Effect of curing time on immobilized Cs and Sr Isotopes leached from cement matrices

To assess the conditions for the safe disposal of radioactive wastes by encapsulation in cements, the effect of curing time on the leaching of radionuclides prior to the commencement of leaching experiments has been investigated. Leach tests were carried out on various cement matrices, using a modified IAEA method recommended by Hespe¹.     

Innovative stabilization/solidification processes of fly ash from an incinerator plant of urban solid waste

Fly ash samples from an incineration plant of urban solid waste (USW) were submitted to a stabilization/solidification process based on encapsulation with a polyester resin. With this process, a very limited increase of about 25% in weight and a compressive strength as high as 1200 kg/cm² can be obtained. The efficiency of the process to stabilize/solidify the residues and to reduce the pollutant release was evaluated by performing both mechanical and leaching tests following the IRSA–CNR standard method. The leaching test was based on treating the sample with an acetic acid solution adjusted to pH 5.2 for 24 h under magnetic stirring. Toxic metals (Pb, Cd, and Cu) and organic pollutants (PAHs, PCBs, and OCPs) were determined in raw fly ash samples and in the leaching solutions of treated samples. Raw residues showed higher concentrations of trace metals than the regulatory limits, whereas the stabilized/solidified residues showed a concentration of all the pollutants lower than the regulatory limits and a compressive strength much higher than the suggested minimum value. Finally, a critical comparison with conventional stabilization/solidification processes based on the use of Portland cement highlighted that the polyester resin-based process performed much better in terms of the release of both organic and inorganic pollutants, thus substantially lowering the environmental impact of these residues.     

Trace metal and mineral speciation of remediated wastes using electron microscopy

Electron microscopic techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalyses (EPMA), were used to evaluate metal species and mineralogical phases associated with metal-bearing contaminated soil and industrial wastes that have been solidified and stabilized with Portland cement. Metals present in the wastes included arsenic, barium, cadmium, chromium, copper, lead, nickel, and zinc. In addition, mineral alterations and weathering features that affect the durability and containment of metals in aged remediated wastes were analyzed microscopically. Physical and chemical alteration processes identified included: freeze-thaw cracking; cracking caused by the formation of expansive minerals, such as ettringite and thaumasite; carbonation; and the movement of metals from waste aggregates into the surrounding cement matrix. Preliminary results show that although the extent of degradation after 6 years is considered slight to moderate, evaluations of durability and permanence of metals containment cannot be based on leaching and bulk chemistry analyses alone. The use of electron microscopic analyses is vital in studies that evaluate trace metal and mineral species and that attempt to predict the long-term performance of metal containment in solidified and stabilized wastes.     

Effect of container adsorption on the210Pb/210Bi secular equilibrium relationship in spiked aqueous solutions

The radioactive boric acid wastes generated from the nuclear power plants have been solidified with cement. One of the properties required for solidified radioactive wastes is resistance to leaching. The leachability of¹³⁷Cs from solidified waste specimens prepared by various formulation has been studied according to the proposed ANS 16.1 Standard Leach Test. For the evaluation of radiological safety in the solidified radioactive waste disposal, the leachability indices have been determined from the leaching test data. The results have turned out to be 5.97–7.60, depending on formulation and solidifying matrix.     

A new standardized leaching test on stabilized wastes

A new long-term leaching test on stabilized and solidified waste material have been developed and standardized in the frame of the Standards, Measurements and Testing (SMT, formerly BCR) programme of the European Union (EU). The project was coordinated by Dr. H. A. Van der Sloot from ECN (Energy Research Foundation, The Netherlands). Twenty-five European laboratories from EU and EFTA countries participated in the intercomparison exercise. The solidification/stabilization treatment of municipal solid waste incinerator fly ashes, using cement as a matrix, was performed by INTRON B. V. (The Netherlands). The resulting solidified waste material was then used to produce the requested specimens for the intercomparison study. Before distribution to participants, specimen homogeneity was tested according to the state-of-the-art technology for physical-mechanical testing of cement samples as well as for consistency of chemical composition of the solid and stabilized waste. The results of tank leaching test for the above mentioned interlaboratory study are reported and the advantages of this new procedure for the study of the environmental impact of solidified wastes are discussed.     

