b) The following is a description of a grinding circuit at a uranium mine in Canada. The circuit consists of a 4.42m by 2.0m long SAG mill in open cicuit with a single sizing screen. Screen oversize reports to a 2.7m diameter by 3m long ball mill. The ball mill operates in closed circuit with two sizing screens, the undersize from all these screens reports to the neutral thickener. The feed rate to the ball mill is 65 tonnes/hour and the product size is 80% passing 300pm and 45% passing 75um. The work index of the ore is 23.7 kWh/tonne. (i) (ii) Sketch a flowsheet of the grinding circuit. [3] If electrical power is available at 30c/KWh, using Bonds'equation estimate the power cost in dollars per 24 hour day, required for comminution of the ore. List the assumptions made in your calculations. [4] (iii) Using a grinding ball size of 0.1m, calculate the percentage critical speed if the SAG mill rotates at 15 rpm. [3]