Utilization of natural hematite as reactive barrier for immobilization of radionuclides from radioactive liquid waste

Selective separation and purification of cerium (III) from concentrate liquor associated with monazite processing by cationic exchange resin as adsorbent

The present study is directed to find the optimal conditions required for efficient separation and purification of Ce3+ as an analog for lanthanides from Fe3+, Th4+, and Zr4+ (interfering ions) using Amberlite IR120H (AIR120H) resin as a strongly cationic exchange adsorbent. The main factors affecting the separation processes had been investigated and optimized. Ce3+ (Ln3+) as an admixture with Fe3+, Th4+, and Zr4+ was successfully separated by batch and column techniques. The sorption efficiency (S, %) from different acidic media was in this order: HCl > HNO3 > H2SO4. In a quaternary mixture with Fe3+ and Th4+, the maximum separation factor between Ce3+ and Zr4+ was ~ 13 after 90 min of equilibration, and the sorption capacity of AIR120H resin for Ce3+ was 8.2 mg/g. The rate of adsorption was found to follow a pseudo-second-order kinetic model. Separation of the absorbed ions was achieved by desorption processes. Firstly, 98 ± 2% of loaded Ce3+ is fully desorbed by 1 M sodium acetate solution without interfering ions. Moreover, ~ 95% of Zr4+ is desorbed by 1 M citric acid solution. Finally, 85% of loaded Fe3+ and Th4+ ions are desorbed with 8 M HCl solution. The batch technique was applied to separate and purify Ln3+-concentrate in chloride liquor (LnCl3), coming from the caustic digestion of Egyptian high-grade monazite. However, the enhanced radioactivity in LnCl3 due to radium -isotopes (228Ra2+, 226Ra2+, 224Ra2+, 223Ra2+) and radio-lead (210Pb2+) is initially reduced by a factor of 92% (i.e., safe limit) by pH-adjustment. As result, it can be recommended that the sorption process by AIR120H resin is efficient and promising for exploring pure lanthanides from its minerals.

Decontamination of 137Cs,95Zr, 154Eu and 144Ce from aqueous solutions using polyacrylamide titanium tungstosilicate

Polyacrylamide titanium tungstosilicate (PAM/TiWSi) composite was synthesised using a sol–gel process and characterized via FT-IR, SEM, XRD, and TGA methods. The effects of several factors on the adsorption of Cs+, Eu3+, Ce3+and Zr4+ have been studied, including contact duration, pH, temperature, and starting concentration. PAM/TiWSi sorption of Cs+, Eu3+, Ce3+and Zr4+ was studied in terms of isotherms and kinetics. The Freundlich model was better linked with isotherm data than the Langmuir model. Cs+, Eu3+, Ce3+and Zr4+ have maximum sorption capacities (Qmax) of 30.7, 26.6, 25,3 and 29.7 mg.g−1, respectively. Furthermore, the sorption process was found based on pseudo-second-order.

Applications of Nano Hydroxyapatite as Adsorbents: A Review

Nano hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has aroused widespread attention as a green and environmentally friendly adsorbent due to its outstanding ability in removing heavy metal ions, radio nuclides, organic pollutants and fluoride ions for wastewater treatment. The hexagonal crystal structure of HAp supports the adsorption mechanisms including ionic exchange reaction, surface complexation, the co-precipitation of new partially soluble phases and physical adsorption such as electrostatic interaction and hydrogen bonding. However, nano HAp has some drawbacks such as agglomeration and a significant pressure drop during filtration when used in powder form. Therefore, instead of using nano HAp alone, researchers have worked on modificationsand composites of nano HAp to overcome these issues and enhance the adsorption capacity. The modification of cationic doping and organic molecule grafting for nano HAp can promote the immobilization of ions and then increase adsorption capacity. Developing nano HAp composite with biopolymers such as gelatin, chitosan and chitin has proven to obtain a synergetic effect for improving the adsorption capacity of composites, in which nano HAp fixed and dispersed in polymers can playmuch more of a role for adsorption. This review summarizes the adsorption properties and adsorbent applications of nano HAp as well as the methods to enhance the adsorption capacity of nano HAp.

