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.

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.

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.

An investigation of machine learning techniques to estimate minimum horizontal stress magnitude from borehole breakout

Borehole breakout is a widely utilised phenomenon in horizontal stress orientation determination,and breakout geometrical parameters,such as width and depth,have been used to estimate both horizontal stress magnitudes.However,the accuracy of minimum horizontal stress estimation from borehole breakout remains relatively low in comparison to maximum horizontal stress estimation.This paper aims to compare and improve the minimum horizontal stress estimation via a number of machine learning(ML)regression techniques,including parametric and non-parametric models,which have rarely been explored.ML models were trained based on 79 laboratory data from published literature and validated against 23 field data.A systematic bias was observed in the prediction for the validation dataset whenever the horizontal stress value exceeded the maximum value in the training data.Nevertheless,the pattern was captured,and the removal of systematic bias showed that the artificial neural network is capable of predicting the minimum horizontal stress with an average error rate of 10.16%and a root mean square error of 3.87 MPa when compared to actual values obtained through conventional in-situ measurement techniques.This is a meaningful improvement considering the importance of in-situ stress knowledge for underground operations and the availability of borehole breakout data.

不同结构地浸钻孔在新疆铀矿山的应用及运行效果评价

基于地浸采铀钻孔浸采效率问题,研发了新型开窗切割式钻孔;通过填砾式钻孔与开窗切割式钻孔的现场施工和溶浸效果对比,分析了两种钻孔结构的优缺点。研究表明,开窗切割式钻孔施工质量可控,钻孔运行稳定时间长,溶浸效果好,浸出液铀浓度上升快,回采率高。两种结构钻孔的对比使用,为地浸采铀矿山的开采提供了重要的理论依据与实践经验,开窗切割式钻孔有助于提高铀资源开发利用率。

Research of in-situ hydraulic test method by using double packer equipment

Double packer equipment for hydraulic test can be used to measure pressure of test zone directly, and it is frequently used to perform many kinds of hydraulic tests and take groundwater sample from borehole. The test method of this equipment mainly includes the test design, implementation, interpretation and synthetic analysis. By adopting the double packer equipment for hydraulic test, the parameter distribution of rock permeability along borehole can be acquired, as well as the connectivity, water conductivity and water bearing capacity of the disclosed structure and the chemical characteristics of the deep groundwater. It is a necessary method for the research and evaluation of the complex hypotonicity terrace site selection under geological conditions. This method is not only suitable for the geological disposal of high level radioactive waste, but also can be used in the site selection of underground facilities such as storage of petroleum and carbon dioxide. Meanwhile, it has a good application prospect in other hydrogeological investigation fields.

地浸采铀钻孔过滤器建造与过滤机理研究

系统研究了多种型式过滤器的过滤机理和效果。在假定颗粒为等粒圆球体且呈斜方体排列的前提下,计算得到砾石过滤器和陶粒贴砾过滤器的最小孔隙直径初始值分别为0.310、0.155 mm,因隔滤作用,孔隙直径随时间延长会逐步变小,过滤效果好;无砾料包网过滤器孔眼直径为0.180~0.270 mm,装配后直径大体一致,只有隔挡作用,过滤效果差。过滤器部位没有充填砾石或充填不密实的钻孔,孔壁可能会垮塌或掉砂,浸出液中夹带的碎屑偏多。压汞试验测试砂岩铀矿层中的最大孔喉直径为0.032 mm,所有过滤器对于失稳的粉砂黏土碎屑和化学沉淀物基本没有隔挡作用。

测井方法在地浸成井质量检测中的应用及建议

地浸采铀作为第三代铀矿采冶技术,在我国铀矿采冶领域有着举足轻重的地位。地浸钻孔作为地浸采铀的“咽喉”,其成井质量的好坏对地浸采铀技术能否成功应用起着至关重要的作用。对几种常用的钻井质量检测测井方法的概念、原理、用途及优缺点进行了介绍,并研究了这几种方法在内蒙古某铀矿实际检测钻孔质量的解释应用。研究结果表明:在钻井质量检测中单独使用某一种测井方法,在某些特定情况会产生偏颇或不足,但联合使用井温测井与密度测井方法则会弥补各自的不足,可以起到更加准确确定投砾界面、判断水泥胶结质量以及是否有串层现象和漏液现象发生的作用,同时还可以清晰判定过滤器的安装位置及工作状况等信息,对后续生产运行、资源判断以及孔位布置等工作具有明确的指向性。

