Experimental study on the leaching performance of U(VI) solidified by uranium tailing cement with different admixtures and ratios

Environmental Technology & Innovation 17 (2020) 100506

Contents lists available at ScienceDirect

Environmental Technology & Innovation journal homepage: www.elsevier.com/locate/eti

Experimental study on the leaching performance of U(VI) solidified by uranium tailing cement with different admixtures and ratios ∗

Fuliang Jiang a,b , , Jintao Guo a , Xiaoli Wang a , Yong Liu a,b , Xiangyang Li a,b , Guan Chen a , Zhe Wang a , Jin Yang a , Biao Tan a a b

School of Resource & Environment and Safety Engineering, University of South China, Hunan 421001, PR China Hunan Province Engineering Technology Research Center of Uranium Tailings Treatment, Hunan 421001, PR China

article

info

Article history: Received 21 June 2019 Received in revised form 11 October 2019 Accepted 19 October 2019 Available online 23 October 2019 Keywords: Uranium tailings Cement solidified waste form Fly ash Slag powder U(VI) Leaching performance

a b s t r a c t Research into radionuclide leaching behavior in the treatment of low-level radioactive waste solidification has been a widespread concern. To study the leaching performance of U(VI) in solidified bodies in simulated groundwater environment, fly ash and slag powder were mixed in different ratios with uranium tailing cement. The U(VI) leaching results from solidified bodies prepared using pure Portland cement, fly ash, slag powder, fly ash, and slag powder were compared and analyzed. The results showed that the leaching performance of solidified U(VI) decreased with increased pH, but the effects were different and had similar inhibitory effects on U(VI) leaching in neutral and alkaline environments. The variation trend of leaching concentrations was also different with admixture changes. When fly ash was added, the U(VI) leaching concentration trend first increased, then decreased, and finally became stable. However, there was no increasing process between pure Portland cement and slag powder, which might have been due to the different admixture chemical compositions. Comparing the leaching rate at 42 d in a neutral environment, it was found that the leaching rate of 15% slag powder was the lowest, at 2.47296 ×10−5 cm/d. © 2019 Published by Elsevier B.V.

1. Introduction Nuclear energy is the only energy source that can be used to replace large amounts of fossil fuels and has been widely used in defense and industrial applications (Abdel Rahman et al., 2011). The uranium mining process is accompanied by the generation of radioactive waste, such as uranium tailings, which contain U(VI) with high water solubility (Yan et al., 2010). Uranium tailings are classified as low and intermediate level radioactive waste, which can seriously threaten human health and ecological environments. For low and intermediate level solidified radioactive waste, solidification methods are first applied and the products deep-buried, as practiced by most professionals (Brookins, 2012; Guo et al., 2011). In many curing methods, cement solidification technology is the main method for radioactive waste treatment, which has the advantages of a simple process, small secondary pollution, and stable aquatic products (Glasser, 1992; Kuang et al., 2019). However, after curing with ordinary Portland cement, solidified radioactive waste bodies are porous and nuclides easily diffuse to the environment through pores after being immersed in groundwater. Therefore, nuclide retention to ∗ Corresponding author at: School of Resource & Environment and Safety Engineering, University of South China, Hunan 421001, PR China. E-mail address: [email protected] (F. Jiang). https://doi.org/10.1016/j.eti.2019.100506 2352-1864/© 2019 Published by Elsevier B.V.

2

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

Table 1 Physical properties of Portland cement. Test items

Density (g cm−3 )

Specific surface area, (m2 kg−1 )

Initial setting time (min)

Final setting time (min)

Test results

3.1

373

149

211

Compressive strength (MPa) 3d

28d

27.4

47.5

Table 2 Chemical composition of raw materials. Raw material

Chemical components (mass fraction, %)

Fly ash Slag powder Cement

SiO2

Al2 O3

Fe2 O3

CaO

MgO

Others

56.50 39.58 24.70

24.70 15.68 5.10

2.87 0.87 3.40

2.80 35.42 59.80

1.02 7.14 4.60

12.11 1.31 2.40

Table 3 Compositional analysis results of uranium tailings. Chemical component

Na

Al

Si

P

S

K

Ca

Fe

As

Rb

Zr

Content (%)

