Microwave irradiation assisted sodium hexametaphosphate modification on the alkali-activated blast furnace slag for enhancing immobilization of strontium
Introduction
An obviously industrial expansion in nuclear industries has been achieved in decades in China, which causes a large amount of radioactive wastewater from the operation process (Su-Xia et al., 2014; Zhang et al., 2019a). Progress has been slow in dealing with nuclear waste and waste fluids containing radionuclides (Gonzalez et al., 2013; Carey et al., 2018). 90Sr2+ is one of some radioactive metal ions commonly existing in the radioactive wastewater, has approximately one third of the lifetime of 238Pu and relatively a lower density. 90Sr has been widely applied in radioisotope thermoelectric generators (RTGs) as a power source and used in 90Sr/90Y generator for obtaining 90Y for medical applications (Dixon et al., 2016; Chakravarty et al., 2012). Recycling 90Sr ions from radioactive wastes is desirable (Ashworth et al., 2018; Vicente Vilas et al., 2018). However, the recovery of Sr2+ from the low and medium-level radioactive wastes or wastewaters is high-cost and easily produces secondary pollutants, thereby increasing the amount of low-to-medium radioactive waste to be disposed of (Tangestani et al., 2017; Feng et al., 2018; Lupa et al., 2018; Ghalami et al., 2019). 90Sr is also considered to one of the most hazardous radiotoxic ions due to its high solubility. An inadvertent leakage into the environment can induce an easy accumulation in biosphere and cause a continuous radiation to the surrounding ecosystem (Ashworth et al., 2018; Pittet et al., 2019).
A deep disposal of immobilized high-level radioactive wastes for a long-term isolation from the surface geochemical environments has been accepted at large by some main nuclear use countries (Disposal of high-level radioactive wastes in geologic repositories, 1979; Roh et al., 2015; Kurihara et al., 2018; Wu et al., 2018). The development of new cementitious matrices and super-inert wrapping materials has been considered key for avoiding the premature breach of radionuclides from barrier systems, optimizing radioactive management, and upgrade the disposal technique (Ei-Eswed et al., 2017; Shiota et al., 2017; Ashworth et al., 2018; Huang et al., 2019; Zhang et al., 2019a). Furthermore, an unprecedented release of radionuclides with a high radioactivity from Fukushima accident not only makes people understand the terrible nature of radioactive pollution also emphasizes the need to find efficient binder materials in case of unforeseen unclear accidents (Hancock et al., 2019; Nakama et al., 2019; Ohira et al., 2019; Zhang et al., 2019b). Blast furnace slag (BFS) produced from smelting iron procedure has become one of hot-spot materials for the preparations of geopolymer and cementitious materials. Most of silicon-aluminum compounds in BFS are formed by a dramatic cooling process (Colangelo and Cioffi, 2013; Vilaplana et al., 2013; Salihoglu, 2014; Meena et al., 2015). BFS-based geopolymers and cements have been fully characterized and also prepared for the capture of some divalent heavy metal (HM) ions such as Pb2+, Cd2+, and Cu2+, etc. (Koplik et al., 2016; Tae and Morita, 2017; Bae et al., 2018). Smaller leaching values and better mechanic performances are observed in BFS-based solidification compared with the ordinary Portland cement (Ozkan et al., 2007; Zhou et al., 2017; Gijbels et al., 2019). Therefore, BFS has potential for Sr2+ immobilization as a binder precursor.
However, the early-strength formation of BFS-based synthesis is clearly inadequate in rapidly processing for Sr-contaminated wastes. Some vitreous structures retained in BFS further restrict the incorporation of Sr2+ into the newly formed matrix during hydration process (Ozeki et al., 2014; He et al., 2016). To strength the immobilization of Sr in the solidified products, increase the durability of BFS-based cement and geopolymer, and improve irradiation tolerance, a suitable activation method should be sought and explored. Microwave irradiation activates materials by the dipole rotation, molecule vibration, and ionic conduction (Hildago-Oporto et al., 2019; Na et al., 2019; Zhou et al., 2019). It can significantly increase the temperatures inside substances using quite a short time. Microwave irradiation has been used for the preparation of the inorganic thin films, electrode catalyst, and porous carbon materials (Luo et al., 2013; Surendran et al., 2017; Nguyen et al., 2018; Yuan et al., 2018; Lee et al., 2019). Its heating mechanism makes it easier to achieve a more uniform heating and dramatic temperature increases between inorganic molecules and inside the mineral structures at the same time. Severe temperature changes can further enhance the instability of amorphous silicon-aluminum compounds in BFS, which facilitates the dissolution of raw microstructures and induces a generation of nucleation and grain crystallization (Salihoglu, 2014; Goodarzi and Movahedrad, 2017; Wang et al., 2018; Kuo et al., 2019). Hence, the feasibility of microwave irradiation to change the cementitious characteristics of BFS samples is worth exploring. Besides, the potential advantages of microwave irradiation for the inorganic minerals have been rarely explored from the solidification mechanism, which requires a further study.
