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The energy requirements of your grinding circuit are an important factor determining your project economics.


SGS has unrivaled expertise in conducting bench-scale tests, such as the MacPherson Autogenous Grindability Test to design power-efficient grinding circuits. We have evaluated more than 750 ore samples from more than 300 deposits using the MacPherson 18” mill test.

The MacPerson Autogenous Grindability Test determines the MacPherson Correlated Autogenous Work Index*. This can be used in conjunction with the Bond Rod and Ball Mill Work Indices to determine power requirements, and to suggest circuit configurations for autogenous grinding (AG) and semi-autogenous grinding (SAG) circuits. Bond’s Third Theory of Comminution is used to calculate net power requirements.

The test is a closed circuit, dry grindability test run in a small standard SAG mill using mill charge level control and air classification to give a minus 14 mesh product. The test is run continuously, similar to a small pilot plant, for a minimum of six hours and until a steady-state is achieved.

 A correlation was determined between the operating work index, determined from full scale and pilot plant operations, and the gross work index determined from small scale tests.

At test completion, all the products are submitted for particle size analysis, and the mill charge is dumped and observed. The charge is submitted for particle size analysis as well as size-by-size specific gravity determinations. This allows the evaluation of any preferential coarse build-up or particle density concentration in the mill charge. The mill power draw, throughput and product size distribution are used to compute a specific energy input and the MacPherson autogenous work index (AWI).

Although the importance to achieve steady-state in a grinding test is widely accepted (Bond tests), the MacPherson test remains the only small-scale AG/SAG mill test that offers this option. Steady-state is especially important in AG/SAG mills where a harder component can build up over time and negatively affect operations.

Another advantage of this test is the generation of a seasoned charge. This has particular value when considering autogenous circuits where the larger lumps must be present in the mill to provide grinding media.

SGS's team of experienced metallurgists will conduct the MacPherson Autogenous Grindability Test in combination with other bench-scale tests and circuit simulation.  The use of many methodologies provides you with a bankable solution that is unmatched in its rigor. Contact us to optimize the comminution design for your orebody.

Feed Sample Requirements

175 kg of minus 1 1⁄4” ore. Preparation from minus 4” feed by the testing group is preferred since the feed size distribution is critical.

* MacPherson A. R., and Turner R. R., “Autogenous Grinding from Test Work to Purchase of Commercial Unit”, Mineral Processing Plant Design, A.L. Mular and R.B. Bhappu, eds., AIME, New York, 1978, pp. 279-305.