Quantifying the impact of mineralogical heterogeneity on reactive transport modeling of CO_(2)+O_(2) in-situ leaching of uranium

CO_(2)+O_(2) in-situ leaching(ISL)of sandstonetype uranium ore represents the third generation of solution mining in China.In this study,reactive transport modeling of the interaction between hydrodynamic and geochemical reactions is performed to enable better prediction and regulation of the CO_(2)+O_(2) in-situ leaching process of uranium.Geochemical reactions between mining solutions and rock,and the kinetic uranium dissolution controlled by O_(2)(aq)and bicarbonate(HCO_(3)-)are considered in the CO_(2)+O_(2) ISL reactive transport model of a typical sandstone-hosted uranium ore deposit in northern China.The reactive leaching of uranium is most sensitive to the spatial distribution of the mineralogical properties of the uranium deposit.Stochastic geostatistical models are used to represent the uncertainty on the spatial distribution of mineral grades.A Monte Carlo analysis was also performed to simulate the uranium production variability over an entire set of geostatistical realizations.The ISL stochastic simulation performed with the selected geostatistical realizations approximates the uranium production variability well.The simulation results of the ISL reactive transport model show that the extent of the uranium plume is highly dependent on mineralogical heterogeneity.The uncertainty analysis suggests the effect of uranium grade heterogeneity was found to be important to improve the accurate capture of the uncertainty.This study provides guidance for the accurate simulation and dynamic regulation of the CO_(2)+O_(2) leaching process of uranium at the scale of large mining areas.

Factors influencing in-situ leaching of uranium mining in a sandstone deposit in Shihongtan, Northwest China

The Shihongtan uranium deposit in northwest China is a sandstone-type deposit suitable for alkaline in-situ leaching exploitation of uranium. Alkaline leaching tends to result in CaCO3 precipitation there by affecting the porosity of the ore-bearing aquifer. CaCO3 deposits can also block pumping and injection holes if the formulation parameters of the leaching solution are not well controlled. However, controlling these parameters to operate the in-situ leaching process is challenging. Our study demonstrates that the dissolved uranium concentration in the leaching solution increases as HCO3-concentration increases. Therefore, the most suitable HCO3-concentration to use as leaching solution is defined by the boundary value of the HCO3-concentration that controls CaCO3 dissolution-precipitation. That is, the dissolution and precipitation of calcite is closely related to pH, Ca2+ and HCO3-concentration. The pH and Ca2+ concentration are the main factors limiting HCO3-concentration in the leaching solution. The higher the pH and Ca2+ concentration, the lower the boundary value of HCO3-concentration, and therefore the more unfavorable to in-situ leaching of uranium.

Improved uranium leaching efficiency from low-permeability sandstone using low-frequency vibration in the CO_(2)+O_(2) leaching process

Extraction of uranium from low-permeability sandstone is a long-standing challenge in mining.The improvement of sandstone permeability has therefore become a key research focus to improve the uranium leaching effect.To address the low-permeability problem and corresponding leaching limits,leaching experiments are performed using newly developed equipment that could apply low-frequency vibration to the sandstone samples.The test results indicate that low-frequency vibration significantly improves the uranium leaching performance and permeability of the sandstone samples.The leaching effect of low-frequency vibration treatment is approximately nine times more effective than ultrasonic vibration treatment,whereas the concentration of uranium ions generated without vibration treatment is not detectable.Mathematical model that considers the combined action of physico-mechanical vibration and chemical erosion is established to describe the effect of low-frequency vibration on the permeability.The calculated results are in good agreement with the tested permeability values.This study thus offers a new method to effectively leach more uranium from low-permeability sandstone using CO_(2)+O_(2)and provides an insight into the impact of low-frequency vibration on the uranium leaching process.

Pyrite Oxidation in Leaching Process ofRadionuclides and Heavy Metals fromUranium Mill Tailings

Pyrite is a sensitive mineral in the geological environment, and its oxidation produces an important geochemical and environmental effect on the control of the redox and pH conditions. Column experiment results were used for modeling the geochemical processes in uranium mill tailings under leaching conditions. Oxidation of pyrite dominates the control of the tailings leaching process. The experimental and modeling results show that the leachate chemistry changes substantially with the decrease in pyrite consumption. In the initial stage of the leaching experiment, the pyrite is consumed several hundred times greater than that in the later stages, for much more oxygen is present in the tailings in the initial stage. As the experiment continues, the tailings is gradually saturated with water and the oxygen concentration greatly decreases and so does pyrite consumption. The experimental and modeling results are useful for the design of mill tailing decommissioning: oxidation process and transport of radioactive nuclides and heavy metals can be constrained by controlling the oxygen concentration of tailings and the infiltration of meteoric water.

