testwork
| Testwork Programs That Deliver Multiple Data Sets
Mining projects are applying the age-old notion of "check your work" against comminution circuit design, mill power requirement estimates and mill throughput estimates. The best way to test the results of one comminution modelling system is to replicate the calculation in a different modelling system. Unfortunately, the most common comminution modelling systems require largely incompatible test programs to provide input parameters. This paper presents some example protocols for sample collection and preparation from drillcore that simultaneously returns comminution datasets suitable for a Bond Work Index based method, an Axb dataset, and a set of SPI results. By carefully collecting data for all three methods, high quality geometallurgical dataset can be created.
(Presented at Procemin 2008, Santiago, Chile)
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Mining projects are applying the age-old notion of "check your work" against comminution circuit design, mill ...[↓ read more ↓] [download]
| Alex Doll & Derek Barratt | |
testwork
| Effect of Sample Dimensions on Comminution Testwork
Comminution tests on a particular project have displayed completely different breakage characteristics relative to a database, depending upon which test procedure was performed. Some of these differences are attributed to the dimensions of the sample that is presented to a test, e.g., a Bond crushing test compared to a ball mill test, while other differences can be attributed to a hardness profile that is inherent in a particular size class compared to another coarser or finer size class, e.g., fracture density and mineral filling and/or grain size. Ore types can respond with a characteristic hardness profile by size which may not be identified if only one sampling and testwork regime is used.
(Presented at Procemin 2009, Santiago, Chile)
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Comminution tests on a particular project have displayed completely different breakage characteristics relativ...[↓ read more ↓] [download]
| Alex Doll & Derek Barratt | |
testwork
| Comparison of UCS to Bond Work Indices
Unconfined Compressive Strength (UCS) is a commonly used rockmass strength measurement used by rock mechanics practitioners. This paper examines potential relationships between UCS and Bond Work Index values (crushing, rod mill and ball mill). Data from 11 mines located around the world is analysed for correlations between UCS and various Wi values.
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Unconfined Compressive Strength (UCS) is a commonly used rockmass strength measurement used by rock mechanics ...[↓ read more ↓] [download]
| Alex Doll, Derek Barratt & Ken Wood | |
testwork
| Effect of core diameter on the Bond impact crushing work index test
The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 50 mm and 75 mm in effective diameter. NQ-diameter drill core, frequently used in mineral exploration programs does not meet that specification, it being 45 mm diameter or less.
This paper reports the effect of performing the impact test on contiguous sections of HQ diameter and NQ diameter core, exploring the hypothesis that the contiguous intervals give equivalent results in spite of the core diameter difference.
[↑ read less ↑] [download]
The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 5...[↓ read more ↓] [download]
| Alex Doll, Derek Barratt & Bob Phillips | |
testwork
| Testwork template spreadsheet
Blank spreadsheet that is pre-populated with the field names needed to import laboratory test results into the SAGMILLING.COM circuit model testwork database (subscription required).
Enter your test results, one per row, arranged into the columns indicated.
To import into your testwork database, copy the block of cells starting with the top row down to the bottom of your data. Paste this block into the import field in the website "add testwork" page (do not worry if the text looks scrambled, the website can understand it).
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Blank spreadsheet that is pre-populated with the field names needed to import laboratory test results into the...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Calculating DWi from a drop weight test result
The drop weight test is a common laboratory measurement used to determine the comminution characteristics of rock samples. A common metric derived from a drop weight test is a value "A×b". Another common metric that is derived from the SMC Test™ variant of a drop weight test is a "Drop Weight Index", abbreviated as DWi. This work looks at a public database of test results to determine a relationship for DWi as a function of A×b.
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The drop weight test is a common laboratory measurement used to determine the comminution characteristics of r...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Commentary on the apparatus of the Bond rod mill work index
The Bond "Third Theory" of comminution was originally divided into three size classes reflecting the varieties of comminution equipment common during the time period when Bond (and his collaborators) were gathering the information to calibrate comminution models. The middle size class, represented by rod milling, is fitted to a tumbling test, referred to as the Bond rod mill work index (Wi RM , or RWi).
