Solid Waste Forms Research Articles

Fabrication and Properties of Technetium-bearing Pyrochlores and Perovskites as Potential Waste Forms

Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (UNF). As such, it is targeted in UNF separation strategies such as UREX+, for isolation and encapsulation in solid waste forms for storage in a nuclear repository. We report here results regarding the incorporation of Tc-99 into ternary oxides of different structure types: pyrochlore (Nd2Tc2O7), perovskite (SrTcO3), and layered perovskite (Sr2TcO4). The goal was to determine synthesis conditions of these potential waste forms to immobilize Tc-99 and to harvest crystallographic, thermophysical and hydrodynamic data. Within these studies, Rietveld structure refinement was applied to allow for crystallographic characterization, while a physical property measurement system (PPMS) was used to determine thermophysical properties. The ternary oxides exhibited good crystallinity and their lattice parameters and atomic coordinates could be refined to high accuracy. Low refinement residuals (RBragg) of 2.0, 2.4, and 3.9% were achieved for Nd2Tc2O7, SrTcO3, and Sr2TcO4, respectively. The strontium technetates, SrTcO3 and Sr2TcO4, show superconductivity at rather high critical temperatures of Tc = 7.8K and 7K, respectively. Nd2Tc2O7 did not show any changes in magnetic properties above 3K.

Solidification of borate radioactive resins using sulfoaluminate cement blending with zeolite

The solidification of borate radioactive resins using sulfoaluminate cement (SAC) blending with zeolite was investigated, and the performance of SAC–zeolite matrix for immobilizing borate resin was evaluated based on the compressive strength, leachability and mineral phases of solidified waste forms. The experimental results showed that the 28 d compressive strength of resin SAC–zeolite waste forms was 18.8 MPa, the cemented waste forms meet the requirement of water, freezing, irradiation and impact resistance tests. The leaching processes of Cs + and Co 2+ were diffusion-limit step. The leachability of Cs + was higher than Co 2+ no matter what the matrix contained zeolite or not, but leachability of both cations was reduced by adding 5% zeolite. For SAC–zeolite matrix, the leaching rates of Cs + and Co 2+ were 6.40 × 10 −5 cm/d and 1.62 × 10 −7 cm/d, and the cumulative leaching fractions were 2.9 × 10 −3 cm and 2.3 × 10 −5 cm, respectively. The X-ray diffraction (XRD) analysis suggested that B(OH) 4 − was incorporated by substitution of SO 4 − in the crystalline structure of ettringite (3CaO·Al 2O 3·3CaSO 4·32H 2O).

Cullet use in the production of building materials

Questions concerning the formation of cullet in the form of solid household wastes and at enterprises which reprocess sheet glass are examined. It is shown that cullet is promising for use in manufacturing materials used in different applications. Decorative facing materials — steklokremnezit, steklokeramit, pressed tiles, and smalt can be made with a wide range of colors, different configurations, and dimensions. Heat- and sound-insulating materials based on granular, tile, and block foam glass and slag foam glass are of practical interest.

Stabilization of ZnCl 2-containing wastes using calcium sulfoaluminate cement: Leaching behaviour of the solidified waste form, mechanisms of zinc retention

To assess the potential of calcium sulfoaluminate cement to solidify and stabilize wastes containing high amounts of soluble zinc chloride (a strong inhibitor of Portland cement hydration), a simulated cemented waste form was submitted to leaching by pure water at a fixed pH of 7 for three months, according to a test designed to understand the degradation processes of cement pastes. Leaching was controlled by diffusion. The zinc concentration in the leachates always remained below the detection limit (2 μmol/L), showing the excellent confining properties of the cement matrix. At the end of the experiment, the solid sample exhibited three zones which were accurately characterized: (i) a highly porous and friable surface layer, (ii) a less porous intermediate zone in which several precipitation and dissolution fronts occurred, and (iii) the sound core. Ettringite was a good tracer for degradation. The good retention of zinc by the cement matrix was mainly attributed to the precipitation of a hydrated and well crystallized phase with platelet morphology (which may belong to the layered double hydroxide family) at early age (≤1 day), and to chemisorption onto aluminum hydroxide at later age.