Evaluating the fractionation of ion-adsorption rare earths for in-situ leaching and metallogenic mechanism

The fractionation of ion adsorption rare earths(IAREs) along the depth in a shaft of a deposit at Dajishan,Jiangxi, China was comparatively evaluated using the partition values(PVs) and relative fractionation values(RFVs) of the leached rare earths(REs). It is found that both PVs and RFVs can objectively reflect the migration and fractionation of REs, but RE content and abrasion pH could not. However, the RFVs can provide more information to quantitatively evaluating the migration and fractionation characteristics of REs along the selected direction and region than PVs could, which is of significance for designing the optimal procedures of in-situ leaching based on the determined flow direction of injecting solution. It is demonstrated that the migration of Ce, Pr, and Nd along the depth direction is inert, and that of REs post Sm and Y is active. Meanwhile, the migration of La shows region characteristics which is active in the upper and inert in lower region. More interesting, the dependence of RFVs on atomic number of REs displays a tetrad group variation trend. However, the fractionation of REs among clay minerals with different particle sizes is not evident, especially for the clay in the bottom region. These results indicate that the migration and fractionation of REs not only are dominated by the adsorption of their hydrated ions, but also rely on their hydrolysis tendency, which provide information for understanding the metallogenic mechanism of IAREs.

Surface reconstruction of Se-doped NiS_(2) enables high-efficiency oxygen evolution reaction

Surface reconstruction of electrocatalysts has been widely witnessed during the electrochemical processes.Here,NiS_(2),NiSe_(2), and Se doped NiS_(2)(Se-NiS_(2)) are fabricated for oxygen evolution reaction(OER) through a mild sulfuration and/or selenylation process of Ni(OH)_(2) supported on carbon cloth(CC).Through careful in-situ Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy,surface reconstruction of NiS_(2),NiSe_(2),and Se-NiS_(2) during the OER process has been revealed.A potentialdependent study shows that Se-NiS_(2) undergoes surface evolution at lower potentials and requires the lowest potential for conversion to NiOOH as a highly OER-active species,accompanied by the leaching of SO_(4)^(2-) and SeO_(4)^(2-) that can again be adsorbed on the catalyst surface to enhance the catalytic activity.Density functional theory(DFT) calculations confirm that Se-NiS_(2) is more susceptible to surface oxidation through the OER process.Therefore,Se-NiS_(2) exhibits outstanding OER activity and stability in alkaline conditions,requiring an overpotential of 343 mV at a current density of 50 mA cm^(-2).A novel insight is provided by our work in understanding the surface reconstruction and electrocatalytic mechanism of Ni-based chalcogenides.

地浸采铀钻孔场区氡致周边辐射环境影响研究

氡是铀矿采冶过程中释放的主要气载放射性流出物,地浸钻孔场区的氡释放主要来源于抽液孔,传统高斯模型对此类源项的适用性有限。用CFD方法建立大气扩散数学模型耦合求解,探究了实际地形、氡源项和2019年的气象数据下某典型地浸铀矿山钻孔场区及周边近地面核素氡的浓度分布特征,并由个人剂量年均分布数学模型计算得到其所致的公众年有效剂量。结果表明:地形和大气风速对钻孔场区氡的迁移扩散具有重要的影响,风速占主导作用,风速越大,氡浓度越小,低地势凹洼处易造成排放源附近氡的积聚,局部污染较重;近地面氡的分布范围主要受风速和风向频率的协同作用影响,且随风速和风频的增大而变大;氡浓度衰减速度与扩散距离呈正相关性,但钻孔场区各抽液孔排放氡浓度水平较低,对环境氡浓度贡献值较小,对周边环境和公众辐射影响较小,其所致的个人剂量均不大于0.0011 mSv·a^(-1)。研究结果可为地浸铀矿山钻孔场区布置和辐射安全距离的确定提供理论支持。

