Chemical Model for the Carbonation of a Grout/Water Slurry

Reardon, Eric J.; Dewaele, Paul

doi:10.1111/j.1151-2916.1990.tb09813.x

Cited by 18 publications

(6 citation statements)

References 17 publications

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“…For pH values greater than 8.0 up to 12.5, concentrations of dissolved carbonate were constrained by assuming equilibrium with the solubility of calcite (CaCO,). Calcite is known to precipitate as a result of carbonation reactions occurring with the dissolution of cement Reardon and Dewaele 1990;Smith and Walton 199 1). The concentrations of dissolved calcium were also constrained in the pH range from 8.5 to 12.5 by assuming the leachate is in equilibrium with the solubility of calcite.…”

Section: Conceptual Modelmentioning

confidence: 99%

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Krupka¹,

Serne²

1998

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C o p k r o f h b r t r y~m d r t n d v d r u n d h 8~m m r h t h . N R C~~r AbstractThe U.S. Nuclear Regulatory Commission (NRC) is developing a technical position document that provides guidance regarding the performance assessment of low-level radioactive waste (LLW) disposal facilities. This guidance includes considerations associated with the chemical environment of the vault disposal system and the effects this system may have on the release and mobility of radionuclides. Because the disposal system will contain cementitious materials as structural, waste form, andor bacld'ill materials, the geochemical properties of pore waters buffered by reactions with cement will be very different from those waters associated with the local soil and geology. This environment therefore needs to be considered within the source term calculations if credit is taken for solubility limits andor distribution coefficients for -dissolved radionuclide concentrqtions within disposal units. Geochemical modeling may be used to assess potential chemical conditions in concrete vault disposal units and associated effects on aqueous speciation, solubilities, and sorption of radionuclides that are released from the waste form.In support of NRC7s development of this technical position, two literature reviews were done on information related to the chemical environments associated with the interaction of water with cementitious materials. One review was conducted on methods and associated solid-phase assemblages used to model the composition of pore water resulting from reaction with cementitious materials used in a disposal vault. This literature review also included related information on experimental studies of cemendwater systems, natural analogue studies of cement and concrete, and radionuclide solubilities experimentally determined in cement pore fluids.Based on the results of .this review, geochemical modeling was used to demonstrate the calculation of conservative maximum concentrations for dissolved americium, neptunium, nickel, plutonium, radium, strontium, thorium, and uranium with respect to key geochemical input parameters for two ground-water environments associated with the disposal system. These environments include 1) a cement buffered system, wherein the leachate pH is controlled at values above 10 by the effective buffering capacity of the concrete; and 2) a ground-water buffered system, wherein the leachate pH and related solution parameters are dominated by the local ground-water system.Another literature review was completed on the available data for the sorption potential of selected LLW radionuclides onto "fresh" cement/concretewhere the expected pH of the cement pore waters will equal or exceed 10. The review included data for the radionuclides americium, inorganic carbon, chlorine, iodine, lanthanide elements, niobium, nickel, neptunium, plutonium, radium, strontium, technetium, thorium, and uranium. Based on information gleaned from the literature, a database was developed of preferred minimum distribution coeff...

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Section: Conceptual Modelmentioning

confidence: 99%

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Krupka¹,

Serne²

1998

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“…We tested the hypotheses that if all reactive surfaces are covered with carbonation products (CaCO 3 (s) and SiO 2 (s)), the aqueous concentration of various ions will be equal to that predicted from the chemical equilibrium of a system containing only those products and CO 2 . A chemical equilibrium analysis was performed using an ion association model, PHREEQC, with the Pitzer ion interaction model for the calculation of ion activity coefficients for solutions with high solute concentrations . The equilibrium constants and ion interaction data for reactions at 25 °C were obtained from the literature and shown in the Supporting Information, Tables S.4 and S.5. − …”

Section: Resultsmentioning

confidence: 99%

“…A chemical equilibrium analysis was performed using an ion association model, PHREEQC, 36 with the Pitzer ion interaction model for the calculation of ion activity coefficients for solutions with high solute concentrations. 37 The equilibrium constants and ion interaction data for reactions at 25 °C were obtained from the literature and shown in the Supporting Information, Tables S. 4 and S.5. 38−40 The system modeled for chemical equilibrium composition was a pure aqueous phase in contact with excess calcite and silica, the two carbonation products given by eqs 1 and 2, in the presence of CO 2 gas with partial pressure of 0.21 atm.…”

Section: Co 2 Uptake By Aqueous Cement Suspensionmentioning

confidence: 99%

Physico–Chemical Processes Limiting CO₂ Uptake in Concrete during Accelerated Carbonation Curing

Kashef-Haghighi

Ghoshal

2013

Ind. Eng. Chem. Res.

