatic environment and impacts human health. The annual economic impact of harmful algal blooms is reported to be as high as $25 million for public health and commercial fishery sector, $29 million for recreation/tourism sector and $2 million for monitoring and management. Adsorption is widely considered as an effective and economic strategy to achieve extremely low concentration of phosphorus. The char produced by valorizing various waste biomasses have been gaining attention in phosphorus remediation owing to their availability, their ability to regenerate and reuse. This review paper exclusively focuses on utilizing hydrochar and biochar synthesized from waste biomass, respectively, through hydrothermal carbonization and slow pyrolysis to mitigate phosphorus concentration and potential strategies for handling the spent char. The key mechanisms involved in phosphate adsorption are electrostatic interaction, ion exchange and complexation. The maximum adsorption capacity of hydrochar and biochar ranges from 14-386 mg g^-1 and 3-887 mg g^-1, respectively. Hydrochar and biochar are cost-effective alternative to commercial activated carbon and spent char can be used for multiple adsorption cycles. Furthermore, extensive research studies on optimizing the feedstock, reaction and activation conditions coupled with technoeconomic analysis and life cycle assessment could pave way for commercialization of char-based adsorption technology.

Kinetic Studies of Cs+ and Sr2+ Ion Exchange Using Clinoptilolite in Static Columns and an Agitated Tubular Reactor (ATR)

Natural clinoptilolite was studied to assess its performance in removing caesium and strontium ions, using both static columns and an agitated tube reactor (ATR) for process intensification. Kinetic breakthrough curves were fitted using the Thomas and Modified Dose Response (MDR) models. In the static columns, the clinoptilolite adsorption capacity (qe) for 200 ppm ion concentrations was found to be ~171 and 16 mg/g for caesium and strontium, respectively, highlighting the poor material ability to exchange strontium. Reducing the concentration of strontium to 100 ppm, however, led to a higher strontium qe of ~48 mg/g (close to the maximum adsorption capacity). Conversely, halving the column residence time to 15 min decreased the qe for 100 ppm strontium solutions to 13–14 mg/g. All the kinetic breakthrough data correlated well with the maximum adsorption capacities found in previous batch studies, where, in particular, the influence of concentration on the slow uptake kinetics of strontium was evidenced. For the ATR studies, two column lengths were investigated (of 25 and 34 cm) with the clinoptilolite embedded directly into the agitator bar. The 34 cm-length system significantly outperformed the static vertical columns, where the adsorption capacity and breakthrough time were enhanced by ~30%, which was assumed to be due to the heightened kinetics from shear mixing. Critically, the increase in performance was achieved with a relative process flow rate over twice that of the static columns.

Prediction and optimization of adsorption properties for Cs+on NiSiO@NiAlFe LDHs hollow spheres from aqueous solution: Kinetics, isotherms, and BBD model

In this work, novel NiSiO@NiAlFe layered double hydroxides (LDHs) hollow spheres were prepared by hydrothermal method. It was worth noting that LDHs' grafting towards NiSiO hollow spheres could avoid the LDHs' aggregation, and thus enhanced the material's adsorption capacity. Furthermore, adsorption kinetics, adsorption isotherms, and Box-Behnken Design (BBD) model were conducted. Results indicated that NiSiO@NiAlFe LDHs hollow spheres had sufficient adsorption capability towards Cs⁺. The adsorption kinetics satisfied the pseudo-second-order adsorption model, Temkin model and Langmuir isotherm model. The adsorption process was efficient at the alkaline condition (pH = 10). The adsorption kinetics indicated that the adsorption process could reach the equilibrium in only 20 min. The maximum adsorption capacity of Cs⁺ towards NiSiO@NiAlFe LDHs hollow spheres was estimated to be 61.5 mg g^-1. Moreover, the adsorption thermodynamics indicated that the adsorption process was exothermal, feasible and spontaneous. Thus, NiSiO@NiAlFe LDHs hollow spheres presented a broad potential for treating cesium containing wastewater.

Brushite-infused polyacrylonitrile nanofiber adsorbent for strontium removal from water

The Fukushima Daiichi nuclear disaster and the decommissioning of over a hundred nuclear reactors worldwide led to the increase in the demand for efficient water treatment technologies to remove radionuclides, such as ⁹⁰Sr. Brushite or dicalcium phosphate dihydrate (DCPD) is a potential adsorbent to remove strontium from water. In this study, composite poly(acrylonitrile) (PAN) nanofiber (NF) adsorbents with DCPD (PAN/DCPD) were prepared, characterized, and investigated for strontium adsorption in water. Material characterization revealed mechanically suitable, hydrophilic, and macroporous composite NF adsorbents with average fiber diameters of <500 nm. As-prepared DCPD powder exhibited a superior strontium uptake capacity of 81.7 mg g^-1 at pH ≅ 10 of aqueous Sr²⁺ solution over its biogenic and synthetic predecessor, hydroxyapatite. Increased DCPD loading resulted in higher adsorption. Maximum Sr²⁺ uptake of PAN/DCPD NF with 70 wt% DCPD loading (PAN/70DCPD NF) was 146 mg g^-1 considering the Sips isotherm model. Kinetic studies revealed that Sr²⁺ removal by PAN/DCPD NF was a chemisorption process which involved ion exchange and surface complexation. PAN/70DCPD NF as a dead-end membrane filter exhibited superior removal efficiency over pure PAN NF. The overall results of this study revealed the potential application of PAN/DCPD NF adsorbent for ⁹⁰Sr removal from water.

