The choice between milled and atomised ferrosilicon affects dense medium separation efficiency, medium stability, viscosity, recovery and operating cost. Both forms perform the same basic function: they are mixed with water to create a dense, magnetically recoverable suspension that separates minerals according to relative density. Their particle shape and size distribution, however, produce different behaviour inside cyclones, drums, baths and medium recovery circuits.

In a direct comparison of milled vs atomised ferrosilicon for dense medium separation, atomised material generally offers better flow characteristics at high medium densities. Milled ferrosilicon tends to provide good suspension stability and can be a cost-effective option where the required density and circuit conditions suit its more angular particle shape. Neither type is automatically right for every plant.

Ore characteristics, target cut-point, separator design, circulating medium density, feed contamination and magnetic recovery performance all influence the decision. A product that works reliably in a low-density bath may behave very differently in a high-density cyclone treating finely crushed ore.

The best selection is therefore based on the complete circuit, not simply the purchase price per tonne. Particle-size distribution, rheology, medium losses and achievable separation accuracy must be considered together.

Direct comparison of milled and atomised ferrosilicon

The principal difference is how the particles are manufactured. Milled ferrosilicon is produced by crushing and grinding solid ferrosilicon into the required size range. This creates particles with irregular, angular surfaces. Atomised ferrosilicon is formed by breaking a stream of molten alloy into droplets that solidify as comparatively smooth, rounded particles.

Those shapes affect how the particles interact in suspension. Angular milled particles have more points of contact and greater resistance to movement past one another. Rounded atomised particles flow more freely, especially as the concentration of solids increases.

• Particle shape: Milled ferrosilicon is angular and irregular; atomised ferrosilicon is rounded or near-spherical.
• Viscosity: Atomised material normally produces lower apparent viscosity at an equivalent solids concentration and particle-size distribution.
• Suspension stability: Fine and angular particles generally settle more slowly, although excessive fines can raise viscosity.
• High-density operation: Atomised ferrosilicon is commonly favoured where a high medium density must be achieved without making the suspension excessively viscous.
• Purchase cost: Milled material can have a lower initial price, but the relevant comparison is the cost per tonne of feed treated at the required separation performance.

These are general tendencies. A fine atomised grade can be more viscous than a coarse milled grade, which is why comparisons must be made between actual product specifications and under realistic plant conditions.

How milled ferrosilicon behaves in a DMS circuit

Milled ferrosilicon has a rough, angular morphology produced by mechanical crushing and grinding. The particles form a stable suspension when the grade contains an appropriate balance of coarse material and fines. This stability helps limit rapid settling in sumps, launders, pipework and separators.

The same particle interactions that aid stability also increase resistance to flow. As solids concentration rises, angular particles can interfere with one another and cause a sharper increase in viscosity. This may limit the maximum practical medium density or reduce separation efficiency if the slurry becomes too viscous for particles of ore to move according to density.

Milled ferrosilicon can be suitable for applications with moderate operating densities, less demanding rheological conditions or equipment designed around its characteristics. It is also relevant where a plant’s operating history, pumps, magnetic separators and density-control system are already configured for a particular milled grade.

Its suitability cannot be judged from the words “milled ferrosilicon” alone. Two grades may differ substantially in their top size, proportion of fines and particle-size distribution. Those differences can affect settling rate, medium adhesion to product, magnetic recovery and losses through screens.

How atomised ferrosilicon behaves in a DMS circuit

Atomised ferrosilicon consists of smoother particles formed as molten droplets cool and solidify. Their rounded geometry reduces inter-particle friction. This allows the medium to remain comparatively fluid at solids concentrations that could make an angular powder difficult to pump or control.

Lower viscosity is especially valuable in dense medium cyclones and high-density mineral applications. In a cyclone, both ore and medium are exposed to strong centrifugal forces. The medium must be dense enough to achieve the required cut-point while remaining sufficiently fluid for efficient stratification and discharge.

Rounded particles can settle more readily if the selected grade is too coarse or if circulation is poor. Atomised ferrosilicon is therefore still supplied in controlled size ranges, with enough fine material to support medium stability. Pumps, agitation and correct circuit velocity remain necessary; particle shape does not remove the need for sound medium management.

Atomised material is often selected for demanding separations involving high medium densities, tight control of viscosity or a need to reduce the rheological penalty of increasing solids concentration. The potential operating benefit must be weighed against delivered price, consumption and recovery performance.

Why medium viscosity influences separation accuracy

A DMS suspension must meet two requirements that can pull in opposite directions. It must resist rapid settling so that density remains reasonably uniform, but it must also flow freely enough for the ore particles to separate. Selecting a finer powder improves stability, yet too many fines increase viscosity and can make the separation less efficient.

Excessive viscosity slows the movement of particles through the medium. Near-density material is particularly sensitive because the difference between its density and the cut-point is small. If movement is restricted, particles may report to the wrong product stream, lowering recovery or contaminating the concentrate.

High viscosity can also affect pressure drop, cyclone operation, pump demand and density measurement. Operators may see the correct density reading while obtaining poorer separation because medium density alone does not describe rheology.

Conversely, a medium that is too coarse or unstable can settle in low-velocity sections. This creates density variation, blockages and inconsistent separator performance. Successful selection finds a workable balance between stability and viscosity for the plant’s operating window.

Particle-size grade matters as much as manufacturing method

Ferrosilicon powders are available in different particle-size grades. Grade names can indicate nominal fineness, but naming conventions do not always provide a complete picture. A technical review should use the supplier’s particle-size distribution, including the coarse limit and the proportion passing relevant sieve or sizing points.