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Accelerated curing of fresh concrete using CO 2 is a possible approach for value-added, high-volume usage products from waste CO 2 emitted from stationary sources. The extent of CO 2 uptake and the spatial distribution of the CaCO 3 (s) precipitates formed during accelerated carbonation curing of compacted, 4-h hydrated cement mortar (fresh concrete mixture with fine aggregates) samples were investigated in this study. The maximum carbonation efficiency achieved was 20% of the theoretical uptake. Microprobe imaging was used to analyze the composition of the compacted cement mortar microstructure and showed extensive filling of pores of diameters 4 μm and smaller, with CaCO 3 (s). The carbonation efficiency, however, reached 67% when an aqueous suspension of cement was carbonated in a completely mixed reactor, where interparticle pores do not exist and a higher surface area of cement particles is exposed to dissolved CO 2 . The theoretical efficiency was not achieved because all reactive cement surfaces were saturated with carbonation products, as indicated by equilibrium concentrations of dissolved calcium, silica, inorganic carbon, and pH. This study shows that both deposition of CaCO 3 (s), on reactive surfaces, and pore filling may regulate the extent of CO 2 uptake during accelerated carbonation curing of concrete.

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“…Cesium, like other alkali elements, should be heavily partitioned into the porewater during the initial setting of the cemented wasteform. Upon carbonation, however, cesium likely precipitates as pollucite, CsAlSi 2 O 6 • x H 2 O, due to the higher silica content of porewater that results from carbonation ( , ). Pollucite is very insoluble, and its precipitation would account for lower Cs leachability with increased carbonation (see Figure ).…”

Section: Discussionmentioning

confidence: 99%

Vacuum Method for Carbonation of Cementitious Wasteforms

Venhuis

Reardon

2001

Environ. Sci. Technol.

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The application of carbonation treatment to cement-based wasteforms as a means to reduce the leachability of entrained undesirable substances, both radioactive and nonradioactive, has been the subject of much study over the past decade. Upon carbonation, hydrated cement phases release their water of hydration and are converted into carbonate minerals. The carbonation process has been shown to reduce the pore size distribution and permeability of the cementitious materials since portions of the original pore network become sites for precipitation of secondary carbonate minerals. As a result, the leachability of entrained contaminants can be markedly reduced. Current methods to carbonate cement-based wasteforms after they have cured rely on exposure to high pressure or supercritical CO2 pressures. In this study, a new low-pressure technique is presented. The method provides more complete carbonation than high-pressure techniques. The principle is to remove the water of reaction as it is produced, thereby maintaining an open pore network to facilitate the transfer of CO2 into the specimen. This is accomplished by conducting the reaction at near-vaccum pressures in the presence of a desiccant. The near-vacuum conditions lower the impedance of water transport from the carbonating specimen to the desiccant due to the large mean free path of the water vapor molecules. The technique was applied to a series of wasteform samples with entrained cationic and anionic waste components. Carbonation penetration depths of up to 11 mm were attained within 45 h of reaction for cylindrical wasteform samples prepared with OPC at a water/cement ratio of 0.60. A carbonation penetration depth of 15 mm was attained in a 6 d reaction of blended cement (OPC and 30% Class 'F' fly ash). In standardized leach tests, cationic waste constituents showed lower leachabilities from carbonated samples than from uncarbonated samples. Anionic waste constituents, however, showed greater leachabilities, and anion leachability increased with the degree of carbonation.

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Chemical Model for the Carbonation of a Grout/Water Slurry

Cited by 18 publications

References 17 publications

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Physico–Chemical Processes Limiting CO₂ Uptake in Concrete during Accelerated Carbonation Curing

Vacuum Method for Carbonation of Cementitious Wasteforms

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Chemical Model for the Carbonation of a Grout/Water Slurry

Cited by 18 publications

References 17 publications

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Physico–Chemical Processes Limiting CO2 Uptake in Concrete during Accelerated Carbonation Curing

Vacuum Method for Carbonation of Cementitious Wasteforms

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Product

Resources

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Physico–Chemical Processes Limiting CO₂ Uptake in Concrete during Accelerated Carbonation Curing