低承压水头条件下地浸钻孔施工与成孔工艺特征探讨

在砂岩矿床的地浸试验和生产中,含矿含水层地下水承压水头很低时,地浸钻孔的开拓难度很大且工艺复杂。由于钻孔泥浆冲洗液的加入,使地层压力失衡。如何减少冲洗液对地层的扰动,防止冲洗液漏失;钻孔施工后采用何种有效的洗孔方法,以恢复含矿含水层的原始渗透性,成为低承压水头条件下地浸工艺钻孔施工和成孔的主要问题。

某铀矿地浸采铀钻孔施工中缩径卡钻原因分析及解决措施

针对某砂岩铀矿床地浸采铀钻孔过程中发生的缩径卡钻事故,分析钻孔施工中缩径和卡钻的原因,根据工程现场的地质条件和施工技术水平,结合地浸工艺钻孔施工特点,提出了改进施工技术、调整泥浆配比、配置大功率泥浆泵、减少施工间断时间等解决措施。实践验证明,这些措施能够有效地控制钻孔缩径卡钻事故的发生。

地浸采铀钻孔过滤器对溶液渗流影响的数值模拟

为提高矿体薄、矿砂比小的砂岩型铀矿地浸溶液工作效率,采用数值模拟方法对钻孔过滤器影响溶液在矿层和围岩的流量分布进行了计算,以优化钻孔结构。结果表明,钻孔过滤器向围岩延伸方向及长度,是影响地浸溶液渗流分布的重要因素;采用抽、注孔过滤器分别自矿层向下围岩和上围岩延伸的结构,可以有效增加溶浸液流经矿层的比例;过滤器延伸长度以2～3 m为宜,处于高位的注液孔过滤器延伸长度可略小于低位注液孔,有利于不同方向的均衡浸出。

物探测井技术在地浸采铀钻孔中的应用

针对物探综合测井资料利用率较低,岩层精细划分不够;矿体品位低、厚度大、铀矿石浸出周期短、浸出率低等在地浸采铀过程中存在的问题,提出了岩矿层精细划分与综合测井技术、过滤器长度与电磁流量测井技术、低品位铀矿石浸出与中子测井技术的研究思路,为地浸采铀工程设计和优化提供参考。

投球式机械-液压逆向灌注器的研制

投球式机械 液压逆向灌注器是利用注浆产生的压力,通过投球方式,实现机械位移控制,在地浸钻孔内完成逆向灌浆的封孔操作,并保证其良好的机械性能、工艺性能,和良好的可操作性。

地浸工艺钻孔中的施工技术

地浸工艺钻孔施工方法是地浸采铀的关键技术之一,在钻孔施工设计、孔斜偏离、套管接头密封、钻孔封孔以及洗孔方面尚存在许多问题,从施工技术管理的角度应予以规范和监督,以期保证钻孔的质量。

地浸采铀钻孔套管壁厚的讨论

集国内外地浸采铀套管应用的经验,讨论了地浸采铀钻孔套管的作用,套管壁厚对套管受力的影响,薄壁套管的优势及应用,并对我国开展薄壁套管的试验与应用提出具体的看法。

中国地浸采铀钻孔施工与成井技术研究进展

随着中国地浸采铀矿山生产和建设能力的提升,中国开展了新型钻机、逆向注浆技术、贴砾式可更换过滤器、洗井水综合处理与回收和废弃钻井液无害化处理技术的研发和实践。这些技术的研发和应用,提升了中国地浸采铀钻孔施工和成井的技术水平,加快了施工进度,提高了生产效率,强化了中国地浸采铀矿山的绿色环保措施;同时促进了低成本、环境友好型地浸采铀大基地的建设,推动了地浸采铀技术的进步。