Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

Adsorption of uranium from crude phosphoric acid using activated carbon

The adsorption of uranium from crude phosphoric acid has been investigated using conventional activated carbons. It was found that treatment with nitric acid oxidized the surface of activated carbon and significantly increased the adsorption capacity for uranium in acidic solutions. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated. Equilibrium data were fitted to a simplified Langmuir and Freundlich isotherms for the oxidized samples which indicate that the uranium adsorption onto the activated carbon fitted well with Langmuir isotherm than Freundlich isotherm. Equilibrium studies evaluate the theoretical capacity of activated carbon to be 45.24 g kg^?1.     

Highly efficient removal of uranium(VI) from aqueous solutions by poly(acrylic acid-co-acrylamide) hydrogels

In this study, poly(acrylic acid-co-acrylamide) (PAAAM) hydrogels were used to remove uranium (VI) ions in wastewater and characterized by FTIR, SEM, EDX. The effects of pH value, coexistence of ionic strength, contact time, initial U (VI) ion concentration and adsorption temperature were also studied. Adsorption data fitted well with pseudo-second-order, intra-particle diffusion model and Langmuir isotherm mode, the maximum adsorption capacity of U(VI) was 713.24 mg g^?1. Thermodynamic analysis shows that the adsorption of U(VI) is spontaneous endothermic. PAAAM hydrogel has excellent regeneration performance, after five time adsorption–desorption cycles, the adsorbent still maintained 99.24% adsorption capacity.     

Batch and dynamic extraction of uranium(VI) from nitric acid medium by commercial phosphinic acid resin,Tulsion CH-96

Batch and dynamic extractions of uranium(VI) in 10⁻³–10⁻²M concentrations in 3–4M nitric acid medium have been investigated using a commercially available phosphinic acid resin (Tulsion CH-96). The extraction of uranium(VI) has been studied as a function of time, batch factor (V/m), concentrations of nitric acid and uranium(VI) ion. Dual extraction mechanism unique to phosphinic acid resin has been established for the extraction of uranium(VI). Distribution coefficient (K _d ) of uranium(VI) initially decreases with increasing concentration of nitric acid, reaches a minimum value at 1.3M, followed by increases in K _d . A maximum K _d value of ∼2000 ml/g was obtained at 5.0M nitric acid. Batch extraction data has been fitted into the linearized Langmuir adsorption isotherm. The performance of the resin under dynamic extraction conditions was assessed by following the breakthrough behavior of the system. Effect of flow rate, concentrations of nitric acid and uranium ion in the feed on the breakthrough behavior of the system was studied and the data was fitted using Thomas model.     

The preparation of PZS-OH/CNT composite and its adsorption of U(VI) in aqueous solutions

In this paper, polycyclotriphosphazene coated carbon nanotubes (PZS-OH/CNT) composite material has been synthesized via a facial method. The prepared PZS-OH/CNT was characterized by FTIR, BET, zeta potential and SEM. The material was investigated as an adsorbent for the adsorption towards U(VI) from aqueous solutions. Several parameters like solution pH, contact time and temperature were used to evaluate the sorption efficiency. The results indicated that the adsorption capacity of uranium on PZS-OH/CNT was improved from 41.48 mg g⁻¹ for CNT to 338.98 mg g⁻¹ due to the presence of functional groups on PZS-OH/CNT. The U(VI) sorption on PZS-OH/CNT was well fitted to the Langmuir adsorption isotherm and pseudo-second kinetics models. The thermodynamic parameters (ΔH, ΔS and ΔG) showed the U(VI) adsorption on CNT and PZS-OH/CNT was endothermic and spontaneous in nature.

     

Biosorption of uranium(VI) by a mangrove endophytic fungus <Emphasis Type="Italic">Fusarium sp</Emphasis>. #ZZF51 from the South China Sea

The uranium(VI) accumulation was studied in detail by using the biomass of mangrove endophytic fungus Fusarium sp.#ZZF51 from the South China Sea. The uranium(VI) biosorption process onto the tested fungus powders was optimized at pH 4.0, adsorption time 60 min, and uranium(VI) initial concentration 50 mg L⁻¹ with 61.89% of removal efficiency. According to Fourier transform infrared spectra for the tested fungus before and after loaded with uranium(VI), the results showed that both of hydroxyl and carboxyl groups acted as the important roles in the adsorption process. In addition, the experimental data were analyzed by using parameter and kinetic models, and it was obtained that the Langmuir isotherm model and the pseudo-second-order kinetic model provided better correlation with the experimental data for adsorption of uranium(VI).     

