Sorption of stable and radioactive Cs(I), Sr(II), Co(II) ions on Ti–Ca–Mg phosphates

Sorption study of long-lived 94Nb on laterite: Effects of physicochemical parameters on sorption

Zr-Nb alloy is used as the pressure tube in pressurized heavy water reactors (PHWR). Prolonged neutron irradiation of the pressure tubes leads to the formation of a long-lived radioisotope ⁹⁴Nb. Thus, the discharged pressure tubes possess huge ⁹⁴Nb activity which persists for a prolonged period.If these discharged pressure tubes come in contact with ground water, ⁹⁴Nb isotope may leach and migrate and this can lead to a long-term radiological impact in the environment.In the present study, we have explored the capability of laterite as a filler material for the containment and retarding the migration of ⁹⁴Nb. In this regard, detailed characterization of the laterite soil was carried out using energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD), fourier transform infra-red spectrometry (FTIR), total cation exchange capacity determination, zeta potential measurement and thermogravimetric analysis (TGA). The sorption study of ⁹⁴Nb on laterite was carried and the effects of different physico-chemical parameters like pH, ionic strength, temperature and equilibration time were evaluated. Ionic strength, temperature and time dependent sorption studies assist to explore the probable sorption mechanism of ⁹⁴Nb on laterite, which helps in understanding the migration behaviour of ⁹⁴Nb in natural aquatic environment. This study suggests that laterite is a promising material in containment of ⁹⁴Nb isotope owing to its good cation exchange behaviour in the acidic medium and ability to form surface complex in the neutral medium.

Performance of molybdenum vanadate loaded on bentonite for retention of cesium-134 from aqueous solutions

This article studied the sorption behavior of Cs(I) ions from aqueous solutions onto molybdenum vanadate@bentonite (MoV@bentonite) composite. MoV@bentonite has been fabricated using the precipitation method and was characterized by different analytical tools including, FT-IR, XRD, and SEM attached with an EDX unit. The sorption studies applied on Cs(I) ions include the effect of contact time, pH, initial metal concentrations, ionic strength, desorption, and recycling. The experimental results revealed that in the adsorption process carried out after equilibrium time (300 min), saturation capacity has a value of 26.72 mg·g^-1 and the sorption of Cs(I) ions is dependent on pH values and ionic strength. Sorption kinetic better fit with the pseudo-second-order model; sorption isotherms apply to Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. Data of thermodynamic parameters indicate that sorption is spontaneous and endothermic. Recycling experiments show that MoV@bentonite could be used for 7 cycles and the best eluant for the recovery of Cs(I) ions is 0.1 M HCl (76.9%). All the obtained data clarify that MoV@bentonite is considered a promising sorbent for the sorption of Cs(I) ions from aqueous solutions.

Inorganic Sorbents for Wastewater Treatment from Radioactive Contaminants

The article presents the distribution coefficient (Kd) values of 137Cs and 90Sr tracer radionuclides in solutions of sodium and calcium salts for a wide range of commercially available inorganic sorbents: natural and synthetic aluminosilicates, manganese, titanium and zirconium oxyhydrates, titanium and zirconium phosphates, titanosilicates of alkali metals, and ferrocyanides of transition metals. The results were obtained using a standard technique developed by the authors for evaluating the efficiency of various sorption materials towards cesium and strontium radionuclides. It was shown that bentonite clays and natural and synthetic zeolites are the best for decontaminating low-salt natural water from cesium radionuclides, and ferrocyanide sorbents are the choice for decontaminating high-salt-bearing solutions. The manganese (III, IV) oxyhydrate-based MDM sorbent is the most effective for removing strontium from natural water; for seawater, the barium silicate-based SRM-Sr sorbent is the first-in-class. Results of the study provide a possibility of making a reasonable choice of sorbents for the most effective treatment of natural water and technogenic aqueous waste contaminated with cesium and strontium radionuclides.

Adsorption of Co(II) ions using Zr-Ca-Mg and Ti-Ca-Mg phosphates: adsorption modeling and mechanistic aspects

The environmental pollution by toxic Co(II) ions had a negative impact on living organisms and water resources. The amorphous Zr-Ca-Mg and Ti-Ca-Mg phosphates with varied Zr and Ti content with the mesoporous structure (A_BET = 19-232 m²/g, V_des. = 0.075-0.370 cm³/g, D_des. = 6.2-10.9 nm) were synthesized. The effect of adsorbent chemical composition, the presence of competing ions (0.1-1.0 M NaCl and 0.01-0.1 M CaCl₂ backgrounds), and pH (3.0-7.0) of aqueous solution on adsorption removal of Co(II) ions by Zr-Ca-Mg and Ti-Ca-Mg phosphates was studied. The highest adsorption capacity of Zr-Ca-Mg-1 and Ti-Ca-Mg-1 samples reached 253.3 and 212.8 mg/g. The prepared adsorbents demonstrated high efficiency at pH in the range of 3.0-7.0 and the presence of 0.1-1.0 M NaCl and seawater with a salinity of 35.0 g/L backgrounds. The chemisorption and ion-exchange mechanisms of Co(II) ions removal for Zr-Ca-Mg and Ti-Ca-Mg phosphates were proposed. The adsorption isotherms were well fitted with Sips and Langmuir models that proved the heterogeneous nature of adsorption sites as well as assumed the monolayer adsorption that occurs at specific homogeneous sites within the adsorbent without any interaction between the adsorbed substances. The kinetic data was well described by the pseudo-second-order model that is suitable for chemisorption processes as liming adsorption stage. The presented results shown the prospects of developed adsorbents for the investigation of real wastewater treatment from heavy metal ions and liquid radioactive waste purification.

