Comparison of sustainable biosorbents and ion-exchange resins to remove Sr2+ from simulant nuclear wastewater: Batch, dynamic and mechanism studies

Synthesis and Evaluation of Peptide-Manganese Dioxide Nanocomposites as Adsorbents for the Removal of Strontium Ions

In this study, a novel organic-inorganic hybrid material IIGK@MnO2 (2-naphthalenemethyl-isoleucine-isoleucine-glycine-lysine@manganese dioxide) was designed as a novel adsorbent for the removal of strontium ions (Sr2+). The morphology and structure of IIGK@MnO2 were characterized using TEM, AFM, XRD, and XPS. The results indicate that the large specific surface area and abundant negative surface charges of IIGK@MnO2 make its surface rich in active adsorption sites for Sr2+ adsorption. As expected, IIGK@MnO2 exhibited excellent adsorbing performance for Sr2+. According to the adsorption results, the interaction between Sr2+ and IIGK@MnO2 can be fitted with the Langmuir isotherm and pseudo-second-order equation. Moreover, leaching and desorption experiments were conducted to assess the recycling capacity, demonstrating significant reusability of IIGK@MnO2.

Investigating the influence of bentonite colloids on strontium sorption in granite under various hydrogeochemical conditions

The disposal of high-level radioactive waste in deep geological repositories is a critical environmental issue. The presence of bentonite colloids generated in the engineering barrier can significantly impact the transport of radionuclides, but their effect on radionuclide sorption in granite remains poorly understood. This study aimed to investigate the sorption characteristics of strontium (Sr) on granite as well as on the coexistence system of granite and colloids under various hydrogeochemical conditions, through batch experiments. Fourier transform infrared spectroscopy was employed to analyze the sorption forms of Sr on granite before and after sorption. Several hydrogeochemical factors were examined, including contact time, pH, ionic strength, coexisting ions, and bentonite and humic acid colloid concentration. Among these factors, the concentration of bentonite colloids exhibited a significant effect on Sr sorption. Within a specific range of colloid concentration, the sorption of Sr on the solid system increased linearly with the bentonite colloid concentration. pH and ionic strength were also found to play crucial roles in the sorption process. At low pH, Sr sorption primarily occurred through the outer sphere's surface complexation and Na+/H+ ion exchange. However, at high pH, inner sphere surface complexation dominated the process. As the ionic strength increased, electrostatic repulsion gradually increased, resulting in fewer binding sites for particle aggregation and Sr sorption on bentonite colloids. The results also indicate that with increasing pH, the predominant forms of Sr in the solution transitioned from SrHCO3+ and SrCl+ to SrCO3 and SrCl+. This was mainly due to the ion exchange of Ca2+/Mg2+ in plagioclase and biotite, forming SrCO3 precipitation. These findings provide valuable insights into the transport behavior of radionuclides in the subsurface environment of the repository and highlight the importance of considering bentonite colloids and other hydrogeochemical factors when assessing the environmental impact of high-level radioactive waste disposal.

Advances in the management of radioactive wastes and radionuclide contamination in environmental compartments: a review

Several anthropogenic activities produce radioactive materials into the environment. According to reports, exposure to high concentrations of radioactive elements such as potassium (⁴⁰K), uranium (²³⁸U and ²³⁵U), and thorium (²³²Th) poses serious health concerns. The scarcity of reviews addressing the occurrence/sources, distribution, and remedial solutions of radioactive contamination in the ecosystems has fueled data collection for this bibliometric survey. In rivers and potable water, reports show that several parts of Europe and Asia have recorded radionuclide concentrations much higher than the permissible level of 1 Bq/L. According to various investigations, activity concentrations of gamma-emitting radioactive elements discovered in soils are higher than the global average crustal values, especially around mining activities. Adsorption technique is the most prevalent remedial method for decontaminating radiochemically polluted sites. However, there is a need to investigate integrated approaches/combination techniques. Although complete radionuclide decontamination utilizing the various technologies is feasible, future research should focus on cost-effectiveness, waste minimization, sustainability, and rapid radionuclide decontamination. Radioactive materials can be harnessed as fuel for nuclear power generation to meet worldwide energy demand. However, proper infrastructure must be put in place to prevent catastrophic disasters.

