Direct Measurement of Mineral Dissolution Enhanced by X-ray Irradiation

Developing a predictive understanding of mineral-phase stability in extreme chemical conditions such as those found in nuclear waste is challenging given the unknown influence of ionizing radiation. The long-term impacts of cumulative radiation damage in the solid state and exposure to radiolysis products in solution can impact mineral precipitation, dissolution, and aggregation behavior. Here, we sought to disentangle some of these effects by examining the dissolution of gibbsite platelets in NaOH solutions using atomic force microscopy with an integrated X-ray source that was used to compare dissolution rates when particles were initially irradiated in a dry state versus irradiated in solution, both of which were compared to unirradiated controls. By tracking particle morphology changes and quantifying material lost over time, dissolution rates and particle roughness were found to be enhanced most when irradiation was carried out during dissolution in NaOH, and to a lesser but significant extent when irradiated dry prior to dissolution. The maximum observed dissolution enhancement in the former case suggests the importance of both a direct effect of absorbed dose on gibbsite stability and an indirect effect arising from surface interaction with solution radiolysis products.