Strontium apatite (i.e., Sr10(PO4)6(OH)2) is an insoluble substance, which is formed by incorporating Sr2+ ions into apatite like minerals (Rabone and De Leeuw, 2006; Ozeki et al., 2014; Panpisut et al., 2019). Calcium ions can be easily substituted by strontium ions in the structures of apatite minerals due to their similar electron configurations (Li et al., 2007; Fredholm et al., 2012; He et al., 2016). The formation of strontium apatite undoubtedly will enhance the capture of Sr2+ in the matrix and increase the durability of blocks. In this study, sodium hexametaphosphate was added to BFS samples to enhance the chemical stabilization of Sr2+ ions in the BFS-based cementitious materials. Microwave irradiation was used to increase the binder activity of BFS samples. Four relevant factors of microwave irradiation were adjusted and optimized in an orthogonal experiment. The influence of each factor on the immobilization capacity of Sr2+ (wt.%) in the matrix was quantitatively determined based on the significance analysis and marginal means. The leaching values, compressive strengths, gamma irradiation degradation, and thermal durability of microwave-irradiation treated solidified blocks were comprehensively investigated. X-ray diffraction (XRD, PANalytical B.V., Holland) and a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS, Carl Zeiss AG, Germany) were used to further analyze the solidification characteristics of BFS-based cementitious materials and explore the specific immobilization mechanisms of Sr2+ ions. This work will present a feasible method for the modification of potential binder materials and exploration of new materials to achieve a fast immobilization of Sr2+ from the nuclear wastewater.
Section snippets
Materials
Blast furnace slag (BFS) samples were obtained from a steel mill located in Changzhou, Jiangsu, China. The BFS samples were dried at 100 °C for 12 h (h), grinded using a ball-grinding machine for 2 h, and sieved through a 200-mesh sieve. The chemical composition of BFS is listed in Table S1 in the supporting information (SI). Sodium hexametaphosphate (Na6O18P6, Analytical grade) used in the experiments was purchased from Chongqing CHUANDONG chemical Inc., China. The water glass with a modulus
Optimization of microwave irradiation
Microwave irradiation can dramatically increase temperatures inside mineral structures, which will change the amorphous activity of BFS samples and affect the interactions between Na6O18P6 and Sr2+ ions. To achieve a maximum irradiation performance, the influences of some relevant factors are necessary to be investigated. As shown in Table 1, changes in the experimental factors clearly affected the immobilization capacities of Sr2+ ions in the MA-BFS-Sr0.1 based solidified blocks. Among 16
Discussion on activation mechanisms
XRD peak patterns of the mortars and binder matrices with 0.1 M incorporation concentration of Sr2+ ions are shown in Fig. 4. Sr2+ ions were chemically immobilized in the internal matrices of P–BFS–Sr0.1-based blocks mainly in the forms of strontium hydroxide precipitations (Kuenzel et al., 2015; Jang et al., 2017; Vandevenne et al., 2018) and strontium substituted hydroxyapatites. Sr2+ ions reacted with the alkali activators to form some hydroxide precipitations (Eq. (7) and Eq. (8), e.g.,
Conclusion
An excessive incorporation of Sr2+ ions into BFS-based cements or geopolymer would result in a rapid release of Sr2+ and a dramatic reduction of compressive strengths. An appropriate addition of sodium hexametaphosphate to BFS obviously enhanced the chemical stabilization of Sr2+ ions incorporated into the BFS-based cementitious materials through the hydroxyapatite formation and Sr2+ substitutions. Microwave irradiation further increased the mechanical strengths of BFS-based blocks and
Declaration of competing interest
None.
Acknowledgements
The author has received no financial support for the research, authorship, and/or publication of this article.
References (64)
- et al.
Facile radiochemical separation of clinical-grade (90)Y from (90)Sr by selective precipitation for targeted radionuclide therapy
Nucl. Med. Biol.
(2019) - et al.
