Comminution
Crushing and grinding of ore is a significant capital and operational cost in many mineral processing plants. Up to fifty percent of the operating costs can be attributed to crushing and milling alone.
It is important to fully determine the comminution parameters relevant to the crushing and milling of an ore to enable complete plant design to take place.
AMMTEC provides a testing service able to determine comminution indices and parameters commonly used in the minerals industry.
Unconfined Compressive Strength Test (UCS)
The strength of a mineral specimen can be tested by compression until the sample fractures or fails. The strength, measured in MPa, is used in the selection of crushers and in assessing the suitability of an ore for SAG milling. Drill core can be used for testing or AMMTEC can core cylinders out of rock specimens. The core is cut to a length to diameter ratio of 2.5 to 1.0 and the ends polished before testing.
Autogenous Media Competency Test
This test is used to assess the suitability of a sample for autogenous milling. A sample of coarse rock or PQ core is tumbled in a 1.83m diameter mill for 500 revolutions at 26 rpm. The mill product is sized and the size distribution assists in determining the suitability of the material for autogenous milling.
Impact crushing tests can be carried out on screened products from the milling test to determine the strength of the milled products. The media competency test is often carried out in conjunction with other comminution tests, e.g. Crushing, Rod, Ball and Abrasion Indices to assist in the full assessment of the suitability of the ore for SAG milling.
Bond Crushing Work Index
The Work Index of large pieces of rock specimens can be tested to determine crusher power requirements. The samples are broken in an Impact Crushability test unit. Twin impact hammers strike a -75+51 mm specimen and the energy of breakage is measured. Twenty rock specimens sized at -75+51 mm are supplied for testing. The energy of breakage is applied to Bond formulae to calculate the Crushing Work Index.
JK Drop Weight Test
The Julius Kruttschnitt Mineral Research Centre has developed a procedure for the testing of ores for SAG and FAG mills. A drop weight test device breaks a number of size fractions and collected energy and sizing data can be analysed to determine parameters for use in the JKSimMet simulator software. A sample of 60 to 70 kg of ROM ore or full PQ core is required to carry out the test procedure. AMMTEC carries out the test and the JK Centre provides a full analysis of the test results.
SMC Testing
The SMC (SAG Mill Comminution) test was developed by SMC Testing Pty Ltd to provide a cost effective means of obtaining these parameters from drill core or broken ROM rock samples in situations where limited quantities of material are available.
The SMC test generates a relationship between specific input energy (kWh/t) and the proportion of fragmented/broken product passing a specified sieve size. The results are used to determine the drop-weight index (DWi) which is a measure of the strength of the ore sample when broken under impact conditions. The DWi is directly related to the JK rock breakage parameters A and b and can be used to determine the values of these parameters.
Bond Abrasion Index
This test is used to determine the abrasiveness of a test sample. The index is used by crusher and mill engineers to determine wear rates of liners. A sample of ore is stage crushed and sized to - 19+ 12.7mm and is abraded in a standard test unit. A small metal paddle is abraded by four lots of 400 grams of sample and the metal weight loss noted.
Bond Rod Mill Work Index
The Bond Rod Mill Work Index is used to determine the power draw or energy consumption to rod mill a test sample. A sample of 15 kg is stage crushed to 100% passing 12.7mm.A known volume of sample is milled in a standard Bond rod mill for a nominated number of revolutions and the product screened. Fresh feed is added to replace the under size and the sample milled again. This process is repeated until a recirculating load of 100% is reached.
Bond Ball Mill Work Index
The Bond Ball Mill Work Index is used to determine the power draw or energy consumption to ball mill a test sample. A sample of 10 kg is stage crushed to 100% passing 3.35mm. A known volume of sample is milled in a standard Bond ball mill for a nominated number of revolutions and the product screened. The test screen size is selected to give a product size close to that expected in practice. Fresh feed is added to replace the under size and the sample milled again. This process is repeated until a recirculating load of 250% is reached.
Ultra Fine Grinding
Ultra Fine Grinding is an increasingly common method of grinding employed in the mineral processing industry. Grinding material to less than 5 microns is possible in UFG mills. Fine grinding some gold ores can result in significant increases in recovery.
METPROTECH and SVEDALA mills are available at AMMTEC to carry out grinding tests. Sensors on the mills allow power consumptions to be determined and assist in scale-up calculations.
Autogenous/Semi-autogenous Mill (AG/SAG) Pilot Plant
AMMTEC's recently completed SAG mill pilot plant consists of a thoroughly overhauled SAG mill and new or refurbished materials handling and particle classification ancillaries.
The plant may be operated in either single stage or two-stage configuration with a ball mill. Pebble crushing is also incorporated for use as required. The mill is complete with load cell and power monitoring.
The SAG mill outline specifications are:
- Type: Hardinge
- Dimensions : Length x Diameter, 0.61 x 1.83 m
- Approx Volume: 1350 L
- Throughput: 0.8 to 3 tph
- Motor Power: 18.7 kW
- Mill Speed: 60-80% Critical
- Grates: 10 mm Slot width
- 70 Pebble Ports
KOEPPERN High Pressure Grinding Roller Press (HPGR) Pilot Plant
AMMTEC houses the recently commissioned Koeppern Processes Australia Pty Ltd (KPA) high pressure grinding roller press (HPGR) pilot plant in their Balcatta WA laboratory. The pilot plant is designed to provide customers with a facility to explore the applicability of high pressure comminution for a specific material or mineral. The press is designed for easy transportation to any mine site for larger scale test work or contract grinding process, complete with materials handling system.
The pilot plant is adequately sized to enable sizing of HPGR of industrial process applications. Batch testwork may be executed in the pilot plant's laboratory setting.
HPGR General Specifications are:
- Roller diameter - 750 mm
- Roller width - 220 mm
- Hinged Frame
- Dual output shaft gear reducer with safety coupling
- Hexadur® wear protection
- Installed power 200 kW
- Maximum pressing force - 1600 kN
- Maximum specific pressing force 8.5 N/mm2
- Variable speed drive 6 to 40 rpm