• Nuclear Engineering and Technology
• /
• v.55 no.12
• /
• pp.4527-4542
• /
• 2023

The present microbial reinforcement of rock and soil exhibits limitations, such as uneven reinforcement effectiveness and low calcium carbonate generation rate, resulting in limited solidification strength. This study introduces electroosmosis as a standard microbial grouting reinforcement technique and investigates its solidification effects on microbial-reinforced uranium tailings. The most effective electroosmosis effect on uranium tailings occurs under a potential gradient of 1.25 V/cm. The findings indicate that a weak electric field can effectively promote microbial growth and biological activity and accelerate bacterial metabolism. The largest calcium carbonate production occurred under the gradient of 0.5 V/cm, featuring a good crystal combination and the best cementation effect. Staged electroosmosis and electrode conversion efficiently drive the migration of anions and cations. Under electroosmosis, the cohesion of uranium tailings reinforced by microorganisms increased by 37.3% and 64.8% compared to those reinforced by common microorganisms and undisturbed uranium tailings, respectively. The internal friction angle is also improved, significantly enhancing the uniformity of reinforcement and a denser and stronger microscopic structure. This research demonstrates that MICP technology enhances the solidification effects and uniformity of uranium tailings, providing a novel approach to maintaining the safety and stability of uranium tailings dams.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.14 no.2
• /
• pp.189-200
• /
• 2016

The Republic of Tajikistan has ten former uranium mining sites. The total volume of all tailings is approximately 55 million tonnes, and the covered area is more than 200 hectares. The safe management of legacy uranium mining and tailing sites has become an issue of concern. Depending on the performance requirements and site-specific conditions (location in an arid, semiarid or humid region), a cover system for uranium tailings sites could be constructed using several material layers using both natural and man-made materials. The purpose of this study is to find a feasible cost-effective cover system design for the Degmay uranium tailings site which could provide a long period (100 years) of protection. The HELP computer code was used in the evaluation of potential Degmay cover system designs. As a result of this study, a cover system with 70 cm thick percolation layer, 30 cm thick drainage layer, geomembrane liner and 60 cm thick barrier soil layer is recommended because it minimizes cover thickness and would be the most cost-effective design.

• Nuclear Engineering and Technology
• /
• v.55 no.2
• /
• pp.523-529
• /
• 2023

Cemented uranium tailings backfill created from alkali-activated slag (CUTB) is an effective method of disposing of uranium tailings. Using some environmental functional minerals with ion exchange, adsorption, and solidification abilities as backfill modified materials may improve the leaching resistance of the CUTB. Natural zeolite, which has good ion exchange and adsorption characteristics, is selected as the backfill modified material, and it is added to the backfill materials with cementitious material proportions of 4%, 8%, 12%, and 16% to prepare CUTB mixtures with environmental functional minerals. After the addition of natural zeolite, the uniaxial compressive strength (UCS) of the CUTB decreases, but the leaching resistance of the CUTB increases. When the natural zeolite content is 12%, the UCS reaches the minimum value of 8.95 MPa, and the concentration of uranium in the leaching solution is 0.28-8.07 mg/L, the leaching rate R₄₂ is 9.61×10^-7 cm/d, and cumulative leaching fraction P₄₂ is 8.53×10^-4 cm, which shows that the alkali-activated slag cementitious material has a good curing effect on the CUTB, and the addition of environmental functional minerals helps to further improve the leaching resistance of the CUTB, but it reduces the UCS to an extent.

• Nuclear Engineering and Technology
• /
• v.54 no.10
• /
• pp.3631-3640
• /
• 2022

Uranium mill tailing ponds (UMTPs) are risk source of debris flow and a critical source of environmental U and Rn pollution. The technology of microbial induced calcium carbonate precipitation (MICP) has been extensively studied on reinforcement of UMTs, while little attention has been paid to the effects of MICP on U & Rn release, especially when incorporation of metakaolin and bacillus subtilis (MBS). In this study, the reinforcement and U & Rn immobilization role of MBS -MICP solidification in different grouting cycle for uranium mill tailings (UMTs) was comprehensively investigated. The results showed that under the action of about 166.7 g/L metakaolin and ~50% bacillus subtilis, the solidification cycle of MICP was shortened by 50%, the solidified bodies became brittle, and the axial stress increased by up to 7.9%, and U immobilization rates and Rn exhalation rates decrease by 12.6% and 0.8%, respectively. Therefore, the incorporation of MBS can enhance the triaxial compressive strength and improve the immobilization capacity of U and Rn of the UMTs bodies solidified during MICP, due to the reduction of pore volume and surface area, the formation of more crystals general gypsum and gismondine, as well as the enhancing of coprecipitation and encapsulation capacity.

• Nuclear Engineering and Technology
• /
• v.55 no.8
• /
• pp.2927-2934
• /
• 2023

The influence of the atmospheric radon background on the airborne gamma spectrum can seriously affect researchers' judgement of ground radiation information. However, due to load and endurance, unmanned aerial vehicle (UAV)-borne gamma-ray spectrometry is difficulty installing upward-looking detectors to monitor atmospheric radon background. In this paper, an advanced spectral-ratio method was used to correct the atmospheric radon background for a UAV-borne gamma-ray spectrometry in Inner Mongolia, China. By correcting atmospheric radon background, the ratio of the average count rate of U window in the anomalous radon zone (S5) to that in other survey zone decreased from 1.91 to 1.03, and the average uranium content in S5 decreased from 4.65 mg/kg to 3.37 mg/kg. The results show that the advanced spectral-ratio method efficiently eliminated the influence of the atmospheric radon background on the UAV-borne gamma-ray spectrometry to accurately obtain ground radiation information in uranium exploration. It can also be used for uranium tailings monitoring, and environmental radiation background surveys.

• Economic and Environmental Geology
• /
• v.30 no.6
• /
• pp.567-586
• /
• 1997

Concentrations of several heavy metals in soils derived from black shale and slate have been reported to be higher than the average concentrations in non-polluted soils. This study describes and characterizes soil minerals, and investigates the distribution of heavy metals in soils, and then examines their relationship. Soils in the study area are mainly consist of guartz and feldspars with minor amount of kaolin, illite, vermiculite, chlorite and illite-vermiculite interstratified minerals. Mineral compositions are similar in mountain-, farmland-, and paddy-soils. The residual soils derived from sandy phyllites contain less illites than those from black shale and black slate. Heavy metals appear to be more concentrated in soils than in rocks. The concentrate ratios in soils to rocks ranges 1.1 times for Cr, 2 for Cu, 1.4 for Ni. The contour maps of Cd, Zn, Pb, Cu contents using 0.43N $HNO_3$-extraction imply that these elements are highly concentrated in the soils near the past uranium exploration region, coal seams, black slate beds and tailings than other parts of the study area. The proportions of the day in most soils are less than 10%. In spite of small proportions of the clay, the concentrations of heavy metals from clay fractions to the total concentrations are high: 1~2.4 times for Co, 1.4~2.5 for Cu, 1.2~2.6 for Ni, 1~5 for Pb, 1~2.7 for Zn and 1.6~1.8 for Cr and V. The contents of organic carbons in clay fractions are also 1.5~3.9 times higher than in silt and sand fractions. Cu, Pb and organic carbons show positive relationship in all size fractions. In the size-fractionated soil profile samples, the contents of heavy metals and organic carbons show analogous trends with depth. For the clay fractions of soil profile samples, the contents of heavy metals with depth have analogous trends to abundances of vermiculites, which have the high CEC in main clay minerals.