“Send the same grade as last time” is a convenient purchasing instruction. It is less useful when the feed has changed, the circuit has been modified, or magnetite consumption is creeping up.

The right magnetite grade for dense media separation is the grade whose particle size distribution, magnetic content, and density suit the separator and operating conditions. Magnetite grade selection means looking at how the medium behaves in the plant, including how well the magnetite is recovered afterwards.

The finest product is not automatically the best choice. Neither is the one with the lowest price per tonne. Before changing an order, it helps to be clear about what the plant needs from the material.

What Does Magnetite Grade Mean?

In this context, grade commonly describes the magnetite product’s particle size classification. Names such as Fine, Superfine, and Ultrafine identify products with different sizing characteristics.

Those names should always be read alongside the specification. They are not a universal ranking of quality, and a grade name from one supplier should not be assumed to match the same name from another.

Particle size distribution describes how much of a sample falls below particular sizes. It is more informative than saying the material is “fine”, because a magnetite product contains particles across a range of sizes.

Martin & Robson’s magnetite range includes Maxifine, Ultrafine, Superfine, Fine, Medium and Coarse grades. The published sizing ranges provide a starting point for comparing those products, while the recommended application still needs to be checked with the plant.

How Do You Read a Particle Size Specification?

A specification stating that 90–95% passes 45 microns means that the stated proportion of the tested material is smaller than that size under the specified test method. It does not mean every particle is 45 microns, or that 45 microns is the average particle size.

For example, Martin & Robson publishes a 90-95% passing 45-micron range for Ultrafine and an 80–86% range for Fine. Those figures help show how the products differ. They do not, by themselves, establish which will perform better in a particular DMS plant.

Ask for the full agreed sizing specification and the method used to check it. Comparisons become less reliable when one result comes from a wet screen, and another comes from a different measurement method without explaining the relationship between them.

Why Can Particle Size Change Medium Behaviour?

The magnetite has to remain sufficiently suspended to create a useful separating medium. At the same time, the suspension has to flow through the equipment and allow the feed material to separate.

Finer magnetite generally settles more slowly, which can help medium stability. However, a greater proportion of very fine material can also influence viscosity, or resistance to flow. A medium that remains suspended is not necessarily a medium that separates the feed well under every condition.

Coarser material introduces a different balance. That is why particle size selection belongs alongside medium density, separator design, and feed characteristics.

Think about what happens inside the circuit rather than how impressive a grade name sounds on the quotation. The plant has to process the material after the purchasing decision is over.

Start With the Separator and Operating Density

A dense medium bath and a dense medium cyclone do not expose the medium to identical conditions. The separator type therefore belongs near the top of the information sent to a magnetite supplier.

The intended medium density matters too. A grade recommendation should account for the concentration and behaviour of solids at the plant’s operating conditions, rather than being based on a generic description of coal washing or mineral processing.

For an existing operation, collect the current grade specification, target density, and actual performance records. For a new circuit, use the process design requirements and the equipment supplier’s input.

Keep the terminology clear. The density of the solid magnetite is different from the operating density of the magnetite-and-water mixture. Ordering material with an appropriate solid density does not establish the correct medium density for the plant.

What Else Matters Besides Sizing?

Magnetic content helps describe how much of the supplied material responds to magnetic separation. This is relevant to recovering magnetite from the process for reuse.

Fe content measures iron content. It is useful product information, but it is not interchangeable with magnetic content. Two numbers expressed as percentages can describe quite different characteristics.

Density provides another part of the specification. Buyers should confirm whether the figure refers to material density or bulk density, as these measurements serve different purposes.

Consistency brings those characteristics together. The plant needs deliveries that remain within the agreed limits, supported by testing that makes the results comparable over time.

Can the Plant Recover the Grade Being Considered?

Separation performance is only part of a grade trial. The magnetite also has to pass through the recovery arrangements already installed at the plant.

A change in sizing may affect how the material behaves on screens and through magnetic recovery. If losses rise, the plant needs to establish whether the cause is the grade, equipment condition, operating settings, or another change during the trial.

That is a good reason to involve the operations team early. A supplier can recommend a product, but the people running the circuit know where the recovery system is already under pressure.

Reviewing those limits before the trial is generally easier than explaining an unexpected increase in consumption afterwards.

When Is It Worth Reviewing the Current Grade?

A review makes sense when the operating conditions or the results have changed. That might follow a change in feed, a new separation requirement, equipment modifications, or a persistent performance problem.

It can also be useful when sourcing arrangements change, and the incoming material no longer behaves like the product previously supplied.

Changing grades without identifying the problem makes the result difficult to interpret. If medium density control is unstable because a measurement is unreliable, a new magnetite grade may leave the original problem untouched.

Establish a baseline first. Record the grade, operating conditions, product quality, recovery, and consumption over a representative period. Then decide what the proposed change is intended to improve.

How Should a Magnetite Grade Selection Trial Be Assessed?

Agree the trial with the plant and supplier, including the practical limits on what can be kept consistent. Useful measures include separation performance, medium behaviour, magnetite losses and the resulting operating cost.

Watch for other changes during the same period. A different feed, a repaired screen or an adjustment to recovery equipment can affect the outcome and should be recorded.

The purchasing comparison should then use both delivered price and measured consumption. A more expensive grade may be justified by better results, but that value needs evidence. Equally, a lower-priced grade may be suitable if it achieves the required performance consistently.

The purpose of a trial is to find out, not to defend the decision already made.

What Should You Send to a Magnetite Supplier?

Give the supplier enough information to make a useful recommendation:

  • The application and separator type.
  • Feed characteristics and the required separation result.
  • Target medium density and the current magnetite specification.
  • Recent consumption and recovery information.
  • The performance issue or change being considered.
  • Expected volumes, delivery requirements and proposed trial conditions.

Martin & Robson offers technical support for magnetite operations, including plant audits and research into grade and separation performance. Use that discussion to connect the product specification with what is happening in your circuit.

The right magnetite grade should have a clear reason behind it. When the recommendation can be explained in terms of your equipment, operating conditions, and measured results, the next purchase order becomes a much easier decision.