Non-isothermal kinetic analysis of mercury desorption from acid mud from lead and zinc smelting process

Zinc smelting produces large amounts of mercury-bearing acid mud with 13.27 wt% mercury and high recovery potential. Its harmless treatment and resource reuse are essential, yet the unclear mercury removal mechanism hinders process improvement. We studied its kinetics via thermogravimetry and a self-developed mercury thermal desorption device to clarify the mechanism and validate the dominant model. Two weightless peaks were observed in the thermogravimetry desorption curves: one (521–740 K) corresponds to the mercury thermal desorption process, which is the focus of this study. The process first displays exothermic behaviour −300.917 kJ·mol−1, followed by an endothermic stage167.553 kJ·mol−1; while the other (849–994 K) corresponds to the oxidation of zinc sulfide. Activation energy of mercury desorption process was calculated by 5 model-free methods. The Flynn-Wall-Ozawa method achieved the best fitting effect with Ea = 115.69 kJ·mol−1 (R2 = 0.943). Using both the model fitting method and Z(α) master-plot method, a geometrical contracting volume model R3 was finally determined as the dominant model through the whole reaction. Mercury desorption tests were conducted; data fitted the R3 model well. Findings guide staged mercury removal: heating for the reaction-controlled stage; heating, pore formation and higher carrier flow for the joint-controlled stage.