Assessing nutrient fluxes in a Vietnamese rural area despite limited and highly uncertain data

Material flow analysis (MFA) is a useful methodology to describe and quantify complex systems based on the law of mass conservation. It was further adapted to suit the specific conditions in developing countries where the available data is scarce and uncertain. The ‘adapted MFA’ methodology optimises the number of parameters, describes these parameters as probability distributions and assesses the accuracy and uncertainty of the model values by Monte Carlo simulation. This study illustrates the first successful application of the ‘adapted MFA’ methodology in a small and low-income area including two neighbouring communes in rural northern Vietnam, where environmental sanitation and traditional agricultural practices are strongly interlinked and have an impact on the surrounding environment. Moreover, data on this area is typically scarce and uncertain. The obtained results reveal that the agricultural system was a significant source of nutrients (nitrogen (N) and phosphorous (P)), which affect the surrounding environment mainly due to the overuse of chemical fertilizers. Every year, there were 103 ± 39 tonnes of N released into the atmosphere, 25 ± 3 tonnes of N leached to the surface water and 14 ± 2 tonnes of P accumulated in the soil, all originating from the applied chemical fertilizers. In addition, the sanitation system was also a critical source of nutrients that enter the surface water. 69 ± 6 tonnes of N and 23 ± 4 tonnes of P came from households through effluents of on-site sanitation systems (such as latrines and septic tanks) and were directly discharged to surface water every year. Moreover, the whole system annually generated a large nutrient source (214 ± 56 tonnes of N; 58 ± 16 tonnes of P) in the form of wastewater, faecal sludge, animal manure and organic solid wastes. The validated MFA was used to model different scenarios for the study site. The first scenario demonstrated that if nutrient management is not improved, wastewater as well as faecal sludge and organic solid waste are expected to double in the year 2020 as compared to that in 2008. The second and third scenario revealed possible strategies to significantly reduce environmental pollution and reuse nutrient sources predicted to be available in the year 2020.

Mix design and mechanical properties of oil palm shell lightweight aggregate concrete: a review

To build environmentally sustainable structures, especially in developing countries, the possibility of using some agricultural wastes and industrial by-products from different industries as construction materials will be highly desirable and has several practical and economic advantages. Oil palm shell (OPS) is a form of agricultural solid waste in the tropical regimes. Research over the last two decades shows that OPS can be used as a lightweight aggregate for producing structural lightweight aggregate concrete. The density of OPS concrete is around 20 - 25 lower than normal weight concrete. Generally, mechanical properties of OPS concrete are slightly lower than the other types of lightweight aggregate concrete. It seems that from the summary and analysis of the existing information concerning OPS concrete and comparing it with other lightweight aggregate concrete it appears that significant achievements can be attained.

Cementation of radioactive borate liquid waste produced in pressurized water reactors

The solidification of simulated radioactive borate liquid waste was investigated using sulfoaluminate cement (SAC) as main matrix material. The additives, including Ca(OH) 2, zeolite, accelerator and polypropylene fiber were used to improve the performance of the solidified wastes. The experimental results indicated that the 28 days compressive strength of the solidified waste forms was 13.9 MPa, the leaching rate was 3.39 × 10 −5, 4.45 × 10 −5 and 4.07 × 10 −7 cm/d for Sr 2+, Cs + and Co 2+ respectively, meeting the requirement of the standard in GB 14569.1-1993. The SEM image and XRD pattern of solidified borate liquid waste forms revealed that the main hydrate of SAC improved the matrix strength and reduced the leachability. Boron, in form of B(OH) 4−, incorporated in ettringite (3CaO·Al 2O 3·3CaSO 4·32H 2O) as solid solutions, and the basic structure of ettringite did not change. SAC is appropriate matrix for the solidification of radioactive borate liquid waste.

The effects of temperature and size on the growth, energy budget and waste outputs of barramundi ( Lates calcarifer)