Assessment of the Greenhouse Gas Footprint and Environmental Impact of CO_(2)and O_(2)in situ Uranium Leaching

Under the new development philosophy of carbon peaking and carbon neutrality,CO_(2)and O_(2)in situ leaching(ISL)has been identified as a promising technique for uranium mining in China,not only because it solves carbon dioxide utilization and sequestration,but it also alleviates the environmental burden.However,significant challenges exist in assessment of CO_(2)footprint and water-rock interactions,due to complex geochemical processes.Herein this study conducts a three-dimensional,multicomponent reactive transport model(RTM)of a field-scale CO_(2)and O_(2)ISL process at a typical sandstone-hosted uranium deposit in Songliao Basin,China.Numerical simulations are performed to provide new insight into quantitative interpretation of the greenhouse gas(CO_(2))footprint and environmental impact(SO_(4)^(2–))of the CO_(2)and O_(2)ISL,considering the potential chemical reaction network for uranium recovery at the field scale.RTM results demonstrate that the fate of the CO_(2)could be summarized as injected CO_(2)dissolution,dissolved CO_(2)mineralization and storage of CO_(2)as a gas phase during the CO_(2)and O_(2)ISL process.Furthermore,compared to acid ISL,CO_(2)and O_(2)ISL has a potentially smaller environmental footprint,with 20%of SO_(4)^(2–)concentration in the aquifer.The findings improve our fundamental understanding of carbon utilization in a long-term CO_(2)and O_(2)ISL system and provide important environmental implications when considering complex geochemical processes.

Remediation of in-situ Leach Mining Contaminated Soil by Amendment-plant Synergism

This study aimed to remediate in-situ leach mining contaminated soil by amendment-plant synergism. The results showed that plant species exhibited ex-tremely significant effects on the concentration of nitrate nitrogen; to be specific, the concentration of nitrate nitrogen in soil planted with wheat was reduced from 692.19 mg/kg to lower than 100 mg/kg; when the mass ratio of amendment to soil reached 3：50 and the amendment particle size was 1-2 mm, the concentration of nitrate ni-trogen in soil planted with wheat was reduced to 43 mg/kg. The amendment type exhibited extremely significant effects on the concentration of ammonium nitrogen; to be specific, when the mass ratio of amendment to soil reached 10：50, the concen-tration of ammonium nitrogen in soil added with 2-3 mm zeolite was reduced from 23 593.75 to 3 300 mg/kg on day 15. Amendments and plants mainly exhibited desorption performance for sulfate radical in soil, and the amendment type extreme-ly significantly affected the concentration of sulfate radical; to be specific, the con-centration of sulfate radical in soil added with limestone increased from 370 mg/kg to 900 mg/kg on day 7.

In-situ Chemical Age of the Sandstone-hosted Uranium Deposit in Ningdong Area on the Western Margin of the Ordos Basin, North China

Objective The Ordos Basin located in the westem part of the North China Craton bears various energy resources such as oil, gas, coal and uranium. It is one of the richest uranium-bearing basins in China. Since the discovery of the large-scale Dongsheng, Hangjinqi and Daying uranium deposits in the north of the Ordos Basin, a new breakthrough of uranium exploration has been achieved in the Ningdong area （eastern Ningxia） on the western margin of the Ordos Basin （WMOB） in the past two years （Wang Feifei et al., 2017）.

基于COMSOL+PHREEQC耦合数值模拟的浸出试验--以内蒙古某铀矿浸出工艺试验为例

室内浸出工艺试验是联系科研和工业生产的必要环节,针对可地浸砂岩型铀矿浸出工艺室内试验条件与工业生产条件不同、物理试验组数多、矿岩采取困难等问题,提出了一套基于COMSOL+PHREEQC耦合的地浸采铀柱浸数值模拟模型构建方法,并以内蒙古某铀矿浸出室内试验(物理试验)为例,开展了物理试验与数值模拟试验对比研究。结果表明:采用基于COMSOL+PHREEQC耦合的数值模拟法,在酸法浸出室内柱浸试验模拟方面,具有良好的可行性;相同压力条件下,pH、U、Fe^(3+)、Ca^(2+)、SO_(4)^(2-)等溶出组分的浸出规律基本一致,峰值出现的时间相对较吻合;不同压力条件下,数值模拟模型的结果符合压力调节情况下的一般规律;所建数值模拟模型在U、Ca^(2+)浓度峰值大小方面尚存在差异,需要进一步完善模拟模型。

Enhancing the electrocatalytic performance of nitrate reduction to ammonia by in-situ nitrogen leaching