A coarser grade generally has lower viscosity and drains more readily from product screens. It may, however, settle faster and can be more difficult to keep evenly suspended. A finer grade provides improved stability but can increase medium carry-over, adhesion and viscosity.

Plants sometimes attempt to solve instability by moving immediately to a finer grade. If poor agitation, inadequate circulation or a malfunctioning pump is the real cause, the change can replace a settling problem with a viscosity problem. Circuit conditions need to be checked before changing powder specification.

For an overview of available options, buyers can review the DMS Powders ferrosilicon product range and discuss the required particle characteristics against their plant data.

Key criteria for selecting milled or atomised ferrosilicon

Required operating density and cut-point

The target separation density is the first filter. Higher medium densities require a greater concentration of ferrosilicon. As concentration rises, particle shape becomes increasingly significant. Atomised powder can offer an advantage where the plant needs a dense medium that remains pumpable and responsive.

The required medium density should not be confused with the mineral’s target product specification. Washability or sink-float data, the proportion of near-density material and the expected separation efficiency all help establish the practical cut-point.

Separator type

Dense medium drums and baths operate differently from cyclones. Baths generally have lower velocities and rely heavily on suspension stability, while cyclones introduce high shear and centrifugal forces. A grade that performs well in one device is not necessarily optimal in another.

Cyclone diameter, inlet pressure, apex and vortex finder configuration, throughput and feed size all influence medium behaviour. The ferrosilicon specification must be considered as part of this operating system.

Ore type and feed-size distribution

Coal, iron ore, manganese, chrome, diamonds and other minerals do not create identical DMS conditions. Feed top size, fines content, clay contamination and surface characteristics affect viscosity and medium drainage.

Slimes entering the circulating medium can increase viscosity even if the ferrosilicon specification has not changed. A plant treating weathered or clay-rich material may therefore require stronger desliming and closer rheology control than one processing clean, competent ore.

Medium recovery equipment

Ferrosilicon is magnetically recoverable, which allows it to be collected from dilute medium after rinsing and returned to the correct-medium circuit. Magnetic separator condition, feed dilution, flow distribution and magnetic loading affect recovery.

Particle size also matters. Very fine particles may be more difficult to recover completely, while coarse particles can be lost through inefficient screening or poor drainage arrangements. Losses should be investigated by sampling the product, discard, rinse-water and magnetic separator streams instead of assuming that powder type is solely responsible.

Logistics and continuity of supply

Remote mining operations need to consider lead times, packaging, storage conditions and shipment planning. This is particularly relevant to global operations supplied across long inland and maritime routes. A technically suitable grade is of little use if stock planning does not account for consumption variability and delivery time.

Ferrosilicon powder should be kept dry and handled in accordance with the supplier’s safety information. Wet or damaged packaging can complicate dosing and inventory control. Dust-control measures, suitable personal protective equipment and properly designed transfer systems are also part of responsible powder handling.

Compare total operating cost, not only price per tonne

The lowest powder price does not always create the lowest separation cost. Medium consumption, product recovery, plant availability and concentrate quality can outweigh a difference in purchase price.

A useful cost comparison includes:

• Delivered ferrosilicon cost and applicable logistics.
• Kilograms of medium consumed per tonne of feed.
• Value of mineral recovery and product-quality changes.
• Magnetic separator and screen performance.
• Pumping, mixing and density-control requirements.
• Downtime caused by settling, blockages or unstable operation.
• Medium carried out on product and discard streams.

Consumption data must be compared over a representative operating period. A short test can be distorted by inventory changes, sump clean-outs, commissioning losses or abnormal feed conditions. Reconciled additions and losses provide a better basis for evaluating the commercial result.

A practical plant trial process

Changing ferrosilicon type or grade is best handled as a controlled plant trial. Establish a stable baseline before introducing the alternative powder. Record feed rate, feed grading, ore density distribution, circulating medium density, viscosity or rheological indicators, cyclone pressure, product quality and medium consumption.

1. Define the problem or objective. Examples include achieving a higher density, lowering viscosity, improving recovery or reducing medium loss.
2. Review the current circuit. Check desliming, screening, pumps, agitation, density instruments and magnetic separators before blaming the medium.
3. Obtain comparable product data. Assess manufacturing method, chemical composition, particle-size distribution and handling information.
4. Plan the transition. Allow for mixing with existing circuit inventory and avoid judging the new product before the old medium has been sufficiently displaced.
5. Hold major variables steady. Where practical, avoid simultaneous changes to cyclone geometry, feed preparation and operating pressure.
6. Sample the relevant streams. Measure separation performance as well as medium density and consumption.
7. Review total economics. Evaluate recovery, quality, stability and losses alongside delivered cost.

Laboratory rheology and settling tests can narrow the options, but they cannot reproduce every feature of a working circuit. Plant-scale validation remains valuable, particularly where feed mineralogy varies.

Common selection and operating mistakes

Choosing only by grade name: The full particle-size distribution is more useful than a nominal label. Request data that allows direct comparison between products.

Using density as the only control measure: Two suspensions at the same density can have different viscosity and stability. Observe rheology and separation results as well.

Ignoring non-magnetic contamination: Ore slimes and corrosion products can build up in the circulating medium. They alter rheology but are not corrected simply by adding fresh ferrosilicon.

Assuming finer is always better: Finer powder improves stability only up to the point where viscosity and carry-over become unacceptable.

