Thermodynamic and Kinetic Analysis of Lead Leaching from Pretreated Pb–Ag Jarosite Sludge by Chloride Solution

Waste products of zinc hydrometallurgy, such as Pb–Ag jarosite sludge, represent a significant environmental problem due to toxic properties associated with elevated lead content. At the same time, this material has economic value, making its valorization beneficial from both ecological and financial perspectives. This study investigates the chloride leaching of pretreated Pb–Ag jarosite sludge, which underwent sulphation roasting followed by water leaching. The experiments were conducted with a constant solid/liquid ratio of 1:20, a stirring rate of 150 rpm, and using a 4 mol dm3 MgCl2 solution as the leaching agent, while temperature (40–80 °C) and leaching time (up to 120 min) were varied. The results showed that temperature significantly affects the lead leaching degree, with the highest (95%) achieved at 80 °C after 60 min. Kinetic analysis revealed a diffusion-controlled mechanism, with an activation energy of 18.40 kJ mol−1. Due to the characteristics of the leaching curve, the process was divided into four segments, with corresponding activation energies determined for each segment (16.48, 11.80, 13.88, and 20.50 kJ mol−1). The proposed MgCl2 system enables efficient lead leaching with a reduced amount of leaching agent, thus representing a more sustainable approach to the valorization of Pb–Ag jarosite sludge.