Zeolites for nuclear waste treatment: Co, Ni and Zn uptake into synthetic faujasite X

Pellets of the synthetic zeolite X were loaded with the radioisotopes⁶⁰Co,⁶³Ni and⁶⁵Zn. The pellets were then calcined. A secondary ion-exchange step introduced a large cation, barium, into the zeolites with a view to blocking the release of the radioisotopes under leaching conditions. Leaching was carried out over 84 days with synthetic sea and ground waters as well as deionised water. Leach tests were evaluated in terms of cumulative fraction of isotopes released and as diffusion coefficients derived from leaching profiles. Cobalt containing samples were cement encapsulated and further leach studies carried out. Some minor reduction in isotopes release was observed in the presence of barium but this was not consistent.     

Effect of neutralizing agent content on137Cs leaching from solidified boric acid waste products

For the preservation of environment from radioactive contamination, one of the properties necessary for solidified radioactive wastes is resistance to the release of radionuclides due to leaching by ground water after land disposal. In order to seek the optimum solidifying formulation for cement solidified boric acid concentrate from pressurized water reactor, a variety of specimens were prepared, varying the content of neutralizing agents and neutralization methods. For the leaching measurements, the ANS 16.1 Standard Leach Test was carried out for the specimens which had been mixed with small concentration of¹³⁷Cs to estimate the leachability index. According to our investigation, the optimum contents of neutralizing agents for neutralization of boric acid radioactive waste were determined in view of resistance ability to leaching. Eventually the leachability indices have turned out to be 5.807.91 depending on the formulations.     

Leaching Studies of Inorganic and Organic Compounds from Fly Ash

Fly ash is produced in massive quantities by fossil fuel based power plants and waste incinerators, and contains high levels of potentially toxic chemicals. Various leaching tests exist to determine the available fractions, but the outcome is strongly dependent on the experimental conditions, and these have not yet been harmonised at the international level. In order to test existing protocols for heavy metals, several intercomparisons were organised within the framework of an EU-INCO project "ANALEACH", in which seven institutes from five countries participated. Two existing reference materials were made available for the project and test batches of two new fly ash reference materials were produced. Availability tests, leaching tests and pH-stat tests were studied and critical steps in the procedures were identified. Fly ashes can also contain large amounts of inorganic sulphur and nitrogen compounds, and the determination and leaching behaviour of these compounds were also studied. In one intercomparison for metals, inorganic S and N-compounds were also included. A five-step leaching test was optimised for fly ash in order to link metal fractions to different types of binding. Column leaching experiments were carried out to investigate leaching from fly ash into soil, mimicking the effects of (acid) rain on fly ash deposited on topsoil after atmospheric transport. The major fraction of the leached metal ions was retained by the soil. Also large numbers of organic compounds (including many toxic ones) were identified in fly ash extracts, especially in city waste incinerator ash. Leaching procedures based on ultrasonic extraction were developed for organic compounds and an intercomparison exercise was organised. In a field study at the river Nitra(Slovakia) numerous organic pollutants were found at elevated levels downstream from a major fly ash dump site.     