Electrochemical nitrate reduction reaction (NITRR) is regarded as a “two birds-one stone” method for the treatment of nitrate contaminant in polluted water and the synthesis of valuable ammonia, which is retarded by the lack of highly reactive and selective electrocatalysts .Herein, for the first time, nickel foam supported Co_(4) N was designed as a high-performance NITRR catalyst by an in-situ nonmetal leaching-induced strategy.At the optimal potential, the Co_(4) N/NF catalyst achieves ultra-high Faraday efficiency and NH_(3) selectivity of 95.4% and 99.4%, respectively.Ex situ X-ray absorption spectroscopy (XAS), together with other experiments powerfully reveal that the nitrogen vacancies produced by nitrogen leaching are stable and play a key role in boosting nitrate reduction to ammonia.Theoretical calculations confirm that Co_(4) N with abundant nitrogen vacancies can optimize the adsorption energies of NO_(3)^(-) and intermediates, lower the free energy (Δ G ) of the potential-determining step (*NH_(3) to NH_(3) ) and inhibit the formation of N-containing byproducts.In addition, we also conclude that the nitrogen vacancies can stabilize the adsorbed hydrogen, making H_(2) quite difficult to produce, and lowering ΔG from *NO to *NOH, which facilitates the selective reduction of nitrate.This study reveals significant insights about the in-situ nonmetal leaching to enhance the NITRR activity.

2D电法监测地浸采铀溶浸剂运移过程探讨

为提高砂岩型铀矿地浸开采效率,需要掌握注入含矿层的溶浸剂溶浸范围,但目前铀矿山还没有高效的观测手段。酸法溶浸剂的主要组分是硫酸,其浓度高达15 g/L,会显著改变含矿层中地下水电阻率。电法勘探对地下介质电阻率变化反应灵敏,为溶浸剂运移观测提供了可能。以我国内蒙古某酸法地浸铀矿为背景,通过数值算例,探讨双偶极、温纳、施伦贝尔三种高密度电阻率装置探测因硫酸运移产生电性异常区域,并通过电性异常区域反向圈定硫酸的溶浸区域。结果表明,三种装置均能够观测到100 m深度因溶浸剂运移产生电性变化区域的视电阻率响应,其中双偶极装置的观测效果和圈定效果最好,其反演结果能够较好地划分电性异常区域的左右边界,60 d后的反演低电阻异常区域面积与对应时刻溶浸区域面积较为吻合。井测线观测装置对地下电阻率变化的灵敏度要高于纯地表测线观测方式,但成本也更高。

Constraints on granite-related uranium mineralization in the Sanjiu uranium ore field,SE China provided by pyrite mineralogy,major and trace elements,S-He-Ar isotopes

The Sanjiu uranium ore field,located in the central of Zhuguangshan granitic batholith,is a newly discovered granite-related uranium ore field in South China.The main sulfide in the ore field is pyrite,which is closely related to uranium mineralization.The textures major and trace elements,S-He-Ar isotopes compositions of pyrites in ores of different grade were observed and/or analyzed by optical microscope,scanning electron microscope,electron microprobe,laser ablation inductively coupled plasma mass spectrometry,and noble gas mass spectrometer(Helix-SFT).It is observed that these U-related pyrites are generally euhedral-subhedral with dissolution textures,anhedral variety with colloform texture veinlet and fine particles,and the color of the associated minerals is mostly dark hue,such as purple-black fluorite dark-red hematite,and dark-green chlorite,etc.The analytical results show that the average compositions of major elements in pyrite are FeS1.944.Pyrites are characterized by S-deficiency,low content of Co and Th,and Co/Ni>1which indicate that these ores are of low-temperature hydrothermal origin.We found that the higher the grade of ore,the more deficient in S,the more obvious negative δ^34S,and the higher REE content(close to U-rich granitic pluton)of pyrite.The S-He-Ar isotopic compositions of various varieties of pyrites indicate that the ore-forming fluids mainly come from crust-derived fluids and mixed with mantle-derived fluids.

Uraniferous Black Shale and Related Uranium Mineralization Features in South China

Black shales are marine sediments with argillaceous, silty and siliceous compositions and high contents of organic materials, disseminated pyrite and uranium. Uraniferous black shale has uranium content of more than 20 ppm.

