Immobilization Of Hazardous Wastes Research Articles

Immobilization of Hazardous Wastes on One-Part Blast Furnace Slag-Based Geopolymers

The immobilization of hazardous wastes in ordinary Portland cement (OPC)-based materials has been widely studied and implemented. OPC-based materials have a high carbon footprint associated with their production and geopolymer materials are a sustainable and eco-friendly alternative. Therefore, this work aimed to immobilize two hazardous industrial wastes: copper wastewater sludge and phosphogypsum in one-part geopolymer materials. For that purpose, the precursor was partially substituted by these wastes (5, 10 and 20 wt.%) in the formulations. The geopolymer fresh and hardened state properties were evaluated, and the immobilisation of pollutants was determined through leaching tests. In phosphogypsum pastes (PG5, PG10 and PG20) it was observed that the compressive strength decreased with the increase in its amount, varying between 67 MPa and 19 MPa. In copper sludge pastes, the compressive strength of the specimens (CWS5 and CWS10) reached ~50 MPa. The mortars, MPG10 and MCWSs10, had compressive strengths of 13 MPa and 21 MPa, respectively. Leaching tests showed that pastes and mortars immobilise the hazardous species of the wastes, except for As from copper sludge, whose the best result was found in the compact paste (CWSs10) that leached 2 mg/kg of As. Results suggest that optimized compositions are suitable for the construction sector.

Development of a stoichiometric magnesium potassium phosphate cement (MKPC) for the immobilization of powdered minerals

Ordinary Portland Cement (OPC)-based materials are not systematically adapted for immobilizing industrial hazardous waste, e.g. for aluminium powder or plutonium waste sludge. In such case, Magnesium Potassium Phosphate Cements (MKPC) represent an interesting alternative.The originality of this research is to develop a formulation of a MKPC paste for hazardous waste immobilization, which incorporates a maximum amount of such waste, preferably in powdered form. To this purpose, a stoichiometric MKPC paste is selected, and its properties are improved by powdered waste addition.Firstly, the physico-chemical mechanisms generating expansion in stoichiometric MKPC paste are analyzed. Swelling is attributed to a pH gradient in the paste, due to the progressive sedimentation of MgO particles in the fresh mix.Secondly, over-stoichiometric MgO is replaced by varying amounts of minerals simulating the waste, of different mineralogy and granulometry, in order to achieve sufficient workability and no swelling. An optimal formulation is proposed, which incorporates powdered fly ash at a fine-to-cement mass ratio (F/C) of 1. Its mechanical performance and endogenous dimensional changes are comparable to typical over-stoichiometric pastes, and they stabilize between 7 and 28 days.

B2O3-assisted low-temperature crystallization of pollucite structures and their potential applications in Cs+ immobilization

Pollucite structures present remarkable chemical stability and good corrosion resistance against the leaching medium, which renders them promising for the permanent disposal of radioactive 137Cs. However, it is still challenging to prepare pollucite with dense structures and high immobilization performance at low temperature so far. Additionally, the fundamental understanding of the mechanism underlying the leaching behaviors of Cs+ from pollucite remains largely unexplored. In this paper, we realize the low-temperature production of pollucite by tailoring the nature of geopolymer precursors and employing B2O3 additives. It has been shown that the introduction of B2O3 not only significantly reduces the crystallization temperature of pollucite, but also improves the immobilization performance of Cs through encapsulation effect. Differential scanning calorimetry and X-ray diffraction confirm the formation of crystalline pollucite from amorphous geopolymer at ∼700 °C in the presence of 7.5 wt% B2O3. By further increasing the treatment temperature to 1000 °C, pollucite grains can be well-encapsulated by glass phase, exhibiting leaching rates ∼2 order lower than their unencapsulated counterparts. Moreover, distinct leaching mechanisms that govern the leaching behaviors of Cs+ from specimens being treated at different temperatures are unveiled. We anticipate that the proposed scheme facilitates the low-temperature production of high-quality pollucite structures with promising applications in the immobilization of hazardous wastes.

