内蒙古钱家店铀矿CO₂+O₂地浸采铀后残留铀的产状及成因

The Occurrence and Genetic Mechanism of Residual Uranium after CO₂+O₂ In⁃Situ Leaching in the Qianjiadian Uranium Deposit, Inner Mongolia

摘要

CO₂+O₂地浸采铀后铀储层中残留铀的产状及成因机制对改进地浸采铀工艺及提高铀浸出效率具有重要意义，但国内外对这方面的研究却很少.鉴于此，以内蒙古钱家店铀矿床地浸开采前后钻孔岩心样品为研究对象，利用扫描电镜及能谱分析识别出3种残留铀产状类型：铀矿物、吸附态铀和含铀矿物，其中，铀矿物包括铀石及沥青铀矿两类，多分布在石英、长石等碎屑颗粒的溶孔中、碳质碎屑内部及边缘、高岭石内部及边缘以及高岭石包裹下的黄铁矿边缘，吸附态铀主要以被粘土矿物和碳质碎屑吸附的形式存在，而含铀矿物包括含铀独居石、含铀锆石以及含铀钛矿物等.对比地浸前后岩心样品中铀的产状变化发现：①与碎屑颗粒伴生的铀矿物中，观察到石英、长石、岩屑溶孔内部的铀矿物和与碳质碎屑伴生的铀矿物残留，未观察到云母解理缝内以及碎屑颗粒边缘的铀矿物残留；②与填隙物伴生的铀矿物中，观察到与黄铁矿和高岭石伴生的铀矿物残留，未观察到与菱铁矿相伴生的铀矿物残留；③高岭石与碳质碎屑吸附铀残留；④碎屑颗粒间的含铀矿物残留.以此为基础，探讨了地浸过程中赋矿层中铀残留的4种成因机制：①由于缺乏有效连通孔隙，浸出剂难以充分接触到碎屑颗粒内部铀矿物，导致碎屑颗粒内部铀矿物残留；②高岭石会堵塞流体运移通道使得与其伴生的铀矿物难以被浸出而残留；③高岭石自身结构具有吸附性且在酸性条件下稳定，导致其吸附的铀难以被浸出而残留，而富含碳质碎屑的区域由于其较强的还原能力、吸附能力以及其区域内较差的流通性导致其吸附的铀无法被浸出而残留；④含铀矿物不易与浸出剂反应导致铀无法浸出.研究表明赋矿层中铀的产状是影响其浸出的重要因素，成果将为改进地浸工艺、提高铀浸出效率提供矿物学方面依据.

Abstract

The occurrence and genetic mechanism of residual uranium in uranium reservoirs after CO₂ + O₂ in-situ leaching of uranium are highly important for improving the in-situ leaching process and leaching efficiency of uranium, but few studies have been conducted in this field. Therefore, this work takes mineralized sandstones and drilling core samples after in-situ leaching of uranium as the research object in the Qian II block of the Qianjiadian uranium deposit in Inner Mongolia. Three types of residual uranium were identified via SEM-EDS analyses: uranium minerals, adsorbed uranium and minerals containing uranium. In the samples after in-situ leaching, uranium minerals include coffinite and pitchblende, which are mainly distributed in the dissolved pores of clastic particles or inside and around clay minerals such as kaolinite. The adsorbed uranium is adsorbed mainly by clay minerals and carbonaceous debris, whereas minerals containing uranium include mainly monazite containing uranium, zircon containing uranium and titanium minerals containing uranium. A comparison of the occurrence of uranium in the mineralized sandstones before and after in-situ leaching reveals the following. (1) In the types of uranium minerals associated with clastic particles, the residual uranium minerals inside the quartz, feldspar, rock debris and carbonaceous debris were observed, whereas no residual uranium minerals at the edge of clastic particles, or inside the mica joints were observed. (2) In the uranium minerals associated with interstitial material, residual uranium minerals associated with pyrite and kaolinite were observed, and no residual uranium minerals associated with siderite were observed.(3) Uranium adsorbed by kaolinite and carbonaceous debris was retained. (4) Minerals containing uranium retains between clastic particles. On the basis of above observations and analyses, four genetic mechanisms of uranium residue in uranium reservoirs during in-situ leaching are proposed. (1) Because of the lack of effective interconnected pores, the in-situ leaching solution has difficulty flowing through the uranium minerals inside the clastic particles, resulting in formation of the uranium residual uranium minerals.(2) Kaolinite can block fluid transport channels, making it difficult to leach uranium minerals associated. (3) Kaolinite has adsorption properties and is stable under acidic conditions, which makes it difficult for the adsorbed uranium to be leached out. Uranium cannot be leached in areas rich in carbonaceous debris because of its strong reduction ability, adsorption capacity and poor circulation in the area. (4) Minerals containing uranium have difficulty reacting with the leaching agent, which results in incomplete leaching. This research has shown that the occurrence of uranium in the mineralized sandstone is an important factor affecting its leaching, and the results provide a mineralogical basis for improving in-situ leaching processes and enhancing uranium leaching efficiency.

