Comminution testing

Maximise ore characteristics and predict comminution circuit throughput with the Integrated JK Drop Weight & SMC Test

The Integrated JK Drop Weight & SMC Test was created to combine two industry-standard tests into a single test for use in characterising ore under AG/SAG milling conditions.

The Integrated JK Drop Weight Test provides ore specific comminution parameters that are used in the JKSimMet software to analyse and/or predict crusher and AG/SAG mill performance. This allows for the optimisation of current circuits or flowsheet design for new circuits.

Developed at JKTech, the Integrated JK Drop Weight & SMC Test is a single particle breakage test across 17 size/energy combinations.

Sample requirements: The minimum sample required to provide sufficient particles for testing is 120 kg of crushed rock in the -63+13.2 mm size range. JKTech can prepare a sample to the specified size range from a larger amount if required.

The SMC Test is a metallurgical test that measures ore hardness properties that are relevant to the performance of mineral comminution circuits.

Its outputs include the Drop Weight Index (DWi), the “Morrell” parameters Mia, Mic and Mih, as well as the JK hardness parameter, Axb. These parameters can be used to size crushing, HPGR, and tumbling mill circuits to process a given ore sample. Alternatively, they can be used to predict the throughput of a given ore sample, through a comminution circuit of a specified power.

The SMC Test requires approximately 30 to 40 kg of ore, significantly less sample than the JK Drop Weight Test or JK Rotary Breakage Test. Two sample preparation methods are available: the cut-core method where the ore sample is competent and restricted in quantity; and the crush-and-select method where the ore is available in larger quantities.

Sample requirements: The length of core required for the two methods are shown in the table below.

For larger diameter core, greater lengths are required for the cut core method. Half core, quarter core and crushed rock can also be used. Lengths in the above table must be multiplied by a factor of two for half core and four for quarter core, respectively.

Measuring ore grindability in rod mills

The Bond Rod Mill Work Index is a measure of the resistance of the material to grinding in a rod mill. It can be used to determine the grinding power required for a given throughput of material under rod mill grinding conditions. It is a 'locked cycle' test conducted in closed circuit with a laboratory screen.

Sample requirements: A minimum of 20 kg of material crushed to nominally minus 19 mm is preferred. JKTech would stage crush the sample to minus 12.5 mm, as required for the Bond Rod Mill Work Index test feed. JKTech can prepare a representative sample, stage crushed to minus 12.7 mm, from a larger sample of ore if required.

Measuring ore grindability in balls mills

The Bond Ball Mill Work Index is a measure of the resistance of the material to grinding in a ball mill. It can be used to determine the grinding power required for a given throughput of material under ball mill grinding conditions. It is a 'locked cycle' test conducted in closed circuit with a laboratory screen.

The Bond Ball Mill Work Index can be used in the design calculations and simulations using JKSimMet of a new grinding circuit. A Bond Ball Mill Work Index may also be used in the simulation and optimisation of existing mill(s) and the associated grinding circuit(s).

Sample requirements: A minimum of 8 kg of material crushed to nominally minus 10 mm is preferred. JKTech would stage crush the sample to minus 3.35 mm, as required for the Bond Ball Mill Work Index test feed. When a JK Drop Weight Test is also being carried out, sufficient sample should be available from the JK Drop Weight Test residue.

An improved method using less mass compared to the Bond Ball Mill Work Index test

The JK Bond Ball Mill (JKBBM) test, is a locked cycle grindability test conducted using a standard laboratory Bond Ball Mill with the same steel ball charge and material feed size (100% passing 3.35 mm) as the Bond Ball Mill Work Index test.

The test requires approximately 50% less material than the Bond Ball Mill Work Index test.

The JKBBM test can be reliably applied to samples that have previously been excluded from testing due to mass limitations.

Sample requirements: A minimum of 4 kg of material crushed to nominally minus 10 mm is preferred. JKTech would stage crush the sample to minus 3.35 mm, as required for the Bond Ball Mill Work Index test feed.

For more information view our JK Bond Ball Mill Test Brochure (PDF, 1 MB).

A fast and convenient way to estimate the strength and fracture toughness of an ore

The Point Load Index can be used to simultaneously characterise rock for blastability and comminution processes.

In a Point Load Test, a sample of rock is mounted between two pointed plates and pressure is applied until failure of the sample occurs. The peak applied load is recorded. This is repeated on a minimum of 20, ideally 50 pieces of rock within a sample with the results used to calculate the Point Load Index.

Sample requirements: Sufficient core to break 50 pieces with a length-to-diameter ratio of at least 2.5:1 and a core diameter ideally about 50mm, although 20 to 60 mm is acceptable. Rock pieces in -75+50mm range can also be used - again 50 pieces with 2.5:1 aspect ratio and reasonably parallel end surfaces.

Is the HPGR grinding alternative right for your application?

High Pressure Grinding Rolls (HPGR) are increasingly becoming a part of hard rock processing due to their energy efficiency, ability to induce micro-cracks and preferential liberation, coupled with high throughput and high reduction ratio.

JKTech offers two different High Pressure Grinding Rolls tests using a laboratory-scale Krupp Polysius machine:

Type A test: Ore energy response to HPGR – During this test work, the best comminution to energy response is targeted and a minimum of six tests is normally carried out to achieve an effective characterisation of an ore under different HPGR operating pressures.

Type B test: Ore variability response to HPGR – Ore variability tests are carried out on as many ore types as can be provided, to test the relative response of the ore to the same HPGR process settings.

Sample requirements: The recommended sample size for each HPGR ‘pass’ is between 20 and 30 kg, therefore the HPGR Type A requires between 120-180kg or material to complete 6 passes.

The Steel Wheel Abrasion Test and employs a custom-designed test rig, appropriately called the SWAT, and is based on the standard Rubber Wheel Abrasion Tester (RWAT). The new SWAT is designed to overcome certain shortcomings of the RWAT relating to insufficient stress levels to truly reflect those experienced by grinding media in operating mills. The test procedure involves ore of a given size being fed by gravity into the gap between a rotating steel wheel and a stationary section of the steel to test for wear. The mass of the steel section is measured before and after the test to determine wear and delivers an abrasive wear parameter k₁.

Sample requirements - Steel Wheel Abrasion Test: Approximately 3-4 kg of material in the correct size fraction (-850+300 µm) per combination of grinding media and material type. Grinding media as provided by client, preferably 50 mm diameter cylinders. It is recommended to test approximately 3-5 media cylinder samples for each media/material combination.