The use of halloysite functionalized with isothiouronium salts as an organic/inorganic hybrid adsorbent for uranium(VI) ions removal.

Elimination of U(VI) from nuclear wastes and from the underground water near the uranium mines is the serious problem. Therefore search for new sorbents for U(VI) is still a big challenge for the scientists. This paper investigates of U(VI) ions sorption on halloysite modified with the isothiouronium salts: S-dodecaneisothiouronium bromide (ligand 1), S,S'-dodecane-1,12-diylbis(isothiouronium bromide) (ligand 2), S-hexadecaneisothiouronium chloride (ligand 3), S,S'-naphthalene-1,4-diylbis(methylisothiouronium) dichloride (ligand 4), and S,S'-2,5-dimethylbenzene-1,4-diylbis(methylisothiouronium) dichloride (ligand 5). It was established that halloysite modified by the ligands with four nitrogen atoms in their structure (ligand-5, 2 and 4) was characterized by higher sorption capacity compared with that modified by the ligands with two donor nitrogens (ligand-1 and 3). The maximum sorption capacity of halloysite-5 toward U(VI) was 157 mg U/g and this places the modified mineral among the most effective sorbents for U(VI) removal from wastes. As follows from ATR, XPS and thermal degradation spectra of the sorption products [R-S-C(NH)(NH2)]n = 1-2(UO22+) complexes are formed on the external surface of the halloysite whereas oligomeric hydroxy complexes (UO2)3(OH)5+ and (UO2)4(OH)7+ are present in the interior of halloysite structure and interact predominantly with aluminols.

Metal Ions Removal Using Nano Oxide Pyrolox™ Material.

The paper presents the use of Pyrolox™ containing manganese nano oxides used for the removal of Cu(II), Zn(II), Cd(II), and Pb(II) as well as U(VI) ions. Their concentrations were analyzed using the atomic absorption spectrometer SpectrAA 240 FS (Varian) as well as UV-vis method. For this purpose the static kinetic and equilibrium studies were carried out using the batch technique. The effect of solution pH, shaking time, initial metal ion concentrations, sorbent dosage, and temperature was investigated. The equilibrium data were analyzed using the sorption isotherm models proposed by Freundlich, Langmuir-Freundlich, Temkin, and Dubinin-Radushkevich. The kinetic results showed that the pseudo second order kinetic model was found to correlate the experimental data well. The results indicate that adsorption of Cu(II), Zn(II), Cd(II), and Pb(II) as well as U(VI) ions is strongly dependent on pH. The value of pH 4-7 was optimal adsorption. The time to reach the equilibrium was found to be 24 h, and after this time, the sorption percentage reached about 70%. Kinetics of Cu(II), Zn(II), Cd(II), Pb(II), and U(VI) adsorption on the adsorbent can be described by the pseudo second order rate equation. Nitrogen adsorption/desorption, infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) measurements for adsorbent characterization were performed. Characteristic points of the double layer determined for the studied Pyrolox™ sample in 0.001 mol/dm3 NaCl solution are pHPZC = 4 and pHIEP < 2.

Tetrad effect in the adsorption of the lanthanides on zeolite Y.

The adsorption of the lanthanides (except for Pm) on the zeolite Y was investigated under various solution conditions of nitrate ion concentration ([NO(-)(3)]: 0.001-2 mol/dm(3)) and total lanthanide concentration (from 0.0001 to 0.001 mol/dm(3)). The solutions of the lanthanide nitrates were equilibrated with the zeolite samples at 296 K. The concentrations of lanthanides in the initial and equilibrium solutions were determined by means of spectrophotometrical method with Arsenazo III reagent and distribution constants K(d) of the lanthanides between aqueous and zeolite phases were calculated. The evident concave tetrad effect in the change of logK(d) values (nitrate concentrations 0.4-2 mol/dm(3)) within the lanthanide series was noticed and an attempt at its explanation through the comparison of covalence in LnO bonds existing in triple bond AlO(1/3Ln)Si triple bond species in the zeolite phase and in Ln(NO(3))(2+) complexes forming in the aqueous phase was presented. The weak convex tetrad effect for equilibrium nitrate concentrations 0.001-0.32 mol/dm(3), manifesting in the change of logK(d) values and in the alteration of logK (adsorption constants), is evidence of the complexation of the tripositive lanthanide ions by the oxygens originating both from water molecules and from the zeolite framework.