1,721,121 research outputs found
Use of phosphogypsum in alkali-activated binders: radiological and leaching assessment
No full textIntroduction
In the phosphate industry vast amounts of phosphogypsum (PG) are produced during fertilizer production when the phosphate ore is treated with sulphuric acid. The PG contains impurities such as P2O5, F-, organic substances, alkali metals and enhanced concentrations of naturally occurring radionuclides (NORs), predominately from the 238U series, restricting its use. Worldwide, 170 million tons of PG are disposed annually and the recycling rate is still very low, i.e. less than 5% while the worldwide production is increasing. (IAEA, 2013; Hilton, 2007; Tayibi et al., 2009; Wang et al., 2018)
Alkali-activated materials (AAMs), produced on the basis of by-products or residues, can replace Ordinary Portland Cement (OPC) reducing the CO2-emissions by up to 80% compared OPC while offering comparable technical performance (Van Deventer, 2012). This work focusses on the
incorporation of phosphogypsum in AAMs based on ground granulated blast furnace slag (GGBFS).
Methodology
A combination of GGBFS (Belgian steel company) and PG (IAEA reference material 434) was used as precursor for the production of AAMs. Non-volatile inorganic NORs and non-radiological elements leaching was assessed by means of an up-flow percolation test as described in CEN/TS 16637-3. Thermal and epithermal neutron activation analysis (NAA) was used for 238U and 232Th while other NORs were analysed via gamma spectrometry. ICP-OES and ion chromatography were applied for quantitative analysis of non-radiological elements. A SARAD Radon Scout PMT radon monitor was used to perform a massic radon exhalation study.
Results & conclusion
The matrix properties from the AAM matrix can be adapted to reduce radon release and to develop an optimal immobilisation matrix for the incorporated NORs and and impurities form PG (e.g. F-). For hardened AAMS, the decline in radon exhalation was assigned to the mechanism of physical encapsulation, which is enhanced by lowering both the pore volume and the specific surface area. From the leaching study it was found that both the porosity and formation of multiple leachable and nonleachable complexes are determining factors for the release of elements from the AAMs.
Acknowledgement
This work was supported by the Fund for Scientific Research Flanders (FWO), and the authors would like to acknowledge the networking support of the COST Action TU1301, www.norm4building.org.
References
*International Atomic Energy Agency (IAEA), Radiation Protection and Management of NORM Residues in the Phosphate Industry, Safety Reports Series No. 78, IAEA, Vienna, 2013.
*Hilton, J. 2007. Towards a management and regulatory strategy for phosphoric acid and phosphogypsum as co-products, in: W.C. Gerken (Ed.), Proc. Fifth Int. Symp. Nat. Occur. Radioact. Mater. (NORM V), IAEA, Seville, Spain, pp 281–295.
*Tayibi, H., Choura, M., López, F.A., Alguacil, F.J., López-Delgado, A., 2009. Environmental impact and management of phosphogypsum. J. Environ. Manag. 90, pp 2377–2386.
* Van Deventer J.S.J., Provis, J.L., Duxson, P., 2012. Minerals Engineering 29, pp 89–104.
* Wang, L., Yu, K., Li, J., Tsang, D.C.W., Poon, C.S., Yoo, J., Baek, K., Ding, S., Hou, D., Dai, J., 2018. Low-carbon and low-alkalinity stabilization/solidification of high-Pb contaminated soil. Chem. Eng. J. 351, pp 418–427
Use of phosphogypsum in alkali-activated binders: radiological and leaching assessment
No full textIntroduction
In the phosphate industry vast amounts of phosphogypsum (PG) are produced during fertilizer production when the phosphate ore is treated with sulphuric acid. The PG contains impurities such as P2O5, F-, organic substances, alkali metals and enhanced concentrations of naturally occurring radionuclides (NORs), predominately from the 238U series, restricting its use. Worldwide, 170 million tons of PG are disposed annually and the recycling rate is still very low, i.e. less than 5% while the worldwide production is increasing. (IAEA, 2013; Hilton, 2007; Tayibi et al., 2009; Wang et al., 2018)
Alkali-activated materials (AAMs), produced on the basis of by-products or residues, can replace Ordinary Portland Cement (OPC) reducing the CO2-emissions by up to 80% compared OPC while offering comparable technical performance (Van Deventer, 2012). This work focusses on the
incorporation of phosphogypsum in AAMs based on ground granulated blast furnace slag (GGBFS).
