Radium removal from aqueous solutions by adsorption on non-treated and chemically modified biomass by-product

The adsorption efficiency of a biomass by-product (olive cake) regarding the removal of radium (²²⁶Ra) from aqueous solutions has been investigated prior and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO₂-coating. The separation/removal efficiency has been studied as a function of pH, salinity (NaCl) and calcium ion concentration (Ca²⁺) in solution. Evaluation of the experimental data shows clearly that the phosphorylated biomass by-product presents the highest adsorption capacity and efficiency followed by the MnO₂-coated material and the non-treated biomass by-product. However, regarding the effect of salinity and the presence of competitive cations (e.g. Ca²⁺) on the adsorption/removal efficiency, the MnO₂-coated material shows the lowest decline in efficiency (only 2 % of the relative adsorption efficiency) followed by the non-treated and the phosphorylated biomass by-product. The results of the present study indicate that depending on the physicochemical characteristics of the radium-contaminated water, all three types of the biomass by-product could be effectively used for the treatment of radium-contaminated waters. Nevertheless, the MnO₂-coated material is expected to be the most effective adsorbent and an alternative to MnO₂ resins for the treatment of environmentally relevant waters.     

Uranium adsorption by non-treated and chemically modified cactus fibres in aqueous solutions

The adsorption efficiency of Opuntia ficus indica fibres regarding the removal of hexavalent uranium [U(VI)] from aqueous solutions has been investigated prior and after the chemical treatment (e.g. phosphorylation and MnO₂-coating) of the biomass. The separation/removal efficiency has been studied as a function of pH, uranium concentration, adsorbent mass, ionic strength, temperature and contact time. Evaluation of the experimental data shows that biosorption is strongly pH-depended and that the MnO₂-coated product presents the highest adsorption capacity followed by the phosphorylated and non-treated material. Experiments with varying ionic strength/salinity don’t show any significant effect on the adsorption efficiency, indicating the formation of inner-sphere surface complexes. The adsorption reactions are in all cases exothermic and relatively fast, particularly regarding the adsorption on the MnO₂-coated product. The results of the present study indicate that adsorption of uranium from waters is very effective by cactus fibres and particularly the modified treated fibres. The increased adsorption efficiency of the cactus fibres is attributed to their primary and secondary fibrillar structure, which result in a relative relative high specific surface available for sorption.     

Utilization of olive pomace in nano MgO modification for sorption of Ni(II) and Cu(II) metal ions from aqueous solutions

Magnesium oxide nanoparticles were synthesized and modified by olive pomace (NMOOP700) as a novel sorbent and characterized using Fourier Transform Infrared Spectra, Scanning Electron Microscope, Transmission Electron Microscope, X-ray Diffraction, Differential Thermal Analysis and Thermal Gravimetric Analysis. Sorption of Cu (II) or Ni (II) ions were achieved taking into account important parameters including initial pH of the medium, contact time, initial metal ion concentration and temperature. A comparative study between Magnesium oxide nanoparticles and NMOOP700 material for the sorption of Cu (II) or Ni (II) ions was implemented. The obtained data revealed that the sorption process is significantly improved using NMOOP700. The monolayer capacity of Ni (II) and Cu (II) metal ions on NMOOP700 at pH 5 were found to be 149.93 ± 4.4 and 186.219 ± 6.3 mg/g, respectively. Findings of the present work highlight the potential use of NMOOP700 as a novel and effective sorbent material for the removal of Cu (II) or Ni (II) ions from the liquid phase.     

Sorption of Cu(II) and Eu(III) ions from aqueous solution by olive cake

The sorption of Cu(II) on olive cake, a biomass by-product of olive oil production, has been investigated by potentiometry at pH 6, I=0.1 M NaClO₄, 25 °C and under atmospheric conditions. Numerical analysis of the experimental data supports the formation of surface complexes and allows the evaluation of the corresponding formation constant, which is found to amount log β=5.1±0.4. This value is close to corresponding values given in literature for Cu(II)-humate complexes, indicating that the same type of active sites (e.g. carboxylic and phenolic groups) is responsible for the Cu(II) binding by olive cake. Addition of a competing metal ion (e.g. Eu(III) ion) in the system leads to replacement of the Cu(II) by Eu(III). Evaluation of the potentiometric data obtained from competition experiments indicates on a ionexchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake is found to be log β=5.4±0.9. The results of this study are of particular interest with respect to waste water treatment technologies using biomass products as adsorbent material and environmental impact assessments regarding disposal of biomass by products in the geosphere.     

Treatment of aqueous solutions with a technogenic carbonate-containing reagent to remove lead(II) ions

Russian Journal of Applied Chemistry - The possibility of using a carbonate-containing technogenic waste as reagent for treatment of aqueous solutions to remove lead(II) ions is demonstrated. The...     

Sorption of thallium(III) ions from aqueous solutions using titanium dioxide nanoparticles

Titanium dioxide nanoparticles (NPs) were employed for the sorption of Tl(III) ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, Tl(III) concentration, temperature, and amount of sorbent. The sorption was found to be fast and to reach equilibrium within 2 min, to be less efficient at low pH values, and to increase with pH and temperature. The sorption fits the Langmuir equation and follows a pseudo second order model. The mean energy of the sorption is approximately 15 kJ mol^?1 as calculated from the Dubinin–Radushkevich isotherm. The thermodynamic parameters for the sorption were also determined, and the ΔH ⁰ and ΔG ⁰ values indicate endothermic behavior.     

Sorption of praseodymium(III) ions from aqueous solutions by a natural clinoptilolite-containing tuff

The equilibrium and kinetics of sorption of praseodymium(III) ions from sulfate solutions by a natural clinoptilolite-containing tuff are studied. It is shown that praseodymium is completely extracted from dilute solutions (<0.002 M). The kinetic parameters of the sorption process are determined.     

Thermodynamic and structural features of aqueous Ce(III)

With a single f-electron, Ce(III) is the simplest test case for benchmarking the thermodynamic and structural properties of hydrated Ln(III) against varying density functionals and reaction field models, in addition to determining the importance of multiconfigurational character in their wave functions. Here, the electronic structure of Ce(H2O)x(H 2O)y(3+) (x = 8, 9; y = 0, 12-14) has been examined using DFT and CASSCF calculations. The latter confirmed that the wave function of octa- and nona-aqua Ce(III) is well-described by a single configuration. Benchmarking was performed for density functionals, reaction field cavity types, and solvation reactions against the experimental free energy of hydration, DeltaG(hyd)(Ce(3+)). The UA0, UAKS, Pauling, and UFF polarized continuum model cavities displayed different performance, depending on whether one or two hydration shells were examined, and as a function of the size of the metal basis set. These results were essentially independent of the density functional employed. Using these benchmarks, the free energy for water exchange between CN = 8 and CN = 9, for which no experimental data are available, was estimated to be approximately -4 kcal/mol.     

Recovery of heavy metal ions from aqueous solutions using modified organosilicas

Sorption of Cu(II), Pb(II), Cd(II), and Zn(II) from aqueous solutions on two-component organosilicas was studied as influenced by sorbent composition, contact time, ratio of solid and liquid phases, solution pH, nature and concentration of heavy metal ions, and content of modifying agent. The degrees of sorption of these metal ions from aqueous solutions using organosilicas modified with aluminum(III) added into the siloxane matrix or with copper(II) grafted to the sorbent surface layer were compared.     

Sorption of phosphate ions on iron(III), zirconium(IV), and chromium(III) oxyhydroxides from aqueous electrolyte solutions

The adsorption of phosphate ions from aqueous solutions with an ionic strength of 0.5 on iron(III), zirconium(IV), and chromium(III) oxyhydroxide hydrogels has been studied as influenced by chloride and sulfate ions. Despite the high concentrations of chloride and sulfate ions, they do not inhibit phosphate adsorption on the hydrogels; they only slightly change the isotherm shape. In the range of equilibrium phosphate concentrations equal to 30–50 mmol/l, all isotherms for iron and zirconium oxyhydroxide gels signify the appearance of a second adsorption layer (two-step isotherms). Both steps are satisfactorily fitted by the Langmuir equation. The maximum adsorptions and adsorption constants have been calculated. For chromium oxyhydroxide gels, the intraduction of an electrolyte dramatically decreases the equilibration rate.     

Determination of iron(III) ions in aqueous solutions by secondary-emission mass spectrometry

Model aqueous solutions containing micro impurities of iron(III) are studied by secondary-emission mass spectrometry. The possibility of using this method for the analysis of rain deposits and samples of atmospheric aerosols is discussed.     