Graphical abstract

关键词

CO₂+O₂地浸采铀 / 砂岩型铀矿床 / 工艺矿物学 / 残留铀 / 松辽盆地 / 钻孔 / 石油地质.

Key words

CO₂+O₂ in⁃situ leaching of uranium / sandstone⁃type uranium deposit / process mineralogy / residual uranium / Songliao basin / borehole / petroleum geology

0 引言

原地浸出采铀是砂岩型铀矿的主要采冶方法，是一种通过溶浸液与矿物的化学反应选择性地溶解矿石中的铀，而不使矿石产生位移的集采、冶于一体的铀矿开采方法，包括酸法地浸、碱法地浸和中性（CO₂+O₂）地浸（Abzalov， 2012； 苏学斌和杜志明，2012；张飞凤等，2012；孙占学等，2021）.相比于酸法地浸和碱法地浸，中性地浸反应温和，不易造成矿层孔隙的化学堵塞，易于地下水治理，对高碳酸盐含量的铀矿床浸出效果好，原理是U⁴⁺被O₂氧化形成U⁶⁺与HCO₃^-络合形成碳酸铀酰离子进入溶液中被浸出（王亮等，2016；原渊等，2019；黎广荣等，2021；孙占学等，2021）.

近年来，许多学者开始探索地浸采铀过程中矿物反应和溶液变化规律，以解释原位地浸采铀过程中遇到的困难（吉宏斌，2019；袁新等，2022；张一诺，2022；赵凯等，2023；张成江等，2024；段美铃等，2024；宋昊等，2024；于慧杰等，2024；周靖等，2024）.一些学者通过观察怀俄明州铀矿床ISR原位地浸采铀后的岩心样品，发现矿床中残留的铀主要分布在不透水且富含有机质的区域、蚀变的黄铁矿、绿泥石和粘土矿物上或是以次生铀矿物形式存在（WoldeGabriel et al.， 2014；Gallegos et al.， 2015），却忽视了与地浸前赋矿层中铀产状的对比，导致仍然不清楚残留铀的成因.还有一些学者通过实验模拟CO₂+O₂地浸采铀过程发现沥青铀矿与铀石是主要浸出对象，而云母、粘土矿物和有机质吸附的铀以及类质同相态的铀难以被浸出（段美铃等，2024；于慧杰等，2024），同时在CO₂+O₂地浸环境下黄铁矿氧化形成的三价铁沉淀以及粘土矿物会吸附地浸液中的铀，干扰铀的浸出（Bi et al.， 2013； Johnson and Tutu， 2013； Gallegos et al.， 2015； 张一诺，2022），但这些研究主要是基于实验室模拟CO₂+O₂地浸过程，而忽视了地浸液运移距离、离子浓度变化、矿物支撑结构、地层非均质性以及地浸过程中矿物溶蚀、生长等综合因素的影响，难以反映真实的地浸作业过程以及结果.

鉴于此，本文将以内蒙古松辽盆地钱家店铀矿床为例，采集钱Ⅱ块CO₂+O₂地浸采铀后的岩心样品，观察对比地浸前含矿带岩心样品中铀的产状，探究真实地浸作业后残留铀的类型及其赋存特征，讨论CO₂+O₂地浸过程中影响铀浸出的关键因素及残留铀的成因机制，为改进地浸工艺、提高铀浸出效率提供微观矿物学方面的依据.