Changing products without a baseline: Without reliable data from the existing operation, it is difficult to identify whether a trial improved technical performance or total cost.

Treating medium loss as a single number: Determine where the loss occurs. Screen oversize, magnetic separator effluent, leaks and material adhering to products require different corrective actions.

Which ferrosilicon type is the better choice?

Atomised ferrosilicon is often the stronger candidate for high-density, viscosity-sensitive separations and demanding cyclone applications. Its rounded particles permit high solids concentrations with comparatively favourable flow behaviour.

Milled ferrosilicon remains a practical choice for circuits operating at suitable densities where its stability, availability and economics align with plant requirements. An established circuit can perform consistently with a correctly selected milled grade, particularly when contamination and recovery are well controlled.

A blend may sometimes be evaluated to balance rheology, stability and cost, but blending requires control. Unplanned mixing of different grades can shift the particle-size distribution and make operating results harder to interpret.

The correct answer comes from matching powder morphology and size distribution to the ore, separator and recovery circuit. That is more reliable than selecting atomised or milled material from a general rule.

Frequently asked questions

Is atomised ferrosilicon always better than milled ferrosilicon?

No. Atomised ferrosilicon generally offers lower viscosity at high solids concentrations, but milled material can be technically and commercially suitable at moderate densities or in circuits designed around its characteristics. Required density, separator type, ore contamination, particle-size grade and total operating cost determine the better choice.

Can milled and atomised ferrosilicon be mixed?

They can physically be mixed, and controlled blends may be assessed for specific applications. The resulting medium will have a combined particle-shape and size distribution, so its viscosity and settling behaviour need testing. Accidental or uncontrolled mixing can make plant performance difficult to evaluate.

What information does a supplier need to recommend a ferrosilicon grade?

Useful information includes the mineral being treated, separator type and dimensions, feed-size range, target cut-point, normal medium density, current powder grade, observed viscosity or settling problems, medium consumption, throughput and destination. Details of desliming, screening and magnetic recovery also improve the selection process.

Discuss your DMS medium requirements with DMS Powders

DMS Powders supplies ferrosilicon powders for dense medium separation in the global mining sector. The company’s background and focus on DMS ferrosilicon provide context for procurement teams and plant personnel comparing medium options.

For help evaluating milled vs atomised ferrosilicon for dense medium separation, send DMS Powders your target density, separator type, feed sizing, current grade and operating concern. Contact DMS Powders for a product enquiry and discuss a specification suited to your circuit and supply requirements.

The post Milled vs Atomised Ferrosilicon for Dense Medium Separation first appeared on DMS Powders.

Selecting the right ferrosilicon grade for dense medium separation requires more than choosing a product from a particle-size table. The medium must create a stable, controllable suspension at the required operating density while remaining compatible with the separator, feed material and recovery circuit.

A grade that is too coarse may settle rapidly and produce density instability. An unnecessarily fine grade may increase medium viscosity, reduce separation efficiency and create recovery or handling difficulties. The most economical option is therefore not automatically the cheapest powder or the finest available grade. It is the grade that delivers reliable separation at an acceptable total medium consumption.

Dense medium separation plants also differ considerably. A static bath treating a relatively coarse feed has different medium requirements from a high-pressure dense medium cyclone processing smaller particles. Ore mineralogy, clay content, feed sizing, target cut density and the condition of the magnetic recovery circuit all influence grade selection.

This guide explains how particle size, powder form, medium stability, viscosity and plant operating conditions should be assessed before specifying a ferrosilicon grade.

What does a ferrosilicon grade describe?

In dense medium separation, the term “grade” normally refers primarily to the particle-size distribution of the ferrosilicon powder. Suppliers may identify products by nominal mesh size, micron range, fineness category or a proprietary grade name. These labels are useful, but they should never replace the full technical specification.

Two powders carrying similar grade descriptions may have different proportions of coarse particles, ultrafines and material within the main operating range. Those differences can affect settling behaviour, slurry viscosity, magnetic recovery and medium losses.

The specification should therefore be reviewed for:

• The complete particle-size distribution rather than a single nominal size.
• The percentage retained above the upper size limit.
• The percentage passing the lower size limit or reporting as ultrafines.
• Whether the material is atomised, milled or a defined blend.
• Apparent and particle density data, where supplied.
• Chemical composition and any relevant handling information.
• Batch consistency and the supplier’s test methods.

Grade should not be confused with the silicon content of the alloy. Dense-medium ferrosilicon is selected as a complete medium product, with alloy composition, density, particle shape and size distribution working together. Comparing only the alloy chemistry does not establish how the powder will behave in a plant suspension.

The main criteria for selecting a ferrosilicon grade

Separator type

The first decision is whether the medium will be used in a static or relatively low-force separator, or in a centrifugal device such as a dense medium cyclone.

Baths, drums and similar separators commonly process coarser feed and can often operate with a comparatively coarser medium. The lower viscosity associated with a suitable coarser powder can assist drainage and medium recovery. The grade must still remain sufficiently stable throughout the vessel to prevent an uncontrolled density gradient.

Dense medium cyclones generally require a finer and more stable medium. The suspension must withstand rapid acceleration and complex flow conditions while maintaining the density needed for separation. A grade with excessive coarse material can segregate within the cyclone and contribute to inconsistent performance. Selecting an extremely fine grade without testing is not the answer, however, because excessive fines can raise viscosity and interfere with particle movement.