0.32

4.66

75.94

0.11

0.88

11.84

0.40

5.32

0.18

0.11

0.15

enhance diffusion resistance to nuclide leaching is the current development trend regarding cement curing of low and intermediate level radioactive waste. The leaching behavior of nuclides in solidified bodies is divided into three stages, including the rapid dissolution of nuclides on solidified body surfaces during the initial leaching stage, long-term slow nuclide diffusion in the middle stage, and the late main stage of chemical dissolution of nuclides dissolved in cement hydration products (Dyer et al., 2000; EI Kamash et al., 2006; Patra et al., 2011). In this study, the stability of radioactive waste cement after curing was studied and it was found that the combination of appropriately designed alkaline activator and cement, such as blast furnace slag, fly ash, and metakaolin, showed early and late strengths in the solidified body that were higher than traditional cement solidified bodies (Shi and Fern´andez-Jim´enez, 2006). The encapsulation mechanism of high waste cement solidified bodies on nuclide has been studied and it was found that alkali-activated cement solidified bodies exhibited high compressive strength, low porosity, and low leaching rates (Shen et al., 1994). Composite cementing materials have been formed by adding zeolite and thermally-activated kaolin to alkali slag cement, which had strong curing effects on nuclides Sr-90 and Cs-137 (Li et al., 1999; Scm and Scm, 2005), but for U(VI) curing performance was sufficiently clear. The slag powder containing noncrystalline structural substances and with potential hydraulic gelling properties, exhibited hydraulic gelling properties after treatment as an activator (Du et al., 2014; Liu et al., 2018). Fly ash is a spherical particle, which can be uniformly filled into spaces and the interior matrix causes a significant decrease in the degree of matrix internal cracking (Shi et al., 2019). In this study, fly ash and slag powder were used to modify solidified bodies of uranium tailings, with comparison of different admixtures and ratios and comparisons using pure Portland cement to explore the leaching performance of U(VI) in uranium tailing solidified bodies in simulated groundwater environments with different pH values. 2. Materials 2.1. Experimental materials and equipment The fly ash (FA) used in these experiments was the main solid waste discharged from coal-fired power plants after coal combustion. It was provided from a power plant in Hunan, China, and its main chemical components were SiO2 , Al2 O3 , and Fe2 O3 (the mass fraction sum accounted for >80% of the total). Grade S95 slag powder belonged to the ultrafine granulated blast furnace slag powders, with an activation index that reached 95% after 18 d; its main chemical components are SiO2 , Al2 O3 , and CaO (the mass fraction sum was close to 90% of the total). The physical properties of ordinary Portland cement (P.O 32.5R) are shown in Table 1 and the chemical composition of all above materials shown in Table 2. Uranium tailings were used as the aggregate for preparing solidified bodies to provide uranium for experimental research on leaching behavior of U(VI). The tailings were sampled from a uranium-tailing pond. To reduce the differences between tailing samples, multipoint stratification sampling was used to treat uranium tailings. X-ray diffraction (XRD) test results of uranium tailings samples indicated that the main minerals of uranium tailings were quartz, dihydrate gypsum, microcline feldspar, and albite (Fig. 1). Compositional analysis results of X Ray fluorescence (XRF) analysis of uranium tailings showed that they mainly contained Si, K, and Fe, which accounted for 75.94, 11.84, and 5.32% of the total mass, respectively, indicating that the quartz composition accounted for a greater proportion (Table 3).

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

3

Fig. 1. XRD test results of uranium tailings. Table 4 The ratios of admixtures per cubic meter. NO.

P. O FA-1 FA-2 FA-3 GGBS-1 GGBS-2 GGBS-3 FG-1 FG-2 FG-3

Cement/kg

250.0 212.5 200.0 187.5 212.5 200.0 187.5 212.5 200.0 187.5

Admixture/kg

Mixing amount

Fly ash

Slag powder

0 37.5 50.0 62.5 0 0 0 25.0 33.3 41.7

0 0 0 0 37.5 50.0 62.5 12.5 16.7 20.8

0 15% 20% 25% 15% 20% 25% 15% 20% 25%

Note: The dosage in this area refers to the ratio of the amount of admixture to the total amount (250 kg).