1 地质背景

松辽盆地是我国中、新生代大型陆相盆地，呈北北东方向展布，盆地呈不规则的菱形，面积达26×10⁴ km²，是我国东北最大的沉积盆地.松辽盆地南部钱家店地区铀勘探取得重大成果，在上白垩统姚家组砂岩中探明了一个超大型砂岩型铀矿 床——钱家店铀矿床（夏毓亮等，2003；陈方鸿等，2005；张明瑜等，2005；陈晓林等，2008a，2008b；焦养泉等，2015；荣辉等，2016；张宇辰等，2024）.该矿床位于松辽盆地西南部开鲁坳陷的次级凹陷钱家店凹陷，钱家店凹陷是中、新生代断坳叠合型凹陷，于海西期褶皱基底之上发育，走向为北东向（图1a）.钱家店凹陷主要经历了早白垩世断陷、早白垩世末抬升剥蚀、晚白垩世坳陷及末期的构造反转、抬升剥蚀共4个阶段（殷敬红等，2000；庞雅庆等，2010；陈方鸿等，2005；陈晓林等，2006）.晚白垩世后存在两期构造热演化，分别是晚白垩世‒早古近纪时期的构造隆升剥蚀阶段和近中新世的构造反转，构造活动导致区域热事件与岩浆活动活跃，发育大规模铀成矿作用（Cheng et al.， 2018，2020）.

钱家店地区钻孔所揭露的地层主要包括上白垩统青山口组（K₂qn）、姚家组（K₂y）、嫩江组（K₂n）、新生界（图1b）.青山口组岩性以浅灰色或红色中细砂岩与泥岩互层为主，富含有机质；姚家组是主要的含矿层位，以粗碎屑岩为主，表现为厚层红色、灰色中细砂岩夹薄层泥岩，矿体厚度平均3 m，呈板状或透镜状；嫩江组以大套灰色泥岩为主，富含有机质与生物碎屑（图1b；张明瑜等，2005；陈晓林等，2007；庞雅庆等，2010；荣辉等，2016；金若时等，2017；夏飞勇等，2019；曹民强，2021；程银行等，2024）.姚家组可划分三级层序分别为低位体系域（LST）、湖泊拓展体系域（EST）、高位体系域（HST），其中低位体系域和湖泊扩展体系研究区发育辫状河‒辫状河三角洲沉积，形成了具有良好连通性的铀储层，是主要的含矿层位（图1b；曹民强，2021）.

2 样品与测试方法

本文选用钱家店铀矿床钱Ⅱ块CO₂+O₂地浸采铀后的钻孔岩心制样，共制样16件，取样位置见图2.该区块投产时间为2015年，地浸设计CO₂浓度为0.3~0.5 g/L，O₂浓度为0.2 g/L.本文扫描电镜测试工作于中国地质大学（武汉）构造与油气资源教育部重点实验室完成，扫描电子显微镜型号为EVO_LS 15环境扫描电子显微镜进行样品显微结构及形貌观测，同时通过Aztec X⁃Max 20能谱仪进行矿物化学组成的分析，分析元素范围是4Be⁃98Cf，试验中薄片进行了喷碳处理.环境扫描电镜分辨率：低真空，4.5 nm，30 kV，BSD（VP模式）.环境扫描电镜条件：室温20 ℃，湿度不高于60%.

3 地浸前含矿砂岩中铀的产状

在钱家店铀矿床地浸前含矿砂岩中识别出3种铀的产状：铀矿物、吸附铀以及含铀矿物.

3.1　铀矿物

钱家店铀矿床地浸前常见铀矿物包括沥青铀矿和铀石，常以胶状、团块状、颗粒状形式存在.沥青铀矿与铀石存在两种产状，分别是与石英、岩屑、云母、碳质碎屑、锆石、铁钛氧化物等碎屑颗粒伴生以及与黄铁矿、粘土矿物及少量菱铁矿等填隙物伴生.第一类主要表现为铀矿物充填石英、长石和岩屑内部溶孔或以胶状形式分布于颗粒边缘（图3a， 3b）；充填云母的解理缝中（图3c）；以胶状形式交代碳质碎屑（图3d）；以胶状形式从边缘交代或包裹铁钛氧化物（图3f， 图4d）.第二类则是与黄铁矿、粘土矿物及碳酸盐胶结物伴生的铀矿物，往往交代黄铁矿、粘土矿物或是生长在溶蚀菱铁矿边缘（图3c， 3e）.

