1. ADVANCES IN GRINDING technology
DM Mihir

2. CONTENTS Introduction Bond’s Work Index Different Grinding Equipment's
Crushing
Grinding
Bond’s Work Index
Different Grinding Equipment's
Grinding Circuits
Ball Mill
Rod Mill & Ball Mill
SAG Mill & Ball Mill
HPGR & Ball Mill
Case Study
Results
Conclusion
References

3. INTRODUCTION

4. Stress Forces - 1 courtesy: metso
Tensile

5. Compression

6. Stress Forces - 3 courtesy: metso
Impaction

7. Stress Forces - 4 courtesy: metso
Shearing

8. BOND’S WORK INDEX W= 10Wi ( 1/√P – 1/√F )
Bond’s Work Index (Wi) is the energy required, expressed as kWh/short ton to size reduce a material of infinitely large size particles to a product of 80% passing 100 microns. Following Equation is used to estimate specific power consumption for scale up purposes.
W= 10Wi ( 1/√P – 1/√F )

9. DIFFERENT GRINDING EQUIPMENTS
BALL MILL
In general the length of the mill is slightly higher than the diameter though not a rule.
The grinding media is spherical .
The size dispersion of the product is high.

10. ROD MILL Length is higher than the diameter as a rule.
The grinding media is rods.
Mill product is coarse grind.
ROD MILL

11. SEMI AUTOGENEOUS MILLS
Diameter is very large compared to length.
Grinding media is feed lumps plus % ball charged.
Less sensitive to feed size composition unlike AG mills.
SEMI AUTOGENEOUS MILLS

12. HIGH PRESSURE GRINDING ROLLS
(HPGR)
Two Rotating Rolls one fixed & other sliding against the fixed roll under pressure.
High power saving.
Product discharged as cake.

13. GRINDING CIRCUITS Fig:1 BALL MILL CIRCUIT
1) Ore Bin 2) Ball Mill 3) Mill Discharge sump 4) Mill Discharge Pump to Hydrocyclone 5) Hydrocyclone
Fig:1 BALL MILL CIRCUIT

14. COMBINATION OF ROD & BALL MILL
F = feed, 1) Rod Mill 2) Mill Discharge Sump 3) Pump 4) Hydrocyclone 5) Ball Mill
Fig: 2
COMBINATION OF ROD & BALL MILL

15. COMBINATION OF SAG & BALL MILL
F = feed, 1) SAG Mill 2) Mill Discharge Sump 3) Pump 4) Hydrocyclone 5) Ball Mill
Fig: 3
COMBINATION OF SAG & BALL MILL

16. Fig:4 COMBINATION OF HPGR & BALL MILL
1) Ore Bin 2) HPGR 3) HPGR Discharge Screen Under Size Sump 4) Pump 5) Hydrocyclone 6) Ball Mill 7) Pump 8) Hydrocyclone
Fig:4 COMBINATION OF HPGR & BALL MILL

17. CASE STUDY- 1
1500 TPD Jharmarkotra Phosphate Concentrator is laid in two streams with two ball mills operating in parallel. Each ball mill is driven by a 600 kW motor (fig:1) giving a throughput of 750 TPD.
Energy Consumption in the 1500 TPD plant (Grinding, Floatation, Thickening & Filtration) per ton of the Ore treated was 49 kWh/ton at the best operating conditions.
A roller press (HPGR) with drive motors of 700 kW ( ) was retro fitted into one of the grinding circuit (fig:4) such that the roller press works in tandem with the ball mill.
This has resulted into increased throughput of 3000 TPD.
The power consumption of TPD plant (Grinding, Floatation, Thickening & Filtration) reduced to 31 kWh/ton of the Ore treated at best operating conditions.

18. RESULTS:
TABLE: 1
TABLE: 2

19. Case Study - 2
At Rampur- Agucha lead zinc mines of M/s Hindustan Zinc Ltd, grinding circuits with rod mill – ball mill and SAG mill – ball mill were installed depending on the changing hardness of ore from different mine pits.
For harder ores SAG – ball mill combination is preferred.

20. Power Consumption of Rod/SAG mill Circuits.
Historical record suggests that rod mill-ball mill circuit including secondary crusher consumed kWh per ton of ore to achieve ground product of d80 at 63 microns.
Whereas SAG mill- ball mill including primary crusher consumed kWh per ton of ore to achieve ground product of d80 at 63 microns.

21. Salient features of SAG- Ball Mill circuit
Primary crusher feed is 1.2 meters and the product size is -150 mm.
It may be noted that entire secondary crushing plant is avoided in SAG- BM circuits.
Cost of consumables is 30% higher for SAG – BM circuits compared to RM – BM circuits.
Maintenance cost of RM- BM to SAG- BM circuits is 1: 1.1 .

22. CONCLUSION:
It can be seen that the grinding circuit of HPGR – Ball Mill are highly energy efficient(1,3).
Attempts are being made(4) to replace ball mill from HPGR – Ball Mill circuits with verti mills or stirred media grinding mills where very fine product sizes are acceptable/desired.
RM- BM circuits consume less power, less grinding media/ other consumables and also maintenance cost is less.
SAG – BM circuits do not need secondary crushing, can handle ores with varying characteristics and causes less dust pollution.

23. REFERENCES: Basics in Minerals Processing, Metso, 2012.
(a) Sekhar, D M R., Jain, C L., Jhamarkotra Phosphate Ore Processing Plant, International Mineral Processing Congress, Turkey, 2006.
(b) HPGR in the Grinding Circuit of Phosphate Concentrator,
3 Joachintiarder, A T., Minerals Processing, Volume 53, 07-08/2012.
4 Drozdiak, JA., Klein,B., Nadolski,S.,& Bamber, A., A Pilot Scale Examination of a High Pressure Grinding Roll & Stirred Mills Comminution Circuit., International Autogeneous, Semi Autogeneous Grinding & High Pressure Grinding Roll Technology, Canada, 2011.

24. REFERENCES
5. Srikath Reddi, J Balasubramanian and Laxman Shektawat, Evaluating the Performance of Different Grinding Circuits at Rampura Agucha Mines, MPT- 2014, Andhra University.