The effects of temperature and size on the growth, energy budget and waste output were examined in small (21 g) and large (142 g) juvenile barramundi ( Lates calcarifer) grown for 26 days at one of six temperatures (23 °C, 26 °C, 29 °C, 32 °C, 35 °C and 38 °C). Fish were fed once a day and faeces was collected by stripping at the end of the growth trial to measure the apparent digestibility of dry matter, energy, nitrogen and phosphorous. Survival was not affected by temperature and was high (87–100%) in all treatments. The influence of size (W) on the daily growth rate (DGR, g fish − 1 d − 1 ) was modelled with the power function DGR = αW γ, where α and γ are constants fitted with regressions to incorporate the effect of temperature into the model. Following a parabolic response to temperature, DGR and feed intake were high in both size classes across a temperature range extending from 29 °C to 35 °C. Temperatures for maximum growth and feed intake lay within the thermal zone for optimal feed efficiency from 26 °C to 35 °C. Feed efficiency was higher in small fish than in large fish. Although size had no effect on nutrient digestibility, temperatures influenced the apparent digestibility of dry matter, energy and phosphorous. The partitioning of consumed energy between growth, heat loss, nitrogen excretion and faeces showed increased energy losses through nitrogen excretion at 38 °C. Size and temperature had significant effects on waste outputs in the form of solid, nitrogen and phosphorous waste. In both size classes lowest levels of waste output were seen from 29 °C to 35 °C with levels rising at the cooler temperatures. The energetics and waste output of juvenile barramundi raised at different temperatures are discussed with respect to temperature dependent nutrient digestibility, feed intake and protein turnover.

Energia de briquetes produzidos com rejeitos de resíduos sólidos urbanos e madeira de Eucalyptus grandis

O incentivo ao consumo e à produção em grande quantidade na sociedade atual gera, exageros de resíduos sólidos urbanos que, em alguns casos, podem ser utilizados para a geração de energia. Neste sentido e visando reduzir os resíduos dos aterros municipais e gerar energia, buscou-se produzir briquetes com mistura de rejeitos de resíduos sólidos urbanos (RRSU) e resíduos de madeira de Eucalyptus grandis. Os briquetes foram fabricados com 0, 5, 10, 15, 20 e 25% de RRSU na mistura com resíduos madeireiros contendo 12% de umidade. Os parâmetros analisados para a escolha da melhor mistura, foram: análise de combustibilidade x cinzas, resistência e energia utilizável. Os briquetes com até 10% de RRSU se mostraram com baixa resistência e os acima de 15% apresentaram grande aumento no teor de cinzas; portanto, os que melhor atenderam aos requisitos combustibilidade x cinzas e resistência mecânica, foram aqueles com 15% de RRSU, pois não se conhece a procedência das cinzas. Considerando-se a energia utilizável, o briquete com 25% de RRSU é o que apresenta maior poder calorífico útil na ordem de 17.175 kJ kg-1 motivo pelo qual se indica a produção de briquetes com adição RRSU; ressalta-se, porém, a necessidade de estudos sobre a emissão de gases.

Dimensional stability under wet curing of mortars containing high amounts of nitrates and phosphates

Investigations were carried out in order to solidify in cement some aqueous streams resulting from nuclear decommissioning processes and characterized by a high salinity (300 g/L), as well as important concentrations of nitrate (150–210 g/L) and phosphate ions (0–50 g/L). Special attention was paid to the influence of these compounds on the dimensional variations under wet curing of simulated solidified waste forms. The length changes of mortars containing nitrate salts only (KNO 3, NaNO 3) were shown to be governed by a concentration effect which involved osmosis: the higher their concentration in the mixing solution, the higher the swelling. The expansion of mortars containing high amounts of phosphates (≥ 30 g/L in the mixing solution) was preceded by a shrinkage which increased with the phosphate concentration, and which could be suppressed by seeding the cement used with hydroxyapatite crystals. This transitory shrinkage was attributed to the conversion into hydroxyapatite of a precursor readily precipitated in the cement paste after mixing.

Development of a Novel Depleted Uranium Treatment Process at Lawrence Livermore National Laboratory

A three-stage process was developed at Lawrence Livermore National Laboratory to treat potentially pyrophoric depleted uranium metal wastes. The three-stage process includes waste sorting/rinsing, acid dissolution of the waste metal with a hydrochloric and phosphoric acid solution, and solidification of the neutralized residuals from the second stage with clay. The final product is a solid waste form that can be transported to and disposed of at a permitted low-level radioactive waste disposal site.

Immobilization of borate waste simulate in cement–water extended polyester composite based on poly(ethylene terephthalate) waste, part 3: Behavior of solid waste form during a scenario of flooding accident in the disposal site

