Microwave dielectric properties and thermochemical characteristics of the mixtures of walnut shell and manganese ore

In this work, dielectric properties and thermochemical characteristics of mixtures of walnut shell and manganese ore were systematically investigated. Results indicated that reducing manganese ore by walnut shell was divided into four stages identified by temperatures: <150 °C, 150 °C–300 °C, 300 °C–480 °C, greater than 480 °C. Higher than 200 °C, the dielectric constants (ε_r′), dielectric loss factors (ε_r″)and loss tangent coefficients (tan δ)of mixture at a ore/biomass mixing ratio of 10:1.2 were observed to suddenly drop to low levels, with 5.107 (F/M), 8.5 × 10⁻⁴ (F/M), 1.66 × 10⁻⁴ (F/M), respectively; which were attributed to the MnO₂ reduced by the reductive volatiles produced by biomass pyrolysis. Meanwhile, the volatiles rendered a decrease in density and dielectric properties of the mixture. The work highlights the possibility of reducing manganese ore by walnut shell with microwave heating.