The equipment used in experiments mainly included a laboratory pH meter, a T6 Xinyue visible spectrophotometer (PERSEE Analytics, Inc., Auburn, CA, USA), an IDS-986A computer-controlled intelligent heating station (IDS, Doha, Qatar), and a TYE-600kN compression-testing machine (WUXI JIANYI INSTRUMENT&MACHINERY, Wuxi, China). 2.2. Preparation of uranium tailing solidified bodies Mixed uranium tailing samples were dried in a blast-drying box and the raw materials weighed using an electronic balance. The Chinese standard (Specification for mix proportion design of masonry mortar, 2010) was used as a reference source for the design of cement incorporation ratios and the ratios of the admixtures shown in Table 4. The minimum requirements of the Chinese standard (Performance requirements for low and intermediate level radioactive waste formcemented waste form, 2011) were met by selecting the cement mortar M7.5 and the preparation method carried out in accordance with the standard provisions. A certain amount of raw material was weighed into a blender (PVC mold, size Φ 50 mm × 50 mm) for agitation experiments. Reduction of bubbles on the mold surface was achieved by appropriate vibration during the molding process. After three min of continuous vibration, sample surfaces were smoothed with a tool and the samples removed from the mold after standing in a cool and ventilated environment for 24 h. Finally, samples were placed into a curing box (temperature: 25 ± 5 ◦ C and humidity ≥90%) and cured to 28 d. According to results from the TYE-600KN pressure testing machine, unconfined compressive strengths met the standard requirements (not < 7 MPa). 3. Methods 3.1. Experimental design The U(VI) content was calculated from the spectrophotometer results and the sample standard curve determined (Fig. 2). Wet digestion (Tuzen et al., 2004) was used to process uranium tailing samples that underwent drying and screening (300 mesh). Using this measurement method, the U(VI) content of the original uranium tailing sand sample was obtained, which was 0.398 mg/g. However, the limit of U(VI) emission concentration has been specified in the Chinese

4

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

Fig. 2. Sample standard curve.

standard (Regulations for radiation and environment protection in uranium mining and milling, 2009), which is 0.300 mg/g. As the direct accumulation of tailings for a disposal method is not desirable, it was necessary to carry out curing treatments. The solute containing uranium is produced by erosion of solidified uranium tailings and pollutes the groundwater environment by means of transport. Here, the pH of the leaching agent in experiments was set at 5, 7, and 9 to simulate acid and alkali conditions in the groundwater environments of solidified uranium tailings. Leaching experiments were carried out according to the experimental method specified in the Chinese standard (Standard test method for leachability low and intermediate level solidified radioactive waste forms, 2011). Samples of regular shape were selected from the prepared solidified bodies and the bottom surfaces polished smooth using sandpaper. Then, 500 ml of prepared leaching agent was added to a dry and clean 750 ml polyethylene bottle and the samples tied with chemically-inert nylon rope and suspended in the bottle to ensure that all sample sides were submerged in the leaching agent at least 1–10 cm, and then sealed. The leaching agent was changed on the 1st, 3rd, 7th, 14th, 21st, 28th, 35th, and 42nd days, with the replaced leaching solutions collected and sealed for analysis. 3.2. Analysis method A collected 20 ml volume of leaching solution was placed it into a centrifuge tube, after filtration through a filter paper using ultrapure water. Then, 10 ml of filtrate was placed in a 25 ml volumetric flask and 4 ml of hydrochloric acid, 1 ml of arsenazo III, 1 ml of disodium-EDTA, and 1 ml of buffer solution added the volume adjusted to 25 ml with ultrapure water. The prepared solution without U(VI) was the blank control group and all samples tested by spectrophotometer. The leaching rate and cumulative leaching fractions were calculated using formulas (1) and (2), respectively. The initial values of U(VI) leaching content in the leached experimental samples at each ratio are shown in Table 5. Cn =

bn /b0 (F /V ) · (∆t)n

∑ Qt =

bn /b0

F /V

(1)

