Reactive transport modeling at uranium in situ recovery sites: uncertainties in uranium sorption on iron hydroxides

Groundwater users near uranium in situ recovery (ISR) sites express concerns regarding local groundwater quality, particularly the influences from elevated concentrations of uranium, radium, and radon found within these deposits. The objective of this study is to evaluate the uncertainties in uranium sorption processes on iron hydroxides, which can significantly impact groundwater quality post-recovery. Using reactive transport modeling, we investigate the geochemical changes that may occur due to variations in groundwater flow patterns influenced by the mining activities. Our methodology includes analyzing the parameters affecting uranium's precipitation and sorption, particularly in environments characterized by reducing conditions versus those dominated by oxidized solid phases. The results highlight that when solid-phase materials consist of sandstone with iron hydroxide coatings, uranium sorption is primarily governed by these iron compounds. Additionally, potential reversal in groundwater flow could lead to prolonged uranium interaction with oxidized materials, affecting environmental assessments. This study provides critical insights for groundwater users, regulatory agencies, and stakeholders regarding the long-term impacts of uranium ISR operations on surrounding groundwater quality.