Feed top size and bottom size

Feed sizing affects both separation dynamics and medium contamination. Coarse, narrowly sized material is usually less sensitive to moderate slurry viscosity than fine feed. As the lower feed size decreases, the risk that high viscosity will hinder particle movement becomes more significant.

Desliming performance is especially relevant. Clay, slimes and fine mineral particles entering the dense-medium circuit can accumulate in the circulating medium. This changes rheology even if the fresh ferrosilicon meets its specification. A plant treating clay-bearing ore may therefore need to place greater emphasis on feed preparation, bleed control and circulating-medium testing rather than trying to solve every problem through a change in ferrosilicon grade.

Required separation density

The target operating density determines how much ferrosilicon must be present in the water-based suspension. Higher medium densities generally require a greater solids concentration. As solids concentration rises, viscosity becomes more sensitive to particle-size distribution, particle shape, contamination and water chemistry.

A grade that performs well at one operating density may become too viscous when used at a substantially higher density. Selection trials should consequently be conducted close to the actual density range expected in the plant, not only at a convenient laboratory concentration.

Medium stability

Stability describes the medium’s resistance to rapid settling and segregation. A stable suspension helps maintain predictable density through the separator and associated pipework. Finer ferrosilicon particles generally remain suspended for longer than coarse particles, but stability should be balanced against viscosity.

Too little stability can cause density variations, solids accumulation in low-flow areas and unreliable cut points. Too much stability is not automatically beneficial if it is achieved through an excessive ultrafine fraction that makes the suspension difficult to drain, rinse or separate magnetically.

Medium viscosity

Viscosity affects how freely the feed particles can move relative to the medium. If viscosity is excessive, particles may report to the wrong product because their movement is hindered rather than because their density is above or below the intended cut point. This effect becomes more pronounced for fine feed.

Ferrosilicon particle size is only one influence on rheology. Solids concentration, particle shape, ore fines, clay, temperature and water chemistry can all change the measured result. Grade comparisons should therefore use representative process water and realistic levels of contamination wherever possible.

Atomised and milled ferrosilicon powders

The production route influences particle shape as well as particle size. Atomised ferrosilicon is formed by breaking molten alloy into droplets that solidify into particles with a generally rounded form. Milled ferrosilicon is produced by crushing and grinding solid alloy, resulting in more angular and irregular particles.

Rounded atomised particles can offer favourable flow and rheological behaviour at a given solids concentration. The smoother particle form can help a suspension achieve the required density without the same degree of interparticle resistance associated with highly angular material. Atomised products are widely considered for cyclone applications and other circuits where tight control of medium behaviour is required.

Milled ferrosilicon can be suitable for bath and other dense-medium applications, depending on its sizing and the operating conditions. Its angular particles may produce different settling, viscosity and drainage characteristics from an atomised powder with a nominally similar size.

Neither production route should be selected from shape alone. The correct comparison includes the full particle-size distribution, operating density, rheology, stability, magnetic recovery and delivered performance. Some circuits may also use a controlled blend to obtain a particular balance of characteristics.

The DMS Powders ferrosilicon product range provides a starting point for comparing powders intended for dense medium separation. Plant operators should match the relevant product specification to their own circuit and test conditions.

How particle size changes plant performance

Particle-size distribution influences several parts of the process at the same time. Changing grade to correct one issue can create another if the entire circuit is not considered.

If the grade is too coarse

An excessively coarse medium may settle quickly in tanks, launders or low-velocity pipe sections. Within a separator, it may develop an undesirable density gradient or respond poorly to short-term flow changes. Coarse particles can also behave differently under cyclone forces, contributing to medium segregation between product streams.

Possible operating symptoms include unstable density readings, fluctuating product quality, solids deposits and a greater difference between sampled medium densities at different circuit locations. These symptoms are not proof of an incorrect grade, as pump performance, instrumentation and flow distribution can produce similar effects.

If the grade is too fine

A powder containing more fines than the circuit needs may create a medium that is stable but overly viscous. Drainage from the product can become more difficult, and additional medium may remain attached to wet ore after the drain stage. Very fine particles can also place different demands on magnetic separation and rinse-screen performance.

High medium losses should not automatically be blamed on a fine grade. Damaged screen panels, unsuitable aperture selection, inadequate spray water, poor magnet performance, leakage and incorrect flow balance must also be investigated.

The importance of the distribution between the limits

Plant behaviour is not controlled only by the largest particle or an average size. The shape of the distribution matters. A broad distribution can pack and flow differently from a narrow one, while a small ultrafine fraction may have a disproportionate effect on viscosity.

For meaningful supplier comparisons, request data produced by stated test methods and compare like with like. Sieve analysis and instrumental particle-size methods do not necessarily report identical results, particularly for irregular particles. Sampling and dispersion procedures can also affect the reported distribution.

A practical selection process for a new or existing DMS plant

1. Define the separation duty. Record the separator type, feed rate, feed top and bottom size, target operating density, expected density range and required product split.
2. Characterise the feed. Review ore density distribution, liberation, clay content, degradation during handling and the quantity of fines likely to enter the medium circuit.
3. Assess the water and circulating medium. Use representative process water for testing. If the plant is operating, analyse the circulating medium rather than relying solely on the fresh make-up powder specification.
4. Shortlist suitable powder forms and sizes. Use the separator type and feed sizing to identify realistic atomised, milled or blended options. Remove grades that cannot provide adequate stability or that are likely to create excessive rheology.
5. Compare full technical data. Review particle-size distribution, powder form, chemistry, density information and test methods. Do not treat nominal grade names from different suppliers as directly interchangeable.
6. Conduct laboratory tests. Measure suspension density, settling or stability and rheological behaviour at representative concentrations. Where possible, assess contamination by ore fines and process water.
7. Run a controlled plant trial. Introduce the selected grade under documented conditions. Allow enough time for the new make-up medium to influence the circulating inventory before drawing firm conclusions.
8. Evaluate total performance. Compare separation efficiency, product quality, medium consumption, recovery performance, density control and operating stability rather than focusing on purchase price per tonne alone.

