In-situ leaching (ISL) causes non-negligible groundwater pollution. It is urgent to remediate the groundwater after ISL activities. In this study, we evaluated the effectiveness of flow electrode capacitive deionization (FCDI) to treat a simulated groundwater, the uranium (U) and SO42− concentration of which are comparable to groundwater in acid in-situ leaching (AISL) uranium mine for the first time. Moreover, the removal mechanism of U and SO42− were investigated in-depth. It is found that the operational mode, applied voltage and initial SO42− concentration significantly affect the removal of U and SO42− by FCDI. The removal efficiency of U and SO42− were above 98 % at 75 min under optimal condition, although U in groundwater mainly existed in the form of uncharged UO2(SO4), followed by UO22+ and UO2(SO4)22−. UO22+ and UO2(SO4)22− in groundwater migrated into the two poles and were quickly absorbed by flow electrode, which promoted the dissociation of UO2(SO4) or complexation of UO2(SO4) with SO42−. In addition, the anion exchange membrane can absorb UO2(SO4) through complexation. These resulted in the efficient removal of U(VI). FCDI can reduce the U and SO42− concentration of the contaminated water (CU = 10 mg L−1, CSO42− = 5 g L−1) to a value lower than the Chinese emission limit (U: 300 μg L−1; SO42−: 250 mg L−1) even after 18 cycles with each cycle operated for 120 min, which informed that FCDI system using activated carbon is of great potential for acidic contaminated water treatment.

The use of household waste -derived materials for wastewater treatment has double environmental benefit due to the availability of simultaneous disposal of household waste and wastewater. In this work, we report the facile production of phosphorus -rich carbon from waste paper as a potential adsorbent for the disposal of uranium (VI)containing nuclear wastewater. A simple phosphoric acid activation -carbonization strategy is developed to effectively transform waste paper into carbon. The phosphorus content of the obtained carbon reaches 8.55 at% and large pores with sizes ranging from 2 to 100 nm are observed. Batch and column adsorption experiments verify that waste paper -derived carbon can efficiently adsorb uranium (VI) from aqueous solution under weakly acidic conditions. The maximum amount of uranium adsorption on the carbon attains 492 mg g -1 at pH 4.6, and adsorption of uranium (VI) on the carbon quickly reaches the equilibrium within 20 minutes. The distribution coefficient of uranium (VI) on waste paper -derived carbon is as high as 128 L g -1 . The carbon can be reused for five times with uranium (VI) adsorption efficiencies above 89% and can be used for dynamic adsorption of uranium (VI) in a fix -bed column. Kinetics, thermodynamics and DFT calculations reveal a surface complexation mechanism between uranium (VI) ion and ionized phosphoric acid group. Moreover, to avoid the generation of secondary polluted water during the treatment of uranium -containing nuclear wastewater, a water -saving method is developed for the adsorption preparation and a water -free combustion method is employed for the disposal of uranium -containing spent adsorbent instead of recycling. This study demonstrates the good application potential of household waste -derived materials in wastewater treatment and provides more clues for the amalgamation of multifold subjects.

In this study, the groundwater hydrodynamics of two adjacent well sites were simulated under different pumping-injection ratios. The aim is to select an optimal pumping-injection ratio that can ensure the groundwater of the two well sites don't affect each other. In addition, the sulfur isotope composition of groundwater in the two well sites were analyzed to verify the simulated results. The results show that the flow velocity at different points outside the edge drilling hole decreases exponentially with the distance between the point and the edge hole. The streamline gradually extends outside of the borehole with the increase of leaching time. It is found that the optimal pumping-injection ratio is 1.003. In this case, the maximum distance between the moving front and the injection borehole is 28.44 m after leaching for 5 years. This indicates that the groundwater flow fields of the two well sites are well controlled. The significant difference in sulfur isotopes between the two well-sites further proves that the SO42- in the acid mining zone does not affect the groundwater in the zone leached by CO2+O-2.

Driven by the global imperative for the geological disposal of high-level radioactive waste (HLW), notable progress has been made in predicting radionuclide transport within fractured rocks. Current research has recognized that the presence of colloids may significantly influence radionuclide transport. However, challenges remain in understanding and quantifying this process from a multi-scale perspective. This review provides a comprehensive overview of recent developments in understanding the role of colloids in facilitating radionuclide transport in multi-scale fractured rocks. We first revisit the fundamental characteristics and processes controlling the transport of colloids and radionuclides in fractured rocks, including the properties of fractured rocks, colloids, and radionuclides, as well as their complex interactions. Furthermore, we discuss recent advancements in lab- and field-scale experiments and modeling techniques that shed light on the mechanisms controlling colloid-facilitated radionuclide transport. The focus then shifts to scaling issues, including scale-dependent transport processes and parameters, as well as the upscaling theories that bridge the gap between lab-scale experiments and field-scale assessments. Finally, we identify unresolved problems and promising development trends in colloid-facilitated radionuclide transport, which offer new opportunities for enhancing the accuracy of long-term safety assessments in HLW geological repositories.

