The objective is to develop a realistic curve relating the overall cost of primary grind per ton of feed to the primary grinding capacity considering kw-h per ton of feed and the fineness of primary grind. In this case the overall cost consists of a capital cost component and an operating cost component. Basically, both components must include not only direct costs but grinding’s share of all applicable indirect and overhead cost items. This allowance of non indirect cost needs careful judgment to ensure that the cost assigned to grinding reflects the actual cost of grinding as closely as possible. To keep the work needed for this study within reasonable limits it is important to develop a preliminary estimate for an intermediate base case and a suitable scale exponent estimated and used for deriving all possible cases.
The suggested relationship is (C1/C) = (W1/W)x where C is the estimated total grinding cost per ton for the base case, W is the Kw-h per ton for the base case, C1 and W1 are the corresponding values for any other grind in the range being considered and “x” is the scale exponent. Separate exponents may be used for capital and operating cost components or a single exponent may be found applicable for the total cost. The resulting curve should relate the total grinding cost per ton to the grinding capacity provided. Next graph show the results of a grinding circuit where the flotation process is performed at 90 µm K80.
Effect of Kw-h/t milled on the grinding cost