Sorption of uranium(VI) from aqueous solution onto magnesium silicate hollow spheres

The sorption of uranium(VI) from aqueous solutions was investigated using synthesized magnesium silicate hollow spheres as a novel adsorbent. Batch experiments were conducted to study the effects of initial pH, amount of adsorbent, contact time and initial U(VI) concentrations on uranium sorption efficiency. The desorbing of U(VI) and the effect of coexisting ions were also investigated. Kinetic studies showed that the sorption followed a pseudo-second-order kinetic model. The Langmuir sorption isotherm model correlates well with the uranium sorption equilibrium data for the concentration range of 25–400 mg/L. The maximum uranium sorption capacity onto magnesium silicate hollow spheres was estimated to be about 107 mg/g under the experimental conditions. Desorption of uranium was achieved using inorganic acid as the desorbing agent. The practical utility of magnesium silicate hollow spheres for U(VI) uptake was investigated with high salt concentration of intercrystalline brine. This work suggests that magnesium silicate hollow spheres can be used as a highly efficient adsorbent for removal of uranium from aqueous solutions.     

Highly efficient sorption of U(VI) from aqueous solution using amino/amine-functionalized magnetic mesoporous silica nanospheres

The amino/amine-functionalized magnetic mesoporous silica nanospheres (MSN-DETA) exhibited relatively high sorption capacity (q_m?=?153.68 mg/g) as well as excellent selectivity for U(VI). The U4f_7/2 X-ray photoelectron spectrometry revealed two binding energies at 380.8?±?0.3 eV (with the proportion of 75.2%) and 382.3?±?0.3 eV, which indicated the inner-surface complexation mechanism. The sorption isotherms fitted well with the Langmuir model, whereas the sorption kinetics could be fitted by pseudo-second-order model. The U(VI)-loaded MSN-DETA could be efficiently regenerated by acidified EDTA (0.4 M). These findings indicated that MSN-DETA could be used as a potential material for the efficient sorption/separation of U(VI) from wastewater.

     

Preparation of chemically oxidized porous carbon and its adsorption of uranium(VI) from aqueous solution

The chemically oxidized porous carbon (m-a-NC) materials were prepared by oxidation and activation of N-doped carbon (NC) materials which were produced from the glucose-urea resin primary carbon. Simultaneously, the batch experiments were carried out to investigate the adsorption of U(VI) onto the m-a-NC materials. The m-a-NC materials exhibit the maximum adsorption capacity of 397 mg/g towards U(VI) at 298.15 K and pH = 4.5. The adsorption kinetics was well fitted by the pseudo-second-order kinetic model, and the adsorption isotherm was better described by the Langmuir model. The possible adsorption mechanism of the m-a-NC for U(VI) was ion-exchange and coordination.

     

Liquid–liquid extraction of uranium(VI) using cyanex 272 in toluene from sodium salicylate medium

Liquid–liquid extraction and separation studies of uranium have been carried out from sodium salicylate media using cyanex 272 in toluene. Uranium was quantitatively extracted by 1 × 10⁻³ M sodium salicylate with 5 × 10⁻⁴ M cyanex 272 in toluene. The extracted uranium(VI) was stripped out quantitatively from the organic phase with 1.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 660 nm. The effect of concentration of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of uranium(VI) from other elements was achieved from binary as well as from multicomponent mixtures. The method was extended for the separation and determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ± 2%).     

Validation of a Monte Carlo HPGe detector model against irradiated foil gamma-ray spectroscopy measurements

In order to separate and pre-concentrate uranium from aqueous phase, a novel silica-based adsorbent was prepared by impregnating nalidixic acid (HNA) into a macroreticular silica/polymer composite support (SiO₂-P) with a mean diameter of 60 μm. Adsorption behavior of uranium from aqueous solution onto the adsorbent was studied. Experimental results indicated that HNA/SiO₂-P showed strong adsorption for uranium in a wide range of pH from 3.5 to 10.0, and the maximum adsorption capacity was 35.4 mg g⁻¹. In addition, HNA/SiO₂-P exhibited good selectivity for U(VI) and showed weak or bare adsorption affinity to foreign ions. Kinetic and isotherm of uranium adsorption were in accordance with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model, respectively. Moreover, U(VI) sorption was found to be an endothermic reaction and spontaneous under experimental state. The synthesized adsorbent showed an admirable stability at lower pH values in aqueous solution.

     

Kinetic studies on the solvent extraction of uranium(VI) from phosphoric acid solution with HDEHP using laser-induced optical fiber fluorimetry

The laser-induced optical fiber fluorimetry has been used for the first time to analyse the concentration of uranium(VI) in the kinetic studies on the extraction of uranium(VI) between 0.5 mol L H₃PO₄ solution and HDEHP-cyclohexane system with Lewis cell. The effects of stirring speed, temperature and concentration of uranium(VI) and HDEHP on the rate of extraction were examined. These data show that the extraction rate of uranium(VI) in this system is controlled by the chemical reaction process at the interface. The rate equations and the rate constants of the forward and reverse extractions were obtained. The mechanism of the extraction has been discussed.     