A low-cost photo-evaporation inorganic membrane preparation and treatment of the simulated high salinity radioactive waste water

Solar-driven desalination is an energy-saving and environmentally benign wastewater treatment technology. A method of in situ self-reduction of graphene oxide (rGO) by cheap geopolymer was introduced, and a photo evaporation membrane device (rGOPGC) for treatment of the simulated high salt liquid radioactive waste (HSLRW) was prepared in the present study. Compared with other rGO based photo evaporation membrane materials, geopolymer matrix has the advantages of low cost, reductant free, simple preparation process and mild conditions. After desalination of simulated seawater, the concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ ions reached the WHO standard, and the removal rates of radioactive I^-, Cs⁺ and Sr²⁺ in the simulated high salinity wastewater reached 99.62%, 99.71% and 99.99% respectively; The evaporation rate of rGOPGC remained stable at 1.5 kg/m²/h after 16 cycles in high salinity environment. There was no obvious salt accumulation on the upper surface of the device, indicating its high stability. Furthermore, the evaporation performance at high temperature near the nuclear power plant (NPP) waste water was simulated and tested. Under one solar intensity and 35 °C ambient temperature, the evaporation rate of 1.75 kg/m²/h and the evaporation efficiency of 98.51% were achieved. The results indicated that the rGOPGC device is potential in the concentration evaluation of HSLRW.

Structural Investigation on the Efficient Capture of Cs+ and Sr2+ by a Microporous Cd-Sn-Se Ion Exchanger Constructed from Mono-Lacunary Supertetrahedral Clusters

Visualization of the ion exchange mechanism for 137Cs and 90Sr decontamination bears significance for safe radioactive liquid waste reprocessing and emergency response enhancement to nuclear accident. Here, the remediation of...

Elaboration of composite based on the incorporation of marble particles into polymeric framework for the removal of Co(II) and Eu(III)

The incorporation of marble particles into the framework of composite material through the polymerization of acrylic acid (AA) and acrylamide acid (AM) using induced gamma irradiation was performed. The novel poly[AA-AM]-marble composite was characterized by multiple analytical instruments such as: energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) analysis, differential thermal analysis-thermogravimetric analysis (DTA-TGA), Fourier transformer infrared (FTIR), surface area measurements using Brunauer–Emmett–Teller (BET) method and scanning electron microscope (SEM). Radioisotopes of fission (152+154Eu) and activation products (60Co) are the major environmental threats. Sorption of stable isotopes of cobalt and europium onto the synthesized composite material as the sorbent is applied. Sorption kinetics of Eu3+ and Co2+ were computed. The obtained results were analyzed by pseudo-first- and second-order, intraparticle diffusion, and Elovich kinetic models. It is deduced that the pseudo-second-order was more fitted and a chemisorption mechanism was suggested. The sorption capacity for Eu3+ and Co2+ on the prepared composite material was measured at the contact time (2 h) and pH = 4 (for Eu3+), pH = 6 (for Co2+) and it was found to be 91.2 and 13.1 mg/g, respectively. A promising result for the decontamination of both Eu and Co ions was obtained in various aquatic ecosystem applications such as: river water, tap water and groundwater.

Synergistic effect of carboxyl and sulfate groups for effective removal of radioactive strontium ion in a Zr-metal-organic framework

Rapid removal of radioactive strontium from nuclear wastewater is of great significance for environmental safety and human health. This work reports the effective adsorption of strontium ion in a stable dual-group metal-organic framework, Zr₆(OH)₁₄(BDC-(COOH)₂)₄(SO₄)_0.75 (Zr-BDC-COOH-SO₄), which contains strontium-chelating groups (-COOH and SO₄) and a strongly ionizable group (-COOH). Zr-BDC-COOH-SO₄ exhibits very rapid adsorption kinetics (<5 min) and a maximum adsorption capacity of 67.5 mg g^-1. The adsorption behaviors can be well fitted to the pseudo-second-order model and the Langmuir isotherm model. Further investigations indicate that the adsorption of Sr²⁺ onto Zr-BDC-COOH-SO₄ would not be obviously affected by solution pH and adsorption temperature. The feasible regeneration of the adsorbent was also demonstrated using a simple elution method. Mechanism investigation suggests that free -COOH contributes to the rapid adsorption based on electrostatic interaction, while the introduction of -SO₄ significantly enhanced the adsorption capacity. Thus, these results suggest that Zr-BDC-COOH-SO₄ is a potential candidate for Sr²⁺ removal. They also introduce dual groups as an effective strategy for designing high-efficiency adsorbents.