Sulfate – hydroxide substitutions in basaluminite: structural effects and implications for As retention at high-alpine climatic conditions

The retreat of permafrost in mountain terrains exposes fresh sulfide minerals to atmospheric conditions, which induce their oxidation and subsequent formation of acid rock drainage rich in Al and sulfate. At pH higher than 4.5, basaluminite exerts a strong solubility control on dissolved toxic Al and has been described as a highly efficient scavenger for toxic As. However, it has been shown that the SO4 content in basaluminite is variable due to a substitution with OH, highlighting a possible solid solution between basaluminite and nanoboehmite. The structural changes associated with this solid solution may affect the As adsorption behavior. We propose HEXD experiments with both natural and synthetic basaluminite samples to determinate how the pH and temperature during precipitation affect their nanomineral structure. This analysis will help to obtain a more predictive understanding of the mobility of toxic elements such as As and Al under changing alpine climatic conditions.