Liquefaction of latex glove waste for volume reduction

doi:10.21203/rs.3.rs-3501974/v1

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Liquefaction of latex glove waste for volume reduction

https://doi.org/10.21203/rs.3.rs-3501974/v1

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published 15 Feb, 2024

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The accumulation of dry active wastes (DAWs) such as latex gloves in nuclear facilities has become a serious issue because of the high cost and limited storage area for their management. In this study, the liquefaction of latex gloves, which mainly comprise rubber and CaCO₃, was investigated as a waste reduction technique. When liquefaction occurred at > 270°C, the latex gloves decomposed into gaseous, liquid, and solid products. Cs-, Sr-, and Co-contaminated latex gloves were liquefied at 350°C, and the solid product was subsequently recovered via distillation. Notably, the contaminants comprising CaCO₃ and char only remained in the solid product (~ 33.3 wt.%); thus, the gaseous and liquid products could be regarded as non-radioactive, thereby reducing the volume of radioactive waste (~ 92.7% reduction after compression). Liquefaction is favorable compared to conventional combustion because it generates less harmful gases by converting the organic components to condensed phases.

Dry active waste

Latex glove

Waste reduction

Liquefaction

Calcium carbonate

The operation of nuclear facilities generates a significant amount of dry active waste (DAW), such as gloves, clothes, shoes, and wipes, which are contaminated with radioactive isotopes (RIs) [1, 2]. However, DAWs comprise approximately 85 vol.% low-level radioactive waste [2], which is a cause for concern owing to the high cost of waste management and the limited area for waste storage and disposal facilities. Incineration has been widely adopted to reduce the volume of DAWs [3, 4], and a high reduction in volume is expected upon incineration because the bulk components (organic compounds) of DAW decompose at high temperatures. However, these processes generate large amounts of gaseous products (CO₂ and other toxic gases) and potentially release volatile RIs, such as Cs-137, into the environment [4, 5]. Therefore, obtaining public acceptance of incineration facilities is challenging. Thus, developing an environmentally benign method of disposing of DAW is necessary.

In this study, liquefaction is investigated as an alternative volume-reduction technique to incineration. Liquefaction, which has been extensively studied for use in the extraction of liquid fuels (oils) from organic waste feeds [6–8], produces large amounts of liquid products, in contrast to incineration. During liquefaction, organic components decompose into liquid (major) and gaseous (minor) products, whereas inorganic components generally form solid particles. Further, a small amount of a solid carbonization product (char) derived from the organic components may also remain. By treating DAWs via liquefaction, the oil and gaseous products may not be subject to radioactive waste regulations if all the RIs remain in the inorganic solid product. Thus, only the solid product is regarded as radioactive waste, thereby reducing the waste volume.

Radioactive latex glove waste is an excellent candidate for investigating liquefaction in DAW reduction because it contains organic (rubber) and inorganic compounds as major components [9, 10]. CaCO₃ is a common inorganic filler used in producing latex gloves (more than a few weight percentages) [9, 10], and rubbers are liquefied at elevated temperatures (~ 300°C) [7, 8]. Compared to incineration, the organic components in latex gloves are predominantly converted to the liquid phase (oil) rather than the gas phase during liquefaction at a low temperature, thereby suppressing the volatilization of the RI-containing compounds. Hence, the liquefaction process may reduce environmental pollution and relieve public concern regarding gaseous product generation and RI release. The liquefaction of latex gloves should produce a CaCO₃-based solid product, which can be disposed of easily, compared to the latex gloves, because CaCO₃ can be stabilized in cement and glass matrices as waste forms [11–14].

To demonstrate the viability of liquefaction-based waste reduction, a surrogate for latex glove waste was prepared using non-radioactive isotopes of Cs, Sr, and Co as contaminants. Liquefaction was conducted in a closed vessel at ≤ 350°C, and the liquid and solid products were recovered via vacuum distillation. Compositional analyses of these products were performed to determine their Cs, Sr, and Co contents after liquefaction, and the volume-reduction ratio was calculated by comparing the volumes of the pristine latex gloves and solid product.