3.2　吸附态铀

地浸前吸附态铀表现为粘土矿物吸附铀以及碳质碎屑等有机质吸附铀.钱家店铀矿床中高岭石吸附铀，二者具有密切的空间共生关系（图4a）.碳质碎屑附近往往发育大量胶状、粒状、草莓状黄铁矿，其自身不仅能还原U⁶⁺形成铀矿物，还会吸附铀元素（图3d）.

3.3　含铀矿物

地浸前含铀矿物包括含铀锆石、含铀钛矿物、钛铀矿、含铀磷灰石以及含铀独居石等.含铀锆石、磷灰石、独居石等往往呈自形‒半自形，往往发育裂隙、溶孔（图4e， 4f）.而含铀钛矿物包括自形网格状含铀金红石，胶状、粒状含铀锐钛矿以及碎屑状含铀白钛石，粒径一般为26~75 μm（图3f，图4c， 4d）.

4 CO₂+O₂地浸后铀的产状

CO₂+O₂地浸采铀后样品中残留铀也存在3种产状：铀矿物、吸附态铀和含铀矿物，其中吸附态铀最常见，其次为含铀矿物，而铀矿物则较为少见.

4.1　铀矿物

地浸采铀后残留铀矿物种类主要为铀石和沥青铀矿，残留沥青铀矿多以胶状、团块状形式存在，残留铀石主要以胶状、团块状、颗粒状形式存在.它们往往与石英、长石、岩屑和碳质碎屑等碎屑颗粒及高岭石、黄铁矿等填隙物相伴生.

与碎屑颗粒相伴生的沥青铀矿、铀石多数以团块状、胶状充填于石英、长石、岩屑颗粒内部溶蚀孔洞中（图5a， 5b），此类铀矿物的直径一般在2.5~ 10 μm.此外，还可见胶状铀石交代碳质碎屑（图5f）.

与高岭石相伴生的沥青铀矿和铀石最常见，主要以胶状、星点状、颗粒状生长在高岭石边缘或内部（图5c， 5d），其粒径往往小于5 μm.与黄铁矿伴生的铀矿物分布于黄铁矿边缘，且这些黄铁矿往往与高岭石、碳质碎屑共生（图5e， 5f）.

4.2　吸附态铀

地浸采铀后的样品中吸附态铀的分布较为普遍，主要有被粘土矿物吸附和被碳质碎屑吸附两种存在形式.常见被高岭石吸附的铀（图6），还能观察到碳质碎屑吸附少量的铀，同时还吸附有Ca、Ti、Al、Si、Zr、Fe等元素，周围往往见大量高岭石分布（图7）.

4.3　含铀矿物

地浸采铀后样品中含铀矿物以含铀锆石、含铀钛矿物为主，还发现少量含铀独居石.含铀锆石往往以自形‒半自形存在且裂隙发育，具有一定磨圆特征，粒径一般在10~25 μm，铀主要发育于裂缝发育的部位（图8a）.含铀钛矿物主要以胶状含铀锐钛矿为主，形态完整，且附近往往伴生高岭石、伊利石等粘土矿物（图8c）.独居石是一种常见含铀重矿物，形态以粒状为主，有明显的磨圆特征，内部含有少量铀，其粒径一般在5~10 μm（图8e）.

5 讨论

5.1　CO₂+O₂地浸前后铀的产状变化特征

残留铀矿物往往赋存在石英、长石等碎屑颗粒的孔洞内、碳质碎屑内部及边缘、高岭石边缘和被粘土矿物堵塞的孔隙中（图5），而连通孔隙之间与长石、云母等碎屑颗粒相伴生的铀矿物含量显著减少，黄铁矿、碳酸盐胶结物相伴生的铀矿物几乎不可见.由于长石、云母、黄铁矿、碳酸盐胶结物等矿物易与地浸液反应发生溶蚀（段美铃等，2024；于慧杰等，2024；周靖等，2024），因此，推断与这些矿物相伴生的铀矿物均被浸出.通过对比地浸前后样品中铀产状的变化，发现地浸后的样品有以下4个特点（图9）：①与碎屑颗粒伴生的铀矿物中，观察到石英、长石、岩屑内部的铀矿物和与碳质碎屑伴生的铀矿物残留，未观察到与云母解理缝内以及碎屑颗粒边缘的铀矿物残留；②与填隙物伴生的铀矿物中，黄铁矿和高岭石伴生的铀矿物残留，未观察到与菱铁矿相伴生的铀矿物残留；③高岭石与碳质碎屑吸附的铀残留；④碎屑颗粒间的含铀矿物残留.