Account for the circulating medium, not only fresh powder

Fresh ferrosilicon begins to change once it enters the plant. Preferential losses may remove one part of the size distribution faster than another. Attrition can generate finer particles, while corrosion and oxidation can change particle surfaces. Ore fines and other contaminants may accumulate if they are not adequately controlled.

As a result, the circulating medium can differ materially from the make-up grade. Routine sampling should cover relevant locations such as correct-medium circuits, dilute-medium circuits and separator feed, subject to the plant’s flowsheet. Samples need to be taken consistently because settling within a line or vessel can make an unrepresentative grab sample misleading.

Useful operating measurements include:

• Correct-medium density and its short-term variation.
• Density differences across relevant streams or sampling points.
• Medium viscosity or an agreed site rheology indicator.
• Particle-size distribution of the circulating medium.
• Magnetic and non-magnetic solids in the medium.
• Ferrosilicon make-up consumption per tonne of feed.
• Medium recovery through drain, rinse and magnetic separation stages.
• Product yield, ash or grade results, depending on the mineral processed.
• Separation efficiency indicators such as probable error and misplaced material, where partition testing is available.

Trend data is usually more informative than one isolated result. It helps the plant distinguish a persistent grade mismatch from short-lived disturbances caused by feed changes, water balance or equipment condition.

Check compatibility with the medium recovery circuit

Ferrosilicon selection affects the whole medium circuit. Drain-and-rinse screens must recover adhering medium while preventing excessive product contamination. Magnetic separators must recover the magnetic medium from dilute streams, and pumps and pipework must maintain suitable transport velocities.

Before changing grade, inspect screen condition, spray arrangement, magnetic separator settings, dilution-water control, sumps and pump performance. A finer grade may expose limitations in the recovery circuit that were less visible with a coarser product. Conversely, poor recovery can make an otherwise suitable grade appear uneconomical.

Magnetic recovery performance should be assessed using the plant’s actual dilute-medium stream. Ore-derived magnetic minerals can report with ferrosilicon, while non-magnetic slimes can remain entrained. Measuring only total solids does not show how much recoverable ferrosilicon is present.

Common ferrosilicon selection mistakes

• Choosing by nominal grade name alone. Product naming systems are not necessarily equivalent between suppliers.
• Assuming finer is always better. Additional stability can be outweighed by higher viscosity and difficult drainage.
• Ignoring feed desliming. Clay and mineral fines can alter the circulating medium more than a modest change in fresh powder size.
• Testing with clean laboratory water only. Results may not represent the plant’s process water or contaminant load.
• Changing several variables during a trial. Simultaneous changes to grade, density, pressure and feed sizing make the result difficult to interpret.
• Judging cost only by powder price. Consumption, product recovery, downtime, quality variation and medium losses form part of the operating cost.
• Overlooking inventory turnover. A new make-up grade does not instantly replace all material circulating through the plant.
• Failing to verify instruments. Density gauges and sampling systems should be checked before a powder grade is blamed for instability.

Questions to give a ferrosilicon supplier

A useful technical enquiry contains enough process information for the supplier to narrow the options. Provide the separator type, mineral or ore being treated, feed-size range, target medium density, throughput, current grade and the problem the plant is trying to solve.

It is also helpful to share available circulating-medium analyses, viscosity or stability results, medium consumption trends and details of the recovery circuit. State whether the project is a new plant, an optimisation exercise or a replacement for an existing supply. For a global operation, delivery location, expected volume, packaging requirements and consumption schedule should be addressed separately from technical grade selection.

DMS Powders supplies ferrosilicon powders for dense media separation to the global mining sector. Readers can review information about DMS Powders before starting a product discussion.

Frequently asked questions about ferrosilicon grades

Which ferrosilicon grade is best for a dense medium cyclone?

Dense medium cyclones generally require a relatively fine, stable medium, but there is no single grade that is best for every cyclone. Feed size, cyclone geometry, operating pressure, target density, ore fines and medium recovery performance must be considered. The choice should be confirmed through representative laboratory work and a controlled plant trial.

Can the same ferrosilicon grade be used in a bath and a cyclone?

It may be technically possible in some flowsheets, but the optimum grade is often different. Baths can commonly use a comparatively coarser medium, while cyclones tend to need greater suspension stability. Using one grade for both should be based on measured performance rather than procurement convenience.

Does finer ferrosilicon improve DMS separation?

Finer powder generally improves suspension stability, but it can also increase viscosity. Excessive viscosity can restrict the movement of fine feed particles and raise medium carryover. Improvement depends on finding the balance appropriate to the separator and feed.

Why does circulating medium become more viscous over time?

Ore fines, clay and other contaminants can accumulate in the circuit. Ferrosilicon may also undergo attrition, and parts of the size distribution can be lost preferentially. Water chemistry and solids concentration can contribute as well. Testing the circulating medium helps identify the actual cause.

How should two ferrosilicon products be compared?