Composition-structure-property relationships in Li2O–Al2O3–B2O3 glasses

The past decade has brought borate glasses to the forefront of industrial and technological innovations with the development of resorbable bioactive glasses for tissue engineering, glasses for immobilization of hazardous wastes and crack-resistant glasses for electronic packaging. However, these applications warrant a deeper understanding of the structural origin of various thermal, chemical and physical properties of borate glasses. Furthermore, the combination of borate glasses with SiO2 results in the formation of borosilicate glasses – one of the most important glass systems from scientific, technological and commercial viewpoints. In fact, it has been shown that most structural features in alkali borosilicates are similar to those of alkali borates. It is therefore important to understand the composition–structure–property relationships in borate-based glass compositions before extending them to more complex borosilicates, or aluminoborosilicate systems. In particular, aluminoborate glasses are intriguing as composition-structure-property models in these glasses are still under-developed. Accordingly, this paper is a sequel of our previous article [J. Non. Cryst. Solids. 460 (2017) 54–65] where we investigated the molecular structure of glasses in the system 25Na2O–xAl2O3–(75–x)B2O3 (x varies from 0 and 25 mol%) using magic angle spinning – nuclear magnetic resonance (MAS-NMR) and Raman spectroscopy. Further, the trends observed for the properties of these glasses, for example, density, molar volume, glass transition (Tg), coefficient of thermal expansion (CTE) and chemical durability (in water) have been correlated and discussed on the basis of their molecular structure.

Carbon dioxide use in beneficiation of landfilled coal ash for hazardous waste immobilization

Landfilled coal fly ash and supplementary minerals were processed into a hydraulic cement binder via input of mechanical energy at ambient temperature in the presence of carbon dioxide (CO2) (considered as a gaseous raw material). An experimental program was conducted with the purpose of optimizing the raw materials formulation for achieving a desired balance of cement chemistry for CO2 capture, compressive strength and heavy metals immobilization qualities of the cement hydration products. The optimum formulation was found to complement high levels of CO2 capture with desired material properties offered by the hydration products. Insight into the structure of hydration products was gained by evaluating their chemical bond structure and thermogravimetry attributes.

The influence of Pb addition on the properties of fly ash-based geopolymers

Preventing or reducing negative effects on the environment from the waste landfilling is the main goal defined by the European Landfill Directive. Generally geopolymers can be considered as sustainable binders for immobilization of hazardous wastes containing different toxic elements.In this paper the influence of addition of high amount of lead on structure, strength, and leaching behavior (the effectiveness of Pb immobilization) of fly ash-based geopolymers depending on the geopolymer curing conditions was investigated. Lead was added during the synthesis of geopolymers in the form of highly soluble salt – lead-nitrate. Structural changes of geopolymers as a result of lead addition/immobilization were assessed by means of XRD, SEM/EDS, and 29Si MAS NMR analysis. Investigated curing conditions significantly influenced structure, strength and leaching behavior of geopolymers. High addition of lead caused a sizeable decrease in compressive strength of geopolymers and promoted formation of aluminum-deficient aluminosilicate gel (depolymerization of aluminosilicate gel), regardless of the curing conditions investigated. According to the EUWAC limitations, 4% of lead was successfully immobilized by fly ash-based geopolymers cured for 28 days in a humid chamber at room temperature.

Thermal properties of 60P2O5–20Fe2O3–20Al2O3 glass for salt waste immobilization

Vitrification is the most effective method of hazardous waste immobilization. Toxic elements are incorporated into a glass structure. Iron alumino-phosphate glasses are presently being considered as a matrix for storage of a radioactive waste which cannot be vitrified using conventional borosilicate waste glasses. Influence of Na2SO4 as a one of components such the waste on thermal properties and crystallization ability of 60P2O5–20Fe2O3–20Al2O3 glass was studied. It was observed that Na2SO4 decreases transformation temperature and increases ΔCp. The glass characteristic temperatures, glass crystallization ability and crystallizing phases were determined. Na2SO4 increases the glass crystallization ability which could be related with ΔCp heat capacity accompanying glass transition changes. The glass internal structure rebuilding accompanying the sodium content increase is considered. The obtained results were compared with structural model previously developed for 60P2O5–40Fe2O3 glass and showed the structural similarity between these glasses.

Structural properties of iron-phosphate glasses: spectroscopic studies and ab initio simulations.

