Issue34

Q. Like et alii, Frattura ed Integrità Strutturale, 34 (2015) 543-553; DOI: 10.3221/IGF-ESIS.34.60 546 Under microwave irradiation, the failure of mineral boundary elements is the root cause of the microwave-assisted mineral liberation. The calculation involves taking the mechanical state of the mineral boundary element as the monitoring object, and the ratio of the number of boundary elements around galena in the failure state to the total number of mineral boundary elements is defined as the mineral boundary element failure rate. During calculation and analysis, this study focused on mineral boundary element failure rate changes and the development law under different conditions of irradiation and mineral composition. Under microwave irradiation, the heated rock generates thermal strain and thermal stress. An element after yield is considered to be a failure element in this paper. The calculation assumes several conditions. First, model boundaries are adiabatic, and no heat transfer occurs between the model and the surroundings. The initial temperature of the model is 25 °C. Only galena absorbs microwave energy under microwave irradiation. The model boundary is free of any constraint. Finally, contact between galena and calcite occurs in a fixed manner. Figure 2 : Geometric plot of computed model Material parameters The thermal conductivity and specific heat of galena and calcite are presented in Tab. 1, whereas the thermal expansion coefficient is shown in Tab. 2 [23, 24]. Thermal conductivity coefficient (w/m °C) Specific heat (J/kg °C) 25°C 100°C 227°C 25°C 227°C 727°C Calcite 4.02 3.01 2.55 819 1051 1238 Galena 2.78 2.23 1.92 209 212 234 Table 1 : Thermal conductivity and specific heat capacity of the mineral [23, 24]. 100°C 200°C 400°C 600°C Calcite 1.31 1.58 2.01 2.4 Galena 6.12 6.1 6.32 6.68 Table 2 : Thermal expansion coefficient of the mineral (10 -5 ) [23, 24]. Both galena and calcite adopt the strain-softening model. This model is based on the Mohr–Coulomb model with non- associated shear and associated tension flow rules. Fig. 3 shows the one-dimensional strain softening model. The curve is linear to the point of yield; within this range, the strain is elastic only, e e e  . After yield, the total strain is composed of elastic and plastic parts, e p e e e   . The mechanical parameters are presented in Tab. 3 [21, 25].