The apparatus used to determine this work index was described in 1943 by Bond & Maxson. Unfortunately, there are some laboratories that have deviated from the apparatus specified by Bond & Maxson and there are modern comminution models that are calibrated to this non-standard mill geometry. (document revised 2023-08-09)
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The Bond "Third Theory" of comminution was originally divided into three size classes reflecting the varieties...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Database of public grindability testwork
Spreadsheet that accompanies the Procemin 2016 paper by Alex Doll. This spreadsheet contains a database of public grindability testwork for projects worldwide. The data is collected mostly from conference papers and NI 43-101 reports. The NI 43-101 data may not be used for commercial purposes (hence it is being given away); but it may be used for research purposes such as model calibrations and project benchmarking.
Last updated 2023-12-25.
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Spreadsheet that accompanies the Procemin 2016 paper by Alex Doll. This spreadsheet contains a database of pu...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| A public database of tumbling mill grindability measurements and their relationships
This work presents a public database of over 800 grindability measurements and a set of equations for converting between different grindability tests based on this database. Several laboratory grindability measurements commonly used in the mining industry; each is generally applicable to a particular grindability model and is incompatible with other models. Conversion between different test types is possible using a series of empirical relationships between those tests conducted at similar size classes.
The commonly used grindability tests included in the database are the Bond work indices for ball milling, rod milling and crushing; the drop weight test results A, b, A×b, DWi, Mia, Mic, Mih and ta; SAG grindability index, SGI or SPI™; and other values such as Mib and point load index.
Some examples of power-based model specific energy predictions will be compared to published mill surveys to observe how well the different models predict the specific energy of an industrial mill.
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This work presents a public database of over 800 grindability measurements and a set of equations for converti...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Appendix- Conversions between grindability test results
Appendix to the Procemin 2017 paper.
Provides basis of conversion between different grindability metrics from laboratory test results. Gives equations to convert between:
- Morrell Mia and Bond WiRM (RWi), rod mill work index
- Morrell Mia and drop weight A×b (Eg. JK DWT Axb)
- drop weight Axb and SGI (SAG grindability index & SPI)
- SGI and drop weight Axb
- Bond WiRM (RWi) and drop weight Axb
- Bond WiRM (RWi) and SGI (or SPI)
- SGI and Bond rod mill work index (WiRM, RWi)
- Morrell Mic and drop weight Axb
All relationships were developed from the public testwork database published on SAGMILLING.COM (as of August 2017).
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Appendix to the Procemin 2017 paper.
Provides basis of conversion between different grindability metrics fr...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Correction of Bond Ball Mill Work Index Test for Closing Mesh Sizes
It is commonly known that one must run the Bond ball mill work index test such you pick a closing mesh to give a P80 close to desired grind size. This is because work index frequently changes as a function of the product size in comminution. If target grind size during a project is changed, or if the test is run at the wrong product size, then it is necessarily to provide a correction.
The goal of this work is to create an equation to adjust a Bond ball mill work index from one P80 basis to another. The proposed model consists of two components, the variable coefficient that is determined from a specific work index determination and a fixed exponent determined by a calibration procedure. The model has the benefit of retaining the variability in hardness that is built into a database of work indexes, while using Hukki’s specific energy approach to adjust for P80.
The laboratory test work program was carried out on SAG belt cut and geo-unit samples of two BC copper-porphyry orebodies yielding an exponent of -0.56 across the range of typical ball mill particle size targets. For validation, the equation was run against African data by Levin (1989) revealing that the exponent changes for different ore types, but generally remains constant within an ore type. The results of this investigation confirm a sensible correlation between the existing theories that enable practitioners to calibrate and fit any work index data given the appropriate calibration exponent. Moreover, the experiments observed that Bond’s work index is less sensitive to variation in P80 than Morrell’s Mib index on the ores tested.
Paper was presented at Procemin·GEOMET 2018 in Santiago, Chile.
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It is commonly known that one must run the Bond ball mill work index test such you pick a closing mesh to give...[↓ read more ↓] [download]
| Yardin Josefin, Alex Doll | |
testwork
| Designing an optimal comminution sampling program for geometallurgy
Paper presented at Procemin 2018.
Breakage characteristics of rocks will change as a function of size; this is one reason why there are so many different grindability metrics in use by the Industry. Designing a geometallurgical sampling program for grindability requires understanding a mine's ore breakage characteristics as a function of size so that the optimal mass and dimension of each sample is collected. This requires a multi-stage, iterative procedure where the initial programs collect a wider range of data that will, if possible, be reduced in later programs as the ore breakage is better understood. A procedure is offered where two initial programs are used to design a third "optimal" program.
