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Haque, N., & Norgate, T. (2014). The greenhouse gas footprint of in-situ leaching of uranium, gold and copper in Australia. Journal of Cleaner Production, 84, 382–390.
Abstract: In-situ leaching (ISL) is a chemical method for recovering useful minerals and metals directly from underground ore bodies which is also referred to as ‘solution mining’. ISL is commonly used for uranium mining, accounting for about 45% of global production. The main benefits are claimed to be a lower environmental impact in terms of visual disturbances, emissions, lower energy use, cost compared with conventional open-cut or underground mining methods, and potential utilisation of lower grade resources. However, there is a lack of reported studies on the assessment of the environmental impacts of ISL, particularly greenhouse gas (GHG) emissions using life cycle assessment (LCA) methodology. The SimaPro LCA software was used to estimate the GHG footprint of the ISL of uranium, gold and copper. The total GHG emissions were estimated to be 38.0 kg CO2-e/kg U3O8 concentrate (yellowcake), 29 t CO2-e/kg gold, and 4.78 kg CO2-e/kg Cu. The GHG footprint of ISL uranium was significantly lower than that of conventional mining, however, the footprints of copper and gold were not much less compared with conventional mining methods. This is due to the lower ore grade of ISL deposits and recovery compared with high ore grades and recovery of conventional technology. Additionally, the use of large amount of electricity for pumping in case of ISL contributes to this result. The electricity consumed in pumping leaching solutions was by far the greatest contributor to the well-field related activities associated with ISL of uranium, gold and copper. The main strategy to reduce the GHG footprint of ISL mining should be to use electricity derived from low emission sources. In particular, renewable sources such as solar would be suitable for ISL as these operations are typically in remote locations with smaller deposits compared with conventional mining sites.
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Qiu, W., Yang, Y., Song, J., Que, W., Liu, Z., Weng, H., et al. (2023). What chemical reaction dominates the CO2 and O2 in-situ uranium leaching?: Insights from a three-dimensional multicomponent reactive transport model at the field scale. Applied Geochemistry, 148, 105522.
Abstract: The complex behavior of uranium in recovery is mostly driven by water-rock interactions following lixiviant injection into ore-bearing aquifers. Significant challenges exist in exploring the geochemical processes responsible for uranium release and mobilization. Herein this study provides an illustration of a ten-year field scale CO2 and O2 in-situ leaching (ISL) process at a typical sandstone-hosted uranium deposit in northern China. We also conducte a three-dimensional (3-D) multicomponent reactive transport model to assess the effects of potential chemical reactions on uranium recovery, in particular, to focus on the role of sulfide mineral pyrite (FeS2). Numerical simulations are performed considering three potential ISL reaction pathways to determine the relative contributions to uranium release, and the results indicate that bicarbonate promotes the oxidative dissolution of uranium-bearing minerals and further accelerates the uranium leaching in a neutral geochemical system. Moreover, the presence of FeS2 exerts a strong competitive role in the uranium-bearing mineral dissolution by increasing oxygen consumption, favoring the formation of iron oxyhydroxide, and therefore causing an associated decrease in uranium recovery rates. The simulation model demonstrates that dissolution of carbonate neutralizes acidic water generated from pyrite oxidation and aqueous CO2 dissociation. In addition, the cation concentrations (i.e., Ca and Mg) are increasing in the pregnant solutions, showing that the recycling of lixiviants and kinetic dissolution of carbonate generates a larger number of dissolved Ca and Mg and inevitably triggers the secondary dolomite mineral precipitation. The findings improve our fundamental understanding of the geochemical processes in a long-term uranium ISL system and provide important environmental implications for the optimal design of uranium recovery, remediation, and risk exposure assessment.
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YI, Z. -ji, LIAN, B., YANG, Y. -qun, & ZOU, J. -ling. (2009). Treatment of simulated wastewater from in situ leaching uranium mining by zerovalent iron and sulfate reducing bacteria. Transactions of Nonferrous Metals Society of China, 19, 840.