Electrostatic adsorption and removal mechanism of ochratoxin A in wine via a positively charged nano-MgO microporous ceramic membrane

Ochratoxin A (OTA) is a very important mycotoxin. However, there are few studies on the removal of OTA in wine because of the great influence on product quality and difficulty in practical application. A nano-MgO-modified diatomite ceramic membrane (MCM) with a high positive charge was prepared and applied to remove OTA in wine. The isotherm adsorption between the positively charged membrane and OTA was in accordance with the Langmuir model, with a maximum adsorption capacity of 806 ng/g at 25 °C. All of the changes in adsorption enthalpy (ΔH), adsorption free energy (ΔG) and adsorption entropy (ΔS) were negative, which indicated that the combination of nano-MgO MCM and OTA was a spontaneous exothermic and nonspecific physical adsorption process. The concentrations of OTA in adsorption-treated wines were lower than 2 μg/kg, and the removal rates exceeded 92%. After OTA removal, the composition of wines was preserved to some extent.

A biochar supported magnetic metal organic framework for the removal of trivalent antimony

Metal organic framework (MOF) nanoparticles are recognized for their effective removal of metal ions from aqueous systems. However, the application of nanoparticles in a powder form as synthesized is not practical and recovery is not easy. We prepared a recyclable magnetic MOF nanoparticle phase and used a widely available waste biomass to generate biochar to support magnetic nanoparticles applied in the treatment of aqueous antimony pollution. A mushroom waste biochar was used to support a magnetic UIO-66-2COOH (denoted as BSMU). Adsorption of trivalent antimony (Sb (III)) onto the BSMU was evaluated. The results showed that optimum conditions for preparation of the BSMU were the mass ratio of MMOF to biochar 4:1, the temperature 70 °C, the time 4 h, and the initiator 4 mM. Under such conditions, sorption capacity reached 56.49 mg/g for treatment of Sb (III) solution at 100 mg/L and pH 9.1. Alkaline conditions (such as pH 9.1) are more favorable for adsorption than acidic conditions, and coexisting ions including NO₃^-, Cl^-, SO₄^2-, and PO₄^3- had no significant negative effect in adsorption, and with the use of low dose, higher adsorption density achieved. The adsorption followed a pseudo second order kinetics model and Freundlich isotherm model. It resulted in a higher enthalpy changes (ΔH^θ) and activation energy (E_a) of 97.56 and 8.772 kJ/mol, respectively, and enhanced the rate pf random contact between antimony and the BSMU, as indicated by a higher entropy change (ΔS^θ) up to 360 J/mol·K. As a result, it readily absorbs antimony. These adsorption properties identified in this study would provide a valuable insights into the application of nanoparticles loaded biochar from abundant biomass in environmental remediation.

Development of a radiochemical method for extraction chromatographic separation of Pb and Bi radioisotopes of forensic and environmental interest

This work describes the purification and separation of some radionuclides of 210Pb and/or 210Bi that might be used in calibration of nuclear spectroscopic instruments for forensic purposes and environmental studies. The retention and desorption investigations have been done by Dowex HCR-S/S resin as the cationic exchanger by batch mode. Full retention of metal ions was achieved in 0.1 M HNO3 solution after an equilibration period of 2 h at room temperature. The uptake of Pb and Bi is reached to more than 95 and 85%, respectively. Desorption studies by several reagents indicated that 1 M citric acid and ammonium acetate are efficient to elute and separate Bi and Pb. Taking into consideration all the above obtained results, column applications packed by the Dowex HCR-S/S resin were carried out to separate 214,210Pb and 214Bi radionuclides either in TENORM-concentrate or old certified reference of 226Ra solution. The column application results revealed that the recovery of Pb and Bi radionuclides was ∼93%. In the radiochemical part, the eluted Bi was impure due to presence of 23% Pb. In contrast, 70% of pure Pb was obtained. Thus, the radionuclides 210Pb can be recovered from several waste resources by this method. It can be concluded that the Dowex HCR resin can be an alternative economic material that could be used to produce 210Pb from the TENORM wastes generated from some strategic industries.