Ivory-colored latex gloves (SFTGL1122D, Medicom, Montreal, Canada) were used, and an aqueous mixture of 0.033 M CsNO₃ (99%, Sigma-Aldrich, St. Louis, MO, USA), 0.033 M Sr(NO₃)₂ (98%, Daejung Chemicals, Siheung, Republic of Korea), and 0.033 M Co(NO₃)₂·6H₂O (97%, Daejung Chemicals) was formulated to prepare the surrogate. The solution (10 mL) was placed inside a pair of latex gloves, which was then aged in a convection oven at 70°C for several days to fix the contaminants.

Figure 1 shows the liquefaction reactor equipped with a distillation system. A closed-vessel reactor (4766, Parr Instruments, Moline, IL, USA) with a temperature-pressure monitoring system was used in the liquefaction study, and the maximum reactor temperature was set at 350°C. Upon reaching 350°C and subsequent cooling, the temperature-pressure curve of the reactor containing the latex gloves was plotted to determine the process temperature. The latex gloves were heated at 150, 250, 300, and 350°C for 5 h to investigate the effect of the process temperature on the latex gloves. Liquefaction studies were also conducted using the surrogate latex gloves contaminated with Cs, Sr, and Co at 350°C for 5 h. The reactor was disassembled to examine the reaction products and measure the mass loss caused by gaseous product formation. Subsequently, distillation studies were conducted at 300°C under vacuum after re-assembling the reactor to separate the liquid and solid products. A quartz condenser with cooling water (5°C) circulation was connected to the reactor to recover the vaporized liquid product upon distillation. In addition, a muffle furnace (Thermolyne F47910-33, Thermo Fisher Scientific, Waltham, MA, USA) was used to heat the latex gloves under ambient air.

The amounts of organic elements in the latex gloves were determined using elemental analysis (EA, FLASH 2000 (for C, H, N, S) and FlashEA 1112 (for O), Thermo Fisher Scientific). Energy-dispersive X-ray spectroscopy (EDS, X-MAX, Horiba, Kyoto, Japan) coupled with scanning electron microscopy (S-4800, Hitachi, Tokyo, Japan) was used to identify the inorganic elements in the combusted latex gloves. Inductively coupled plasma (ICP) techniques were applied to quantitatively analyze the Cs (by mass spectrometry (iCAP Qc, Thermo Fisher Scientific)) and Sr and Co concentrations (by atomic emission spectroscopy (iCAP 7400 Duo, Thermo Fisher Scientific)). The phases of the solid product were characterized using X-ray diffraction (XRD, D8 Advance, Bruker, Billerica, MA, USA).

Figure 2 shows a flow diagram of the liquefaction-based waste reduction process of contaminated latex gloves. When the latex gloves are liquefied, they degrade into three phases (gas, liquid, and solid); the gaseous product can be easily separated from the condensed products, which comprise the liquid (oil) and solid (CaCO₃, minor additives, and char) products. The liquid-solid mixture was further distilled to separate the liquid product from the solid product. The solid products contained radioactive contaminants, whereas the gaseous and liquid products were no longer radioactive.

To quantify the organic and inorganic components in the latex gloves before liquefaction, the gloves were fired at 1000°C in air to remove the organic species via combustion (Fig. 3a). Consequently, 3.58 g of ivory-colored ash remained after combustion, which is 13.3% of the initial mass of the latex gloves (26.24 g). Notably, the mass loss is comparable to the amounts of organic elements (C, H, O, N, and S) observed using EA, as shown in Table 1. Thus, ash was deduced to comprise the inorganic components, and no residual carbonization products (black) were expected, based on the color of the produced ash. As shown in Fig. 3b, the EDS results reveal that Ca is the dominant element in the produced ash, with several other minor elements (e.g., Ti, Zn, Si, and Al) also present. CaO, in particular, is a major component of the ash, as shown in Fig. 3c, and it is formed when CaCO₃ decomposes at elevated temperatures (CaCO₃ → CaO + CO₂) [14].