Compare full particle-size distributions, powder form, chemistry, density information and test methods. Then test both products at the plant’s operating density using representative water and contamination conditions. The final comparison should include separation results, medium recovery and consumption, not only the delivered powder price.

Select a grade against measurable plant objectives

The right ferrosilicon grade for dense medium separation is the one that maintains sufficient stability without creating excessive viscosity, supports the intended cut density and can be recovered efficiently by the plant. Separator type and feed sizing establish the starting range, while representative testing confirms the choice.

If you are specifying medium for a new project or reviewing an existing DMS circuit, send DMS Powders the separator, feed, density and recovery details behind your requirement. Contact DMS Powders about ferrosilicon grade selection to discuss an appropriate product from its global DMS supply range and make an enquiry.

The post How to Select the Right Ferrosilicon Grade for Dense Medium Separation first appeared on DMS Powders.

Ferrosilicon for diamond ore dense medium separation provides the controllable slurry density needed to separate liberated diamond-bearing particles from lower-density waste. In a correctly designed circuit, fine ferrosilicon powder is mixed with water and circulated through a dense medium cyclone. Particles that are denser than the effective separation density report to the sinks stream, while lighter material reports to floats.

The medium does not identify diamonds selectively. Diamonds have a relative density of approximately 3.5, but other dense minerals may also enter the sinks fraction. Dense medium separation therefore produces a smaller, higher-density concentrate for downstream recovery rather than a finished diamond product.

Ferrosilicon grade, particle size distribution, slurry stability and magnetic recoverability all affect plant performance. An unsuitable powder can increase medium consumption, impair cyclone separation or create an unnecessarily viscous slurry. Ore preparation and operating control are equally significant, so medium selection should be based on the complete circuit rather than nominal density alone.

This article explains how ferrosilicon behaves in a diamond DMS plant, how to assess available grades and which operating conditions commonly influence recovery, concentrate yield and medium losses.

What ferrosilicon does in a diamond DMS circuit

DMS-grade ferrosilicon is an iron-silicon alloy powder with a high particle density and a magnetic response that allows it to be recovered from process water. Suspended in water at a controlled concentration, it forms a dense medium whose relative density can be adjusted to suit the ore and required separation point.

A typical diamond ore circuit crushes and screens kimberlite, lamproite or another diamond-bearing material into defined size fractions. Scrubbing may be used to break down clay-rich material, followed by screening or classification to remove fines that would interfere with the medium. The correctly sized feed is mixed with the dense medium before entering a cyclone or another gravity separation vessel.

Inside a dense medium cyclone, centrifugal forces amplify the density-based separation. The lower-density fraction generally leaves through the overflow as floats, while denser particles leave through the underflow as sinks. The sinks product then passes to downstream concentration, sorting or diamond recovery stages appropriate to the plant.

After separation, drain-and-rinse screens recover medium from both product streams. The dilute medium is cleaned and concentrated, commonly using magnetic separators, before returning to the correct-medium circuit. This recovery loop is one reason ferrosilicon is well suited to continuous mineral-processing operations.

Diamond recovery begins with effective ore preparation

Even a carefully selected ferrosilicon grade cannot compensate for poorly prepared feed. Dense medium separation works on differences in particle density, so the feed must first be liberated and presented within the size range for which the plant was designed.

Excessively large particles may be poorly liberated or exceed the cyclone’s top-size capability. Very fine material can increase viscosity, contaminate the circulating medium and reduce the sharpness of separation. Clays are particularly troublesome because they can disperse into the process water and change slurry behaviour without causing an obvious change in the amount of ferrosilicon added.

Effective preparation normally requires attention to:

• Controlled crushing: The circuit must liberate diamond-bearing particles while limiting unnecessary breakage and the production of excessive fines.
• Scrubbing: Weathered or clay-rich ore may need sufficient attrition to remove coatings and disaggregate soft material.
• Screening accuracy: Oversize, undersize and misplaced particles can all compromise the separation.
• Desliming: Removing slimes helps protect medium stability, viscosity and magnetic recovery efficiency.
• Consistent feed rate: Sudden variations in solids loading can change cyclone performance even if the measured medium density remains steady.

Ore mineralogy and competency can change across a deposit. Plants should therefore assess how different ore domains affect fines generation, medium contamination and yield rather than assuming that one set of operating conditions will remain optimal throughout the mine life.

How to select ferrosilicon for diamond ore dense medium separation

The correct product is not simply the powder with the highest density or finest particle size. Selection requires a balance between medium stability, viscosity, magnetic recovery, resistance to degradation and the separation density required by the plant.

Particle size distribution

Ferrosilicon must remain sufficiently suspended to form a consistent medium. A distribution that is too coarse can settle rapidly in tanks, launders and low-velocity sections. This creates density variation and may require more agitation or pumping energy. At the other extreme, excessive ultrafines can increase viscosity and make rinsing or magnetic recovery more difficult.

The target distribution should reflect the medium density, cyclone size, circulation rate, pipework and the amount of non-magnetic contamination expected from the ore. A supplier’s product specification should be considered alongside plant trials and medium samples taken under actual operating conditions.

Atomised and milled ferrosilicon

Ferrosilicon powder is commonly produced in atomised or milled form. Atomised material tends to have more rounded particles, while milling produces a more angular particle shape and a different size profile. Particle shape influences packing, slurry rheology, surface area and resistance to physical degradation.

