Abstract
In this work, the dense glass matrix of uranium tailings was successfully fabricated via microwave sintering process with Na2CO3 as a sintering aid. The effects of Na2CO3 additive and sintering temperature on the microstructure and mechanical properties of as-prepared solids were systematically investigated. XRD results confirmed the vitrified forms can be achieved at 1200°C within 30 min with 20 wt.% Na2CO3 addition. Importantly, the Na2CO3 additive significantly reduced the firing temperature from 1500°C to 1200°C and promoted densification. FT-IR analysis demonstrated that the main characteristic peaks of the sintered samples were attributed to the vibration of Si-O-Si. Microstructural studies presented the homogeneous distribution of glass phases. The results of mechanical properties of the sintered forms show that bulk density and Vickers hardness increased with increasing Na2CO3 content as well as sintering temperature, and the highest bulk density (2.45 ± 0.01 g/cm3) and Vickers hardness (823 ± 25 HV) were obtained at the temperature of 1300°C with 20 wt.% Na2CO3 addition, the heating rate of 20°C/min, and the soaking time of 30 min. It implied that the combination of microwave sintering with the appropriate addition of Na2CO3 would provide an efficient method for the immobilization of radionuclides in uranium tailings.
Highlights
With the development of the nuclear industry, the demand for uranium resources increases dramatically, which resulted in a significant increase in uranium tailings [1]. e main pollution in uranium tailings is actinide nuclides and other radionuclides, whose disposal methods are necessary for preventing their migration into water or air [2, 3]. e migration of radioactive contamination into the surrounding would pollute the environment and pose a great threat to human health [1, 4,5,6,7]
For the remediation of the uranium tailings pond, physical remediation, chemical remediation, microbial remediation, and phytoremediation have been considered [10]. e physical remediation [11, 12] method requires simple equipment at a low cost, which can be considered as efficient treatment. e chemical remediation [9, 13, 14] method has expensive costs for large numbers of chemical reagents, which could result in secondary pollution. e microbial remediation and phytoremediation method [15,16,17,18,19] have low cost, while the strong biological selectivity limits their application
Compared with other sintering methods, microwave sintering is a highly efficient heating method without pressure in which the material is heated by the dielectric loss of the material itself, rather than gradually transferring heat to the inner of the material by heating the surface of the material [29]. erefore, a rapid vitrification method and good homogeneity of the cured matrix are the key challenges for the solidified uranium tailings
Summary
With the development of the nuclear industry, the demand for uranium resources increases dramatically, which resulted in a significant increase in uranium tailings [1]. e main pollution in uranium tailings is actinide nuclides and other radionuclides, whose disposal methods are necessary for preventing their migration into water or air [2, 3]. e migration of radioactive contamination into the surrounding would pollute the environment and pose a great threat to human health [1, 4,5,6,7]. Erefore, it is urgent to find an efficient and reliable immobilization method to safely dispose of radionuclides in uranium tailings. For the remediation of the uranium tailings pond, physical remediation, chemical remediation, microbial remediation, and phytoremediation have been considered [10]. E physical remediation [11, 12] method requires simple equipment at a low cost, which can be considered as efficient treatment. In situ vitrification (ISV) technology is commonly considered as an effective alternative to physical remediation to immobilize radionuclides in radioactively contaminated. SPS method could achieve high-density parts of materials at lower sintering temperatures, but it needs to be carried out by applying pressure [28]. Microwave sintering has been employed to immobilize the radionuclides in uranium tailings. As a result of this work, high-density and hardness vitrified forms with homogeneously distributed amorphous glass phases were successfully fabricated. e outcomes provide a theoretical basis for the researchers to solidify radionuclides and have important guiding significance for the engineering application of the beach surface of the uranium tailings reservoir in the later stage
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