Phosphonation of Alginate-Polyethyleneimine Beads for the Enhanced Removal of Cs(I) and Sr(II) from Aqueous Solutions

Although Cs(I) and Sr(II) are not strategic and hazardous metal ions, their recovery from aqueous solutions is of great concern for the nuclear industry. The objective of this work consists of designing a new sorbent for the simultaneous recovery of these metals with selectivity against other metals. The strategy is based on the functionalization of algal/polyethyleneimine hydrogel beads by phosphonation. The materials are characterized by textural, thermo-degradation, FTIR, elemental, titration, and SEM-EDX analyses to confirm the chemical modification. To evaluate the validity of this modification, the sorption of Cs(I) and Sr(II) is compared with pristine support under different operating conditions: the pH effect, kinetics, and isotherms are investigated in mono-component and binary solutions, before investigating the selectivity (against competitor metals) and the possibility to reuse the sorbent. The functionalized sorbent shows a preference for Sr(II), enhanced sorption capacities, a higher stability at recycling, and greater selectivity against alkali, alkaline-earth, and heavy metal ions. Finally, the sorption properties are compared for Cs(I) and Sr(II) removal in a complex solution (seawater sample). The combination of these results confirms the superiority of phosphonated sorbent over pristine support with promising performances to be further evaluated with effluents containing radionuclides.

New Process for the Sulfonation of Algal/PEI Biosorbent for Enhancing Sr(II) Removal from Aqueous Solutions-Application to Seawater

Sulfonic resins are highly efficient cation exchangers widely used for metal removal from aqueous solutions. Herein, a new sulfonation process is designed for the sulfonation of algal/PEI composite (A*PEI, by reaction with 2-propylene-1-sulfonic acid and hydroxylamine-O-sulfonic acid). The new sulfonated functionalized sorbent (SA*PEI) is successfully tested in batch systems for strontium recovery first in synthetic solutions before investigating with multi-component solutions and final validation with seawater samples. The chemical modification of A*PEI triples the sorption capacity for Sr(II) at pH 4 with a removal rate of up to 7% and 58% for A*PEI and SA*PEI, respectively (with SD: 0.67 g L^-1). FTIR shows the strong contribution of sulfonate groups for the functionalized sorbent (in addition to amine and carboxylic groups from the support). The sorption is endothermic (increase in sorption with temperature). The sulfonation improves thermal stability and slightly enhances textural properties. This may explain the fast kinetics (which are controlled by the pseudo-first-order rate equation). The sulfonated sorbent shows a remarkable preference for Sr(II) over competitor mono-, di-, and tri-valent metal cations. Sorption properties are weakly influenced by the excess of NaCl; this can explain the outstanding sorption properties in the treatment of seawater samples. In addition, the sulfonated sorbent shows excellent stability at recycling (for at least 5 cycles), with a loss in capacity of around 2.2%. These preliminary results show the remarkable efficiency of the sorbent for Sr(II) removal from complex solutions (this could open perspectives for the treatment of contaminated seawater samples).

New insights into the interactions between Pb(II) and fruit waste biosorbent

Fruit waste is a sustainable biosorbent for heavy metal removal from wastewater. Elucidation of adsorption mechanism is imperative for the process control and development of effective adsorbents. In this study, watermelon rind (WR) exhibited selective and efficient Pb(II) adsorption with a maximum uptake of 230.5 mg/g at pH 5.0. The WR-packed bed column showed high Pb(II) uptake and robust durability over 10 adsorption-desorption cycles with long breakthrough time of 8-13 h (89-144 bed volume), and 95% of sequestered Pb(II) was rapidly desorbed in 1-2 h by 0.05 M HCl. Spectroscopic characterization by FTIR and XPS identified hydroxyl, carboxyl, amine, and ether groups as the binding sites for Pb(II) via the binding force of complexation. Physicochemical analysis showed that ion exchange with Mg²⁺ and Ca²⁺ accounted for 19% of Pb(II) adsorption by WR; electrostatic attraction and microprecipitation jointly contributed. Quantum chemistry simulation verified the interactions between Pb(II) and binding sites and revealed carboxyl was the preferential functional group. The findings corroborate the applicability of WR in scale-up Pb(II) removal/recovery from wastewater and elaborate the mechanisms of Pb(II) adsorption by the WR biosorbent. This also provides insights into the behavior of heavy metals in other liquid/solid interfaces.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Circular economy based landfill leachate treatment with sulphur-doped microporous biochar