Vitrification is the most effective method for the immobilization of hazardous waste by incorporating toxic elements into a glass structure. Iron phosphate glasses are presently being considered as matrices for the storage of radioactive waste, even of those which cannot be vitrified using conventional borosilicate waste glass. In this study, a structural model of 60P2O5-40Fe2O3 glass is proposed. The model is based on the crystal structure of FePO4 which is composed of [FeO4][PO4] tetrahedral rings. The rings are optimized using the DFT method and the obtained theoretical FTIR and Raman spectra are being compared with their experimental counterparts. Moreover, the proposed model is in very good agreement with X-ray absorption fine structure spectroscopy (XANES/EXAFS) and Mössbauer spectroscopy measurements. According to the calculations the Fe(3+) is in tetrahedral and five-fold coordination. The maximal predicted load of waste constituents into the glass without rebuilding of the structure is 30 mol%. Below this content, waste constituents balance the charge of [FeO4](-) tetrahedra which leads to their strong bonding to the glass resulting in an increase of the chemical durability, transformation and melting temperatures and density.

Thermal properties of phosphate glasses for salt waste immobilization

Vitrification is the most effective method of the hazardous waste immobilization. Toxic elements are incorporated into glass structure. Iron phosphate glasses are presently being considered as a matrix for storage of the radioactive waste which cannot be vitrified using a conventional borosilicate glass. Influence of Na2SO4 as one of the components such the waste on thermal properties and crystallization ability of iron phosphate waste glass was studied. It was observed that Na2SO4 decreases transformation temperature and increases ΔC p. The glass characteristic temperatures, glass crystallization ability, and crystallizing phases were determined. Na2SO4 increases the glass crystallization ability which could be related with ΔC p heat capacity accompanying glass transition changes. The glass internal structure rebuilding, accompanying the sodium content increase, is considered. It is shown that ΔC p is a suitable, structure-sensitive glass crystallization ability, parameter.

Metal Immobilization of Hazardous Waste by Cementation

Metal Immobilization of Hazardous Waste by Cementation

Emanation thermal analysis study of brannerite ceramics for immobilization of hazardous waste

Brannerite based ceramics, designed as a matrix for immobilization of high level radioactive waste (HLW), was investigated from the viewpoint of microstructure changes and atomic transport properties caused by leaching of the ceramics at pH 2 and 11, respectively. Scanning electron microscopy (SEM) and emanation thermal analysis (ETA) techniques were used for this purpose. Surface morphology, microstructure changes and transport properties of both ‘as-leached’ and ‘as-prepared’ samples were compared and the effect of leaching on the thermal behavior of the ceramics samples heated in the temperature range from 20 to 1250°C was characterized. The mobility of radon in the brannerite ceramics was evaluated by mathematical modeling from ETA results. The thermal behavior of the non-leached brannerite ceramics sample and its natural analogue brannerite mineral was compared using the ETA.

Influence of pH, curing time and environmental stress on the immobilization of hazardous waste using activated fly ash

The current work is related to inorganic species in sludge generated from Common Effluent Treatment Plant contaminated with hazardous wastes at relatively high concentration. The environmental sensitive metals studied in the sludge are Pb, Fe, Ni, Zn and Mn. The solidification/stabilization (S/S) of heavy metals within fly ash-cement-based matrix was conducted for low cost treatment and reuse of sludge. The study examines the strength of the S/S product by predicting the effect of supplementary cementing material from efficiency factor ( k) at 60 °C curing temperature. The leaching test was performed at two different pH 7 and 4 to determine the efficiency of heavy metal immobilization. It was observed that replacing 76% OPC by 56% fly ash and 20% sludge for 28 days curing period shows increase in strength as well as rate of stabilization for zinc, iron and manganese at pH 7, lead and nickel were stabilized by 79 and 82%, respectively. Environmental stress test was performed to evaluate the tolerance of extreme adverse environmental condition.

Hydrocalumite-type materials: 1. Interest in hazardous waste immobilization

This study investigated the incorporation of Cr, V and Si oxoanions into hydrocalumite. Hydrocalumite together with ettringite form during the hydration of Portland cement and the use of these materials in hazardous waste immobilization is of current concern. The anion uptake was examined in terms of the structural characteristics by means of thermogravimetric analysis, infrared spectroscopy, X-ray diffraction (XRD) and in situ high temperature X-ray diffraction (HTXRD). The syntheses were carried out by coprecipitation or exchange reaction. The short interlamellar distances observed for Ca 2 Al–V 2 O 7 and Ca 2 Al–SiO 4 phases, 7.90 and 10.93 Å, respectively, are explained by a grafting process onto the hydroxide layers. The good crystallinity of Ca 2 Al–CrO 4 allowed the refinement of the cell parameters in the P -3 space group with a =5.7507(3) Å and c =20.164(2). A structural model is proposed with CrO 4 species close to the seventh coordination position of Ca atoms. In situ HTXRD measurements in the temperature range 25–350 °C reveal different thermal behaviors depending on the oxoanion. At low temperature, a dehydration–hydration process partly reversible was observed for Ca 2 Al–V 2 O 7 and Ca 2 Al–CrO 4 phases, between 100–200 and 50–120 °C, respectively. At higher temperature, strong interlayer contractions were observed due to a pillaring process: Δ d / d =−13% for Ca 2 Al–V 2 O 7 at 200 °C, Δ d / d =−32% for Ca 2 Al–CrO 4 at 250 °C and Δ d / d =−35% for Ca 2 Al–SiO 4 at 135 °C.