Numerous field observations show that the channels in one fracture are narrow and the solute penetration depth might be larger than the width. For this case, the diffusion from a channel into the matrix is more realistic to be modeled as radial diffusion than one-dimensional. In present work, the single channel model with radial diffusion is revisited and a simple and robust analytical solution is developed. This solution takes a convolution form of two functions, in which different transport mechanisms are accounted for. The statistical interpretations of the two functions and the analytical solution aid to develop a simple Time Domain Random Walk (TDRW) algorithm and an extension is made to improve its accuracy, efficiency and applicability. To demonstrate the accuracy and efficacy of the extended algorithm, three groups of simulations are performed and it is found that the results of all approaches are identical. The TDRW algorithm, having the same performance as that of inverse Laplace transform solution, is superior to Gaussian quadrature method in computational time. However, due to Monte Carlo nature of the algorithm, the computational burden of TDRW algorithm is dependent on the number of particles applied, which also influences the calculation accuracy. Therefore, a trade-off between computational burden and calculation accuracy should always be made, once the TDRW algorithm is used.

For the disposal of high-level radioactive waste (HLW), the deep geological disposal is recognized as an effective method. The distribution coefficient (Kd) of radionuclides on buffer/backfill materials or host rock is one of the key parameters used in the safety assessment of geological repository. 137Cs is one of the high-yield (t1/2 = 30.1 y, 6%) fission products in spent fuels, its high solubility makes it likely to migrate through groundwater to the biosphere. Multibarrier system prevents leakage of radionuclides to the environment. The present review discusses the general mechanisms of cesium adsorption by minerals, elaborates the parameters which influence adsorption of cesium contain concentration of cesium, pH, humic acid, competitive cations and properties of minerals. Furthermore, we have collected the Kd values from cesium adsorption studies concerned with the minerals conducted during the past two decades, and analyzed by the probabilistic modelling to obtain the best-estimated Kd values of Cs adsorption on bentonite, granite and clay under different solution conditions.

In recent years, Capacitive Mixing (CapMix) has garnered growing interest as a novel method for harnessing energy from the salinity gradient between seawater and freshwater. However, the challenge of extracting energy in a continuous way remains to be solved in traditional CapMix system. In this study, we demonstrate the feasibility of achieving continuous energy extraction through the use of a two-cell flow electrode Capacitive Mixing (F-CapMix) system. The performance of the F-CapMix system is evaluated under various experimental conditions including the activated carbon loading, carbon black additives, velocity of the flow electrode and feed water and external resistance in the circuit. The results suggest that the power density of the system can be significantly increased by approximately 800 % or 400 % with an increase in the carbon loading or the addition of carbon black additives, respectively. Meanwhile, reducing the flow rate of the flow electrode and feedwater from 20 mL/s to 5 mL/s was found to improve the system's performance. In addition, it is crucial that the external resistance is matched to the internal resistance of the cell for achieving a maximum power density. These results highlight the potential of F-CapMix and provide guidance for its further optimization.

Biotite is an important adsorption carrier in the constituent minerals of Beishan granite. In this work, the effects of compaction density and ionic strength on the diffusion behavior of Se(IV) and Re(VII) in biotite were studied by capillary in-diffusion method and diffusion cell through-diffusion method. When the compaction density decreases or the ionic strength increases, the apparent diffusion coefficient increases, and its values range between 10–11 and 10–9 m2/s. The relationship between De and εacc, ionic strength and εacc was fitted using Archie's law and compared with the parameters of other researchers.

Laboratory experiments and point monitoring of reservoir sediments have proven that stable sulfate reduction (SSR) can lower the concentrations of toxic metals and sulfate in acidic groundwater for a long time. Here, we hypothesize that SSR occurred during in situ leaching after uranium mining, which can impact the fate of acid groundwater in an entire region. To test this, we applied a sulfur isotope fractionation method to analyze the mechanism for natural attenuation of contaminated groundwater produced by acid in situ leaching of uranium (Xinjiang, China). The results showed that delta S-34 increased over time after the cessation of uranium mining, and natural attenuation caused considerable, area-scale immobilization of sulfur corresponding to retention levels of 5.3%-48.3% while simultaneously decreasing the concentration of uranium. Isotopic evidence for SSR in the area, together with evidence for changes of pollutant concentrations, suggest that area-scale SSR is most likely also important at other acid mining sites for uranium, where retention of acid groundwater may be strengthened through natural attenuation. To recapitulate, the sulfur isotope fractionation method constitutes a relatively accurate tool for quantification of spatiotemporal trends for groundwater during migration and transformation resulting from acid in situ leaching of uranium in northern China.

In this work, three variant Time Domain Random Walk (TDRW) algorithms were developed for the problem of solute transport in a single fracture-matrix system, where an arbitrary inlet boundary condition can be applied. One approach performs an additional evaluation of integral in terms of injection boundary and the solution to a Dirac delta case. One method makes use of two functions, dependent on specific boundary conditions, to estimate the particle arrival time. The other additionally introduces the concept of solute injection time, resulting from the injection boundary, into the calculation of particle arrival time. To validate the developed variant algorithms, two benchmark cases are considered with respect to a general Dirichlet injection mode and a Robin injection boundary, respectively. The results from three approaches all make a good agreement with those of inverse Laplace transform method. However, the Monte Carlo nature of the TDRW algorithm implies that the accuracy of the computational result is highly dependent on the number of particles applied in the simulation.