Authors:G. Dell’Agli, G. Mascolo, M. C. Mascolo, and C. Pagliuca
Summary Mechanical mixtures containing zirconia xerogel and increasing amount of crystalline yttria up to 40 mol%, were hydrothermally treated by microwave route at 110°C for 2h. All the treatments were performed in the presence of (KOH+K2CO3) mineralizer solution at concentration 0.2 M. Amorphous and hydrated ZrO2-Y2O3 solid solutions with yttria content up to 33.3 mol% (corresponding to Zr/Y molar ratio equal to 1), resulted after the hydrothermal treatments. A remarkable reduction of the surface area has been detected at increasing yttria content of the amorphous phases with a corresponding increase of the exothermic peak of crystallization. A mechanism of reaction for the formation of the amorphous solid solutions has been proposed.
Controlled heating (in air) of clay minerals leads to transformations into disordered structures and recrystallization into new phases at high temperatures. These phase transformations are of topotactic nature. On the other hand, prolonged dry-grinding treatments of the same silicates causes structural amorphization with no recrystallization into new phases. The mechanical energy relaxation mechanism, invoked to explain these differences, accounts for the particle size changes and the large growth of dislocations. The latters affect sensibly the reactivity of the materials submitted to such solid-state treatments.
These processes are monitored mostly by XRD, DTA and IR spectroscopy. The latter method allows to study in some silicates submitted to progressive grinding the location and nature of OH groups and water molecules.
Fixation of137Cs,144Ce,60Co,90Sr,240Th and233U from aqueous and phosphate media on bentonite clay was studied. The fixation of the radioactive ions on bentonite surfaces
was dependent on the pH behavior of the metal ions. A method was proposed to use bentonite as an absorbent of ions from simulated
radioactive waste as a treatment step.
Gamma-irradiation of treated piggery slurry was studied as a possible way of posttreatment. Biologically non-degradable substances (cellulose, lignin, etc.) were almost completely oxidized at 90–100 kGy radiation doses. TOC values indicated complete oxidation of organic carbon to CO2. Radiation doses of 10 and 50 kGy have not changed the biodegradability of irradiated substances. By -irradiation after chemical and biological treatment it is possible to get highest quality effluent with COD values lower than 40 mg.l–1.
Radionuclide concentrations in digester sludge and effluent samples from Hamilton and Dundas sewage treatment plants, located
at the western tip of Lake Ontario, have been determined by high-resolution γ-ray spectrometry. The radionuclides51Cr,75Se and131I, which are used in nuclear medicine procedures, were found in sludge samples. Very low concentrations of51Cr, entering Lake Ontario through the Hamilton plant effluent discharge, have little effect on lake water quality.
Via the thermal treatment of natural phosphates and their analysis, it was proved that the decrease in their solubility in
the interval 400–550C is an indication of the degree of incorporation of OH groups into the apatite structure of phosphates,
whereas the solubility at 950C is an indication of the degree of incorporation of the non-volatile components. The higherR950, the more extensive this substitution, and the more reactive the natural phosphate.
Synthetic Fe—Mn alkoxide of glycerol samples are submitted to controlled heating conditions and examined by IR absorption spectroscopy. On the other hand, the same sample is studied by infrared emission spectroscopy (IRES), upon heating in situ from 100 to 600°C. The spectral techniques employed in this contribution, especially IRES, show that as a result of the thermal treatments ferromagnetic oxides (manganese ferrite) are formed between 350 and 400°C. Some further spectral changes are seen at higher temperatures.
Different iron hydroxide precipitation processes simulating radioactive waste, treatment have been investigated by Mössbauer spectroscopy at room temperature and at 80 K. Magnetic oxides (hematite or magnetite) partially affected by superparamagnetic relaxation have been observed. The crystallization degree and the particle size depend on the concentration and the addition order of chemicals. Much smaller particles were precipitated with Ca(OH)2 than with NaOH as neutralization reagent.
Authors:A. Dyer, A. Gawad, M. Mikhail, H. Enamy, and M. Afshang
A natural laumontite from the Isle of Skye, Scotland has been examined as a candidate material for aqueous nuclear waste treatment, and its fully Ca exchanged form has been shown to be Sr selective. Laumontite has a good pH stability in acid and alkaline media. The materials used have been characterized by wet chemical analysis, XRD and thermal analysis. The studies include both ion exchange kinetics and equilibrium isotherm studies which tend to confirm simple Kd tests.
Authors:Sangita Pal, Suchismita Mishra, S. Satpati, G. Pandit, P. Tewari, and V. Puranik
“In-House” resin Polyacrylhydroxamic acid (PHOA) has been synthesized and utilized targeting ground water remediation; recovery
of uranium from low concentration aqueous solution e.g., mining activities related water, flooding of excavated or deplumed
areas, nuclear plant washed effluent and process generated effluents in nuclear plant during front-end as well as back-end
treatment. In the present study, treatment of field effluent containing heavy metals and radio-nuclides from contaminated
mining sites reflected preference for uranium with respect to manganese. The specific complexation between the extractant
and metal ion especially uranium provides high distribution co-efficient (Kd) for uranium (Kd,U = 1,450 mL/g from inlet of Effluent Treatment Plant (ETP) and Kd,U = 74,950 mL/g for synthetic solution) compared to high level impurity (1,000 times higher concentration) of manganese (Kd,Mn = 111 mL/g from inlet of ETP and Kd,Mn = 10,588 mL/g for synthetic solution). The “In-House” resin showed significant extractability (70–95% elution efficiency)
and indicates a possibility of selective removal/recovery of the valuable metal ions even from secondary sources. As a specialty,
resin can be regenerated and reused.