Size Reduction and Milling

In a grain milling operation conforming to Rittinger's law ($E = K_R \left[\frac{1}{d_2} - \frac{1}{d_1}\right]$), grinding grain from an initial average size of $d_1 = 5.0\text{ mm}$ to $d_2 = 1.0\text{ mm}$ consumes $8.0\text{ kW}\cdot\text{h/tonne}$. If the material is further ground to $d_3 = 0.5\text{ mm}$, the total energy required from the original 5.0 mm size in kW$\cdot$h/tonne is: