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INTRODUCTION

Predicting the size distribution in the product and the power requirements of a pilot scale Vertimill. INTRODUCTION.

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INTRODUCTION

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  1. Predicting the size distribution in the product and the power requirements of a pilot scale Vertimill

  2. INTRODUCTION • Vale, the second largest mining company in the world, has instigated a detailed study for the utilization of Vertimills as an alternative to conventional tube ball mills in pellet feed grinding applications.

  3. INTRODUCTION • Three samples were prepared with mixtures of different feeds. Normally, the grinding circuits in pelletizing plant receive the product from different mines with different properties in size distributions, hardness, density etc. Then, the preparation of distinct mixtures for testing is important.

  4. COMMINUTION MODEL

  5. COMMINUTION MODEL

  6. SAMPLES

  7. VERTIMILL PILOT TESTS • The Vertimill was operated with screw speed of 87 rpm in direct circuit configuration closed with a Derrick Vibrating Screen. Samples of new feed, mill discharge and screen oversize and undersize were collected during the tests for solids density and size distribution analysis.

  8. BALL SIZE DISTRIBUTIONS

  9. LAB TESTS • Each batch grinding test is carried out in a diferent time interval in dry basis. An additional grinding test is carried out with water at the desired solids concentration.

  10. LAB TESTS • The tests are designed to reach the desired product size distribution specified as a P80 value. In order to achieve this, grinding times are calculated assuming first order breakage and the previous test result at a shorter grinding time.

  11. LAB TESTS

  12. PARAMETERS • The grinding parameters were determined using a specialized optimization software developed by Mineral Technologies International, Inc. – MTII called BatchMillTM. The software interpolates the size distribution of each milling time in order to determine the model parameters

  13. PARAMETERS The parameter S1E was multiplied by 1.35 to correct for the higher efficiency of the Vertimill with respect to the standard ball mill.

  14. SIMULATIONS • Data from mass balance of each test was used to perform simulations using the Herbst-Fuesternau ball mill model implemented in the Modsim plant-wide Simulator. The feed and product size distributions of the mill were considered to check the accuracy of the model.

  15. MIX 2 Simulation

  16. MIX 3 Simulation

  17. MIX 4 Simulation

  18. CONCLUSIONS • As a preliminary conclusion it is very likely that the grinding mechanisms that prevail in a Vertimill are the very same grinding mechanisms that occur in the conventional ball mill. • The difference between these two types of mills is basically their energy efficiency.

  19. CONCLUSIONS • It is recommendable to validate this methodology with coarser ore samples because it is possible that other factors may influence the product size distribution and the net power drawn in the Vertimill, as for example the settling velocity in the classification and the grinding zones of the Vertimill.

  20. QUESTIONS?

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