Compositional changes in cement-stabilized waste during leach tests--comparison of SEM/EDX data with predictions from geochemical speciation modeling

Cement-based stabilization/solidification (s/s) is a widely used treatment process for hazardous wastes containing toxic metals. The treated waste consists of a complex mixture of several solid phases produced by cement hydration reactions. Understanding and predicting the effects of leaching on these individual phases is essential for assessing the long-term immobilization of metal contaminants in s/s waste exposed to rain and groundwater. In this paper, particles of crushed Portland cement doped with copper, lead, and zinc nitrates were leached with nitric acid solutions maintained at constant pH in the range pH 4-7. Changes in solid composition at the microscopic scale were measured by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDX). The geochemical equilibrium model SOLTEQ-B, which accounts for the incongruent solubility behavior of calcium silicate hydrate, was used to simulate the compositional changes in the hydration gel for increasing extents of leaching. Measured concentrations of calcium, silicon, and sulfur were successfully predicted at all extents of leaching. Aluminum, lead, and zinc concentrations were also in good agreement with model predictions, except in the remineralization zones that form when metals solubilized in the outer regions of the s/s waste particles diffuse toward the interior and reprecipitate at higher pH. Copper was less accurately modeled at high extents of leaching. Accounting for the incorporation of contaminant metals into the cement hydration gel (in opposition to assuming the presence of individual metal hydroxides) is crucial for successfully predicting contaminant metal concentrations in the hydration gel at low and intermediate extents of leaching.     

Studies of Thermal Transformations of Petrochemical Wastes For Obtaining Mineral-carbon Sorbents

In the present work an attempt was made to obtain mineral-carbon sorbents by thermal decomposition of solid waste materials containing, besides to mineral components, solid petroleum derivatives. The amount and the homogeneity of distribution of coal product formed in decomposition of organic matter on the surface of the mineral matrix, as well as the porous structure of the sorbents obtained depend largely on the conditions of calcination of the wastes used. The aim of this work was to find optimum conditions of the process. The sorptive properties of the obtained material were checked in the process of reduction of pollutants contained in industrial wastes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bone cell activity responsive drug release from biodegradable apatite/collagen nano-composite cements--in vitro dissolution medium responsive vitamin K2 release

A biodegradable drug delivery system with perforated macro pores was established using an apatite/collagen composite cement containing menatetrenone (VK2). The drug-release capabilities of the device were investigated in vitro under osteoblast and osteoclast-like conditions (SOB and SOC). A bulk powder of apatite cement containing 2.5% VK2 and 20% bovine collagen was obtained by grinding, kneaded with phosphoric acid, and poured into molds, producing fixed blocks with 0-60 perforated macro pores. The characteristics of these samples were measured by X-ray powder diffraction analysis and Fourier-transformed and infrared spectroscopy, and found to be very similar to those of natural bone. Drug release tests were performed under SOB in simulated body fluid (pH 7.8), and then under SOC in acetate buffer (pH 4.5) at 37.0±0.1 °C, and the process repeated twice. The device released almost no drug in SOB, but a significant amount in SOC. The drug release in SOC was not proportional to the number of macro pores in the first test, but was in the second. The device showed dissolution medium-responsive drug release.     

Comparative behavior of britholites and monazite/brabantite solid solutions during leaching tests: a combined experimental and DFT approach

In the field of the specific immobilization of actinides, several phosphate-based ceramics have already been proposed as suitable candidates. Among them, britholite and monazite/brabantite (now called monazite/cheralite) solid solutions have been considered as serious candidates on the basis of several properties of interest. Although both matrices appear almost similar from a chemical point of view, their chemical behavior during leaching tests appear to be strongly different with normalized dissolution rates of typically (2.1 +/- 0.2) g.m(-2).day(-1) for Th-britholites (10(-1)M HNO(3), theta = 25 degrees C, dynamic conditions) and (2.2 +/- 0.2) 10(-5) g.m(-2).day(-1) for Th-brabantites (10(-1)M HNO(3), theta = 90 degrees C, dynamic conditions). To understand such difference from a crystallographic point of view, comparative leaching tests have been performed using either high or low renewal of the leachate. The results obtained clearly revealed a lower chemical durability of An-britholites compared to that of (Ln, Ca, An)-monazite/brabantite solid solutions. As a confirmation of this point, density functional theory calculations clearly showed some great differences in the cohesive energy of calcium in both crystal structures, which can explain this strong difference in the chemical durability of both materials.     