前人通过实验证明了长石、云母、菱铁矿和黄铁矿及其伴生铀矿物在CO₂+O₂条件下会被溶解浸出（段美铃等，2024；于慧杰等，2024；周靖等，2024），所以①、②中碎屑颗粒内部溶蚀孔洞中的铀矿物、碳质碎屑伴生的铀矿物和与高岭石、黄铁矿伴生的铀矿物在地浸过程中未被完全浸出，主要是缺乏有效连通孔隙使得浸出液难以与铀矿物发生反应，而流通孔隙内的黄铁矿和碳酸盐矿物等填隙物相伴生的铀矿物可以与地浸液充分反应而浸出（图9），主要反应式如下（朱鹏等，2011；Reynolds， 2013； 田增辉等，2024）：

2USiO₄（铀石）+4H⁺+O₂ +2H₂O→2UO₂²⁺+2H₄SiO₄，_（1）

UO₂（沥青铀矿）+0.5O₂+2H⁺→UO₂²⁺ +H₂O,

（2）

UO₂²⁺+nHCO₃^-→UO₂(CO₃)₂^2-2n+nH⁺ ,^（3）

综上所述，碎屑颗粒溶孔内的铀矿物、碳质碎屑伴生的铀矿物、高岭石伴生的铀矿物、高岭石包裹下黄铁矿伴生的铀矿物、高岭石和有机质吸附的铀以及含铀矿物是CO₂+O₂地浸过程中难以浸出或无法浸出的类型.

5.2　CO₂+O₂地浸过程中铀残留的原因

上述研究已经识别出不同产状下的铀在地浸前后的差别，下面将讨论碎屑颗粒伴生的铀矿物、填隙物伴生的铀矿物、高岭石与碳屑吸附的铀以及含铀矿物这4种产状下铀残留的成因机制.

（1）碎屑颗粒伴生的铀矿物.通过对比地浸前后碎屑颗粒伴生铀矿物发现，碎屑颗粒溶孔内部的铀矿物和与碳质碎屑伴生的铀矿物未被完全浸出.碎屑颗粒溶孔内部的铀矿物残留的原因主要是由于浸出液缺乏充分进入溶孔内部的连通孔隙，而石英、长石较难在CO₂+O₂地浸条件下溶解，使得浸出剂无法与其溶孔内部铀矿物反应而残留.即使中性CO₂+O₂地浸条件下长石能与浸出液反应发生溶蚀（周靖等，2024），在镜下发现长石溶蚀形成伊利石而内部存在铀矿物残留的现象（图5c），说明长石在CO₂+O₂地浸过程中蚀变为伊利石、高岭石等层状硅酸盐矿物亦会堵塞浸出液的流动孔隙导致铀矿物难以完全浸出（周靖等，2024）.而碳质碎屑由于其自身较强的还原能力会中和浸出液，使得碳质碎屑伴生的铀矿物难以被氧化浸出.

所以，碎屑颗粒伴生的铀矿物主要是缺乏有效运移通道难以与浸出液反应，所以往往难以被完全浸出.

（2）前文研究发现与填隙物伴生的铀矿物中主要以高岭石相伴生的铀矿物和高岭石包裹下与黄铁矿相伴生的铀矿物未被完全浸出（图5c， 5d， 5e），前人认为高岭石会堵塞铀储层孔隙，降低孔隙度、渗透率，其吸水发生膨胀也会限制浸出液流动（杜超超和周义朋，2019；黎广荣等，2021；袁新等，2021；刘石玉等，2022；赵凯等，2023），而且CO₂+O₂地浸过程中高岭石的结构难以被溶解破坏（周靖等，2024），所以与填隙物伴生的铀矿物残留的原因主要是由于高岭石等粘土矿物堵塞孔隙导致相关铀矿物难以被完全浸出.

由此可知，高岭石等粘土矿物会堵塞流体运移通道，导致地浸液无法与填隙物伴生的铀矿物反应，致使铀矿物无法被完全浸出，所以高岭石等粘土矿物堵塞是造成铀浸出率低的重要因素.

