Microwave drying of nickel-containing residue: dielectric properties, kinetics, and energy aspects

Abstract

Nickel-containing residue (NCR) is a hazardous solid waste from battery production lines. Recently, the interest in recovering valuable metals from NCR has increased because sustainable utilization of resources is more and more valued. Drying is a key part of the recovery process. In this study, we measured the dielectric properties of the NCR for different moisture contents and temperatures using the cavity perturbation method at 2.45 GHz. The microwave absorption characteristics of NCR had a positive correlation with the moisture content, while it was less efficient in the 20-180°C temperature range. Then found that the microwave drying data at different microwave powers (400-700 W) and for different sample weights (60-120 g) have a better fit with the Midilli-Kucuk model. The activation energy (Ea) was received as 9.76 W/g using an exponential expression based on the Arrhenius equation. Finally, the energy consumption reduce 110 W·h/kg than that of drying with a single microwave power by optimizing the microwave drying process.

Microwave Drying of Sewage Sludge: Process Performance and Energy Consumption

“…The main reasons for the decrease in drying rate are as follows: (1) The bound water in the sludge is attached to the interior or the surface of the solid matrix via chemical or hydrogen bonds [10], requiring more energy to break than free water. (2) The dielectric constant of the matrix is much smaller than that of water [42,64]. Therefore, the overall dielectric constant of the sludge gradually decreases with decreasing moisture content, leading to a decrease in the absorbed microwave energy and water evaporation as the drying progresses.…”

“…As a result, the heat efficiency gradually decreases as the drying progresses. The main reasons for the increase in energy consumption are as follows: The dielectric constant of the solid matrix is much smaller than that of water [42,64]; therefore, the microwave energy decreases with a decrease in M t ; moisture is mainly present in the form of bound water, which requires more energy to evaporate than free water; microwave energy is used to evaporate the moisture as well as increase the temperature; the drying rate of the sludge gradually decreases as the drying progresses.…”