Abstract: Batch and column experiments were conducted to determine whether zerovalent iron (ZVI) and sulfate reducing bacteria (SRB) can function synergistically and accelerate pollutant removal. Batch experiments suggest that combining ZVI with SRB can enhance the removal of U(?) synergistically. The removal rate of U(?) in the ZVI+SRB combining system is obviously higher than the total rate of ZVI system and SRB system with a difference of 13.4% at t=2 h and 29.9% at t=4 h. Column experiments indicate that the reactor filled with both ZVI and SRB biofilms is of better performance than the SRB bioreactor in wastewater basification, desulfurization and U(?) fixation. The results imply that the ZVI+SRB permeable reactive barrier may be a promising method for treating subsurface uranium contamination.
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Zhou, Y., Li, G., Xu, L., Liu, J., Sun, Z., & Shi, W. (2020). Uranium recovery from sandstone-type uranium deposit by acid in-situ leaching – an example from the Kujieertai. Hydrometallurgy, 191, 105209.
Abstract: The factors influencing uranium recovery in water-rock systems during acid in-situ leaching (ISL) were studied at the Kujieertai uranium deposit in Xinjiang. Using an ISL unit, a field leach trial (FLT) had been carried out to test the sequential effects of a leaching solution without oxidant (H2SO4 solution 4–8 g/L) and a leaching solution with oxidant (H2SO4 3–7 g/L, and Fe (III) 2–6 g/L). The observation of the leaching process revealed clearly defined stages of uranium release from the solid mineral to solution. Uranium mobilization from solid mineral into solution can be described in four stages. At the beginning of the acid ISL process, there was no oxidant to be added to the leaching solution and the desorption of hexavalent uranyl ions in the open pores, as well as dissolution of hexavalent uranium minerals, led to a short-term peak in the pregnant solution, which happened while pH decreased from about 5.3 to 2.62. Following the depletion of the adsorbed hexavalent uranium and a decline in uranium dissolution intensity, the addition of Fe(III) facilitated the oxidation of tetravalent uranium, which enabled intensive uranium mobilization again. During this process, the dissolution of uranium had a strong positive correlation with the reduction of Fe(III) and Eh in the leach solution. Beside hydrochemical factors, the deportment of uranium was also an important factor affecting uranium recovery. Uranium located in the open pores can be completely exposed to the solution and the mobilization intensity was significantly affected by hydrogeochemical conditions; but the uranium present in microfissures and in the ore matrix could not be fully exposed to the solution, so, their dissolution intensity was primarily controlled by corrosion and permeability of the ore. In general, the hydrogeochemical conditions and the deportment of uranium were the external and internal factors that significantly affected the dissolution and recovery of uranium in the early and middle stages of the FLT. However, in the latest stages, due to uranium depletion, enhancing the chemical potential of the leaching solution, specifically acidity and/or the amount of oxidant, had little improvement on uranium recovery.
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Pastukhov, A. M., Rychkov, V. N., Smirnov, A. L., Skripchenko, S. Y., & Poponin, N. A. (2014). Purification of in situ leaching solution for uranium mining by removing solids from suspension. Minerals Engineering, 55, 1–4.
Abstract: This study investigated the process of in situ leaching (ISL) method of uranium mining, and the removal of solid particles from the leaching solution. Investigations were carried out for 4months. The content of firm suspensions in the productive solutions arriving from the well field was up to standard of 3–5mg/l. After keeping in a settler of productive solutions within one hour concentration of suspensions decreases to 2–2.5mg/l. To increase the life of the wells requires more fine purification of the ISL solutions. The best results can be obtained but using filtration. Bag filters were used in experiments carried out at the extraction site. All samples of polypropylene bag filter was produced by the Tamfelt Corporation. The best results were obtained for fabrics S-51M03-L2K4 (pore size 3μm). After three month of trials following indicators of wells work were fixed: on the trial cell decrease in intake capacity did not occur; on the other cells of well field injectability of holes for the same period of time decreased for 15–40%. The results illustrated the high efficiency of this method, which allows injection wells to reach a constant intake capacity, making it possible for technological cells to achieve a constant productivity and balance. Purification of solutions allows to reduce acidulation term of new technological cells from 3–4 to 1.5–2months.
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