The synergistic effect on the product distribution for the co-pyrolysis of tannery wastes

•Harmless disposal of tannery wastes by co-pyrolysis was explored.•Co-pyrolysis of tannery wastes produced much more high-quality oil and gas.•Synergistic co-pyrolysis effect was found when more tanning sludge (TS) was added.•Synergistic co-pyrolysis effect was owing to the catalytic effect of mineral in TS. The resource management and decontamination of tannery wastes are greatly desired in the tannery industry. The co-pyrolysis of three tannery wastes (chrome tanned buffing dust (CTBD), chrome shavings (CS), and tanning sludge (TS)) were explored for optimizing the pyrolysis process and product, which significantly increased the yield of tar/gas, the fraction of light tar and the specific surface area of char. The results showed that different materials interacted in the pyrolysis progress, and the influence of the CTBD/CS/TS ratio further confirmed the existence of a synergistic effect. TS played a key role in the co-pyrolysis process, which notably promoted the secondary reaction process of char to tar/gas and upgraded the produced volatiles. Moreover, further investigation into the effect of mineral components revealed that the synergistic effect of co-pyrolysis derived from the catalytic effect of mineral components such as Fe2O3 and CaCO3 in TS, accounted for the significantly-improved co-pyrolysis performance of tannery wastes. The excellent co-pyrolysis performance of tannery wastes may provide a promising technical route for their resource utilization.