(2)

where Cn is the leaching rate of U(VI) in the nth leaching cycle, cm/d; bn the mass of leached uranium in the nth leaching cycle, g; b0 the initial leached U(VI) content in the leaching test sample, g; F the sample geometric surface area in contact with the leaching agent, cm3 ; V the sample volume, cm3 ; (∆t)n the number of days of the nth leaching cycle, d; and Qt the cumulative leaching fraction of U(VI) at time t, cm. 4. Results and discussion The leaching rate of solidified solids was closely related to the raw materials used in the preparation of solidified solids (Cantrell et al., 2014; Zheng et al., 2016). Under the condition of uranium tailings as a solidified aggregate, solidified uranium tailings with different contents were prepared by changing the proportions of cement, fly ash, and slag powder. The leaching resistance of solidified uranium tailings was improved by introducing admixtures.

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

5

Table 5 Initial value of U(VI) leaching content in each sample. NO.

Spectrophotometric average

U(VI) concentration/(mg/L)

U(VI) content/mg

FA-1 FA-2 FA-3 GGBS-1 GGBS-2 GGBS-3 FG-1 FG-2 FG-3 P. O

0.025 0.019 0.032 0.019 0.014 0.017 0.019 0.025 0.016 0.013

0.121 0.093 0.152 0.093 0.072 0.082 0.093 0.118 0.078 0.066

0.015 0.012 0.019 0.012 0.009 0.010 0.012 0.015 0.010 0.008

Fig. 3. Leaching concentration and cumulate fraction leached of U(VI) in solidified bodies with ordinary Portland cement.

4.1. Leaching concentration and cumulate fraction leached of U(VI) in solidified bodies with ordinary Portland cement The leaching concentration of U(VI) in solidified bodies with ordinary Portland cement tended to decrease under the three applied pH conditions. The whole process presented three stages, including rapid decline, slow decline, and steady trends (Fig. 3). Compared with the three curves, when the pH value was 5, the leaching concentration was higher than with the other two pH conditions. Compared with the three stages, the leaching concentration at the beginning was quite different. With prolonged leaching time, the difference gradually decreased. The reason for this might have been that the pH value of the leaching agent was different and scale formed on the surface by the leaching agent tended to be saturated with reactions between the leaching agent and solidified body. As a result, the leaching effect was lower in the later stage. Moreover, the leaching concentrations of uranium tailings on the first day were clearly higher than in the other two. For uranium tailing solidified bodies with cement alone, it was observed that U(VI) leaching of uranium tailings under acidic conditions was greater than leaching under alkaline and neutral conditions, which had certain inhibitory effects. Research (Pöml et al., 2011) has shown that high pH solutions for a long time can maintain the stability of solidified bodies. However, it is easy to produce decomposition effects under lower pH conditions and the stability can be poor. At the same time, it was found that the cumulative leaching fraction of U(VI) under these conditions varied with leaching agent pH and the difference was clear, particularly in an acidic environment, which was higher than in neutral and alkaline conditions (Fig. 3). This curve (Fig. 3) facilitated comparative analysis. Longitudinally, the cumulative leaching fraction decreased with increased leaching agent pH. The cumulative leaching fraction of 42 d U(VI) solidified bodies was 0.01249, 0.01017, and 0.00883 cm, respectively. The cumulative leaching fraction increased with increased leaching time and finally tended to stabilize. 4.2. Leaching concentration and cumulate fraction leached of U(VI) in solidified bodies mixed with fly ash The leaching concentration and cumulative leaching fraction of U(VI) in three pH environments with 15, 20, and 25% fly ash showed that the leaching agent pH had an effect on the leaching concentration and cumulative leaching fraction of U(VI) (Fig. 4). With increased pH, the leaching concentration and cumulative leaching fraction of U(VI) showed a decreasing trend. At the same time, the leaching concentration of U(VI) and its cumulative leaching fraction and leaching time had different trends. With extended leaching time, the leaching concentration of U(VI) first increased, then decreased, and

