1. Once mining unit operations produce the broken ore (i.e., muck) through drilling and blasting operations, the top fragment size of the muck can be as large as 1 m or larger. The 80 percent passing (P80) size distributions of run-of-mine ore (ROM) can be as large as 36 inches. Subsequently, the ROM is passed through various sizes of crushers for ease of handling (e.g., transportation) and to improve processibility. To get a sense of how energy requirement changes in conventional size reduction with respect to the varying product size required for processing, estimate the Horsepower needed to crush 1000 tonnes/hour of hard rock ore with a work index of 14.0 kWh/tonne. Assume that the crushing will be carried out successively from a P80 of 36 inches in the ROM size range to a P80 of 0.05 inch while keeping the size reduction ratio (i.e., F80/P80) constant at 3 in all stages. Also, assume that this work index remains valid for the whole range.

a) Tabulate and plot the power (in HP) calculated as a function of P80 representing the range (note: the graph to be constructed) should have six data points when complete). 10 marks.

b) Based on the data plotted, what can you conclude about the energy requirement when the particle size decreases beyond the P80 of inch that represents the boundary between crushing and grinding (i.e. rod milling) in conventional size reduction practice? 4 marks.

2) The following diagram shows a simplified process diagram for the flotation recovery of copper from a polymetallic sulphide ore, consisting of roughers and scavengers representing the primary stage. Suppose that sampling around the circuit has indicated the copper grades given on the diagram (in % by weight). The copper-bearing mineral in the ore is chiefly chalcopyrite (CuFeS2).

a) Considering the % Cu in pure chalcopyrite (34.63%), determine how pure the copper is concentrated in the first stage (C1) and the second stage (C2) by expressing the purity relative to the case of pure chalcopyrite (i.e., 100% corresponding to the 34.63%Cu, the theoretical maximum grade attainable). 3 marks.

b) You will realize that the percentage purity of C1 and C2 is in no way close to chalcopyrite. This is because of the co-flotation of other minerals in the polymetallic sulphide ore. In the primary stage, operators always pay more attention to the recovery of concentrate in a large mass than the selectivity between different metal-bearing minerals. The selectivity can be achieved in subsequent stages (e.g., cleaners, recleaners etc). However, we are not concerned with the subsequent stages here. Determine the ratio of concentration in the roughers and scavenger sections (i.e., C1 and C2). 5 marks.

c) What is the % Cu recovery in the roughers and scavengers, respectively, based on the same fresh ore with 0.81% Cu and the combined overall recovery? 5 marks. d) Construct a 2-point grade-recovery curve showing the circuit performance based on the cumulative grade and the cumulative overall recovery for copper. What can you conclude about how it is shaped? 7 marks.