Concentration of U(VI) on a complexing sorbent for its determination by the spectrophotometric method

A complexing sorbent based on Zn, Al-layered double hydroxide intercalated with EDTA (Zn, Al-EDTA) for the concentration of U(VI) and its subsequent spectrophotometric determination in natural and waste waters of the uranium mining industry with a high salt content has been proposed. The conditions of U(VI) extraction from waters and its desorption for subsequent determination with arsenazo III in strongly acid medium were determined.     

Layered double hydroxides intercalated with EDTA as effective sorbents for U(VI) recovery from wastewater

The performance of the synthetic hydrotalcite-like sorbents, initial {[Zn₄Al₂(OH)₁₂]CO₃·nH₂O} and heat-treated (Zn₄Al₂O₇) forms and the form intercalated with EDTA and prepared in a nitrogen atmosphere from [Zn₄Al₂(OH)₁₂]Cl₂·nH₂O, was evaluated and compared. Increased concentrations of hydrocarbonate and carbonate ions do not noticeably affect the degree of U(VI) recovery from wastewaters with pH 8, which is due to tight binding of U(VI) with EDTA anions in the interlayer space of layered double hydroxides. [Zn₄Al₂(OH)₁₂]EDTA·nH₂O is one of the most effective and cheapest synthetic sorbents for recovering from aqueous media not only cationic but also anionic U(VI) species, which is particularly important. Therefore, the sorbent can be recommended for practical use.     

Montmorillonite modified with polyethylenimines as a sorbent for recovering U(VI) from wastewaters

Clay minerals modified with polyethylenimines (Mn-t-PEI) show promise for sorption treatment of wastewaters to remove U(VI) and for U(VI) preconcentration in determination of its low concentrations. Conditions are found for preparing modified sorbents: The optimal pH range for PEI sorption to prepare the modified sorbents is ≥9.0, which suggests electrostatic interaction of PEI with montmorillonite. The maximal sorption of the linear and branched polymers on montmorillonite, calculated from the sorption isotherms, is 0.32–0.38 g PEI/g mineral. The U(VI) sorption value on natural montmorillonite is considerably lower than on Mn-t-PEI, where the isotherm at low U(VI) concentrations is practically linear and the degree of U(VI) sorption exceeds 97% (depending on the uranium content).     

Bioleaching of heavy metals from wastewater sludge by ferrous iron oxidizing bacteria

Experiments on bacterial leaching of heavy metals from aerobically stabilized surplus activated sludge at the Bortnichi aeration plant in Kiev have been conducted with addition of FeSO₄ ? 7H₂O as a stimulant of iron-oxidizing bacteria. The mechanism of heavy metal leaching involving the ferrous iron oxidation by bacteria with subsequent formation of Fe(OH)₃ was confirmed. This process is accompanied by the reduction of pH level of wastewater sludge that results in leaching of heavy metals.     

Sorption of U(VI) on montmorillonite with aluminum and iron hydroxides deposited on its surface,studied in the presence of citric and oxalic acids

Sorption of U(VI) on montmorillonite from the Cherkassy deposite with Al(III) and Fe(III) hydroxides deposited on its surface (metal weight fraction 0 and 5%: M-0, MAl-5, and MFe-5) was studied in the presence of complexing agents: citric and oxalic acids. Citric acid suppresses the uranium sorption from weakly acidic solutions more strongly than does oxalic acid. At equimolar concentrations of ligands and U(VI) in solution, ternary surface complexes can be formed on the surface of the examined samples.     

Desorption of U(VI) from montmorillonite with aluminum and iron hydroxides deposited on its surface

Decontamination of uranium-containing samples based on montmorillonite from the Cherkassy deposit, with Al(III) and Fe(III) hydroxides (weight fraction with respect to metal 0 and 5%: M-0, MAl-5, and MFe-5) deposited on its surface, by desorption with complexing agents (EDTA, citric acid, oxalic acid, sodium carbonate) was studied. With respect to efficiency of U(VI) desorption from the sample surface, the ligands can be ranked in the following order: citric acid > oxalic acid > ETDA ≥ sodium carbonate. In neutral solutions, citric acid is the most effective and environmentally suitable. From M-0 and MAl-5 samples, U(VI) is desorbed completely, whereas in the case of MFe-5 about 15% of U is irreversibly bound to the surface.     

Effect of aluminum and iron hydroxides deposited on the montmorillonite surface on the U(VI) sorption

Sorption of U(VI) on montmorillonite (M) of the Cherkassy deposit, with Al(III) and Fe(III) deposited on its surface in various amounts (1 and 5 wt %), was studied. The presence of such hydroxides increases the U sorption in the range pH 4.0–8.0. The U(VI) sorption increases in the order M < [M + 1% Al(III)] < [M + 5% Al(III)] < [M + 1% Fe(III)] < [M + 5% Fe(III)]. The U sorption isotherms on all the sorbents were obtained. The effect exerted on the sorption by artificial (ethylenediaminetetraacetic acid) and natural (fulvic acids) complexing agents was examined. Original Russian Text ? G.N. Pshinko, A.A. Bogolepov, S.A. Kobets, A.A. Kosorukov, 2009, published in Radiokhimiya, 2009, Vol. 51, No. 2, pp. 187–190.     

The removal of heavy metals from aqueous solutions by montmorillonite modified with polyethylenimine

We have shown a possibility of using montmorillonite modified with polyethylenimine for the removal of ions of heavy metals (Co(II) and Ni(II) from aqueous solutions. It has been found that the employment of such a composite sorbent is promising for purification of medium- and highly-mineralized wastewaters with the neutral value of the pH. The complexation influence of the reagents on the purification process has been shown and determined a dose of a reagent for obtaining the maximum possible degree of purifying aqueous solutions.     

Influence of the nature of oxygen-containing minerals on their sorption ability toward U(VI)

Sorption of U(VI) on natural and synthetic oxygen-containing minerals was studied. With respect to the sorption ability toward U(VI), natural minerals can be ranked in the order iron-containing > aluminum-containing > silicon-containing, and synthetic minerals, in the order iron-containing ≈ silicon-containing ≫ aluminum-containing. It was demonstrated by the example of Fe(OH)₃, α-FeO(OH), and γ-FeO(OH) that crystalline minerals bind U(VI) at pH values corresponding to natural media (pH > 7.5) better than do amorphous minerals. The ionic strength does not affect the U(VI) sorption owing to formation of strong inner-sphere complexes on the mineral surface. The presence in solution of complexing agents in small amounts can enhance the U(VI) sorption owing to formation of ternary surface complexes, whereas large excess of the ligand decreases the sorption because of the shift of the equilibrium toward formation of soluble complexes migrating in the environment by long distances with water streams.     

Removal of toxic metals from aqueous solutions by layered double hydroxides

The article has investigated the possibility of using layered double hydroxide intercalated by diethylenetriaminepentaactetic acid for the removal of toxic metals from aqueous solutions. It has been shown that sorption of Ni(II), Co(II), and Pb(II) from aqueous solutions on the indicated sorbent is determined by several mechanisms of sorption: complexation, ionic exchange and precipitation of metal hydroxides. Comparative research of the efficiency of removing toxic metals by carbonate and chelate forms of sorbents was conducted.