Neither description should be treated as a complete purchasing specification. Different grades can exist within each production route, and suitability depends on the circuit. High-density applications or plants requiring tightly controlled rheology may favour a particular atomised grade, while other operations may achieve the required result with an appropriately specified milled or blended product. Comparative testing should use the intended operating density and representative process water.

Medium viscosity and stability

A stable medium resists rapid settling, but stability achieved through an excessive proportion of fine particles can create high viscosity. A viscous medium restricts the movement of particles relative to the fluid, potentially causing misplaced floats and sinks. It can also affect cyclone pressure, pumping and screen drainage.

Density and viscosity should consequently be assessed together. Two media at the same relative density can perform differently because of ferrosilicon size distribution, clay contamination, water chemistry or degradation of the circulating powder.

Magnetic response and recovery

Ferrosilicon’s magnetic properties allow dilute medium to be recovered after rinsing. Effective magnetic separation reduces losses and limits the amount of alloy discharged with tailings, concentrate or effluent. Product selection should therefore account for magnetic susceptibility as well as fresh-medium behaviour.

Recovery performance is also governed by magnetic separator condition, feed dilution, flow distribution and the accumulation of non-magnetic solids. Poor recovery should not automatically be attributed to the supplied powder without checking the recovery circuit.

Consistency between deliveries

Stable DMS control depends on predictable feed material. Procurement specifications should define the parameters that matter to the plant, supported by appropriate supplier documentation and incoming quality checks. Relevant parameters may include size distribution, apparent or particle density, moisture, chemical composition and magnetic behaviour.

Mining operations can review the available ferrosilicon powder products from DMS Powders and discuss grade selection against the plant’s cyclone configuration, target medium density and ore characteristics.

Medium density is not the same as separation density

Operators often monitor the density of the circulating medium because it can be measured and adjusted relatively quickly. However, the measured medium density does not necessarily equal the effective cut density achieved inside the cyclone.

The actual separation is affected by cyclone geometry, inlet pressure, feed solids, particle size, medium rheology and the density differential between the cyclone overflow and underflow. A stable density reading at one sampling point may conceal segregation elsewhere in the circuit.

Partition testing provides a more useful assessment of separation efficiency. Representative particles or density tracers are passed through the circuit, and their distribution between sinks and floats is analysed. The results can indicate the density at which particles have an equal probability of reporting to either stream and reveal how sharply the separation occurs.

For diamond ore, the selected cut point must reject enough low-density waste while retaining the dense particles that could contain diamonds. Setting the cut density too low can produce an unnecessarily large concentrate, increasing the load on downstream recovery. Setting it too high can increase the risk of valuable material reporting to floats, particularly where particles are partially liberated or have composite densities.

Operating variables that influence cyclone performance

Ferrosilicon quality is only one part of a functioning DMS circuit. Several interacting variables determine whether the cyclone produces a consistent and efficient separation.

• Feed pressure: A dense medium cyclone requires operation within its designed pressure range. Fluctuating or unsuitable pressure changes the internal flow pattern and separation behaviour.
• Medium-to-ore ratio: Insufficient medium can overload the cyclone with solids, while excessive circulation adds pumping and recovery demand without necessarily improving separation.
• Feed size range: Wide size distributions can separate less sharply because fine and coarse particles respond differently inside the cyclone.
• Cyclone wear: Wear to the inlet, vortex finder, body or spigot changes the cyclone geometry and can gradually shift performance.
• Spigot condition: Partial blockages or unsuitable spigot dimensions affect underflow discharge and density differentials.
• Process water: Dissolved salts, suspended clay and changing water sources may alter medium rheology and corrosion behaviour.
• Instrumentation: Density gauges, pressure instruments and flow meters require inspection and calibration. A stable but inaccurate reading can lead to confident operation at the wrong condition.

Control-room trends should be compared with physical samples and metallurgical results. Visual observations of drain-and-rinse screens, magnetic separator discharge and cyclone products can expose problems that a single density measurement misses.

Reducing ferrosilicon consumption and medium losses

Ferrosilicon is continuously recovered and reused, but every DMS plant experiences some loss. The useful objective is to identify avoidable losses without compromising rinsing, separation stability or concentrate quality.

Medium can leave the circuit through adhesion to ore particles, inefficient rinsing, screen damage, spillage, leaks, magnetic separator inefficiency and deliberate bleed streams used to control contamination. Fine or degraded ferrosilicon may also be harder to recover than material within the intended particle size range.

A practical loss investigation should establish where the material is going. This normally means sampling floats, sinks, rinse water, magnetic separator products and discard streams rather than calculating only the difference between deliveries and stock levels.

Useful corrective actions may include:

• Checking drain-and-rinse screen panels for wear, damage and incorrect aperture selection.
• Maintaining effective spray coverage and suitable rinse-water pressure without overwhelming the dilute-medium circuit.
• Inspecting launders, sumps and pipework for settled material and hidden leakage.
• Testing magnetic separator feed conditions and recovered-medium quality.
• Controlling clay and slimes before the DMS stage.
• Monitoring the particle size distribution of circulating medium to identify degradation or selective losses.
• Keeping accurate fresh-medium addition and production records on a consistent basis.

The cheapest powder per tonne is not necessarily the lowest-cost medium in operation. Consumption rate, recovery efficiency, separation performance, concentrate volume and plant availability all contribute to the real cost of use.

Common causes of unstable or poor separation

Medium density changes rapidly

Rapid variation may result from inconsistent fresh-medium dosing, water ingress, an unstable sump level, poor agitation or changing returns from the dilute-medium circuit. Sampling at several points can distinguish a control problem from density segregation within the plant.