Detoxification of municipal solid waste incinerator (MSWI) fly ash by single-mode microwave (MW) irradiation: addition of urea on the degradation of Dioxin and mechanism
J. Hazard Mater.
(2019) - et al.
Highly efficient capturing and adsorption of cesium and strontium ions from aqueous solution by porous organic cage: a combined experimental and theoretical study
Appl. Surf. Sci.
(2019) - et al.
Radiological and non-radiological leaching assessment of alkali-activated materials containing ground granulated blast furnace slag and phosphogypsum
Sci. Total Environ.
(2019) - et al.
Stabilization/solidification of zinc-contaminated kaolin clay using ground granulated blast-furnace slag and different types of activators
Appl. Geochem.
(2017) - et al.
Transgenerational effects of historic radiation dose in pale grass blue butterflies around Fukushima following the Fukushima Dai-ichi Nuclear Power Plant meltdown accident
Environ. Res.
(2019) - et al.
Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation
Ceram. Int.
(2016) - et al.
Immobilization of trace heavy metals in the electrokinetics-processed municipal solid waste incineration fly ashes and its characterizations and mechanisms
J. Environ. Manag.
(2019) - et al.
Encapsulation of Cs/Sr contaminated clinoptilolite in geopolymers produced from metakaolin
J. Nucl. Mater.
(2015) - et al.
Performance demonstration of 4pibeta(LS)-gamma coincidence counting system for standardization of radionuclides with complex decay scheme
Appl. Radiat. Isot. : Incl. Data, Instrum. Methods Agric. Ind. Med.
(2016)
Cesium-adsorption capacity and hydraulic conductivity of sealing geomaterial made with marine clay, bentonite, and zeolite
Soils Found.
Chemical composition, crystal size and lattice structural changes after incorporation of strontium into biomimetic apatite
Biomaterials
Chemical stabilization of chromate in blast furnace slag mixed cementitious materials
Chemosphere
Temporal decrease in air dose rate in the sub-urban area affected by the Fukushima Dai-ichi Nuclear Power Plant accident during four years after decontamination works
J. Environ. Radioact.
Porous metal oxides derived from Cu-Al layered double hydroxide as an efficient heterogeneous catalyst for the Friedel-Crafts alkylation of indoles with benzaldehydes under microwave irradiation
Heliyon
Strength properties of concrete incorporating coal bottom ash and granulated blast furnace slag
Waste Manag.
Determination of (89)Sr and (90)Sr in fresh cow milk and raw urine using crystalline synthetic tunnel manganese oxides and layered metal sulfides
Anal. Chim. Acta
Stabilization of cesium in alkali-activated municipal solid waste incineration fly ash and a pyrophyllite-based system
Chemosphere
The treatment of radioactive wastewater by ultrasonic standing wave method
J. Hazard Mater.
Incorporating Cs and Sr into blast furnace slag inorganic polymers and their effect on matrix properties
J. Nucl. Mater.
Green remediation of contaminated sediment by stabilization/solidification with industrial by-products and CO2 utilization
Sci. Total Environ.
Stable solidification of silica-based ammonium molybdophosphate by allophane: application to treatment of radioactive cesium in secondary solid wastes generated from fukushima
J. Hazard Mater.
Model experimental study on Cs removal from clay minerals by ion exchange under microwave irradiation
Chem. Eng. Process
Decontamination of radioactive wastewater: state of the art and challenges forward
Chemosphere
Influence of urban surface roughness on build-up and wash-off dynamics of road-deposited sediment
Environ. Pollut.
Reductive solidification/stabilization of chromate in municipal solid waste incineration fly ash by ascorbic acid and blast furnace slag
Chemosphere
Effect of humic acid & bacterial exudates on sorption-desorption interactions of (90)Sr with brucite
Environmental Sci. Process. Impacts
Removal of Hexavalent Chromium in Portland Cement Using Ground Granulated Blast-Furnace Slag Powder
Removal of Cs, Sr, U and Pu species from simulated nuclear waste effluent using graphene oxide
J. Radioanal. Nucl. Chem.
Availability of yttrium-90 from strontium-90: a nuclear medicine perspective
Cancer Biother. Radiopharm.
Use of cement kiln dust, blast furnace slag and marble sludge in the manufacture of sustainable artificial aggregates by means of cold bonding pelletization
Materials (Basel)
The influence of Sr doses on the in vitro biocompatibility and in vivo degradability of single-phase Sr-incorporated HAP cement
J. Biomed. Mater. Res. A
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