Ash properties will change during storage. CO2 and moisture from the air spontaneously reacts with the ash and form hydroxides, carbonates, bicarbonates and other minerals like gypsum and ettringite Etiégni& Campbell, 1990Steenari. et al., 1999. This is part of the reason why different methods of stabilizations are used to harden the raw ash.
Hardened ash is less reactive and the solubility of many elements is reduced. The reactivity of an ash product is also reduced by the formation of larger agglomerate particles and stabile dense structures Steenari. et al., 1998. Stabilization and agglomeration methods used today usually involves the addition of water to the ash and then either pellets formation, granulation or spontaneous stabilization combined with crushing Ibid. Åbyhammar. et al., 1994.