Effect of Short Carbonation on Element Mobility in Wood Ash

Abstract During carbonation of wood ash, carbon dioxide reacts with alkali or alkaline earth components in the ash-forming carbonates. The impact of a short carbonation on the mobility of elements in wood ash was investigated. The aim was therefore to apply a sequential extraction approach to investigate the influence of a short carbonation process on the mobility of environmentally relevant metals and plant nutrients in wood ash. Results show that short carbonation results in differences in the chemical bonding form of ash-forming elements and thus their potential mobility. The mobility of almost all examined metals (with the exception of Zn) increased after short carbonation treatment compared to the untreated ash. The extractable fractions of Cd, Cu, and Ni increased from 16.5 to 21.2%, 14.7 to 18.1%, and 20.3 to 24.5%, respectively. Pb and Cr also exhibited slight increases in element mobility, while for Zn, the overall extraction efficiency decreased from 19.6% to 15.8%. Also plant nutrients (phosphorus─more oxidizable and magnesium─more acid-soluble) exhibited increased mobility after carbonation. Overall, the results demonstrate that short carbonation is not a purely stabilizing process but a dynamic transformation governed by changes in pH, carbonate formation, and mineral equilibria. While carbonation can contribute to immobilization, it may also temporarily increase element mobility. These findings improve the mechanistic understanding of ash–CO2 interactions and provide a basis for targeted ash conditioning strategies.