Hybrid Pectin-Based Sorbents for Cesium Ion Removal

In this paper, beads-shaped hybrid sorbents composed of pectin and Prussian blue were prepared. Various ratios of pectin and Prussian blue in hybrid sorbents were tested. Obtained sorbents had high and roughly constant sorption capacity in a broad pH range (4–10), in which also the swelling index and stability of sorbents were satisfactory. The preliminary sorption studies proved that almost 100% of cesium removal efficiency may be achieved by using the proper sorbent dose. The sorption capacity of the hybrid sorbent with a 1:1 ratio of pectin to Prussian blue equaled q = 36.5 ± 0.8 mg/g (dose 3 g/L, pH = 6, temp. = 22 ± 1 °C, t = 24 h). The obtained results showed that the prepared hybrid pectin-based sorbents are promising for cesium ions removal.

Field technical applicability and cost analysis for microwave based regenerating permeable reactive barriers (MW-PRBs) operating in Cs-contaminated groundwater treatment

The present study tests the potentiality of a novel microwave based regenerating permeable reactive barrier (MW-PRB) system as combined treatment for Cs-contaminated groundwater. Granular activated carbon (GAC) was selected as adsorptive materials in batch and column MW-regeneration experiments. Experimental and modeling data were elaborated for technical and economic considerations in order to assess the MW-PRB feasibility jointly with essential information regarding its real field applicability. Batch experiments investigated the effects of 10 adsorption-MW regeneration cycles under different MW irradiation conditions (applied electric field = 200-460 V m^-1; irradiation times = 1-15 min) by assessing GAC variation properties in term of regeneration yield (δ), specific area and weight loss (WL) variation. Column tests were carried using a dedicated setup essentially including a column filled with GAC implanted in a MW oven cavity (MW electric field of 385 V m^-1, irradiation times 5-15 min). Lab-scale results shown the ability of MW in Cs removal from GAC as demonstrated by regeneration yield (δ = 79-110%) and WL (6.78% for 10 cycles) values. This was confirmed in dynamic conditions by data from MW-column tests highlighting the highest Cs removal of ~80% when the maximum regeneration time was applied. Residual Cs concentration in breakthrough curves fitted well with the proposed Yoon and Nelson model (R² = ~0.97). Results from techno-economic analysis revealed the MW-PRB viability and its advantages also in comparison with conventional PRB systems, demonstrating the concept of combined MW-PRB treatment. Saved cost obtained demonstrated in fact the potential cost effectiveness of MW-PRB system and, consequently, the implementation of novel approach is encouraged. Calculated PRB longevity vs groundwater velocity curves are useful in order to predict long-term PRB performance and the response of the remediation activities, as well as for guiding the design and the scaling-up of MW-PRB treatment.

Synthesis and Sorption Properties towards Sr-90 of Composite Sorbents Based on Magnetite and Hematite

The article describes the synthesis of composite sorbents by immobilizing iron oxide in a polymer matrix with subsequent hydrothermal treatment at a temperature of 175 °C. The sorbents based on magnetite and hematite were synthesized, their magnetic properties and phase composition were evaluated, and the iron content was determined. Sorption characteristics of the composites towards microconcentrations of Sr-90 radionuclide in solutions with different mineralization and pH were investigated. It was shown that the sorbent based on magnetite was the most efficient. In alkaline media with pH above 11, the composite sorbent based on magnetite exhibited increased selectivity towards Sr-90 and proved to be suitable for application under dynamic sorption conditions with subsequent desorption of the radionuclide with a solution of HNO₃.

Investigation of interaction behaviours of cesium and strontium ions with engineering barrier material to prevent leakage to environmental

This study deals with performance of removal of cesium (Cs⁺) and strontium (Sr²⁺) ions from synthetic aqueous solution using amino pyridine sulfone amid resin as a barrier material for nuclear waste storage areas to reduce environmental risk. The effects of adsorbate concentration, temperature and contact time on the efficiencies of the engineering barrier material for Cs⁺ and Sr²⁺ ions were investigated and evaluated. It was found that total adsorption capacity was higher for cesium ions than strontium ions. Dubinin-Radushkevich (D-R) isotherm model was well fitted to the adsorption data for both ions. The micropore capacity of the barrier material was found as 4.20 mg for strontium ions and 5.40 mg for cesium ions. ΔH values were indicated that the interaction process is exothermic for both ions. The positive value of entropy for both ions show that randomness at the solid-solution interface increased. Pseudo-second-order model was well fitted the kinetic data.