There is now increasing interest in the creation of a more 'circular economy', with a particular aim to eliminate waste - by design, within which products are optimised to be reused, restored or returned. Here, a sulphur functionalised microporous biochar was synthesised from an abundant biomass waste material (cherry kernels), for the selective removal of Pb(II) from landfill leachate as a representative heavy metal. The production process utilises renewable waste material and removes toxic chemicals. Characterisation of the biochar showed that pyrolysis and functionalisation formed an adsorbent with a microporous structure and rich surface chemical functionality. The adsorption process was optimised using a 'response surface methodology - Box-Behnken Design'. Lead removal efficiency approached 99.9% under optimised experimental conditions, i.e., where the solution pH was 6.0, the biochar dose was 4.0 g/L and the contact time was 47 min. The adsorption process was best described using a Freundlich model. The maximum amount of Pb(II) adsorbed was 44.92 mg/g. The main adsorption mechanisms occurred through outer-sphere (electrostatic attraction) and inner-sphere complexation. Desorption studies showed that three successful regeneration cycles (with acidic deionised water) could be used post pyrolysis. The biochar removed 97% of Pb(II) from landfill leachate samples, as compared to 9.4%, and 7.6% for two commercial activated carbon adsorbents. These findings demonstrate the high selectivity of this biochar towards Pb(II) and its applicability even in the presence of high concentrations of many potentially interfering inorganic and organic ions and compounds.

Magnetite nanoparticles grafted with murexide-terminated polyamidoamine dendrimers for removal of lead (II) from aqueous solution: synthesis, characterization, adsorption and antimicrobial activity studies

In this study, new, efficient, eco-friendly and magnetically separable nanoadsorbents, MNPs-G1-Mu and MNPs-G2-Mu, were successfully prepared by covalently grafting murexide-terminated polyamidoamine dendrimers on 3-aminopropyl functionalized silica-coated magnetite nanoparticles, and used for rapid removal of lead (II) from aqueous medium. After each adsorption process, the supernatant was successfully acquired from reaction mixture by the magnetic separation, and then analyzed by employing ICP-OES. Chemical and physical characterizations of new nanomaterials were confirmed by XRD, FT-IR, SEM, TEM, and VSM. Maximum adsorption capacities (q_m) of both prepared new nanostructured adsorbents were compared with each other and also with some other adsorbents. The kinetic data were appraised by using pseudo-first-order and pseudo-second-order kinetic models. Adsorption isotherms were found to be suitable with both Langmuir and Freundlich isotherm linear equations. The maximum adsorption capacities for MNPs-G1-Mu and MNPs-G2-Mu were calculated as 208.33 mg g^-1 and 232.56 mg g^-1, respectively. Antimicrobial activities of nanoparticles were also examined against various microorganisms by using microdilution method. It was determined that MNPs-G1-Mu, MNPs-G2-Mu and lead (II) adsorbed MNPs-G2-Mu showed good antimicrobial activity against S. aureus ATTC 29213 and C. Parapsilosis ATTC 22019. MNPs-G1-Mu also showed antimicrobial activity against C. albicans ATTC 10231.

Removal of strontium by in situ electrochemical synthesis of Zn–Al LDHs using a bidirectional pulse method

The Sr2+ removal rate is 99.26%, and the energy consumption of the reaction process is 5.01 kW h m−3.

Natural and anthropogenic radionuclides in water and wastewater: Sources, treatments and recoveries

Water-energy nexus in the context of changing climate amplifies the importance of comprehending the transport, fate and recovery of radioisotope. While countries have been more interested for zero/low greenhouse gas emission technologies, energy production from nuclear power plant (NPP) can be a prominent solution. Moreover, radioisotopes are also used for other benefits such as in medical science, industrial activities and many more. These radionuclides are blended accidently or intentionally with water or wastewater because of inefficacious management of the nuclear waste; and therefore, it is an imperative task to manage nuclear waste so that the harmful consequences of the waste on environment, ecology and human health can be dispelled. Due to generation of significant amount of waste throughout its utilization, a noticeable number of physical, chemical and biological processes has been introduced as remediation processes although mechanisms of optimum removal process are still under investigation. Removal mechanisms and influencing factors for radionuclide removal are elucidated in this review so that, further, operation and process development can be promoted. Again, resource recovery, opportunities and challenges are also discussed for elevating the removal rates and minimizing the knowledge gaps existing in development and applications of novel decontamination processes.