（3）高岭石和碳质碎屑吸附的铀. 高岭石作为层状硅酸盐矿物具有比表面积大、阳离子交换能力强的特点，对铀具有较强的吸附能力，能吸附浸出液中的碳酸铀酰离子（杜超超和周义朋，2019；黎广荣等，2021；袁新等，2021；刘石玉等，2022；赵凯等，2023；周靖等，2024），同时周靖等（2024）通过CO₂+O₂地浸实验发现粘土矿物吸附的铀在地浸过程中难以被浸出，认为是由于其层片状、薄片状结构无法在CO₂+O₂地浸条件下破坏导致的.所以，由于高岭石自身结构具有吸附性，能稳定吸附铀导致其难以被浸出而残留，降低了对铀的浸出效率.

碳质碎屑作为铀矿床内部沉积来源的有机质，是铀储层中重要的组成部分，对铀具有较强的吸附、络合和还原能力，常见其吸附铀酰离子或被铀石、沥青铀矿交代（刘汉彬等，2007；Dai et al.， 2015； Bone et al.， 2017； 焦养泉等，2018；Rong et al.， 2019； Zhang et al.， 2019，2021）.同时，前人研究发现钱家店铀矿床中含矿段碳质碎屑受到辉绿岩侵入事件或铀辐射的影响，其成熟度往往高于其他分带（Sassen， 1984； Smieja⁃Król et al.， 2009； Havelcová et al.， 2014； Rong et al.， 2019），而碳质碎屑在成岩热演化、成熟或被厌氧菌分解过程中往往会产生腐殖酸、H₂S、干酪根以及CH₄等还原物质，有助于络合铀酰离子或还原U⁶⁺ （向伟东等，2000；尹金双等，2005；李艳青和程相虎，2018；李子颖等，2022）.此外，碳质碎屑成熟或受菌群分解所释放的有机酸会造成pH降低局部呈酸性环境，长石、云母等矿物会在这种环境下溶蚀向粘土矿物发生蚀变（Dill， 2010，2016； 宁君等，2023），导致富含碳屑的岩石内部高岭石含量升高堵塞孔隙.而且，受到碳质碎屑熟化产生的H₂S影响，附近往往生长大量的黄铁矿，在铀储层内形成强还原屏障有利于还原铀形成铀矿物，却会消耗浸出剂阻碍铀的浸出（荣辉等，2016；焦养泉等，2018；乐亮，2021；Yue et al.， 2022）.所以，虽然富含碳质碎屑的部位有利于铀富集，也会因其较强的还原性消耗浸出剂或发育高岭石堵塞孔隙导致铀难以浸出，这也是地浸后样品中碳质碎屑伴生铀残留的原因（图5f，图7a）.

综上所述，高岭石自身结构具有吸附性，能稳定吸附铀导致其难以被浸出而残留，而富含碳质碎屑的区域拥有较强的还原性与吸附性可能会还原、吸附地浸液中的铀或是中和浸出液，同时碳屑成熟释放的有机酸会造成局部的酸性环境溶蚀长石等碎屑颗粒，有利于高岭石的形成，堵塞孔隙，导致区域内的流通性变差，致使碳质碎屑吸附的铀无法被浸出而残留.

（4）含铀矿物. 含铀锆石、含铀磷灰石以及含铀独居石中的铀是类质同相态的铀，指U与Ca、Zr和La系元素通过类质同象发生置换进入载体矿物晶格从而使该矿物含铀（孙冰等，2020），最终使载体矿物成为含铀矿物.锆石内部赋存的铀被认为是锆石的自辐射损对其晶格造成了破坏产生了微裂隙，流体通过这些裂隙进一步促进其内部发生蚀变，导致了U、Pb等元素的交换和迁移，并使Al、Fe、Ca等元素与Zr、Si发生交换，使得蚀变部位的铀含量增加（Nasdala et al.， 2010； 孙钰函等，2020；Sun et al.， 2021； 焦养泉等，2022）.独居石［CePO₄或（Ce、La）PO₄］作为一种稀土矿物，也是常见的含铀矿物.锆石、磷灰石以及独居石在低温型沉积盆地中赋存，往往具有典型的磨圆特征（图4f， 图8a， 8e），表明均是自沉积期搬运来的矿物.前人普遍认为以上含铀矿物中的铀在CO₂+O₂地浸下难以被浸出，需要强酸或是强碱的条件才能将其浸出（吉宏斌，2019；段美铃等，2024），所以这些含铀矿物是因为难以在CO₂+O₂地浸条件下反应溶蚀导致内部的铀无法浸出.

