Long-term leaching of stabilized wood ash

The long-term leaching of two wood ashes, a granulated ash from a circulati ng fluidized bed boiler (CFB) and a grate-fired boiler (GF) ash, stabilized by wetting and agglomeration, was simulated in laboratory experiments and theoretically, with a kinetic model. Ash particles extracted from forest so il 2 yrs after spreading were also analysed. The results showed that leachi ng rates for nutrients depend on particle size, durability of ash aggregate s and nutrient speciation. The hard CFB ash granules released less of their salt content than did the more fragile GF ash aggregates. Differences in m atrix durability as well as in Ca speciation also rendered the CFB ash gran ules the lowest Ca leaching rates. The Ca leaching rates predicted for diff erent particle sizes by the kinetic model were significantly higher than th ose obtained experimentally. This discrepancy is probably due to factors su ch as decreasing porosity and chemical inhibition of calcite dissolution du ring experiments.