Low-cost chitosan-calcite adsorbent development for potential phosphate removal and recovery from wastewater effluent

Phosphorous (P) recovery from wastewater will become increasingly vital in the future as terrestrial rock phosphate deposits are expended. Effective management of P as a critical resource will require new techniques to recover P from wastewater, ideally in a form that can be used in agriculture as fertiliser. In this study, batch and fixed-bed column conditions were tested using a novel KOH deacetylated calcite-chitosan based adsorbent (CCM) for P removal from aqueous solutions and wastewater effluents. The unique characteristics of this adsorbent as a phosphate adsorbent were the result of rich surface functionality (amine and sulphur functional groups of the chitosan and proteins) and the CaCO₃ content (providing donor ligands; and additionally beneficial if the material were used as fertiliser, buffering soil acidification caused by nitrogen application). The maximum P adsorption capacity was determined to be 21.36 mgP/g (at 22 °C) and the endodermic process reached equilibrium after 120 min. The experimental data was best described using a Langmuir isotherm and a pseudo-second order kinetic model. The diffusion kinetic analysis highlighted the importance of both film and intraparticle mass-transport. Material characterisation suggested that the adsorption process involved interactions between P and functional groups (mostly -NH₃⁺) due to electrostatic interaction on the chitosan chain or involved ligand exchange with CO₃^2-. Analysis of materials using X-Ray Powder Diffraction (XRPD) and Thermogravimetric Analysis (TGA) indicated a microprecipitation-type mechanism may occur through the formation of hydroxylapatite (Ca₅(PO₄)₃(OH)). Desorption studies demonstrated that the P-laden CCM (derived from crab carapace) had the potential to be reused in soil amendment as a slow-release P fertiliser. The effects of different operating parameters were explored in a fixed-bed column, and the experimental data fitted well to the Clark model (R² = 0.99). The CCM also showed excellent P adsorption potential from secondary and final wastewater effluent in dynamic conditions, even at low P concentrations. Finally, a scale-up approach with cost analysis was used to evaluate the price and parameters needed for a potential large-scale P recovery system using this adsorbent.

Synthesis optimisation and characterisation of chitosan-calcite adsorbent from fishery-food waste for phosphorus removal

Here, Box-Behnken design (BBD) approaches were utilised to optimise synthesis methodology for the chitosan-calcite rich adsorbent (CCM) made from fishery-food waste material (crab carapace), using low-temperature activation and potassium hydroxide (KOH). The effect of activation temperature, activation time and impregnation ratio was studied. The final adsorbent material was evaluated for its phosphorus (P) removal efficiency from liquid phase. Results showed that impregnation ratio was the most significant individual factor as this acted to increase surface deacetylation of the chitin (to chitosan) and increased the number of amine groups (-NH₂) in the chitosan chain. P removal efficiency approached 75.89% (at initial P concentration of 20 mg/L) under optimised experimental conditions, i.e. where the impregnation ratio for KOH:carapace (g/g) was 1:1, the activation temperature was 105 °C and the activation time was 150 min. Predicted responses were in good agreement with the experimental data. Additionally, the pristine and CCM material were further analysed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), Brunauer-Emmett-Teller technique (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Characterisation showed enhancements in surface chemistry (introducing positively charged amine groups), textural properties and thermal stability of the CCM.

A review of the potential utilisation of plastic waste as adsorbent for removal of hazardous priority contaminants from aqueous environments

There is growing global awareness of the presence and negative impacts of waste plastic in the marine environment. Risks to wildlife include ingestion and entanglement for macro-plastic (larger than 5 mm in length), alongside food chain transfer for micro-plastics (less than 5 mm in length). Plastics in the marine environment have also been shown to adsorb and accumulate contaminants from seawater, e.g., heavy metals and hydrophobic organic compounds. This means that plastics can additionally act as vectors for transport of contaminants, permitting ecotoxicological risks to be spatially extended. However, the ability of waste plastic to adsorb pollutants also offers potential opportunity, if they can be used for the decontamination of wastewater. Here, we provide an overview of marine plastic types and distribution, and then systematically assess their potential to be repurposed as novel adsorbents. Data published in recent years are interrogated to gain an overview of the interaction mechanisms between marine plastics and both organic and inorganic contaminants. In addition, factors that may be exploited to enhance their performance in removal of contaminants are also reviewed and prioritised, e.g., surface modification and activation. This paper highlights the novel potential of repurposing plastic waste for wastewater treatment applications and seeks to identify key knowledge gaps and future research priorities for scientists and engineers.