Recovery of zinc and lead by simultaneously leaching from lead slag fuming dust with ammonium chloride solution

The effects of leaching temperature (60−105 °C), NH₄Cl concentration (3−7 mol/L), liquid/solid ratio (4:1−12:1 mL/g), stirring speed (150−750 r/min), and leaching time (5−90 min) on the leaching rates of Zn and Pb were investigated. The leaching kinetics of Zn- and Pb-rich fuming dust with a NH₄Cl solution was also studied. The leaching rates of Zn and Pb respectively reached 98.2% and 75.6% at leaching temperature of 100 °C, an NH₄Cl concentration of 7.0 mol/L, a liquid/solid ratio of 10:1 mL/g, a stirring speed of 450 r/min and leaching time of 60 min. The kinetics results indicate that the leaching of Zn and Pb conforms to the shrinking unreacted core model and is controlled by the internal diffusion of NH₄Cl through the reacted fuming dust layer and external diffusion of NH₄Cl through the leaching solution boundary layer, respectively. The apparent activation energies of Zn and Pb are 23.922 and 19.139 kJ/mol, respectively. This study demonstrates that the use of NH₄Cl solution, without ammonia, is an environmentally friendly method for simultaneous extracting Zn and Pb from the fuming dust of lead blast furnace slag.