Table 1

Elemental analysis results of the latex gloves.
Element	C	H	N	S	O	Total
Content (wt.%)	67.81	8.89	0.43	1.54	8.26	86.93

Upon liquefaction of the latex gloves, the pressure in the vessel increases owing to the formation of gaseous and evaporable liquid products; thus, the pressure may be used as an indicator of liquefaction. Figure 4 shows the temperature and pressure of the latex glove-containing vessels with respect to time upon heating and cooling. In the initial heating stage, the pressure slowly increases with time (or temperature) owing to the expansion of air in the vessel and residual water on the surfaces of the latex gloves. An abrupt change in pressure was observed at > 270°C, indicating that thermal decomposition of the latex gloves commences. Notably, the pressure within the reactor remained high after cooling, indicating the presence of gaseous products in the reactor.

Figures 5a–e show the respective reaction products in the closed vessel before and after liquefaction at 150, 250, 300, and 350°C. Remarkably, no noticeable differences, except for a change in color, were observed after heating at 150°C (Fig. 5b). At 250°C, the color of the latex gloves turned considerably darker, which may be attributed to the partial decomposition of the organic components, but their overall shapes were retained (Fig. 5c). At ≥ 300°C, the latex gloves decomposed into a mixture of liquid and solid products (Figs. 5d–e), indicating successful liquefaction. This behavior is consistent with the temperature-pressure relationship shown in Fig. 4. The latex gloves were also treated at 350°C in air using the muffle furnace for comparison (Fig. 5f). No liquid product was obtained after the reaction, leaving only a solid product, indicating that the organic components were converted into volatile species. The solid product was black, suggesting the formation of a char and CaCO₃ mixture. Notably, the sample lost approximately 76.6% of its initial mass after air treatment, suggesting that most of the organic compounds (~ 86.9 wt.% in Table 1) were eliminated via gas generation, even at 350°C in air.

To demonstrate the technical viability of liquefaction in waste reduction, the surrogate of the contaminated latex gloves containing non-radioactive Cs, Sr, and Co was treated at 350°C in the closed vessel (Fig. 6a), and the reaction products in the condensed phases were subsequently distilled under vacuum. Cs, Sr, and Co were used as contaminants in this study because they are the most common sources of environmental pollution [15–17]. Figure 6 shows the experimental procedure used in the latex glove treatment. During liquefaction, the contaminated latex gloves decomposed and a mixed product was obtained (Fig. 6b). In this study, a gaseous product was released when the reactor was opened, but it may be collected or treated further, if necessary. The reactor was resealed for distillation at 300°C under vacuum. Figure 6c shows the escape of oil vapor from the reactor; this vapor was then cooled to form a liquid in the condenser connected to the receiver. Consequently, the black solid (Fig. 6d) and brown liquid products (Fig. 6e) were recovered separately. Figure 6f shows a considerable reduction in the volume of the latex gloves after liquefaction. The XRD analysis confirmed that the major phase of the final solid product is CaCO₃ (Fig. 7). The color of the solid product suggests the presence of char derived from the organic compounds, similar to that observed following combustion in air (Fig. 5f).

The initial mass of the pair of contaminated latex gloves introduced into the reactor for liquefaction-distillation is 12.99 g (Fig. 6a). When the reactor was disassembled after liquefaction, the mass of the sample decreased to 11.45 g (Fig. 6b), indicating that 11.9 wt.% was lost owing to gaseous product formation during liquefaction. Conversely, the organic component was almost completely lost to the atmosphere upon treatment in air, as shown in Fig. 5f (76.6 wt.% loss). The closed-vessel system suppressed the formation of gaseous products, leaving significant amounts of the condensed liquid and solid phases; thus, air pollution caused by gaseous products (CO₂, etc.) can be significantly reduced by adopting liquefaction. The solid product recovered after distillation weighed 4.33 g (Fig. 6d), which is 33.3% of its initial mass. Meanwhile, the recovered liquid product only weighed 4.91 g (Fig. 6e), which is lower than the expected value (11.45–4.33 = 7.12 g). This may be attributed to the loss of liquid product (Fig. 6c) via partial vapor-phase loss to the vacuum pump during distillation and oil residue remaining in the reactor and condenser owing to its viscosity. However, the loss of the liquid product may be reduced by optimizing the distillation equipment and conditions. Alternatively, a simple physical separation technique, such as centrifugation and filtration, may be applied as a pre-treatment to recover the solid product with a lower oil content prior to distillation. Hence, the loss of the liquid product during distillation may be minimized with pre-treatment.