Laboratory scale testing program was conducted to investigate the feasibility of using water extended polyester cement composite (PCC) based on poly- (ethylene terephthalate) waste (PET) as immobilization matrix for borate waste, originated from pressurized water reactors (PWRs), during prolonged term of disposal process and in scenario of flooding accident. Twenty-eight days cured solid blocks prepared as a premix of 3% by weight of the water extended polyester (WEP) and ordinary Portland cement (OPC) past having 40% by weight water were subjected to static immersion in three type of leachants, namely tap, sea, ground water. Weight changes, compressive strength variations, porosity, water absorption, and some other physical properties of the solid PCC waste forms were evaluated during 260 days of the static immersion. X-ray diffraction (XRD), infrared analysis (IR), and electron scanning microscope were performed for the waste forms at the end of immersion prolonged period to follow the internal changes in the solid waste forms that may occur due to the corrosion action of the different leachants. The results obtained from the different measurements confirm the performance of the PCC solidified waste form, based on the mentioned formulation, as an acceptable matrix in the various disposal sites and for extended disposal time even at the worst flooding environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4113–4120, 2007

Formation of leadhillite and calcium lead silicate hydrate (C–Pb–S–H) in the solidification/stabilization of lead contaminants

In this study, we have investigated the structure of Pb-doped solidified waste forms (SWF) for assessment of lead fixation. A large quantity of lead precipitates produced during the S/S, based upon the results of cement–water solution analysis, X-ray diffraction and electron probe microanalysis/electron dispersive spectroscopy investigations, have been shown to be principally leadhillite (lead carbonate sulfate hydroxide, Pb 4SO 4(CO 3) 2(OH) 2), lead carbonate hydroxide hydrate (3PbCO 3 · 2Pb(OH) 2 · H 2O) and two other unidentified lead salts. In the long curing, the lead species dissolved from the lead precipitates are fixed into the cement matrix, forming a gelling calcium lead silicate hydrate during cement-based solidification. On leaching the lead precipitates such as leadhillite were markedly dissolved/released and some dissolved lead species were adsorbed to silicate-rich surface of leached SWF with the subsequent formation of mainly amorphous gel of calcium lead silicate hydrate.

THE MICROSTRUCTURE OF Pb-DOPED SOLIDIFIED WASTE FORMS USING PORTLAND CEMENT AND CALCITE

An electron probe microanalysis (EPMA) investigation can provide quantitative and qualitative insight into the nature of the surface and bulk chemistry on solidified waste forms(SWF). The proportion of Pb in grain areas is below 0.3 wt. %, and the proportion near the border of the grain slightly increases to 0.98 wt. % but in the inter-particle areas farther from the grain, the concentration of Pb markedly increases. It is apparent that very little Pb diffuses into the tricalcium silicate() particles and most of the Pb exists as precipitates of sulfate, hydroxide, and carbonate in the cavity areas between grains. Calcite additions on Pb-doped SWF are also observed to induce deeper incorporation of lead into the cement grains with EPMA line-analysis of cross-sections of cement grains. The line-analysis reveals the presence of weight % Pb over from cement grain boundaries. In the inter-particle areas, the ratio of Ca, Si, Al and S to Pb is relatively similar even at some distance from the grain border and the Pb (wt. %) ratio is reasonably constant throughout the whole inter-particles area. It is apparent that the enhanced development of C-S-H on addition of calcite can increasingly absorbs lead species within the silica matrix.

Effect of calcite on Pb-doped solidified waste forms in leaching

The alkalinity of cementitious materials rectifies a low pH of leachant to be over 12 in leaching. The rapid change of leachant pH produces the remarked variation of solubility of heavy metals in the toxicity characteristic leaching procedure. The release of lead on cementitious solid waste forms in leaching was observed in the pH range of particularly 12. The release of lead is significant dependant on the changed values of leachant pH. The pH static leaching procedure (PSLP) was implemented for assessing a quantitative measurement of total potential leachability with the continuing addition of acidic leachant up to the point of no change of leachant pH. The release of lead on Pb-doped solidified waste forms (SWF), in the PSLP, was 27.0% of initial concentration at the maximum meq CH 3COOH (about 24.0) added to g dry solidified wastes. In this study, the immobilization effect of calcite on SWF was investigated in the acidic condition by the PSLP. Calcite additions to SWF make a good fixation efficiency of about 92%. Calcite addition abundantly provides the acid neutralization capacity to protect SWF from the attack of acid, with the marked development of hydrated minerals (mainly portlandite and C–S–H) in accordance with the accelerating effect of cement hydration.

