Abstract
Mineral fertilizers were prepared using three different types of sewage sludge incineration ash (SSA) and CaCO3 by means of calcination. The raw mixtures with varied CaO contents were calcined in an electric furnace at different temperatures. To evaluate the fertilizer performance, water soluble SiO2, citric acid soluble P2O5 and mineral composition were analyzed.
The results showed that the formation process and dissolution behavior of minerals varied depending on the composition of the raw SSA.
Calcining higher Al2O3 ash with a CaO content increased to 55.0% produced a mixture of gehlenite and Ca14.92 (PO4)2.35 (SiO4)5.65, with citric acid solubility of P2O5 and water solubility of SiO2 improved up to 98 and 86%, respectively. Calcining lower Al2O3 ash with a CaO content increased to 57.5% produced dicalcium silicate, with both citric acid solubility of P2O5 and water solubility of SiO2 improved to over 98%.
Consequently, it was found that regardless of the chemical composition of raw SSA useful mineral fertilizers with high solubilities of P2O5 and SiO2 could be obtained by adjusting the CaO content properly.