The behaviors of the contaminants during liquefaction are the most critical factors in developing waste treatment processes. The respective amounts of Cs, Sr, and Co added to the latex gloves were approximately 0.044, 0.029, and 0.020 g (0.33 mmol each). The Cs, Sr, and Co contents in the liquid and solid products were analyzed using ICP techniques, and the results are shown in Table 2. Notably, the amount of contaminants in the liquid product was lower than the detection limit (1 ppm), confirming that the liquid product may be regarded as non-radioactive. Meanwhile, the contaminants were incorporated into the CaCO₃-based solid product (4.33 g) in amounts comparable to those used in preparing the contaminated latex gloves. Therefore, only the solid product should be treated as radioactive waste after liquefaction.

Table 2

Results of inductively coupled plasma analysis of the solid product recovered after liquefaction and distillation
Element	Cs	Sr	Co
Added (g)	0.044	0.029	0.020
Content in liquid product (wt.%)	N.D.	N.D.	N.D.
Content in solid product (wt.%)	0.97	0.62	0.49
Mass in solid product (g)	0.042	0.027	0.021
N.D., not detected.

The reduction in volume was estimated by measuring the density of the solid product. The tap density of the as-recovered solid product was 0.76 g cm^–3, which could be further increased to 1.44 g cm^–3 after compression (30 MPa). The mass of a bundle of latex gloves tightly packed in a box (240 × 121 × 75 mm = 2178 cm³) was approximately 687.4 g, and the expected mass of the solid product that may be obtained via the liquefaction-distillation of the package was 229.1 g (33.3% of the initial amount). Thus, the respective volumes of the as-recovered and compressed solid products of the package were 301.4 and 159.1 cm³, which are equivalent to 86.2% and 92.7% decreases in volume without treatment and with simple compression, respectively.

Liquefaction-based processes offer several advantages in managing radioactive latex glove waste. The area required for temporary storage or final disposal may be significantly reduced via volume reduction. Furthermore, organic compounds generally form mobile complexes in the geological environment; thus, their underground disposal is disfavored [18–20]. The organic components in the latex gloves decompose into gas, oil, and char after liquefaction, but the char and inorganic CaCO₃ are retained in the final solid product, which is more suitable for underground disposal than the latex gloves. The stabilities of solid products in disposal can be further improved by fabricating proper waste forms (e.g., cement and glass) [11–14]. Consequently, the burden of storing/disposing latex glove waste generated by nuclear facilities may be reduced by using liquefaction to lower the cost of waste management.

Liquefaction-based volume reduction of latex gloves was suggested as a technical option in treating accumulated radioactive latex glove waste in nuclear facilities. Latex gloves were liquefied at > 270°C and decomposed into gas, liquid, and solid phases. The liquefaction of Cs-, Sr-, and Co-contaminated latex gloves was conducted at 350°C, and the CaCO₃-based solid product was then recovered after subsequent vacuum distillation at 300°C. Notably, the contaminants only remained in the solid product. The mass and volume of the compressed recovered solid product were approximately 33.3% and 7.3% (in the compressed state), respectively, of their initial values, indicating that latex glove waste was significantly reduced via liquefaction. Compared to conventional combustion, gas-phase generation could be minimized using this technique because the organic components in latex gloves were mainly converted into condensed phases. Furthermore, the solid product, a mixture of CaCO₃ and char, no longer contains organic species, which are unstable during long-term storage and disposal, thus simplifying waste management. The solid product may be treated further (e.g., cement waste form fabrication) for underground disposal. This process may also be used to treat other liquefiable wastes generated in nuclear facilities, such as plastics and sludge.

DAW	Dry active waste
RI	Radioactive isotope

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this article.

Acknowledgements

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MISP) (RS-2022-00155421).

