Mineralogical Composition Evolution and Thermogravimetric Characteristics of Sewage Sludge Ash at Different Ashing Temperatures

The characterization and comparison of sludge ashes at various ashing temperatures were carried out to study the relationship between the ashing fusibility, physicochemical properties and thermogravimetric characteristics. The low temperature ashes were black gray and had the characteristic of the coexistence of irregular and rounded particles, which contained a certain proportion of residual unburned combustible material. As the ashing temperature increased, the flake–like crystals transformed into long columns with a compact arrangement. Agglomeration of the ash samples became significant and provided the supporting effect of a skeleton structure. The ash samples at a low ashing temperature had lower ash characteristic temperatures. As the ashing temperature increased, the characteristic temperature increased, which implied that the minerals with high melting points provided the supporting effect of a skeleton structure. The main mineral compositions of the ash samples at the low ashing temperature were...