Elimination of Cs+ from aquatic systems by an adsorbent prepared by immobilization of potassium copper hexacyanoferrate on the SBA-15 surface: kinetic, thermodynamic, and isotherm studies

For elimination of cesium from aqueous solutions, mesoporous SBA-15 was synthesized and employed as the support for immobilization of potassium copper hexacyanoferrate. The synthesized adsorbent was characterized by various techniques and was used for adsorption of cesium. The results indicated that its adsorption capacity was 174.80 mg/g and superior to many studied adsorbents. The adsorbent represented good selectivity in the presence of some studied co-existing. The Temkin, Redlich-Peterson, Sips, Langmuir, and Freundlich isotherm models were used to evaluate the experimental data. The error analysis performed by EABS, ERRSQ, and HYBRID methods showed that the data was in good agreement with the Langmuir model indicating that the process was monoenergetic and the uptake of cesium forwarded through monolayer process. The pseudo-second-order model was recognized as the adequate model to describe the kinetic data of the adsorption process. The adsorption process was endothermic and spontaneous. The regeneration tests revealed that the adsorbent retained most of initial capacity after recovery.

Hybrid porous magnetic bentonite-chitosan beads for selective removal of radioactive cesium in water

Easy-to-obtain magnetic bentonite-chitosan hybrid beads (Bn-CTS) were prepared by immobilizing bentonite within a porous structure of chitosan beads to achieve a hybrid adsorption effect for the removal of cesium ion (Cs⁺) from water. The hybrid adsorbent, which had a porous structure and abundant binding sites contributed by both chitosan and bentonite, ensured superb adsorption characteristics. The paramagnetic character of the beads enabled their facile separation for recycling. The chitosan/bentonite ratio, pH and contact time were optimized to achieve the optimal Cs⁺ efficiency, and the adsorption kinetics and isotherms were thoroughly discussed. The adsorption kinetics obeyed the pseudo-second-order model, and the best fitted equation for equilibrium data was the Langmuir isotherm model. The maximum adsorption capacity of the bentonite-chitosan beads was 57.1 mg g^-1. The adsorbent had excellent selectivity towards Cs⁺ adsorption in the presence of abundant cations (Li⁺, Na⁺, K⁺ and Mg²⁺). The adsorbent was able to be recycled by treating the beads with 0.1 mol L^-1 of MgCl₂ to quantitatively desorb Cs⁺ from the beads. Overall, the magnetic bentonite-chitosan beads can be used as a highly efficient adsorbent for radioactive waste disposal and management.

The adsorption of Cs+ from wastewater using lithium-modified montmorillonite caged in calcium alginate beads

The increasing nuclear energy consumption has posed serious environmental concerns (e.g. nuclear leakage), and the removal of radionuclides such as cesium becomes an urgent issue to be solved currently. In this research, a novel non-toxic adsorbent lithium-modified montmorillonite clay encapsulated in calcium alginate microbeads (MCA/Li) was fabricated by using ion-exchange method and then used successfully in the remediation of cesium-contaminated wastewater. Analyses of scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the physicochemical properties of adsorbent MCA/Li, such as internal crystal structure, constituent elements, and functional groups. The effects of concentration ratios (sodium alginate/montmorillonite), solution pH, contacting time and initial Cs⁺ concentration on the adsorption behavior were carefully investigated via batch adsorption experiments. The adsorbent MCA/Li exhibited higher selectivity and removal efficiency towards Cs⁺ with the maximum adsorption capacity of 100.25 mg/g. In the kinetics study, the pseudo-first-order fitted the cesium adsorption data of MCA/Li better than the pseudo-second-order. The adsorption mechanism studies revealed the process followed the Langmuir isotherm model, which suggested that Cs⁺ adsorption onto MCA/Li is a monolayer homogeneous adsorption process. The research findings indicated this novel adsorbent MCA/Li demonstrated great potential in radioactive wastewater treatment due to its convenience in synthesis, high adsorption capacity, and low cost.

Strontium selectivity in sodium nonatitanate Na ₄Ti₉O₂₀·xH₂O

We study the extraction of strontium by sodium nonatitanate powder from nitrate strontium and acetate sodium mixture. Experiments show that adsorption is quantitative. The excess Gibbs free energy has been modeled by various models (ideal, 2D Coulomb, regular solution model) for the solid phase. We find that the free energy of the solid phase is controlled by short-range interactions rather than long-ranged Coulombic forces. The selectivity is the consequence of a competition between the liquid and solid phases: both phases prefer strontium rather than sodium but the solid contribution is predominant.

Adsorption removal of cesium from drinking waters: a mini review on use of biosorbents and other adsorbents

Radiocesium (Cs) removal from waters becomes an emerging issue after the Fukushima Daiichi Nuclear Power Plant Disaster, during which a total of approximately 3.3×10(16) Bq Cs was released to contaminate the environment. This mini-review provided a summary on literature works to develop efficient adsorbent for removing Cs from waters. Adsorbent made of raw and modified minerals, composites particles, and biosorbents that are highly specific to Cs in the presence of other alkali and alkali earth metals were summarized. Development of Prussian blue (PB) nanoparticles on Cs removal and its potential use in drinking waterworks was discussed. This review is a unique report for adsorption removal of Cs from contaminated waters.