Effect of ball size on the performance of grinding and flotation circuits: the Sarcheshmeh copper mine case S. Banisi* and M. Farzaneh At the Sarcheshmeh copper mine, 41 000 t ore per day with an average grade of 0 . 9%Cu is ground to 70% passing 75 mm. Grinding is effected in eight parallel lines of 865 m ball mills in a closed circuit with cyclones. The makeup balls are 80 mm forged alloy steel balls and the average ball consumption is 750 g t 21 ore ground. In order to optimise ball size distribution inside the mill, based on the previous investigation, instead of using only 80 mm makeup balls, a combination of 80 and 60 mm (75 and 25 wt-%) ball charge was used in one of the grinding lines. To evaluate the performance of three ball types, namely, forged alloy steel balls (A), ductile cast iron (C), high chromium cast iron (D) and also a combined (80 and 60 mm) charge of forged alloy steel balls (B), four identical parallel mills were charged accordingly. These four mills were sampled during a period of 1 year. The amount of material finer than 75 mm cyclone overflows was selected as a criterion for the performance evaluation. It was observed that in a mill with the combined makeup balls, the amount of fines (,75 mm) produced was 4% higher than that of the other mills. The consumption of ball types A, C and D were 730, 710 and 534 g t 21 respectively. The results of laboratory flotation tests showed that owing to an improvement in the production of fines, an increase of 1 . 4% in the overall copper recovery is obtainable. Owing to the promising results, the new makeup ball regime was implemented in all mills in the plant. Keywords: Ball size, Flotation, Grinding, Liberation degree Introduction The Sarcheshmeh copper ore body that may rank as the third or fourth largest in the world contains one billion tonnes averaging 0 . 90% copper and 0 . 03% molybdenum. It is located southeast of Iran and has been pro- cessing 41 000 t d 21 ore since 1982. The mine produces 140 000 t copper and 3500 t molybdenite concentrate per year. After three stages of crushing, the ore with a 12 . 7 mm F 80 is fed to eight parallel ball mills working in closed circuit with cyclones to produce a product 70% finer than 75 mm. The concentrate of the first stage of flotation is reground and the tailing constitutes the main component of the plant final tailings. A concentrate with an average grade of 31%Cu is obtained after cleaning and recleaning stages. Total recovery of the plant varies between 84 and 88% depending on the operating conditions and ore type. At the Sarcheshmeh complex, 52% of total electrical energy is consumed in the concentration plant. Grinding section uses 72% of the energy consumed in the plant which in turn is only 5% of the total grinding cost. Therefore, an improvement in the grinding operation not only is economically important but actually has a direct effect on the performance of the downstream separation process, i.e. flotation. In the grinding circuit, 80 mm forged alloy steel balls are used with an average consumption of 750 g t 21 ore milled. This translates into more than $100 000 . 00 per month for each mill, ,80% of the total grinding costs. The relatively high cost of grinding balls and their critical effect on the grinding efficiency initiated a project into a detailed study of their quality and size distribution. The significant effect of ball size on the grinding efficiency has been mentioned in literature in many istances. 1–7 Only in one case, the size distribution of the entire charge of a 2 . 7563 . 05 m ball mill was measured and reported. 8 It is believed for the first time that at the Sarcheshmeh copper mine, a mill in much larger size was emptied and the ball size distribution was measured. A detailed study on this subject was reported elsewhere. 9 Background New makeup ball regime The ball size distribution was obtained from the examination of entire charge (280 534 balls with a mass Mining Engineering Department, Shahid Bahonar University of Kerman, PO Box 761-133, Kerman, Iran *Corresponding author, email banisi@mail.uk.ac.ir ß 2006 Institute of Materials, Minerals and Mining and The AusIMM Published by Maney on behalf of the Institute and The AusIMM Received 25 October 2005; accepted 5 July 2006 DOI 10.1179/174328506X128805 Mineral Processing and Extractive Metallurgy (Trans. Inst. Min Metall. C) 2006 VOL 115 NO 3 165