Evolution of metallurgical balance

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WILKE, A.V., CARRASCO, P.C. and CORTES, M.G. Evolution of the estimation of the metallurgical balance. Fourth World Conference on Sampling & Blending, The Southern African Institute of Mining and Metallurgy, 2009.

Evolution of the estimation of the metallurgical balance
A.V. WILKE, P.C. CARRASCO and M.G. CORTES
*El Teniente Codelco ChileThe metallurgical balance is a tool usually applied in the mining industry. The final result is used for different objectives. All the existing software for the calculation of the metallurgical balance fits the numbers in such way that a logical correspondence between the input and output materials exist. Nevertheless, the accuracy of the metallurgical balance strongly depends on the quality of theinput data. Division El Teniente of Codelco Chile has been optimizing the metallurgical balance system the last 14 years. As well, it has participated in the development of corporate norms to optimize the operations of sampling and weighting systems. As a consequence, the precision and the accuracy of the metallurgical balance have been improved in a significant way. Also the understanding ofprocess variability was enhanced. The improvements have allowed Codelco to discover and minimize hidden losses and to better support top management decisions. The present paper describes the main aspect of the continuous improvement process.

Introduction
The metallurgical balance (BM) is an inheritance of the Kennecott American pre-nationalization administration. The calculation model of the BM inthe Division Teniente was computerized in 1980 considering the process control elements existing at that time, see Figure 1. With all the information, the difference between the

concentrate tonnage sent by the concentrator and the tonnage of the concentrate received by the smelter was estimated. Then, the tonnages and grades were fitted in order obtain a zero closing difference. Later, therecoveries and official figures of production were estimated. As the measurements of almost all the control points were inaccurate and imprecise, the closing differences were also

1. 2.

Mineral feeder Incorrect weight system Mineral feeder Incorrect sampling system

3. 4. 5. 6. 7.

Process concentrate Incorrect sampling system Concentrator general tail Incorrect sampling system Internaltail Correct sampling system Internal tail Incorrect sampling system Concentrate received in smelter (calculated) Incorrect sampling and weight system Concentrate received in smelter (calculated) Incorrect sampling system

8.

9. Secondary material Incorrect sampling system 10. Slag’s Incorrect sampling system

11. Final product (metallic copper) Correct weight system

Figure 1. Sampling andweight 1994

EVOLUTION OF THE ESTIMATION OF THE METALLURGICAL BALANCE

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biased and imprecise. As a consequence of the fitting process, the adjustment constantly harmed the concentrator and benefitted the smelter (Figure 2). In this scheme, the actual causes of problems were hidden by the MB process. As a consequence, bad decisions andunnecessary actions were taken along the mining value chain, from rock to anodes. Also, the tonnage of concentrates stockpiles was artificially inflated.

Improvements at the concentrator
The improvements conducted in the concentrator were the following ones: Weighting systems A high standard weighting system was installed to improve the accuracy and precision of the estimation of the concentratetonnage at the transfer point. Later, this standard was applied to all the weighting systems associated with the calculation of the BM in the concentrator. Corporative Norm CNAM 014, ‘Weighting systems in Conveyor belts’11 was implemented. Back analysis proved that the application of this norm has been fundamental in the improvement process of the quality of the MB. It is in line with other...
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