6

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

Fig. 4. Leaching concentration and cumulate fraction leached of U(VI) in solidified body mixed with fly ash.

then tended to stabilize. The trend of the cumulative leaching fraction of U(VI) increased rapidly, then slowed, and became stable. When the fly ash content was 15%, the cumulative leaching fractions of fly ash in the three pH environments were 0.00727, 0.00613, and 0.00549 cm, respectively, but they were lower than those of cement alone. The leaching concentration of uranium increased from ∼0.05 ppm to over 0.1 ppm during the increasing phase and the leaching concentration more than doubled. The leaching concentration of uranium reached its highest under acidic conditions, reaching 0.131 ppm. The subsequent leaching process was similar to that of cement. When 20% fly ash was added, the leaching concentration and cumulative leaching fraction were clearly less than that when 15% fly ash was added and the decline greater than that of the latter. For convenience of comparison, pH 5 conditions were selected. The former decreased from 0.083 to 0.027 ppm in the process of leaching from the 3rd to 42nd day, with a decrease of 67%, while the latter decreased from 0.061 to 0.035 ppm, with a decrease of 43%. By comparing the leaching concentration with leaching time, it was found that the difference of leaching concentration among three pH values was found to be not clear in the later stage of leaching when 15% fly ash was added. This showed that not only was the leaching of U(VI) inhibited by additives, but the leaching resistance was also improved by changing the additive proportions within a certain range. With increased fly ash content, to 25%, the change trend of leaching concentration was different from that of the first two. The main manifestation was that the leaching concentration of U(VI) sharply declined in the process of stabilization in the later leaching stage, while both of the two fly ash contents were present an excessive stage. During leaching time from the 7th to 28th days, the leaching concentration level was higher than that of 20% fly ash, which might have been caused by the 25% fly ash. Studies have shown that proper fly ash blending can achieve long-term stability of the solidified bodies during the treatment (Cong et al., 2016). When the fly ash blending amount was within a certain range, it had little effect on the cement strength performance, but it was beyond the scope of this study. At the same time, the effect of fly ash on the cement hydration heat was very clear, which affected the surface crack generation. However, from 42nd day leaching results, the leaching concentration remained at a minimum. Combined with the above analytical results, the leaching resistance of uranium tailing solidified bodies were seen to be effectively improved by adding fly ash. With increased fly ash content, the leaching concentration and cumulative leaching fraction of U(VI) decreased, especially when 25% fly ash was added. 4.3. Leaching concentration and cumulate fraction leached of U(VI) in solidified bodies mixed with slag powder When slag powder was added, the leaching concentration changed from high to low with increased leaching time and finally became stable (Fig. 5). The cumulative leaching fraction increased to a steady state with increased leaching time.

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

7

Fig. 5. Leaching concentration and cumulate fraction leached of U(VI) in solidified bodies mixed with slag powder.

