Effects of kaolin and calcium carbonate additives on ash fusion characteristics of various tannery wastes during combustion.

The leather industry produces substantial amounts of solid waste, including tanning sludge and various leather wastes, presenting significant environmental challenges. This study explores the influence of additives (kaolin and CaCO) on the ash fusion characteristics of leather mixed solid waste (LMSW) during combustion. The effects of these additives on ash fusion temperatures (AFTs) and mineral transformation were systematically investigated using X-ray diffraction, X-ray fluorescence, and thermodynamic equilibrium calculations. The results show that the sum of CaO and FeO in the ash of LMSW exceeds 60%, increasing the proportion of wet blue leather in the waste slightly elevates the softening temperature (ST). Notably, kaolin-commonly employed to enhance coal ash fusion properties-reduces the AFTs of LMSW, particularly at the base/acid ratio is close to 1. In contrast, CaCO addition significantly improves AFTs, especially when the B/A ratio exceeds 1. Thermodynamic analysis further reveals that kaolin accelerates liquefaction in LMSW, with melting behavior aligning well with experimental AFTs trends. Additionally, this study evaluates the applicability of traditional coal ash fouling and slagging indicators to LMSW, demonstrating a strong correlation between these indicators and AFTs. However, when basicity exceeds 1, the indicators and AFTs exhibit opposing trends. To optimize ash melting behavior, additives should be selected based on the waste ash's B/A ratio to prevent it from approaching 1.