Geochemical reactions altering the mineralogical and multiscale pore characteristics of uranium-bearing reservoirs during CO2 + O2in situ leaching
Xingyu Zhou, Wei Wang, Qinghe Niu, Qizhi Wang, Xuebin Su, Genmao Zhou, Lixin Zhao, Zhongmin Ji, Xiaofei Qi, Lanlan Tian, Jianhui Zhang, Beibei Sun
Abstract
CO 2 + O 2 in situ leaching has been extensively applied in uranium recovery in sandstone-type uranium deposits of China. The geochemical processes impact and constrain the leaching reaction and leaching solution migration; thus, it is necessary to study the CO 2 + O 2 –water–rock geochemical reaction process and its influence on the physical properties of uranium-bearing reservoirs. In this work, a CO 2 + O 2 –water–rock geochemical reaction simulation experiment was carried out, and the mineralogical and multiscale pore characteristics of typical samples before and after this simulation experiment were compared by X-ray diffraction and high-pressure mercury intrusion porosimetry (HPMIP). The results show that the CO 2 + O 2 –water–rock geochemical reaction has complicated effects on the mineral compositions due to the various reaction modes and types. After the CO 2 + O 2 –water–rock geochemical reaction, the femic minerals decrease and the clay minerals in the coarse sandstone, medium sandstone, fine sandstone, and siltstone increase, while the femic minerals and clay minerals in sandy mudstone show a contrary changing trend. The CO 2 + O 2 –water–rock geochemical reaction decreases the total pore volume of uranium-bearing reservoirs and then promotes pore transformation from small scale to large scale. The fractal dimensions of macropores are decreased, and the fractal dimensions of mesopores, transition pores, and micropores are increased. The effects of felsic mineral and carbonate dissolution, secondary mineral precipitate, clay mineral swelling, and mineral particle migration are simultaneously present in the CO 2 + O 2 in situ leaching process, which exhibit the positive transformation and the negative transformation for the uranium-bearing reservoirs. The mineral dissolution may improve reservoir permeability to a certain degree, while the siltation effect will gradually reveal with the extension of CO 2 + O 2 in situ leaching. This research will provide a deep understanding of the physical property response of uranium-bearing reservoirs during CO 2 + O 2 in situ leaching and indicate the direction for the efficient recovery of uranium resources.