Instrumental neutron activation analysis of lanthanides and coexisting elements in monazite samples and group separation using synthesized inorganic ion exchangers

Samples of Egyptian monazite ore obtained from black sand of Abu-Khashaba, Rashied (Rosetta) area on the Mediterranean Sea coast were analyzed for some lanthanides and coexisting elements using instrumental neutron activation analysis (INAA). The analyses were carried out qualitatively and quantitatively for the elements Ce, Nd, Eu, Gd, Tb, Yb and Sc, La as well as the accompanying elements Co, Cr, Fe, Hf, Nb, Zn, Zr in addition to the actinides Th and U; whereas after relatively longer decay time the following lanthanide elements were analyzed: Ce, Nd, Eu, Gd, Tb, Yb and Sc, beside the accompanying elements Co, Cr, Fe, Hf, Nb, Zn, Zr and Th. Two certified reference materials (CRM) were used in this study. For sorption studies, radioactive isotopes 141Ce, 160Tb, 169Yb, 95Zr, 181Hf, and 95Nb were prepared by neutron irradiation to trace the adsorption behaviors of their corresponding elements under certain conditions. Furthermore, radiochemical separation of the analyzed elements in the irradiated monazite samples in sulfuric acid solutions was carried out. Ion exchange technique was applied under static and dynamic conditions and the employed inorganic ion exchangers were locally synthesized and characterized using FT-IR and scanning electron microscopy (SEM) tools. Good group separation of the analyzed lanthanide elements from the accompanying elements was achieved.

Evaluation of electrokinetics coupled with a reactive barrier of activated carbon loaded with a nanoscale zero-valent iron for selenite removal from contaminated soils

The range between dietary deficient and toxic levels for selenium is quite narrow. In this study, the synergistic effects of electrokinetics (EK) and a permeable reactive barrier (PRB) on the reductive sequestration of Se(IV) oxyanions from spiked soils were investigated in detail. Activated charcoal (AC)-supported Fe(II) and nanoscale zero-valent iron (nZVI) were prepared as the PRB media for use in an electrolyzer. In aqueous equilibrium adsorption tests, the AC-supported nZVI medium had a higher adsorption capacity than that of the other adsorbents. The Se(IV) removal isotherms were well-fitted using the Langmuir model. The Se(IV) removal rates were accurately predicted by both pseudo-first- and pseudo-second-order kinetic models. For the coupled systems, a moderate increase in the number of PRBs and decrease in the PRB thickness in the electrolyzer enhanced the removal and catalytic recovery of Se(IV) from the spiked soil samples. A Se(VI) removal efficiency of approximately 95% and Se(VI) reduction efficiency of 90% were achieved in the optimized electrochemical system. The Se(IV) species were reduced to Se° and FeSe by the AC-supported nZVI regardless of the pH distribution. The experimental results provide guidance for the multichannel recovery of Se from abandoned ore tailings or solid wastes.

Comparison of some organic and inorganic ion exchangers concerning the sorption of Ce(III), Te(IV), Zr(IV), Hf(IV) and Nb(V)

The sorption behaviors of Ce(III), as a representative of trivalent lanthanide ions, and Te(IV), Zr(IV) and Nb(V) as fission products representatives, as well as Hf(IV), from various aqueous media on some synthesized inorganic exchangers, as well as commercially available organic ion exchangers were studied and compared. Organic cation exchanger Dowex-50WX8 and organic anion exchangers AG-1X8 and AG-2X8 were utilized. Synthesized inorganic ion exchangers were zirconium titanium phosphate (ZrTiP) of different Zr:Ti mole ratios and ceric tungstate (CeW). The sorption was carried out from mineral acid solutions as well as EDTA and DTPA solutions. The radioactive isotopes, 95Zr, 95Nb, 123mTe, 141Ce and 181Hf were used to trace the sorption behaviors of the corresponding elements, which were studied in mixtures of them. The differences between the sorption behaviors of the studied metal ionic species on both kinds of ion exchangers were interpreted and discussed in this work.