Effect of Mineral Density for Milling Magnetite Ores

Transcription

1 Effect of Mineral Density for Milling Magnetite Ores Alex Jankovic Phil Baguley Walter Valery Peter Holtham Metso Process Technology & Innovation IRON ORE July Perth, Western Australia

2 Overview Introduction Industrial surveys Laboratory test work Comments Conclusions 2 / 21

3 Introduction 3 / 21

4 Introduction Ball mills in closed circuit with cyclones PRODUCT Feed CYCLONE BALL MILL 4 / 21

5 Discussion Topic Bond methodology used for sizing ball mill circuits Mineral density affects cyclone classification performance Ball mill circuits for magnetite ore underperform 5 / 21

6 Industrial circuit example Circuit capacity around 25% below design Two surveys were undertaken Samples were sized down to 20 µm, the sized fractions assayed by XRF data were mass balanced on a size-by-size and mineral basis using Limn silica, magnetite, CaO, MgO and Al 2 O 3 content of each stream compared on a sizeby-size basis 6 / 21

7 Cyclone streams silica in all the streams is significantly coarser than the magnetite corrected cut size (d50c) for magnetite was 29 µm, for silica 68 µm. Classification efficiency for -53 µm fraction: magnetite 42%, silica 65% 7 / 21

8 Ball mill performance Silica in the ball mill product is coarser than the magnetite in the ball mill feed Most of the circulating load in the ball mill circuit is liberated magnetite If classification of the silica and magnetite occurred at the same cut size, throughput would be higher Survey Mineral F80 (µm) Survey 1 Survey 2 P80 (µm) Reduction ratio Magnetite Silica Remainder Circ. load % Magnetite Silica Remainder / 21

9 Laboratory test work Can effect of magnetite density on grinding performance be simulated in laboratory conditions? Laboratory testwork carried out by Metso PTI vacation students in collaboration with CSIRO in Brisbane. 9 / 21

10 Modified locked cycle tests Test 1. Standard Bond ball mill test, 250 % circulating load and 100 % classification efficiency Test 2. Simulates a typical industrial ball mill in closed circuit with cyclones, 250 % circulating load and 50 % classification efficiency Test 3. Simulates a ball mill in closed circuit with high frequency screens, 100 % circulating load and 90 % classification efficiency Test 4. Takes into account cyclone density effect, 250 % circulating load and 50 % classification efficiency for non-mags, 30% for mags (error in the paper!!) 10 / 21

11 Bond test 11 / 21

12 Modified locked cycle test Test 1. Standard Bond ball mill test, 250 % circulating load and 100 % classification efficiency 12 / 21

13 Modified locked cycle test Test 2. Simulates a typical industrial ball mill in closed circuit with cyclones, 250 % circulating load and 50 % classification efficiency Test 3. Simulates a ball mill in closed circuit with high frequency screens, 100 % circulating load and 90 % classification efficiency Test 2, 50% Test 3, 10% 13 / 21

14 Modified locked cycle test Test 4. Takes into account cyclone density effect, 250 % circulating load and 50 % classification efficiency for non-mags, 30% for mags 14 / 21

15 Test results grinding capacity Test Classification Eff. % Circ. Load % P 80 µm Grindability (g/rev) Relative grinding capacity (%) % Non-mags, 30% Mags (error in the paper!!) 15 / 21

16 Comments Laboratory testwork confirms grinding capacity reduction due to magnetite density effect Laboratory testwork conducted at much coarser grind compared to industrial example. Tests at finer grind should be carried out. Laboratory testwork with the magnetic separation step time consuming Magnetic separation step has crucial effect on test results Test need further improvements 16 / 21

17 Conclusions A convectional ball mill in closed circuit with hydro cyclones grinding magnetite ore had 25% lower capacity than predicted using Bond methodology. Industrial surveys and detailed analysis on a size-by-size and mineral basis confirm reduced classification efficiency, finer cut size and over grinding of magnetite. Laboratory modified locked cycle testwork confirms grinding capacity reduction due to magnetite density effect. Modified locked cycle test with magnetic separation step need further development. Consult experts when selecting ball mill for magnetite milling!! 17 / 21

18 company/metso metsoworld metsogroup metsoworld metsogroup

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