Study on physicochemical characteristics, solidification and utilisation of tannery sludge gasification ash.

Gasification is an attractive method for tannery sludge (TS) disposal because of its advantages: volume reduction, stabilisation, harmlessness, and energy recovery. TS reduction ash (A) and TS oxidation ash (A), simulated from a downdraft fixed bed gasifier (DFBG) and an updraft fixed bed gasifier (UFBG), were investigated on their physicochemical characteristics, solidification behaviour, and value-added utilisation. Results showed that the main mineral matters in A and A consisted of Fe-oxids and Fe-Cr compounds, and the DFBG was more suitable for TS gasification than the UFBG because of the lower content of Cr(Ⅵ) in A. With the addition of waste glass bottles (W), the ash fusion temperatures (AFTs) and leaching concentrations of heavy metals in A and A decreased significantly, and the heavy metals in A and A were successfully immobilised by the wrapping effect of the molten W. Moreover, gasification ash, as an auxiliary material for rock wool, reduced the AFTs and viscosity coefficient of the main chemical compositions in rock wool. With the addition of A, the occurrence of Fe-containing compounds and the extremely low risk of leaching toxicity of heavy metals were observed. The maximum addition proportion of gasification ash was dependent on the maximum content of FeO allowed in the raw materials of rock wool, and its addition ratio must be below 15%.