Potential for U sequestration with select minerals and sediments via base treatment

Temporary base treatment is presented as a potential remediation technique for heavy metals through adsorption, precipitation, and co-precipitation with minerals. The objective of this research was to evaluate changes in uranium mobility and mineral dissolution with base treatments using sodium hydroxide, ammonium hydroxide, and ammonia gas in laboratory batch experiments. The methodology involved manipulating pH with ammonia gas injection, which is particularly advantageous in vadose zone environments as it avoids adding liquids that could enhance groundwater flux. Results indicated a significant increase in the partitioning of uranium to the solid phase by several orders of magnitude following base treatment, contingent upon the presence of various minerals and natural sediments from the Hanford site. The presence of dissolved calcium and carbonate was found to substantially influence uranium precipitation and co-precipitation at elevated pH levels. Additionally, incongruent dissolution of bulk mineral phases was observed, likely leading to the formation of secondary mineral phases that could effectively sequester uranium through adsorption and precipitation processes as the pH shifted back to natural conditions.