The effect of sodiumlignosulphonate on cement properties for conditioning the hazardous wastes

Sodiumlignosulphonate was added to sulphate resisting cement as chemical additive to modify its physical and chemical properties for conditioning hazardous and radioactive wastes for long term disposal. The effect of some organic and inorganic chemicals on sulphate resisting cement was investigated. The physical properties such as density, porosity percent and absorption percent for all the studied samples as well as the compressive strength values and the leaching properties were also determined. The thermal stability and the radiation stability were also investigated.     

FTIR-ATR study of the surface of a tubular zeolite NaA membrane ultrasonically reacted with water and acetic acid.

For the dehydration process of biomass alcohol using a zeolite NaA (LTA) membrane supported by an alumina porous support tube, it is very important to understand damage of the surface crystal, which may be caused by acetic acid. Therefore, the surface structure and the chemical composition of the LTA membrane that reacted with water or acetic acid (pH 3-4) were investigated by the Fourier Transform Infrared Attenuated Total Reflectance method (FTIR-ATR), with a diamond prism as the waveguide, scanning electron microscope and an energy-dispersive X-ray analysis. For leaching experiments using water and acetic acid, ultrasonication was applied to promote the leaching rate and to surely prepare damaged membranes as a model experiment. The Si-O asymmetric stretching vibration spectra of the original LTA membranes showed a bimodal peak. LTA membranes after water leaching also showed the same peak. However, for the LTA membrane reacted with acetic acid of pH 3, damage of the surface LTA crystal and the loss of sodium by dissolution were clearly observed. Also, its Si-O spectral shape was broad, which suggests amorphous-like substances secondarily formed on the membrane surface. Sodium acetate was not detected for all LTA membranes reacted with acetic acid. To evaluate surface-damaged and sodium-loss membranes, FTIR-ATR can sensitively detect a Si-O spectral change corresponding to the surface structure and the chemical composition of the LTA membrane.     

Hydrothermal solidification of municipal solid waste incineration fly ash

Hydrothermal solidification of municipal solid waste incineration (MSWI) fly ash has been conducted under saturated steam pressure at 200 °C for up to 48 h with quartz addition. To enhance the strength of solidified specimens further, the raw fly ash was pre-treated by water-washing and mixed with NaOH solution (2 M) as reaction solvent. Experimental results showed that curing time and temperature had significant effects on strength development. Strength development was found to be mainly due to tobermorite formation, and addition of quartz and NaOH solution promoted tobermorite formation. The raw fly ash could also be used as an additive to solidify MSWI bottom ash, and with raw fly ash addition (10%) the flexural strength of solidified specimens reached more than 21 MPa, suggesting high potential to recycle 100% MSWI ash (e.g. as 10% fly ash + 90% bottom ash). Leaching tests were conducted to determine amounts of heavy metals dissolved from solidified specimens. The results showed that under the hydrothermal conditions of this study, leaching of heavy metals was very low. As such, the hydrothermal processing method might have high potential for recycling/reusing MSWI fly ash on a large scale.     

Leaching behavior of137Cs in cement

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of¹³⁷Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.¹ The leachability was measured as a function of bentonite clay to cement ratio. The fraction of¹³⁷-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.^2,3     

"Acid extractable" metal concentrations in solid matrices: a comparison and evaluation of operationally defined extraction procedures and leaching tests

Different frequently used methods to determine the influence of acid conditions on heavy metal release from soils, sediments and waste materials, namely pH_stat leaching tests and acid extractions with acetic acid (HOAc) (0.11 M and 0.43 M) and sodium acetate (NaOAc) (1 M) were compared for 30 samples (soils, sediments and waste materials) with different physico-chemical properties and a different degree of contamination. However, no distinct relationship was found between physico-chemical sample characteristics, total element concentrations and acid-extractable metal concentrations in the presented dataset.