Kinetics and mechanism of radium-isotopes dissolution in TENORM scale waste associated with petroleum production using certain organic carbon source: lactic acid solution-case study

The present study is conducted to explore the dissolution as inferred from the kinetic mechanism for radium-isotopes (²²⁸Ra, ²²⁶Ra, and ²²⁴Ra) in the TENORM scale waste deposited in oilfield pipes and equipment, Gulf of Suez, Egypt. The main efficiency factors for Ra²⁺-compound dissolution by lactic acid (LA) solution, e.g., reactive organic carbon (i.e., electron-donor source), have been investigated, and optimum chemical conditions have been determined. The obtained data were also employed to predict the leaching kinetics and mechanism of the Ra²⁺-isotopes removal by three shrinking core models (SCM, liquid film process-chemical controlled process-diffusion controlled process) and Arrhenius model. The maximum leaching percentage of Ra²⁺-isotopes reached to 55-60% at the optimal leaching conditions (0.3 M LA, 5 h, 25 °C, ϕ < 1 mm, S/L ratio 10/50 g mL^-1). The Ra-isotopes removal proceeds kinetically by diffusion-controlled process. Activation energy (E_a) of the leaching process was 10.51 kJ mol^-1. This value conforms that the leaching process for removal of Ra²⁺-isotopes in the TENORM scale waste by LA solution is controlled by a diffusion process. Values of thermodynamic parameters (∆G^o, ∆H^o, ∆S^o) were determined and indicate that dissolution of Ra²⁺-isotopes in the studied waste is non-spontaneous and temperature dependent. Moreover, the leaching mechanism may be attributed to the dissolution of soluble exchangeable and acidic species of Ra²⁺-species and/or these due conversions of insoluble Ra-sulfate to more soluble Ra-sulfide and/or Ra-hydrogen sulfide by LA solutions.

Removal of 209Po from aquatic environment and its equilibrium and thermodynamic parameters

In this study, removal of ²⁰⁹Po from aqueous media using a natural zeolite as an adsorbent material was investigated. The adsorption experiments were performed by batch technique. The influence of specific process parameters such as initial concentration, pH of solution, contact time and temperature was studied to predict the optimum conditions for effective removing of ²¹⁰Po. Initial and equilibrium activity concentration of ²⁰⁹Po in solutions was counted by a ZnS(Ag) alpha scintillation counter. Adsorption yield of ²⁰⁹Po onto the zeolite was determined as 90 ± 2% at pH: <3 and 25 °C for 40 min of contact time. The applications of the isotherm models such as Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were studied to evaluate adsorption characteristics of ²⁰⁹Po onto natural zeolite. Results indicated that the Dubinin-Radushkevich and Freundlich models gave a better fit to the experimental data than Langmuir isotherm models. The thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption process were calculated. The change in entropy (ΔS^o) and enthalpy (ΔH^o) were estimated to be -0.0003 J nmol^-1 K^-1 and 0.1008 kJ nmol^-1, respectively.

Modification of perlite to prepare low cost zeolite as adsorbent material for removal of 144Ce and 152+154Eu from aqueous solution

The expanded perlite and base activated perlite (Zeolite-NaA) results from treating perlite has a SiO2:Al2O3 ratio ~2 were used as an adsorbents for the removal of 144Ce and 152+154Eu. The two adsorbents were fully characterized. The factors affecting the sorption of radionuclides onto expanded and modified perlite including contact time, pH, ion concentration were investigated. The modification process of expanded perlite enhanced the removal of 152+154Eu from 17.0 to 97.0 %, while for 144Ce from 22.0 to 91.0 %. Both 144Ce and 152+154Eu obey Langmiur isotherm model in case of using modified perlite (Zeolite-NaA) and expanded perlite.

Using graphene quantum dots for treating radioactive liquid waste

The use of smart materials, especially the carbon-based nanomaterials, is increasing each day. Among the several carbon-based nanomaterials, graphene quantum dots are one of the most impressive ones, not only by its quantum behavior but due to the adsorption quality conferred by electrostatic interactions from the negatively charged groups as the huge surface area (2.630 m2/g). In this study, we developed and tested graphene quantum dots (GQDs) as smart nano-adsorbents of uranium (²³⁸U) from the radioactive industry waste. The GQDs were developed in a size range of 160-220 nm using a totally green route. The results showed that the GQDs were capable to adsorb almost 40% of the uranium (²³⁸U) in alamine 3366 solution. Also, the results demonstrated that using GQDs treatment-like smart nanomaterials for radioactive waste in a volume reduction of almost 90% is achieved, helping the storage process as the final disposal of this material. We may conclude that GQDs may represent a smart device for the treatment of radioactive waste as an alternative of absorbent in the radioactive industry.