The effects of leaching agent pH on the leaching process were that the leaching effect of U(VI) decreased with increased pH. From the peak value of leaching concentration and leaching time curve, when 15% slag powder was added, the peak value of U(VI) leaching concentration in the three pH environments occurred in the first day of leaching time, showing was 0.117, 0.094, and 0.083 ppm, respectively. Under all conditions, the leaching capacity of U(VI) was lower than that of cement alone. With continuous leaching, the leaching capacity of U(VI) in each leaching stage was clearly weaker than that of the latter. The long-term stability of uranium tailing solidified bodies was also improved by adding slag powder. When 20 and 25% slag powder were added, the U(VI) leaching trend in these bodies were the same as that in 15% and the change in leaching concentration not significant. The leaching resistance performance of these bodies was observed not to be clearly improved with increased amounts of slag powder within a certain range. On the whole, the leaching concentration of U(VI) decreased with increased slag powder content. By comparing the leaching process of mixed fly ash and slag powder, the difference between them was clear. The leaching concentration of U(VI) did not rise with increased time when slag powder was added, which was similar to that when cement alone was added, but the concentration first increased and then decreased when fly ash was added. This might have been due to admixture differences. By comparing the chemical composition of fly ash and slag powder (Table 2), most of the two admixtures had the same composition. However, the content of calcium oxide and magnesium oxide were quite different, with the content in slag powder higher than that of fly ash, especially in terms of calcium oxide. A white scale with compact structure that was produced during uranium leaching led to reduced uranium leaching capacity. Studies (Yan, 1980) have shown that the scale chemical composition was mainly calcium, ∼36.3%, followed by magnesium oxide. The leaching ability of uranium was observed to decrease due to the attachment of more calcium and magnesium ions to the surface of slag powder solidified bodies. With extended leaching time, scale adhered to the surface tended to be saturated, thus showing a downward trend in leaching concentration, which was also the main reason for the eventual stabilization of leaching concentration under various admixtures in these experiments. 4.4. Leaching concentration and cumulate fraction leached of solidified U(VI) when fly ash and slag powder were mixed The leaching effects of U(VI) from adding fly ash and slag powder at the same time were observed to decrease to a certain extent, compared with that by adding cement alone (Fig. 6). Due to the addition of slag powder in the admixture, the trend of U(VI) leaching concentration was different from the first rising stage when fly ash was added alone, but the overall trend was downward. Some studies have shown that, when slag powder and fly ash are added simultaneously, the hydration heat of cement is significantly reduced (Cong et al., 2016), thus reducing the influence on surface cracks of solidified bodies, such that there was no rising stage when only fly ash was added.

8

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

Fig. 6. Leaching concentration and cumulate fraction leached of solidified U(VI) when fly ash and slag powder are mixed at the same time.

In terms of leaching concentration, the anti-U(VI) leaching effect of 15% slag powder and fly ash was better than that of 15% fly ash because of slag powder addition. At 42 d, the leaching concentration decreased significantly, below 0.02 ppm. When 25% slag powder and fly ash are added, the leaching concentration anomaly of 1-day U(VI) can be found. After removal, it was seen that the peak value of U(VI) leaching concentration decreased with increased slag powder and fly ash content, but the decrease was not significant. The results showed that the leaching resistance with the two additives was improved when the two additives increased simultaneously, but the leaching performance of U(VI) was in general not significantly altered. Comparing the leaching process in acid–alkali environments, the leaching concentration in neutral and alkaline environment was observed to be almost the same from the 1st to the 7th days, indicating that the leaching performance of leaching agents at pH 7 and 9 were the same when slag powder and fly ash were added simultaneously. The leaching concentration was found to tend to stabilize at a faster rate than that under the above-mentioned doping conditions and this trend was observed after the 21st day, while the other doping conditions were basically constant after the 28th day and even after the 35th day. 4.5. Leaching rate of U (VI) solidified by uranium tailings cement with different admixtures and ratios The leaching rate was used to measure the release rate of radionuclides and to reflect the durability of these solidified materials. For ease of comparison, solidified bodies under the dosage of the above several U(VI) leaching conditions were considered under the demands of the national standard regarding the leaching rate of deionized water on conditions, so as to compare at pH 7 leaching rate changes. The leaching rate of single cement and fly ash, slag powder, and compound cement are shown in Fig. 7a, b, and c, respectively. The leaching rate of U(VI) with a single cement was clearly seen to be higher than that with other additives, especially in the early leaching stage. The leaching rate in the first day with only cement was 0.00215 cm/d and the peak leaching rate of the other three additions at 0.00109, 0.00104, and 0.00158 cm/d, respectively. In terms of leaching time, with increased time, the difference between the U(VI) leaching rate and other additions gradually decreased, which was related to uranium leaching saturation. The minimum leaching rate of fly ash, slag powder, and the admixture at the 42nd day appeared at the dosage of 25% fly ash, 15% slag powder, and 20% compound admixture. The leaching rates were 2.95677 × 10−5 , 2.47296 × 10−5 , and 3.06287 × 10−5 cm/d, respectively. The relationship between the leaching rate and leaching time when the leaching rate was lowest on the 42nd day showed that the curve of 25% slag powder and 20% slag powder were almost coincident (Fig. 7d). 5. Conclusions In this research, the leaching behaviors of U(VI) from solidified uranium tailing bodies with different added proportions of cement, fly ash, and slag powder added to the solidified body were examined and leaching experiments of U(VI)