The first program will use feed conveyor belt cuts, bulk samples collected from tunnels, or composites of large diameter drill core to "map" the rock breakage characteristics by size. This program requires some coarse samples; for example, whole HQ-diameter core.
The second program is a reduced variability sampling program that will ultimately become part of the overall geometallurgy data set interpolated into the mine model. Results of this initial variability program are examined to identify if any size classes are redundant and may be excluded from future sample collection.
The final program is the optimized variability sampling program that draws on the two earlier programs to use only the necessary laboratory testing at the smallest sample dimension. The combined results of the second and third programs become the overall geometallurgy data set.
This iterative procedure drives toward smaller sample dimensions and minimum laboratory testing, yielding the optimal program costs without sacrificing quality.
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Paper presented at Procemin 2018.
Breakage characteristics of rocks will change as a function of size; this i...[↓ read more ↓] [download]
| Alex Doll | |
testwork
| Bond's Work Index: What it is and what it isn't
Bond's work index is one of the mostly widely used metrics of mineral grindability. In spite of its ubiquity, users are often not aware of the nuances of the work index family: what are its strengths and weaknesses. Moreover, the operating work index frequently gets confused for a specific energy (SEC) consumption in documents such as National Instrument (NI) 43-101 reports. Understanding where the work index fits into the family of power-based grinding metrics will help operators correctly apply the work index and avoid making mistakes.
Understanding your ore's variation of work index by size is particularly useful for SAG mill troubleshooting and production forecasting. Examples of the variation in work index at Centerra's Mount (Mt.) Milligan mine and the implications for mill operation and design will be discussed.
A revised definition of work index is offered that makes clear the distinction between specific energy consumption and work index.
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Bond's work index is one of the mostly widely used metrics of mineral grindability. In spite of its ubiquity, ...[↓ read more ↓] [download]
| Alex Doll & Berge Simonian | |
testwork
| Reference Table for Drill Core-Grinding test compatibility
The table shows the minimum core length and diameter for a given test to be viable assuming a 2.75 t/m³ ore is used. This reference table has also been reviewed and was given feedback by Alex Doll of Alex G Doll consulting, Ltd.
Tests included are: Bond work indexes for ball milling, rod milling, & crushing, JK DWT, SAGDesign SMC, and SPI/SGI.
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The table shows the minimum core length and diameter for a given test to be viable assuming a 2.75 t/m³ ore i...[↓ read more ↓] [download]
| Munashe Kurisa & Alex Doll | |
testwork
| Secrets of the Bond Ball Mill Grindability Test
The Bond ball mill grindability test is one of the most common metrics used in the mining industry for ore hardness measurements. The test is an important part of the Bond work index methodology for designing and measuring the efficiency of mineral grinding circuits. In spite of being called “Bond’s Law”, the work index equations are not a law of nature; but rather an empirically measured regression of a large data set collected by the Allis-Chalmers corporation in the period between 1930 and 1952. As a regression, it is valid within a specific “calibration space”, and great care is required when deviating the test procedures or observing results that are outside of that calibration space.
This paper is a collected summary of other works by the Authors that describe feed sizes, product sizes, quality control checks, and other information about interpreting the test and using its results. Examples of adjustments that are sometimes required when using the test are: changing the test product (P 80), and coping with a feed that is too fine to apply the “proper” feed preparation steps (such as is sometimes observed from HPGR or SAGDesign product testing). Related metrics, like the Morrell Mib value and Levin B value will be discussed, along with recommendations for their use on design projects.
The intended audience is any user laboratory work index test data.
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The Bond ball mill grindability test is one of the most common metrics used in the mining industry for ore har...[↓ read more ↓] [download]
| Alex Doll, Vladimir Nikolić | |
testwork
| Effect of core diameter on the Bond impact crushing work index test
The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 50 mm and 75 mm in effective diameter. NQ-diameter drill core, frequently used in mineral exploration programs does not meet that specification, it being 45 mm diameter or less.
This paper reports the effect of performing the impact test on contiguous sections of HQ diameter and NQ diameter core, exploring the hypothesis that the contiguous intervals give equivalent results in spite of the core diameter difference.
[↑ read less ↑] [download]
The Bond low energy impact (crushing) work index test is specified to be performed on rock specimens between 5...[↓ read more ↓] [download]
| Alex Doll | |