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.
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.
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.
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.
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.
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.
Authors:F. Franco, L. Pérez-Maqueda, and J. Pérez-Rodríguez
Kaolinites from well-known sources (KGa-1 and KGa-2) were used to study the influence of the particle-size reduction on the
dehydroxylation process. Size reduction of particles was obtained by ultrasound treatment to avoid the effect of the progressive
amorphization of the structure, which takes place with the traditional grinding treatment. The particle-size reduction causes
an increase of the mass loss between 140 and 390°C attributed to the loss of the hydroxyl groups exposed on the external surface
of kaolinite; a shift to lower temperatures of the endothermic effect related with the mass loss between 390 and 600°C; and
a shift of the end of dehydroxylation to lower temperatures. The first modification can be explained by an increase of the
number of hydroxyls exposed on the external surface of kaolinite which is proportional to the new surface generated in the
particle reduction process, whereas the shift of the dehydroxylation to lower temperatures is related to the reduction of
the dimensions of the particles which favour the diffusion controlled mechanisms. Comparing between the DTA curves to the
TG curves of the studied samples shows that the observed modifications in the thermal properties induced by the particle-size
reduction are greater for the low-defect kaolinite. The intensity of these modifications depends on the effectiveness of the
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.
The number of the cities with canalized water and sewage treatment stations has increased lately and consequently having in
mind the great concern on environment preservation and the quality of the water used by society. However, these stations are
nowadays causing another kind of problem: a huge quantity of sludge as residue. Due to the implication of the residue on the
environment and, consequently, to human life quality, performing of an accurate investigation about the components of such
sludge, as well as the thermal stability of this residue in the environment become necessary. This paper presents a study
on sludge from water and sewage treatment station, as well as the thermal characterization of residue. Such study was performed
through FTIR, atomic absorption, thermoanalytical (TG/DTG, DTA) techniques, that made it possible to observe that the main
components of the sludge are clay, carbonates and organic substance, presenting a low rate of metals and a unique thermal
behavior since the sludge from the treatment station has a higher thermal stability.