Simultaneous removal of uranium and humic acid by cyclodextrin modified graphene oxide nanosheets

Cyclodextrin-modified graphene oxide nanosheets (denoted as CD/GO) were synthesized by an in-situ polymerization method and characterized by as well as Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and potentiometric acid-base titration. The characterization results indicated that CD was successfully grafted onto GO surfaces by forming a chemical bond. Mutual effects on the simultaneous removal of hexavalent uranium and humic acid by CD/GO from aqueous solution were investigated. The results indicated that U(VI) and humic acid (HA) sorption on CD/GO were greatly affected by pH and ionic strength. The presence of HA enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH, whereas the presence of U(VI) enhanced HA sorption. The surface adsorbed HA acted as a “bridge” between U(VI) and CD/GO, and formed strong inner-sphere surface complexes with U(VI). Sorption isotherms of U(VI) or HA on CD/GO could be well fitted by the Langmuir model. This work highlights that CD/GO can be used as a promising material in the enrichment of U(VI) and HA from wastewater in U(VI) and humic substances obtained by environmental pollution cleanup.     

Poly(cyclotriphosphazene-co-phloroglucinol)PCPP as a solid phase extractant for preconcentrative separation of uranium(VI) from aqueous solution

Poly(cyclotriphosphazene-co-phloroglucinol) (PCPP) microspheres, a new solid phase extraction for extracting uranium(VI), synthesized via one-pot precipitation copolymerization. The PCPP microspheres were characterized by FT-IR, SEM/EDS, zeta potential and N₂ adsorption/desorption isotherms. Through the extraction experiment to evaluate the extraction behavior of the PCPP microspheres for uranium(VI). The extractant can achieve the optimal effect under the conditions of contact time with 60 min, pH = 3.5, initial concentration 100 mg L⁻¹ and extractant dosage 0.70 g L⁻¹. The extraction behavior obeyed with the pseudo second-order model and Langmuir isotherm model.

     

Adsorption of uranium (VI) from aqueous solution by tetraphenylimidodiphosphinate

The adsorption of uranium (VI) using tetraphenylimidodiphosphinate (Htpip) was studied. Factors of affecting sorption efficiency have been investigated and results showed the adsorption of uranium (VI) was equilibrium at pH 4.5, time 20 min, adsorbent dosage 0.005 g and initial concentration 50 mg L^?1 reaching 99.86 mg g^?1 of adsorption capacity and 99.86% of removal efficiency. Additionally, the interfering ions studies showed that the adsorbent possessed excellent adsorption selectivity of uranium (VI). The surface morphology of Htpip was investigated by SEM. The adsorption process of uranium (VI) onto Htpip fit the pseudo-second-order kinetic model and the Freundlich isotherm model very well.     

Adsorption of uranium(VI) from aqueous solution by diethylenetriamine-functionalized magnetic chitosan

In this paper, the modified magnetic chitosan resin containing diethylenetriamine functional groups (DETA-MCS) was used for the adsorption of uranium ions from aqueous solutions. The influence of experimental conditions such as contact time, pH value and initial uranium(VI) concentration was studied. The Langmuir, Freundlich, Sips and Dubinin–Radushkevich equations were used to check the fitting of adsorption data to the equilibrium isotherm. The best fit for U(VI) was obtained with the Sips model. Adsorption kinetics data were tested using pseudo-first-order and pseudo-second-order models. Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model, indicating that the chemical adsorption was the rate-limiting step. The present results suggest that DETA-MCS is an adsorbent for the efficient removal of uranium(VI) from aqueous solution.     

Recovery of Uranium(VI) from Sulfate Leach Liquor using Modified Duolite

Silicate mercapto Duolite composite ( SMDC ) and activated Duolite A 101 D ( AD ) were prepared, characterized, and tested for uranium removal from sulfate solution using batch experiment technique. The capability of newly adsorbents for sorption of uranium was estimated and optimized under different controlling variables, including the impact of uranium initial concentration, pH of the medium, equilibrium time, temperatures, dose and interfering ions. Testing of different adsorbents for adsorption isotherms revealed that the achieved experimental data were fitting well with the Langmuir isotherm model with 68.02 mg · g^–1 and 208.33 mg · g^–1 as theoretical capacity for AD and SMDC , respectively. Thermodynamic parameters have been resulted in negative values for ΔH and ΔS indicating an exothermic and decreased randomness behavior for uranium(VI) adsorption, while negative values of ΔG indicate spontaneous uranium adsorption. The kinetics studies showed that the adsorption process was controlled expressed by pseudo-second order model. Finally, the optimized factors have been applied for uranium(VI) recovery from Gattar leach liquor producing a uranium concentrate (Na₂U₂O₇) with uranium concentration of 70 % and purity of 93.33 %.