Methodology
A combination of GGBFS (Belgian steel company) and PG (IAEA reference material 434) was used as precursor for the production of AAMs. Non-volatile inorganic NORs and non-radiological elements leaching was assessed by means of an up-flow percolation test as described in CEN/TS 16637-3. Thermal and epithermal neutron activation analysis (NAA) was used for 238U and 232Th while other NORs were analysed via gamma spectrometry. ICP-OES and ion chromatography were applied for quantitative analysis of non-radiological elements. A SARAD Radon Scout PMT radon monitor was used to perform a massic radon exhalation study.
Results & conclusion
The matrix properties from the AAM matrix can be adapted to reduce radon release and to develop an optimal immobilisation matrix for the incorporated NORs and and impurities form PG (e.g. F-). For hardened AAMS, the decline in radon exhalation was assigned to the mechanism of physical encapsulation, which is enhanced by lowering both the pore volume and the specific surface area. From the leaching study it was found that both the porosity and formation of multiple leachable and nonleachable complexes are determining factors for the release of elements from the AAMs.
Acknowledgement
This work was supported by the Fund for Scientific Research Flanders (FWO), and the authors would like to acknowledge the networking support of the COST Action TU1301, www.norm4building.org.
References
*International Atomic Energy Agency (IAEA), Radiation Protection and Management of NORM Residues in the Phosphate Industry, Safety Reports Series No. 78, IAEA, Vienna, 2013.
*Hilton, J. 2007. Towards a management and regulatory strategy for phosphoric acid and phosphogypsum as co-products, in: W.C. Gerken (Ed.), Proc. Fifth Int. Symp. Nat. Occur. Radioact. Mater. (NORM V), IAEA, Seville, Spain, pp 281–295.
*Tayibi, H., Choura, M., López, F.A., Alguacil, F.J., López-Delgado, A., 2009. Environmental impact and management of phosphogypsum. J. Environ. Manag. 90, pp 2377–2386.
* Van Deventer J.S.J., Provis, J.L., Duxson, P., 2012. Minerals Engineering 29, pp 89–104.
* Wang, L., Yu, K., Li, J., Tsang, D.C.W., Poon, C.S., Yoo, J., Baek, K., Ding, S., Hou, D., Dai, J., 2018. Low-carbon and low-alkalinity stabilization/solidification of high-Pb contaminated soil. Chem. Eng. J. 351, pp 418–427
Crystallographic changes in lead zirconate titanate due to neutron irradiation
Get PDFPiezoelectric and ferroelectric materials are useful as the active element in non-destructive monitoring devices for high-radiation areas. Here, crystallographic structural refinement (i.e., the Rietveld method) is used to quantify the type and extent of structural changes in PbZr0.5Ti0.5O3 after exposure to a 1 MeV equivalent neutron fluence of 1.7 × 1015 neutrons/cm2. The results show a measurable decrease in the occupancy of Pb and O due to irradiation, with O vacancies in the tetragonal phase being created preferentially on one of the two O sites. The results demonstrate a method by which the effects of radiation on crystallographic structure may be investigated
Solubility and speciation of plutonium(VI) with orthophosphate
No full textPu(VI) speciation and solubility with phosphate was examined at pH from 0.3 to 12.2, Pu(VI) concentrations from 5 \times\ {\rm 10}\sp{-5} M to 1.3 \times\ {\rm 10}\sp{-3} M and phosphate concentrations up to 0.6 M. Absorption spectroscopy, solubility experiments, scanning electron microscopy and photon correlation spectroscopy were utilized.The species PuO\sb2{\rm H}\sb2{\rm PO}\sb4\sp{+} and PuO\sb2{\rm (H}\sb2{\rm PO}\sb4{\rm )}\sb2 formed at pH 2.4. The aqueous plutonium concentration was 10\sp{-5} M at pH from 3.5 to 6 and 10\sp{-6} M at pH from 6 to 8. Plutonium(VI) favored complexation with phosphate only at Pu(VI) concentrations greater than 1.5 \times\ {\rm 10}\sp{-4} M. Evidence exists that mixed phosphate-carbonate species were formed.The species (PuO\sb2{\rm HPO}\sb4)\sb{\rm n} and (PuO\sb2{\rm NaPO}\sb4)\sb{\rm n}, characterized by absorption bands at 842.3 0.05 nm and 846 0.05 nm, are formed at pH between 2.4 and 9. The species (PuO\sb2{\rm HPO}\sb4)\sb{\rm n} has = 340 20, log = 4.32 + 10.73n (0.20 + 0.41n) and log \beta\sp{T} = log + 1.2n (0.10 + 0.41n). The species (PuO\sb2{\rm NaPO}\sb4{\rm )}\sb{\rm n} has = 380 20 and log \beta\sp{T}\sb{846} = log \beta\sp{T}\sb{842} - (4.4 0.3)n. At pH 9, Pu(VI)-phosphate species formed with absorption bands at 857 1 nm ( = 200 30) and 866 nm ( = 123 15).Made available in DSpace on 2011-05-07T14:00:38Z (GMT). No. of bitstreams: 2
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Source receptor modeling of airborne particles collected over the Great Lakes
