The leaching of ash in sulfuric acid (pH 1.0, 25EC, S/L 1:10) was studied as a function of time. Data for the extraction of trace elements are presented. The study embraced ash from the combustion of two Turkish lignites (Yata?an and Tunçbilek), one asphaltite (Silopi) and the briquettes of Swedish softwood sawmill residues (Fränsta). Conclusions are drawn regarding suitable residence times for an industrial washing process as well as the chemical nature of trace elements in the untreated ashes. The kinetics of trace element (Cd, Co, Cr, Cu, Mo, Ni, V and Zn) dissolution followed a shrinking core model and extended times (> 32 h) were required to reach maximum extraction from the ashes. Comparisons with data for the dissolution of dominant ions point at association with aluminum or iron containing phases (clays). Th and U reached high extraction yields after 8 h in solution, which suggests either surface association or association with rapidly dissolved Ca or Mg containing phases. Time-dependent Ba and Pb dissolution was observed below the limit set by the solubility of the corresponding sulfides.