Ferrosilicon settles in tanks or pipework

Settling can indicate inadequate agitation, low line velocity, an unsuitable particle size distribution or extended shutdowns without the correct restart procedure. Simply adding finer powder may increase viscosity, so the hydraulic cause should be checked first.

The medium becomes progressively more viscous

Clay ingress, ore fines, corrosion products and accumulated ultrafine ferrosilicon can all increase viscosity. Medium density may remain on target while separation sharpness deteriorates. Desliming performance and circulating-medium composition should be examined before changing the density set point.

Concentrate yield rises unexpectedly

A higher sinks yield can reflect a genuine change in ore mineralogy, a lower effective cut density, cyclone wear, feed-size changes or medium rheology. It does not automatically indicate improved diamond recovery. Yield should be interpreted with partition data and downstream recovery results.

Ferrosilicon consumption increases

Check for damaged screens, poor rinsing, magnetic separator inefficiency, leaks and increased surface moisture or fines in the feed. Comparing ferrosilicon concentration in each loss stream is more reliable than making repeated adjustments to the fresh-medium grade.

Sampling and quality control for reliable DMS operation

A useful monitoring programme combines frequent operational checks with periodic metallurgical assessment. Operators may track correct-medium density, cyclone pressure, sump levels, flow rates and fresh-medium additions during each shift. Laboratory or plant metallurgical teams can then assess circulating-medium size distribution, contamination, viscosity and magnetic recovery at suitable intervals.

Representative sampling is essential. Ferrosilicon settles when flow stops and can segregate in moving streams, so poorly positioned sample points or inconsistent procedures produce misleading results. Samples should be taken from established, well-mixed flows using the same documented method each time.

Density tracers and partition studies are especially valuable after commissioning, significant ore changes, cyclone component replacement or persistent recovery concerns. These tests connect operating settings to actual separation performance rather than relying on assumptions based on design values.

Storage, handling and safe use of ferrosilicon powder

Fresh ferrosilicon should be stored in dry conditions and protected against contamination. Packaging and bulk-handling systems should prevent water ingress, uncontrolled dust release and mixing with other grades. Stock rotation also helps maintain traceability between deliveries and plant performance.

Fine mineral and metal-alloy powders require suitable occupational hygiene controls. Facilities should follow the supplier’s current safety data sheet, conduct a site-specific risk assessment and use appropriate enclosed transfer, extraction, housekeeping and personal protective equipment. Potential ignition sources and combustible-dust risks must be assessed for the actual powder and handling method rather than assumed from the product name alone.

Wet ferrosilicon slurry also needs disciplined housekeeping. Spills can create slip hazards, settle in drains and result in avoidable product loss. Maintenance work on sumps, tanks and pipework should follow the mine’s isolation, confined-space and stored-energy procedures.

Information to provide when requesting a ferrosilicon recommendation

A productive supplier discussion starts with process detail. Before requesting a quotation or trial material, compile the information needed to assess technical suitability and logistics.

• Ore type and relevant mineralogical characteristics.
• Nominal top and bottom feed sizes.
• Target medium density and available partition-test results.
• Cyclone diameter, configuration and typical operating pressure.
• Current medium grade and any identified performance concern.
• Circulating-medium viscosity or particle-size data, where available.
• Fresh-medium consumption and measured loss locations.
• Packaging, storage, delivery volume and destination requirements.

This information helps distinguish a powder-selection issue from an ore-preparation, hydraulic or recovery-circuit problem. It also supports a more meaningful comparison between candidate grades.

DMS Powders supplies ferrosilicon powders for dense media separation to the global mining sector. More information about the business is available on the DMS Powders company page.

Frequently asked questions about ferrosilicon in diamond DMS

Why is ferrosilicon used instead of plain water?

Water does not have sufficient density to separate diamond-bearing dense particles from many common gangue minerals. Adding high-density ferrosilicon creates an adjustable medium while retaining the fluid properties needed for pumping and cyclone separation.

Does dense medium separation recover only diamonds?

No. DMS separates particles according to effective density, not mineral identity. Diamonds and other dense particles report to the sinks fraction, which is processed further to recover and identify diamonds.

Can a finer ferrosilicon grade prevent settling?

A finer grade may improve stability, but excessive fines can increase viscosity and reduce separation efficiency. Agitation, circulation velocity, contamination and shutdown procedures should be checked before changing grades.

How is ferrosilicon recovered after the cyclone?

Medium is drained and rinsed from the sinks and floats products. Dilute ferrosilicon slurry is then concentrated with magnetic separation and returned to the circulating-medium system, subject to the plant’s cleaning and control arrangement.

How should a mine compare ferrosilicon suppliers?

Compare technical consistency, particle size distribution, density, magnetic behaviour, supporting documentation, packaging and delivered logistics. Plant performance, medium consumption and separation results provide a better commercial comparison than purchase price alone.

Discuss ferrosilicon requirements with DMS Powders

Reliable diamond DMS depends on matching the ferrosilicon powder to the ore, required separation density, cyclone design and medium recovery circuit. A technically suitable product should support stable operation, effective magnetic recovery and controlled viscosity across realistic plant conditions.

For assistance selecting ferrosilicon for diamond ore dense medium separation, contact DMS Powders with your plant and delivery requirements. Include the operating density, feed size, cyclone details and any current medium-loss or rheology concerns so that the enquiry can be assessed in the correct process context.

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