Assessment of Fossil Fuel Fly Ash Formulations in the Immobilization of Hazardous Wastes

In this work, a simple and inexpensive method is introduced for the immobilization of the hazardous elements Cd, Pb, and Fe from their aqueous solutions in compressed fossil fuel fly ash formulations, as candidates for waste forms. The molded formulations were prepared by initially mixing the hazardous waste solutions with the fossil fuel fly ash material at a constant ratio (17%). Then the resulting pastes were pressed at the appropriate pressure using a manual hydraulic press. The compressed formulations revealed good water resistance, compression strength, and radiation resistance. Leachability investigations of the molded matrices were performed in terms of the accelerated leach test, the toxicity characteristic leaching procedure (TCLP), and long-term leach tests. The TCLP results obtained for Cd and Pb were well below their TCLP limits. On the other hand, the accelerated and long-term leach tests showed a similar behavior. The properties of the compressed formulations revealed their high performance...

5595724 Treated Calcium/oxyanion-containing particles for medical diagnostic imaging

This study investigated the incorporation of Cr, V and Si oxoanions into hydrocalumite. Hydrocalumite together with ettringite form during the hydration of Portland cement and the use of these materials in hazardous waste immobilization is of current concern. The anion uptake was examined in terms of the structural characteristics by means of thermogravimetric analysis, infrared spectroscopy, X-ray diffraction (XRD) and in situ high temperature X-ray diffraction (HTXRD). The syntheses were carried out by coprecipitation or exchange reaction. The short interlamellar distances observed for Ca2Al–V2O7 and Ca2Al–SiO4 phases, 7.90 and 10.93 Å, respectively, are explained by a grafting process onto the hydroxide layers. The good crystallinity of Ca2Al–CrO4 allowed the refinement of the cell parameters in the P-3 space group with a=5.7507(3) Å and c=20.164(2). A structural model is proposed with CrO4 species close to the seventh coordination position of Ca atoms. In situ HTXRD measurements in the temperature range 25–350 °C reveal different thermal behaviors depending on the oxoanion. At low temperature, a dehydration–hydration process partly reversible was observed for Ca2Al–V2O7 and Ca2Al–CrO4 phases, between 100–200 and 50–120 °C, respectively. At higher temperature, strong interlayer contractions were observed due to a pillaring process: Δd/d=−13% for Ca2Al–V2O7 at 200 °C, Δd/d=−32% for Ca2Al–CrO4 at 250 °C and Δd/d=−35% for Ca2Al–SiO4 at 135 °C.

Synthesis, Crystal Chemistry and Stability of Ettringite, A Material with Potential Applications in Hazardous Waste Immobilization

ABSTRACTRecent results on synthesis, crystal chemistry, structure and stability of ettringite*, with specific reference to use of this material in hazardous waste immobilization, are presented. Ettringites with selenate, chromate, borate, sulfite and carbonate replacing sulfate have been synthesized and characterized by XRD for phase purity and structure. In X-ray powder diffractograms, selenate and chromate etringites have the normal trigonal P31cettringite structure, whereas the borate, sulfite and carbonate ettringites can be indexed on a hexagonal unit cell with a halved c parameter. In excess of 95% of the Se and B in solutions spiked with various concentrations of these elements has been removed by precipitation of ettringite. Ettringites appear to be unstable in solutions outside of the approximate pH range 11.0-12.5, and there is a potential for some oxyanion exchange between ettringites and oxyanion-containing solutions. Buffering of pH, and dissolved Ca, Al and sulfate activities by other components of ettringite-based hazardous waste forms, combined with low-reactivity C-S-H matrices, could largely mitigate these concerns.

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Simulation of solidification temperature profiles in the polyester process for immobilization of hazardous wastes

Simulation of solidification temperature profiles in the polyester process for immobilization of hazardous wastes