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

9

Fig. 7. Leaching rate of U (VI) solidified by uranium tailing cement with different admixtures and ratios.

in simulated groundwater environment performed. The results yielded the leaching concentration, cumulative fraction leached, and leaching rate, which showed that the leaching agent pH affected U(VI) leaching and the leaching process was hindered by high leaching agent pH. Moreover, fly ash and slag powder hindered the leaching of U(VI) to varying degrees, respectively. For the 10 samples of this study, U(VI) had different leaching processes and effects, which were affected by the admixture pH and leaching agent. Thus, when considering the use of cement curing technology to treat uranium tailings, it was important to consider both the groundwater and admixture environments. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This research was supported by the National Natural Science Foundation of China (No. 11475081, 11875164), Project Approved by the Research Foundation of Education Bureau of Hunan Province, China (No. 17B228), the Double First Class Construct Program of USC (No. 2017SLY05), Hunan Provincial Innovation Foundation For Postgraduate, China (No. CX20190726), Project Approved by Hunan Province Engineering Research Center of Radioactive Control Technology in Uranium Mining and Metallurgy & Hunan Province Engineering Technology Research Center of Uranium Tailings Treatment Technology (No. 2018YKZX1004), Open Fund Project of Hunan Cooperative Innovation Center for Nuclear Fuel Cycle Technology & Equipment (No. 2019KFZ01).