06/00107 A decision supported system based on thecombination of fuzzy expert estimates to assess the financial risks in high-level radioactive waste projects: Fiordaliso, A. and Kunsch, P. Progress in Nuclear Energy, 2005, 46, (3–4), 374–387

This paper reports on the development of accelerated tests for evaluating microbial influenced degradation (MID) of cement-solidified wastes. An existing U.S. Nuclear Regulatory Commission accelerated test cannot distinguish between degradation caused by biogenic acid produced under optimal conditions in a bioreactor and that caused by active biofilms formed on the waste materials. Nutrient limitations were also observed that would significantly limit the activity of any developing biofilm. Results from this work have shown that it is possible to modify this test to remove nutrient limitations and enable the effects of MID resulting from active biofilms to be examined. Aggressive MID microorganisms can form a biofilm on the surface of cement-solidified waste so that when nutrients are provided the microbes remain active. Elemental mass loss data from exposed solidified waste forms indicate the continued development and growth of microbes on the surface of samples.

Effect of calcite on lead-rich cementitious solid waste forms

The effect of calcite on lead-rich solidified waste forms generated using Portland cement has been investigated. Samples of cementitious wastes in the absence and presence of Pb and in the absence and presence of calcite were examined separately at 2, 7, 14 and 28 days of hydration by X-ray diffraction and SEM/EDS and for compressive strength. The presence of lead was observed to produce lead carbonate sulfate hydroxide (Pb 4SO 4(CO 3) 2(OH) 2), lead carbonate hydroxide hydrate (3PbCO 3·2Pb(OH) 2·H 2O) and two other unidentified lead salts in cavity areas, and was observed to significantly retard the hydration of cement. Calcite addition to the Pb wastes was found to induce the rapid crystallization of calcium hydroxide coincident with the onset of C–S–H gel germination. The rapid dissolution of lead precipitates was observed with the subsequent development of very insoluble gel products of the form C–Pb–S–H. These products are formed by chemical incorporation of re-dissolved Pb species into silicate structures.

1172. 岩石固化体からのヨウ素浸出メカニズムの解明

In Japan, a preliminary safety assessment for geological isolation of TRU waste has reported that the rate of radioactive exposure can be controlled by radioactive iodine (I-129). In order to decrease the rate of radioactive exposure, the HIP (Hot Isostatic Pressing) solidified method has been developed for an iodine adsorbent waste (silver loaded silica gel) to produce a stable "HIP rock solidified waste form".Static leaching tests for the HIP rock solidified waste form, which were performed in a reducing condition with 3×10-3M Na2S solution for 300 days, showed that the normalized leaching rates for I and Si were extremely low (10-7-10-8g/dm2/day). For initial 60 days of the tests the cumulative amount of leached iodine was proportional to square root of time, which indicates that the leaching can be controlled by diffusion.Therefore, this phenomenon will be controlled by diffusion. By TEM analysis for the reacted waste form surface, formation of sulfides was observed at quartz grain boundary, which indicates that the diffusion path of iodine can be the grain boundary.Consequently, it is possible to adapt "grain boundary diffusion model" as iodine-leaching mechanism of the HIP "rock" solidified waste.

Development of test methods for assessing microbial influenced degradation of cement-solidified radioactive and industrial waste

This paper reports on the development of accelerated tests for evaluating microbial influenced degradation (MID) of cement-solidified wastes. An existing U.S. Nuclear Regulatory Commission accelerated test cannot distinguish between degradation caused by biogenic acid produced under optimal conditions in a bioreactor and that caused by active biofilms formed on the waste materials. Nutrient limitations were also observed that would significantly limit the activity of any developing biofilm. Results from this work have shown that it is possible to modify this test to remove nutrient limitations and enable the effects of MID resulting from active biofilms to be examined. Aggressive MID microorganisms can form a biofilm on the surface of cement-solidified waste so that when nutrients are provided the microbes remain active. Elemental mass loss data from exposed solidified waste forms indicate the continued development and growth of microbes on the surface of samples.

Dose rate and temperature effects in radiation disorder creation in SrTiO 3

An important aspect of assessing the physical and chemical stability of SrTiO 3 phase under radiation is to evaluate the disorder caused by α-decays in the actinide loaded nuclear waste form during the repository time. Indeed, radiation can affect considerably the chemical durability of the solid waste forms, especially for α-emitter immobilisation. It is already known that amorphisation in SrTiO 3 can be described at room temperature, by the cascade-overlap model with an additional term representing the initial disorder creation. In the present work, it is shown by using Pb-ion beam to simulate the α-recoil nuclei for creating the disorder that Pb-dose rate and sample temperature during irradiation are two important factors that affect SrTiO 3 susceptibility to proceed toward amorphisation.