J. B. Park, C.-W. Kim, S.-H. Kim and J. Y. Kim, Ann. Nucl. Energy, 42, 89 (2012).
J. H. Schulte and P. N. McNamara, in: Waste management 88: symposium on radioactive waste management, R. G. Post Ed., University of Arizona Nuclear Engineering Dept., Tucson, AZ (1988).
D. Alexandre, S. Asazuma, A. Bertini, G. Ferenczy, Y. Fitamant, S. Khubetsov, M. Kienhofer, R. Kohout, K. Lal, R. Mellenamin, L. Mergan, A. Morales León, J. Neubauer, S. Pettersson, P. Ronx, L. Sukhanov and A. Tsarenko, Status of technology for volume reduction and treatment of low and intermediate level solid radioactive waste, International Atomic Energy Agency, Vienna (1994).
S. W. Long, The incineration of low-level radioactive waste: a report for the advisory committee on nuclear waste, United States Nuclear Regulatory Commission, Washington, DC (1990).
J. I. Yoo, T. Shinagawa, J. P. Wood, W. P. Linak, D. A. Santoianni, C. J. King, Y. C. Seo and J. O. L. Wendt, Environ. Sci. Technol. 39, 5087 (2005).
A. R. K. Gollakota, N. Kishore and S. Gu, Renew. Sustain. Energy Rev., 81, 1378 (2018).
N. Ahmad, F. Abnisa and W. M. A. W. Wan Daud, Fuel, 218, 227 (2018).
L. Zhang, B. Zhou, P. Duan, F. Wang and Y. Xu, Chem. Eng. J., 285, 157 (2016).
H. G. I. M. Wijesinghe, W. G. T. W. Gamage, P. Ariyananda, H. A. S. L. Jayasinghe and A.N.R. Weerawansha, Int. J. Sci. Res. Publ., 6, 266 (2016).
C.-M. Deng, M. Chen, N.-J. Ao, D. Yan and Z.-Q. Zheng, J. Appl. Polym. Sci., 101, 3442 (2006).
M. Balonov, M. Dubourg, V. Efremenkov, J. Gilpin, R. Rabun, P. Wong and M. Wright, Management of waste containing tritium and carbon-14, International Atomic Energy Agency, Vienna (2004).
H.-C. Eun, H.-C. Yang, H.-J. Kim, S.-J. Kim, M.-K. Jeon, K.-Y. Lee and B.-K. Seo, J. Radioanal. Nucl. Chem. 331, 3735 (2022).
H.-C. Eun, H.-C. Yang, H.-J. Kim, S.-J. Kim, K.-Y. Lee and B.-K. Seo, J. Radioanal. Nucl. Chem. 328, 627 (2021).
P. K. Gallagher and D. W. Johnson Jr., Thermochim. Acta. 6, 67 (1973).
A. R. Lang, D. L. Engelberg, C. Walther, M. Weiss, H. Bosco, A. Jenkins, F. R. Livens and G. T. W. Law, ACS Omega. 4, 14420 (2019).
Y. Xie, J. Wang, Q. Sun, Y. Hu, M. Men, S. Wang, G. Liu and A. Mi, Prog. Nucl. Energy. 154, 104453 (2022).
T. Y. Kim, J. E. Hong, H. M. Park, U. J. Lee and S.-Y. Lee, J. Radioanal. Nucl. Chem. 323, 903 (2020).
L. R. van Loon and W. Hummel, The role of organics on the safety of a radioactive waste repository, Paul Scherrer Institut (1993).
B. F. Greenfield, M. H. Hurdus, N. J. Pilkington, M. W. Spindler and S. J. Williams, MRS Online Proc. Libr., 333, 705 (1993).
J. Kim, J. Kim, H. Jung and J.-C. Ha, Nucl. Eng. Des. 265, 841 (2013).

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Journal Publication

published 15 Feb, 2024

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Editorial decision: Minor Revisions Needed
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Reviewers invited by journal
05 Nov, 2023
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You are reading this latest preprint version

Liquefaction of latex glove waste for volume reduction

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1. Introduction

2. Materials and methods

3. Results and Discussion

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