Microwave drying method investigation for the process and kinetics of drying characteristics of zinc-leaching residue.

Due to the high moisture content in the zinc-leaching residue, it is easy to cause safety problems when directly entering the kiln. Microwave drying can minimize particle agglomeration and promote cracks on the mineral surface, which benefits the subsequent recovery and smelting of zinc-leaching residue. The results showed that increasing microwave power and particle size range could improve the maximum drying rate and reduce the drying time. The maximum drying rate of 20 g zinc-leaching slag with a microwave power of 700 W, a particle size of 1-10 mm, and a moisture content of 20% can be higher than 0.365%/s and reach complete drying within 120 s. The drying results were fitted and statistically analyzed using nine common kinetic models of drying, the surface diffusion coefficient changes were further analyzed at four levels, and the reaction activation energy (Ea) was calculated. According to Fick's second law, when the average particle size increased from 0.044 to 5.5 mm, the surface diffusion coefficient increased from 6.2559 × 10-9 to 3.8604 × 10-6 m2/s, which showed that the effect of particle size change on microwave drying process was significant. The Ea of the drying reaction was 18.1169 kJ/mol. This method provides an idea for efficiently treating secondary resources containing valuable metals.