No full textHigh-volume air samplers were used to collect aerosol samples on Whatman 41 air filters at the Canadian air sampling stations Burnt Island, Egbert and Point Petre. Once collected, the samples were analyzed for trace elements by neutron activation analysis. Air concentrations of over thirty trace elements were determined. A special focus was made to utilize Compton suppression gamma-ray spectroscopy and epithermal irradiations to enhance the detection limits of neutron activation analysis. These vanguard techniques allowed for the determination of trace elements at very low levels. Advancements were also made for the determination of Br through short-lived irradiations.After the air concentrations were determined for trace elements from the neutron activation analysis data, the trends, sources and origin of the atmospheric aerosols were investigated. Exploration of the seasonal trends revealed that elements from a salt source like Na, Cl and Br were highest in the winter while elements originating from crustal weathering like Al, Ca and Si were highest in the summer. Many elements of anthropogenic origin demonstrated no seasonal trend. Enrichment factor analysis revealed elements from non-crustal sources including the elements Ag, As, Br, Cl, I, In, Sb, Se, Sn and Zn. Factor analysis exhibited trends that indicate oil and coal combustion, mining, incineration, and smelting as anthropogenic sources to aerosols of the rural Great Lakes. Potential source contribution function analysis indicated that many of the anthropogenic atmospheric pollutants in the Great Lakes originate from industrial centers in the eastern and southeastern United States. Study of the trace metal dry deposition into Lakes Huron and Ontario indicated that the majority of the total deposition resulted from crustal materials. However, dry deposition is a significant pathway for many toxic anthropogenic trace metals into the Great Lakes.Made available in DSpace on 2011-05-07T12:00:13Z (GMT). No. of bitstreams: 2
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Characterization of environmental tobacco smoke by neutron activation analysis as a source of hazardous metals in indoor air pollution
No full textThe characterization of environmental tobacco smoke (ETS) as a source of heavy metals has been performed. Thirty elements were determined in 15 brands of cigarettes and their components. Five elements, Br, Cd, Cl, K, and Zn were found to be major elemental sources in the particulate phase of ETS. The elemental distribution in cigarette components was examined using a mass balance before and after cigarette smoking. The results show that most elements retain their major fraction in cigarette ash; only cadmium has a large emission (44%) in sidestream smoke, which thus makes cadmium a very important element of exposure to passive smokers. Elemental particle size distribution in ETS was measured in a room size chamber. The mass mean diameters ranged from 0.20 m to 0.35 m.Instrumental neutron activation analysis was improved for air filter samples by using epithermal neutrons and Compton suppression counting techniques. The detection limits have been reduced to a few nanograms for Cd and less than a half nanogram for As and Sb. The method provides a means for large scale multi-element determination.The evaluation of cadmium as a marker of ETS was carried out. Cadmium concentration in ETS free indoor air was measured to be less than 2 ng/m\sp3. The cadmium source in tobacco of American cigarettes was determined to be 1.25 0.18 g/g, of which about 60% of the cadmium in consumed tobacco was released as ETS. Cadmium in ETS was found to exist in small particles (less than 1 m), and Cd concentration in ETS was observed to decay slowly, and increase linearly with the strength of the source.The One-Compartment Model was chosen in this study for validating the experimental results. A parameter, deposition velocity, in the model was measured by the experiments, with a value of 0.04 m/h. The elemental and total suspended particulate (TSP) emission factors were measured both in sidestream smoke and in the chamber, and results show that they strongly depend on smoking conditions, except for Cd. The predictions of TSP concentrations agree with the experimental results. The amount of TSP and cadmium in ETS inhaled by a passive smoker was estimated.Made available in DSpace on 2011-05-07T14:00:11Z (GMT). No. of bitstreams: 2
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Previous issue date: 1993Embargo set by: Seth Robbins for item 72617
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