Study of the chemical activation of hydroxyapatite rich ashes as raw materials for geopolymers

Abstract The behaviour of ashes, deriving from mixed vegetal and animal biomass incineration, was studied in different alkaline and acidic environments, in order to assess their suitability as primary raw material for low-temperature chemical consolidation. Mixed biomass ashes are mainly based on calcium phosphate and secondly on aluminosilicate compounds; they still represent an unexplored source material to be used in alternative ceramics production. Their chemical behaviour was studied as a function of pH and chemical nature of the leaching solutions, to identify the suitable conditions for ashes chemical consolidation. Preliminary results indicated that acidic digestion of ashes, regardless acid counterion nature, is able to determine the complete decomposition of complex calcium-phosphate phases. Then it allows recombination of dissolved phases into new ones, thus promoting chemical consolidation. Alkaline media were found to be less effective, however, biomass ashes might be successfully regarded as partially reactive fillers for alkali-activated materials.