Magnetic Composite Sorbents for Trapping Heavy Metals from Liquid Waste and Their Immobilization in a Mineral-Like Matrix

Magnetic sorbents were prepared by addition of ferrospheres to zirconia-silica gel followed by thermal treatment at 500 °C. The ferrosphere narrow fraction E -0.063+0.050 mm from fly ash resulted from combustion of Ekibastuz coal was used as a magnetic component. The surface of magnetic composites was additionally functionalized by grafting of – POONa and – NH2 groups. Under equilibrium conditions sorption capacities of the sorbents with respect to Се3+ used as a U4+/Th4+ simulator and Pb2+ were measured by means of determination of sorption isotherms which were fitted by the Langmuir model. It was established that extraction of Се3+ and Pb2+ from aqueous solutions is characterized by distribution coefficients of 104–106 ml/g. Temperature conditions for solid-phase crystallization of the sorbents resulting in polyphase systems with the content of zircon phase of 50 wt. % were found

U-Pb zircon in situ dating with LA-MC-ICP-MS using a mixed detector configuration

The LA-MC-ICP-MS method applied to U-Pb in situ dating is still rapidly evolving due to improvements in both lasers and ICP-MS. To test the validity and reproducibility of the method, 5 different zircon samples, including the standard Temora-2, ranging in age between 2.2 Ga and 246 Ma, were dated using both LA-MC-ICP-MS and SHRIMP. The selected zircons were dated by SHRIMP and, after gentle polishing, the laser spot was driven to the same site or on the same zircon phase with a 213 nm laser microprobe coupled to a multi-collector mixed system. The data were collected with a routine spot size of 25 μm and, in some cases, of 15 and 40 μm. A careful cross-calibration using a diluted U-Th-Pb solution to calculate the Faraday reading to counting rate conversion factors and the highly suitable GJ-1 standard zircon for external calibrations were of paramount importance for obtaining reliable results. All age results were concordant within the experimental errors. The assigned age errors using the LA-MC-ICP-MS technique were, in most cases, higher than those obtained by SHRIMP, but if we are not faced with a high resolution stratigraphy, the laser technique has certain advantages.

Microstructure characterization of nanocrystalline ZrSiO4synthesized by ball-milling and high-temperature annealing

Microstructure characterization and phase transformation kinetics of a high-energy ball-milled and post-annealed stoichiometric (1:1 mol%)m-ZrO2and amorphous (a-) SiO2powder mixture have been investigated by Rietveld analysis of X-ray powder diffraction data. The experimental results reveal that the ball-milling of stoichiometric powder results in the formation ofc-ZrO2/t-PSZ phases only. The ZrSiO4phase was not found to form even after 30 h of milling. However, an almost stoichiometric ZrSiO4(commercially known as zircon) phase is found to form even when a sample that was ball-milled for 5 min was post-annealed at 1473 K for 1 h. It appears that the intermediatet-PSZ phase plays an important role in zircon phase formation. The content of ZrSiO4phase increases very sharply within 15 min of milling and remains almost unchanged after 30 h of ball-milling. It is also found that nanocrystalline zircon particles are almost free from lattice strain. Contamination by an α-Fe2O3phase from the milling media results in a colour gradient (white to reddish) in the nanocrystalline ZrSiO4phase.

Zirconia-mullite ceramics made from composite particles coated with amorphous phase: Part II. Effects of boria additions to the amorphous phase

Mullite and zirconia-mullite ceramics have been prepared by coating alumina/zirconia particles with an amorphous silica layer. The effect of composition change of the amorphous silica layer by adding B2O3 was investigated. For the zirconia-free compositions, the addition of B2O3 remarkably accelerates the kinetics of the crystallization of the amorphous coating layer, the viscous sintering, and the mullitization. For the zirconia-containing ceramics, the addition of B2O3 enhanced the viscous sintering kinetics and delayed the decomposition of the transient zircon phase and the subsequent t- to m ZrO2 transition, thus resulting in a higher ratio of t- to m-ZrO2. The B2O3-containing zirconia-mullite composites exhibit the same level of fracture toughness (Kic) as the B2O3-free zirconia-mullite composites.

Effect Of Dopants on the Crystallization of Zircon From Zirconium Silicate Gels

ABSTRACTZirconium silicate gels containing small amounts of foreign cations were found to exhibit different crystallization behavior as compared to undoped gels. The reaction to form the zircon phase was enhanced by the presence of these dopants, with zinc oxide additions causing the largest decrease in crystallization temperature. The crystallization behavior of these gels is compared to that of zircon prepared from alternative processing techniques.