10

F. Jiang, J. Guo, X. Wang et al. / Environmental Technology & Innovation 17 (2020) 100506

References Abdel Rahman, R.O., Ibrahium, H.A., Hung, Y.T., 2011. Liquid radioactive wastes treatment: A review. Water (Switzerland) 3 (2), 551–565. http: //dx.doi.org/10.3390/w3020551. Brookins, D.G., 2012. Geochemical Aspects of Radioactive Waste Disposal. Springer Science & Business Media. Cantrell, K.J., Um, W., Williams, B.D., Bowden, M.E., Gartman, B., Lukens, W.W., . . . Mausolf, E.J., 2014. Chemical stabilization of Hanford tank residual waste. J. Nucl. Mater. 446 (1–3), 246–256. http://dx.doi.org/10.1016/j.jnucmat.2013.10.060. Cong, L., Qi, W., Qina, S., Junfeng, L., 2016. Effects of mineral admixtures on cementation of radioactive wastes. Mater. China 35 (7), 509–517. Du, Y., Wei, M., Reddy, K.R., Liu, Z., Jin, F., 2014. Effect of acid rain pH on leaching behavior of cement stabilized lead-contaminated soil. J. Hard Mater. 271, 131–140. http://dx.doi.org/10.1016/j.jhazmat.2014.02.002. Dyer, A., Las, T., Zubair, M., 2000. The use of natural zeolites for radioactive waste treatment: Studies on leaching from zeolite/cement composites. J. Radioanal. Nucl. Chem. 243, 839–841. EI Kamash, A.M., EI Naggar, M.R., EI Dessouky, M.I., 2006. Immobilization of cesium and strontium radionuclides in zeolite-cement blends. J. Hard Mater. 136, 310–316. http://dx.doi.org/10.1016/j.jhazmat.2005.12.020. GB 23727-2009, 2009. Regulations for Radiation and Environment Protection in Uranium Mining and Milling. Inspection and Quarantine of the People’s Repablic of China, Beijing, China. Glasser, F.P., 1992. Progress in the immobilization of radioactive wastes in cement. Cem. Concr. Res. 22 (2–3), 201–216. Guo, X., Xu, C., Yang, W., Wu, H., Fan, Z., 2011. Radiation protection. Radiot. Prot. 31 (3), 184–192. Kuang, Y., Zou, S., Xu, L., Huang, B., Liu, Y., Kou, X., Xi, W., 2019. Effect of mixing parameter on property of cenment solidified radioactive waste form. At. Energy Sci. Technol. 53 (2), 234–242. Li, Y., Qian, G., Yi, F., Shi, R., Fu, Y., Li, L., Zhang, J., 1999. Study on rich alumina alkali-activated slag clay minerals cementitious materials for immobilization of radioactive waste. Chin. J. Nucl. Sci. Eng. 19 (4), 379–384. Liu, X., Tang, B., Yin, H., Emile, M., 2018. Durability and environmental performance of bayer red mud–coal gangue-based road base material. Chin. J. Eng. 40 (4), 438–445. http://dx.doi.org/10.13374/j.issn2095-9389.2018.04.006. Patra, A.C., Sumesh, C.G., Mohapatra, S., Sahoo, S.K., Tripathi, R.M., Puranik, V.D., 2011. Long-term leaching of uranium from different waste matrices. J. Environ. Manag. 92 (3), 919–925. http://dx.doi.org/10.1016/j.jenvman.2010.10.046. GB 145691-2011, 2011. Performance Requirements for Low and Intermediate Level Radioactive Waste Form-Cemented Waste Form. Ministry of Ecology and Environment of the People’s Republic of China, Beijing, China. Pöml, P., Geisler, T., Cobos-sabaté, J., Wiss, T., Raison, P.E., Schmid-beurmann, P., Deschanels, X., 2011. The mechanism of the hydrothermal alteration of cerium- and plutonium-doped zirconolite. J. Nucl. Mater. 410, 10–23. http://dx.doi.org/10.1016/j.jnucmat.2010.12.218. Scm, A.A., Scm, A.A., 2005. Feasibility of immobilizing simulated radioactive slurry based on Alkali-activated Slag-clay minerals composite cement. At. Energy Sci. Technol. 39 (4), 311–317. Shen, X., Yan, S., Wu, X., Tang, M., Yang, L., 1994. Immobilization of simulated high level waste into waste form. Cem. Concr. Res. 24 (4), 133–138. Shi, C., Fern´andez-Jim´enez, A., 2006. Stabilization/solidification of hazardous and radioactive wastes with alkali-activated cements. J. Hard Mater. 137, 1656–1663. http://dx.doi.org/10.1016/j.jhazmat.2006.05.008. Shi, Y., Zhu, J., He, D., Luo, X., Wu, T., Du, S., 2019. Effect of mineral admixture on mechanical properties and cracking tendency of concrete. J. Chin. Ceram. Soc. 47 (11), 1–6. http://dx.doi.org/10.14062/j.issn.0454-5648.2019.11.11. JGJT 98-2011, 2010. Specification for Mix Proportion Design of Masonry Mortar. Shaanxi Research & Design Institute of Architecture Sciences, Xi’an, China. GB/T 7023-2011, 2011. Standard Test Method for Leachability Low and Intermediate Level Solidified Radioactive Waste Forms. Inspection and Quarantine of the People’s Repablic of China, Beijing, China. Tuzen, M., Sari, H., Soylak, M., 2004. Microwave and wet digestion procedures for atomic absorption spectrometric determination of trace metals contents of sediment samples. Anal. Lett. 37 (9), 1925–1936. http://dx.doi.org/10.1081/AL-120039436. Yan, T.Y., 1980. Calcite control in in-situ uranium leaching process. J. Pet. Technol. 32 (11), 2068–2074. Yan, S., Hua, B., Bao, Z., Yang, J., Liu, C., Deng, B., 2010. Uranium(VI) removal by nanoscale zerovalent iron in anoxic batch systems. Environ. Sci. Technol. 44 (20), 7783–7789. Zheng, D., Ji, T., Wang, C., Sun, C., Lin, X., Muhammed, K., Hossain, A., 2016. Effect of the combination of fly ash and silica fume on water resistance of Magnesium – Potassium Phosphate Cement. Constr. Build. Mater. 106, 415–421. http://dx.doi.org/10.1016/j.conbuildmat.2015.12.085.