pH played an important role in explaining the release of metals from the contaminated soils, sediments and waste materials. The pH-shift after extraction with the different acetic acid solutions (0.11 M and 0.43 M) was both explained by the initial pH of the sample and its acid neutralizing capacity. The pH of the NaOAc extract was well buffered and the release of elements from solid matrices by NaOAc was both the result of the complexation with acetate and pH (pH 5). Generally, a linear correlation was found between the amount of Zn and Cd extracted by 0.11 M HOAc, 0.43 M HOAc and 1 M NaOAc. The amounts of Zn and Cd extracted with HOAc (0.11 M and 0.43 M) were comparable with amounts of respectively Zn and Cd released during pH_stat leaching at pH 4. However, for Cu, Pb and As, it was often not possible to relate the results of a pH_stat leaching test to the results of single extractions with acetic acid solutions.     

Electrosprayed core-shell nanoparticles of PVP and shellac for furnishing biphasic controlled release of ferulic acid

Coaxial electrospraying was explored to organize polymer excipients in a core-shell manner for providing biphasic controlled release of active ingredient. With ferulic acid (FA) as a model drug, and shellac and polyvinylpyrrolidone (PVP) as the core and shell polymeric matrices, core-shell nanoparticles were successfully fabricated. A series of tests were carried out to characterize the prepared core-shell nanoparticles and also the nanoparticles prepared using a single fluid electrospraying of the shell or core fluids alone. The core-shell nanoparticles had an average diameter of 530?±?80 nm with clear core-shell structure. The contained FA was converted to an amorphous state both in the core and the shell parts due to the favorable hydrogen bonding between the components. In vitro dissolution tests demonstrated that the core-shell nanoparticles were able to provide the desired biphasic drug-controlled release profiles. Coaxial electrospraying is a useful tool for the development of novel nanodrug delivery systems from polymers.     

Factors affecting the leaching mechanism of Mg bearing oxide impurities in Hydrogen Assisted Magnesiothermic Reduction (HAMR) of TiO2

Titanium production by a direct TiO₂ reduction route which is highly energy-efficient and environment-friendly compared to commercial Kroll's process, known as HAMR (Hydrogen Assisted Magnesiothermic Reduction) process has been developed in recent times to meet the growing global demands of low-cost pure Ti. Removal of the Mg compounds after each reduction and de-oxygenation step in the HAMR process by leaching, is essential to ensure good purity and mechanical properties of the final Ti powder. In this study, we investigate the effects of temperature, particle size, and pH on the dissolution kinetics of Mg from Mg-bearing compounds such as MgO and MgCl₂ that remain after the HAMR Process. We also report the underlying mechanism and rate-controlling steps of Mg removal using HCl in connection with the HAMR process. The dissolution kinetics followed a logarithmic rate kinetic model for diffusion through a porous medium that is commonly used for battery research. Kinetics of leaching were significantly improved using finer particles with 99.96 wt.% Mg removal and corresponding Ti loss of only 1.8 wt. %. The rate of dissolution exhibited a weak dependence with the pH and did not abide by the rate-controlling steps of dissolution of ionic oxides like MgO proposed by previous kinetic models.     

Studying the ash behaviour of agricultural residues using thermal analysis

In this paper, the ash behaviour of some typical Mediterranean agricultural residues, such as peach stones, cotton gin wastes and grape residues is studied via simultaneous, (DTA/TG), thermal analysis methods. Furthermore, the effect of various pre-treatment techniques, such as fractionation and leaching, on the ash behaviour of the specific residues is also studied. Fractionation improves some of the main biomass properties such as calorific value, volatiles and ash content but deteriorates significantly the ash chemical composition of the remaining ash fraction. Leaching improves both the main properties of the treated biomass samples and the chemical composition of the remaining ash fraction, while the combination of the two pre-treatment methods results in a merge of their main advantages leading to an even larger improvement of the ash thermal behaviour. This revised version was published online in July 2006 with corrections to the Cover Date.