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IsaMill

IsaMill is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand IsaMill rather than just read about it. In short: The IsaMill is a type of efficient stirred grinding mill for fine and coarse griding used in mineral industry. It was jointly developed in the 1990s by Mount Isa Mines Limited ("MIM", a subsidiary of MIM Holdings Limited and now part of the Glencore Xstrata group of companies, Australia) and Netzsch Feinmahltechnik ("Netzsch"), a German manufacturer of bead mills.

IsaMill — main illustration
IsaMill — illustration

Key takeaways

  • IsaMill belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect IsaMill to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of IsaMill from memory before moving on to harder problems.

Reference excerpt

The IsaMill is a type of efficient stirred grinding mill for fine and coarse griding used in mineral industry. It was jointly developed in the 1990s by Mount Isa Mines Limited ("MIM", a subsidiary of MIM Holdings Limited and now part of the Glencore Xstrata group of companies, Australia) and Netzsch Feinmahltechnik ("Netzsch"), a German manufacturer of bead mills. The IsaMill is primarily known for its ultrafine grinding applications in the mining industry, but is also being used as a more efficient means of coarse grinding. By the end of 2008, over 70% of the IsaMill's installed capacity was for conventional regrinding or mainstream grinding applications (as opposed to ultrafine grinding), with target product sizes ranging from 25 to 60 μm.

Introduction

While most grinding in the mineral industry is achieved using devices containing a steel grinding medium, the IsaMill uses inert grinding media such as silica sand, waste smelter slag or ceramic balls. The use of steel grinding media can cause problems in the subsequent flotation processes that are used to separate the various minerals in an ore, because the iron from the grinding medium can affect the surface properties of the minerals and reduce the effectiveness of the separation. The IsaMill avoids these contamination-related performance issues through the use of an inert grinding medium. First used in the Mount Isa lead–zinc concentrator in 1994, by May 2013 there were 121 IsaMill installations listed in 20 countries, where they were used by 40 different companies.

IsaMill Operating Principles The IsaMill is a stirred-medium grinding mill, in which the grinding medium and the ore being ground are stirred rather than being subjected to the tumbling action of older high-throughput mills (such as ball mills and rod mills). Stirred mills often consist of stirrers mounted on a rotating shaft located along the central axis of the mill. The mixing chamber is filled with the grinding medium (normally sand, smelter slag, or ceramic or steel beads) and a suspension of water and ore particles, referred to in the minerals industry as a slurry. In contrast, ball mills, rod mills and other tumbling mills are only partially filled by the grinding medium and the ore.

In stirred-medium mills, the stirrers set the contents of the mixing chamber in motion, causing intensive collisions between the grinding medium and the ore particles and between the ore particles themselves. The grinding action is by attrition and abrasion, in which very fine particles are chipped from the surfaces of larger particles, rather than impact breakage. This results in the generation of fine particles at greater energy efficiency than tumbling mills. For example, grinding a pyrite concentrate so that 80% of the particles are less than 12 μm (0.012 mm) consumes over 120 kilowatt-hours per tonne (kWh/t) of ore in a ball mill using 9 mm balls, but only 40 kWh/t in an IsaMill using a 2 mm grinding medium.

The IsaMill usually consists of a series of eight disks mounted on a rotating shaft inside a cylindrical shell (see Figure 2). The mill is 70–80% filled with the grinding medium, and is operated under a pressure of 100 to 200 kilopascals. The disks contain slots to allow the ore slurry to pass from the feed end to the discharge end (see Figure 3). The area between each disk is effectively an individual grinding chamber, and the grinding medium is set in motion by the rotation of the disks, which accelerate the medium toward the shell. This action is most pronounced close to the disks. The medium flows back toward the shaft in the zone near the midpoint between the disks, creating a circulation of the grinding medium between each pair of disks, as shown in Figure 4.

The average residence time of the ore in the mill is 30–60 seconds. There is negligible short-circuiting of the grinding zone by the feed, as a result of having multiple grinding chambers in series. The ground product is separated from the grinding medium at the discharge end of the mill. This is achieved without using screens by using a patented product separator that consists of a rotor and a displacement body (see Figure 2 and Figure 4). The relatively short distance between the last disk results in a centrifugal action that forces coarse particles towards the mill shell, from where they flow back towards the feed end. This action retains the grinding medium within the mill. The product separator is a very important part of the IsaMill design. It avoids the need to use screens to separate the grinding medium from the ground particles. Using screens would make the mills high-maintenance, as they would be prone to blocking, necessitating frequent stoppages for cleaning. Fine particles are not as susceptible to the centrifugal forces and stay closer to the center of the mill, where they are discharged through the displacement body at a rate equal to the mill's feed rate. The design of the IsaMill results in a sharp product size distribution, meaning that the IsaMill can operate in open circuit (i.e. without the need for an external separation of the discharged particles in screens or hydrocyclones to allow coarse over-size product to be returned to the mill for a second pass). It also means that there is less overgrinding at the finer end of the size distribution, such as occurs during the operation of tower mills.

… excerpt ends here. Continue reading the full article.

Illustrations

IsaMill: Figure 2. Schematic view of an IsaMill showing the principles of its operation.
Figure 2. Schematic view of an IsaMill showing the principles of its operation.
IsaMill: Figure 3. Photograph of an IsaMill disk being pushed into place on the mill's shaft. The slots in the disks are clearly shown. The orange device behind the second disk is the product separator.
Figure 3. Photograph of an IsaMill disk being pushed into place on the mill's shaft. The slots in the disks are clearly shown. The orange device behind the second disk is the product separator.
IsaMill: Figure 4. Schematic diagram showing the flow patterns of the grinding medium inside an IsaMill.
Figure 4. Schematic diagram showing the flow patterns of the grinding medium inside an IsaMill.
IsaMill: Figure 5. Photograph on an IsaMill with the split-shell design to allow easier replacement of the shell liner.
Figure 5. Photograph on an IsaMill with the split-shell design to allow easier replacement of the shell liner.
IsaMill: Figure 6. Schematic diagram of an IsaMill showing how the shell slides away from the shaft and grinding disks to allow easy access to the mill's internal components.
Figure 6. Schematic diagram of an IsaMill showing how the shell slides away from the shaft and grinding disks to allow easy access to the mill's internal components.

Worked examples

Example 1 — a first encounter with IsaMill

Start with the simplest possible case. Write down what IsaMill claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to IsaMill before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about IsaMill ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of IsaMill

In research
IsaMill appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses IsaMill in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
IsaMill is common in secondary-school and first-year university syllabi. It links to neighbouring topics Grinding mills, so understanding it makes those chapters shorter.
In everyday life
Look for IsaMill outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study IsaMill in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what IsaMill means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain IsaMill out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IsaMill in simple terms?

The IsaMill is a type of efficient stirred grinding mill for fine and coarse griding used in mineral industry. It was jointly developed in the 1990s by Mount Isa Mines Limited ("MIM", a subsidiary of MIM Holdings Limited and now part of the Glencore Xstrata group of companies, Australia) and Netzsc…

Why does IsaMill matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study IsaMill?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on IsaMill.

Tags

  • Grinding mills

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