而地浸后与铁钛氧化物伴生的铀，其存在形式主要为胶状的含铀钛矿物或是铀矿物以星点状分布在钛氧化物内部（图8c），部分学者认为砂岩型铀矿床中胶状的含铀钛矿物是以类质同相态存在或是以钛铀矿形式存在且难以被浸出（段美铃等，2024；于慧杰等，2024）.然而，受含铀盆地演化过程中的温度条件与流体性质影响，铁钛氧化物与铀的关系仍存在争议，部分学者认为是铁钛氧化物的蚀变提高了对铀的吸附能力（Payne， 1999； Bonnetti et al.， 2015，2017），还有学者研究认为钛铁矿蚀变对铀进行预富集后自催化还原成矿（丁波等，2020；Ding et al.， 2022； 刘红旭等，2023），而Yin et al.（2024）研究发现松辽盆地内锐钛矿向金红石蚀变过程中发育的纳米孔隙会吸附铀，后期被还原形成铀氧化物的纳米颗粒而非是以类质同相态或钛铀矿形式存在，是具有可开发价值的.然而，受不同成岩成矿条件的约束，不同铀矿床中与铁钛氧化物伴生的铀的产状也存在差异（Ding et al.， 2022；刘红旭等，2023；张宇辰等，2024），所以不同类型铁钛氧化物伴生的铀被浸出的可能性以及浸出所需的条件还需进一步探索.

综上，碎屑颗粒间的含铀锆石、含铀独居石等具有类质同相态铀的含铀矿物在CO₂+O₂地浸条件下无法被浸出，含铀钛矿物内部的铀也难以被完全浸出，但铀与铁钛氧化物具有密切的空间关系且这种产状的铀具有可开采潜力，所以研究铁钛氧化物相伴生的铀浸出的相关问题是进一步提高砂岩型铀矿铀浸出效率的关键.

6 结论

（1）钱Ⅱ块CO₂+O₂地浸后残留铀可分为3种产状，分别是铀矿物、吸附态铀以及含铀矿物.铀矿物包括铀石及沥青铀矿，主要分布在石英、长石等碎屑颗粒的溶孔中、碳质碎屑内部及边缘、高岭石等粘土矿物内部及周缘以及高岭石包裹下的黄铁矿边缘，吸附态铀主要以被粘土矿物和碳质碎屑吸附的形式存在，而含铀矿物主要包括含铀独居石、含铀锆石以及含铀钛矿物等.

（2）地浸前后样品中铀的产状变化规律表现为4种特点：①与碎屑颗粒伴生的铀矿物，观察到石英、长石、岩屑内部的铀矿物残留，未观察到云母解理缝内以及碎屑颗粒边缘的铀矿物残留；②与填隙物伴生的铀矿物中，观察到与黄铁矿和高岭石伴生的铀矿物残留，未观察到与菱铁矿相伴生的铀矿物残留；③高岭石与碳质碎屑吸附铀残留；④碎屑颗粒间的含铀矿物残留.

（3）总结了4种铀残留的成因机制：①由于缺乏有效连通孔隙，浸出剂难以充分接触到碎屑颗粒内部铀矿物，导致碎屑颗粒内部铀矿物残留；②高岭石会堵塞流体运移通道使得与其伴生的铀矿物难以被浸出而残留；③高岭石自身结构具有吸附性且在酸性条件下稳定，导致其吸附的铀难以被浸出而残留，而富含碳质碎屑的区域由于其较强的还原能力、吸附能力以及其区域内较差的流通性导致其吸附的铀无法被浸出而残留；④含铀矿物不易与浸出剂反应导致铀无法浸出.

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基金资助

中国铀业有限公司‒东华理工大学核资源与环境国家重点实验室联合创新基金项目(2023NRE⁃LH⁃17)

中核铀业全国重点实验室基金项目(NKLUR⁃2024⁃YB⁃011)