Removal of SO_4^(2-),uranium and other heavy metal ions from simulated solution by sulfate reducing bacteria

在在原处铀沥滤的情况中，自从 leachant 被注入忍受铀沉积物的水，为地下水的原始 geochemical 环境被改变。这增加 SO42 的集中 ? ，在地下水污染的铀和另外的重金属离子和结果。SO42 的减小上的模仿的解决方案的 pH 值的效果？并且由减少细菌(SRB ) 的硫酸盐的铀和另外的重金属离子的移动被学习。结果看那模仿的答案的 pH 价值是否是大约 8， SO42 的减小率吗？由 SRB 和铀的移动率， Mn2+ ， Zn2+ ， Pb2+ 和 Fe2+ 将到达他们的最高的价值。为在在原处沥滤的地下水的补习的一种 bioremediation 技术铀矿能被开发。

Development and Prospect of China Uranium Mining and Metallurgy

The development of industry of uranium mining and metallurgy in China has been reviewed generally,emphasizing on investigation approaches and application levels of uranium mining technologies such as in-situ leaching,heap leaching,stope leaching:on the basis of analysis on status of uranium mining and metallurgy and problems existed,also considering the specific features of deposit resources,the development orientation of uranium mining and metallurgy in China is pointed out.The industry of China uranium mining and metallurgy is faced to new opportunity of development and challenge in 21st century,the only way to realize sustainable development of uranium mining and metallurgy and harmonious development between economy and environment is to develop new technology on mining,ore beneficiation and metallurgy,increase the utilization level of uranium resources,low down impact on environment caused by mining and metallurgy.

独居石优溶渣浸出过程研究

独居石是典型伴生铀、钍的稀土矿资源,通过现有的碱溶转化、优溶等步骤提取稀土后,所得优溶渣是富含铀、钍、稀土的重要二次资源。为与稀土提取保持一致的盐酸体系,研究优溶渣的盐酸浸出过程对整体回收工艺十分关键。采取单因素试验考察浸出过程条件对铀、钍、稀土浸出率的影响。结果表明,使用下述优化参数:盐酸浓度6 mol/L、浸出时间1.5~2 h、浸出温度60℃、液固体积质量比3 mL/g时,优溶渣中铀、钍、稀土的浸出率分别可达90%~95%、92%~93%、>60%,实现了较高的资源回收率。浸出渣的工艺矿物学分析表明,其主要由锆石、钍化合物和石英等脉石矿物组成。剩余的稀土组分则主要集中在未分解的独居石中,其余为少量磷钇矿和褐钇铌矿。试验结果可为独居石优溶渣的综合回收技术提供基础数据和支撑。

地浸采铀注液井小直径潜水泵抽水洗井试验

某地浸采铀试验采区注液井周边含矿层堵塞严重。注液井套管内径仅有80 mm,在常规空压机抽水洗井结束后,在3口注液井中开展了小直径潜水泵抽水洗井试验。初始抽水量均在4.5 m_(3)/h左右,期间最小抽水量为3.4 m_(3)/h,其中2口井的第1股最浑浊洗井水的含砂量分别为4.36、5.19 kg/m_(3)。粒度、电镜扫描和化学组成分析显示,洗井水沉降干渣中的矿物碎屑主要为粉砂、细砂碎屑,少量黏土碎屑;化学沉淀主要是CaCO_(3)、MgCO_(3)和FeCO_(3);潜水泵抽水洗井累计运行约27.5 h,未出现任何故障。试验表明,小直径潜水泵抽水洗井可行且投资少、成本低、安全性高、实施方便。

内蒙古芒来铀矿石酸法柱浸试验

为获得溶浸液在不同硫酸质量浓度条件下的铀浸出特征及试验参数,探究内蒙古芒来铀矿床矿石酸法浸出的可行性,开展了不同硫酸质量浓度(5、10、15、20 g/L)的溶浸液下室内柱浸浸铀试验。试验结果表明,随着溶浸液硫酸质量浓度的增高,浸出液铀质量浓度及铀浸出率随之增高,浸出周期缩短,故酸法工艺适合该矿床铀浸出。试验后期浸出液流量降低与长石类矿物的黏土化蚀变有关。针对铀平均品位为8.8×10^(-5)的矿石,铀浸出率为49.80%~54.35%,从浸出率、防堵塞及浸铀成本等方面综合分析,认为质量浓度为10 g/L的硫酸溶浸液较适合该铀矿酸法地浸开采。

某独居石优溶渣二段逆流浸出试验研究

针对某独居石优溶渣,研究了采用一段常规浸出—二段逆流浸出工艺浸出铀、钍、稀土。考察了各因素对浸出效果的影响。结果表明:采用一段常规浸出法时,适宜条件下的铀、钍、稀土浸出率分别为98.66%、95.37%、64.23%;采用二段逆流浸出法时,铀、钍、稀土浸出率均可提高0.5%~1.0%,浸出液余酸降低50%以上,矿浆固液分离性能得到了一定改善。