Extraction of Ce(III) with naphthenic acid from nitrate solutions

Extraction of Ce(III) with naphthenic acid from nitrate solutions was studied. The composition of solvation complexes, extraction constants, and Gibbs energies of extraction were found from the dependences of the distribution coefficients on pH and compositions of the aqueous and organic phases.     

Sorption of cadmium ions from aqueous solutions onto nanoporous modified carbon sorbents

Physicochemical properties of nanoporous modified carbon sorbents and sorption of cadmium ions (0.1–20 mg L^?1) onto them from nitrate solutions at pH 5–7 were studied. The acid-base nature of functional oxygen-containing groups on the carbon surface of the sorbents was determined. The ability to sorb cadmium ions depends on the kind of chemical modification of the sorbent surface.     

Studies on crystalline zirconium phosphate-IV self-diffusion of La(III) and Ce(III) ions

Radioisotopes were used to determine self-diffusion parameters for the movement of La(III) and Ce(III) ions in crystalline α zirconium phosphate. Conclusions are drawn as to the mechanism of ion movements in this medium.     

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

Extraction kinetics of iron(III) from aqueous nitrate solutions to toluene solutions of tri-n-butylacetohydroxamic acid

The forward and reverse extraction rate of Fe³⁺ at time zero between aqueous nitrate solutions and toluene solutions of tri-n-butylacetohydroxamic acid, HX, has been studied as function of the composition of the system and the stirring speed of the two phases. Experimental information has been also obtained on the degree of aggregation of HX, its surface active properties, its solubility in the aqueous phase as well as on the equilibrium distribution of Fe(III). Rate equations have been derived. The rate determining step of the extraction reaction has been shown to be the reaction of the free and hydrolyzed iron ions, Fe³⁺ (hydrated) and FeOH⁺ (hydrated), with the HX undissociated molecules. The reactions occur simultaneously in the aqueous phase (homogeneous path) and at the interface (heterogeneous path). A correlation between the rate constants and the equilibrium constant of the extraction reaction of Fe(III) has been established.     

Adsorption of lanthanides(III) from aqueous solutions by fullerene black modified with di(2-ethylhexyl)phosphoric acid

Fullerene black (FB) - a product of electric arc graphite vaporization after extraction of fullerenes - was modified with the di(2-ethylhexyl)phosphoric acid (D2EHPA). The distribution of D2EHPA between FB and aqueous HNO₃ solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of D2EHPA concentration in the sorbent phase on the adsorption of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates from HNO₃ solutions by D2EHPA-modified FB are considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanides’ adsorption increases with an increase in the element atomic number. A considerable synergistic effect has been observed upon the addition of the neutral bidentate tetraphenylmethylenediphosphine dioxide ligand to D2EHPA in the sorbent phase.      

Spectroscopic,electrochemical, and structural aspects of the Ce(IV)/Ce(III) DOTA redox couple chemistry in aqueous solutions

The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V versus SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)_aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a t_1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same t_1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA^2?) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)_aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S₂O₃^2?. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand.     

Removal of nickel (II) ions from aqueous solutions using modified activated carbon: A kinetic and equilibrium study

Removal nickel from the aquatic environment is a serious environmental problem in view of public health. The present article studies the applicability of activated carbon, obtained from graphite, as a source of adsorbents to remove nickel from the aqueous polluted water. Activated carbon was obtained by steam activation of graphite and then was oxidized by nitric acid followed by modification with Tetraethylenepentamine (TEPA). The applicability of graphite activated carbon (GAC), and modified activated carbon by Tetraethylenepentamine (GACA) to remove nickel ions Ni(II) from aqueous media was studied. The effect of pH, initial concentration, contact time, and the temperature was evaluated during Ni(II) removal operating in a batch process. Experimental results show that the studied activated carbon have a good adsorption capacity for Ni(II) ions and could reduce the concentrations of it in the groundwater. A maximum removal efficient of Ni(II) was observed at 55°C. The experimental data showed an endothermic and spontaneous process, which was fitted to Langmuir isotherm. Based on our results, we can conclude that it is possible to use GAC and GACA for removing Ni(II) effectively from groundwater.