Promotion of Para-Chlorophenol Reduction and Extracellular Electron Transfer in an Anaerobic System at the Presence of Iron-Oxides

Anaerobic dechlorination of chlorophenols often subjects to their toxicity and recalcitrance, presenting low loading rate and poor degradation efficiency. In this study, in order to accelerate p-chlorophenol (p-CP) reduction and extracellular electron transfer in an anaerobic system, three iron-oxide nanoparticles, namely hematite, magnetite and ferrihydrite, were coupled into an anaerobic system, with the performance and underlying role of iron-oxide nanoparticles elucidated. The reductive dechlorination of p-CP was notably improved in the anaerobic systems coupled by hematite and magnetite, although ferrihydrite did not plays a positive role. Enhanced dechlorination of p-CP in hematite or magnetite coupled anaerobic system was linked to the obvious accumulation of acetate, lower oxidation-reduction potential and pH, which were beneficial for reductive dechlorination. Electron transfer could be enhanced by Fe2+/Fe3+ redox couple on the iron oxides surface formed through dissimilatory iron-reduction. This study demonstrated that the coupling of iron-oxide nanoparticles such as hematite and magnetite could be a promising alternative to the conventional anaerobic reduction process for the removal of CPs from wastewater.

Removal of 210Po from aqueous media and its thermodynamics and kinetics

In this study, the composite adsorbent as granule was prepared by mixing of polyacrylonitrile (PAN) and a natural zeolite (clinoptilolite) in specific conditions. The prepared composite adsorbent was used for investigating the adsorption behaviour of ²¹⁰Po. Adsorption of ²¹⁰Po was studied in a column system. The effective parameters such as initial activity concentration of ²¹⁰Po, pH of the aqueous solution, contact time and temperature of solution for adsorption behaviour of ²¹⁰Po were studied. Adsorption yield of ²¹⁰Po on composite adsorbent from aqueous solution in optimum conditions were determined as 75.00 ± 0.15%. The adsorption equilibrium data was examined using various well-known isotherm models such as Freundlich, Langmuir, Dubinin and Radushkevish and Tempkin, and it was observed that the experimental equilibrium data well fitted and found to be in good agreement with the Tempkin model. Adsorption thermodynamics and kinetics of the polonium were studied. It was found that the processes for ²¹⁰Po were exothermic and spontaneous. The kinetic data conformed better to the pseudo-second order equation.

Non-invasive characterization of colorants by portable diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and chemometrics

During the last years the need for non-invasive and non-destructive analytical methods brought to the development and application of new instrumentation and analytical methods for the in-situ analysis of cultural heritage objects. In this work we present the application of a portable diffuse reflectance infrared Fourier transform (DRIFT) method for the non-invasive characterization of colorants prepared according to ancient recipes and using egg white and Gum Arabic as binders. Approximately 50 colorants were analyzed with the DRIFT spectroscopy: we were able to identify and discriminate the most used yellow (i.e. yellow ochres, Lead-tin Yellow, Orpiment, etc.), red (i.e. red ochres, Hematite) and blue (i.e. Lapis Lazuli, Azurite, indigo) colorants, creating a complete DRIFT spectral library. The Principal Component Analysis-Discriminant Analysis (PCA-DA) was then employed for the colorants classification according to the chemical/mineralogical composition. The DRIFT analysis was also performed on a gouache painting of the artist Sutherland" and the colorants used by the painter were identified directly in-situ and in a non-invasive manner.

Preparation of activated carbon from doum stone and its application on adsorption of 60Co and 152+154Eu: Equilibrium, kinetic and thermodynamic studies

Removal of radionuclides from wastewater before discharging to environment is necessary for the safety of living beings. Activated carbon prepared from doum stone (DS), an agricultural waste by-product, has been used for the sorption of ⁶⁰Co and ^152+154Eu radionuclides from aqueous solutions. DS has been characterized by different analytical tools. The efficiency of the adsorbent was investigated using batch sorption technique under different experimental conditions. The equilibrium sorption data were analyzed using Freundlich and Langmuir isotherm models. The kinetic experimental data were analyzed using four kinetic models including pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion model to examine the mechanism of sorption and potential rate-controlling step. The maximum capacity of DS was found to be 121 mg/g and 166 mg/g for cobalt and europium, respectively. Sorption efficiency of DS to remove ⁶⁰Co, ^152+154Eu and ¹³⁴Cs from real radioactive wastewater and environmental (river water and sea water) samples was also investigated. The results revealed that the prepared DS as low cost could be used as a promising material for the simultaneous removal of different radionuclides such as ⁶⁰Co, ^152+154Eu and ¹³⁴Cs, or trivalent actinides such as ^{241, 242m,243}Am from real radioactive waste and environmental water samples.