Dense Media Separation For Lithium Pegmatite Ore

A dense media separation (DMS) plant can provide an effective pre-concentration step for lithium-bearing pegmatite, particularly where spodumene occurs with lighter quartz, feldspar and mica. The process separates crushed ore according to density, allowing a portion of barren or low-value rock to be rejected before finer grinding and flotation.

For Australian lithium projects, this can reduce mill feed, reagent consumption, tailings volumes and downstream operating costs. The right result depends on ore texture, spodumene liberation, feed sizing, gangue density and the stability of the dense medium circuit. A flowsheet must therefore be developed from representative testwork rather than copied from another deposit.

DMS is especially attractive for hard-rock operations in Western Australia, where deposits may be located far from established infrastructure and skilled labour. At Greenbushes, Pilgangoora, Wodgina or Kathleen Valley, every tonne removed before fine processing can influence haulage, water demand, power use and plant footprint.

The practical objective is a robust circuit that produces a consistent heavy fraction for lithium recovery while keeping spodumene losses in the floats stream low. This requires careful control of crushing, screening, medium density, cyclone performance, water recovery and product handling.

Ore Characteristics And DMS Suitability

Lithium pegmatite is commonly hosted in coarse-grained rock containing spodumene, petalite or lepidolite, together with quartz, feldspar, mica and accessory minerals. Spodumene has a higher specific gravity than most of the principal gangue minerals, which creates the basis for gravity separation. However, the contrast is not unlimited, and some iron-bearing silicates or dense accessory minerals may report with the spodumene product.

The key question is whether the lithium mineral is present as liberated crystals or as composite particles after reasonable crushing. Coarse, well-liberated spodumene generally responds well to DMS. If it remains locked inside quartz-feldspar particles, a heavy fraction may still be produced, but its grade and recovery can be less predictable.

Ore variability is significant across a pit and between mining zones. A spodumene-rich domain may respond differently from a mica-rich pegmatite or weathered near-surface material. Variability samples should therefore cover grade, hardness, alteration, mineralogy and expected mine scheduling.

Heavy liquid separation, sink-float testing and pilot-scale DMS work can establish the appropriate cut density, size range, mass yield and lithium distribution. These results should be combined with crushing and screening tests to define a flowsheet that is technically sound and commercially realistic.

Primary Crushing And Feed Preparation

Run-of-mine ore normally passes through a primary jaw or gyratory crusher, followed by secondary crushing and, where necessary, tertiary size reduction. The aim is to expose spodumene without creating excessive fines. Over-crushing can generate slimes and composite particles that reduce DMS efficiency.

A typical plant removes very fine material before dense media treatment because fines consume medium, hinder separation and increase water-treatment requirements. The desliming cut-off is selected through testwork and may vary with ore type. Coarse particles can be treated in a DMS cyclone, while a finer fraction may require spirals, reflux classifiers, flotation or another gravity circuit.

Screen efficiency is critical. Poorly sized feed creates an unstable cyclone response and makes medium density control less meaningful. Plant designers should allow for spray water, screen blinding, wear, maintenance access and the abrasive nature of Australian hard-rock ore.

In remote Western Australian operations, crushing equipment may face long delivery times and limited local inventories for specialised components. Modular structures, standardised pumps and accessible wear parts can help reduce downtime when a mine is several hours from Perth or a major regional centre.

Dense Medium Circuit Configuration

The prepared feed enters a mixing or medium-contacting stage where crushed ore encounters a suspension of water and finely ground ferrosilicon. The medium is adjusted to a density between the principal float and sink populations. In a dense medium cyclone, particles are separated by centrifugal forces: lower-density gangue exits through the overflow, while denser spodumene-bearing material reports to the underflow.

The sink product is usually rinsed on drain-and-rinse screens. Recovered ferrosilicon is returned to the medium circuit, while wash water and diluted medium pass through magnetic separators for medium recovery. The float product follows a similar drainage and rinsing arrangement before being conveyed to stockpile or waste handling.

A simplified plant sequence is:

• Run-of-mine ore receiving and controlled feeding
• Primary, secondary and optional tertiary crushing
• Screening, fines removal and size classification
• Dense medium mixing and cyclone separation
• Drain-and-rinse screening of sink and float products
• Magnetic medium recovery and density adjustment
• Sink product storage and downstream lithium processing
• Float disposal, possible by-product recovery and water recycling

Cut density must be controlled continuously. Variations in ferrosilicon concentration, feed rate, particle size or water addition can shift the separation boundary. Automated density gauges, sampling points and feedback control are valuable, although operators still need clear procedures for upset conditions.

Product Quality And Downstream Recovery

The DMS sink stream is a pre-concentrate, not automatically a saleable lithium product. It may proceed to ore sorting, re-crushing, grinding, mica removal and spodumene flotation. The selected route depends on whether the target product is a lithium concentrate for conversion, a lower-grade intermediate, or a blend for another processing stage.

Grinding should be limited to the degree needed for liberation. Coarse DMS concentration can substantially reduce the mass entering the grinding circuit, but the retained material may still contain locked spodumene. The grinding duty must be assessed alongside flotation response, circulating load and energy consumption; guidance on dry and wet grinding also illustrates why moisture and material characteristics matter when selecting a comminution route.

The plant should track lithium recovery by size fraction and stream, not just final concentrate grade. A high sink yield can look attractive while carrying excessive quartz and feldspar into the mill. Conversely, an aggressive rejection setting may lower operating cost but discard valuable coarse spodumene.

Stockpiling and blending are also important. Separate handling of high-grade and low-grade DMS products can give the concentrator more flexibility, especially when mine feed changes during wet-season access constraints or when shipments must meet a contracted specification.

Water, Medium And Tailings Management

DMS uses process water for medium preparation, screen sprays and product rinsing. Water recovery thickeners, clarification ponds, pumps and recycle lines should be sized for normal operation as well as storm events. In the Pilbara and Goldfields, water supply, borefield licensing and evaporation can materially affect the project design.

Recycled water chemistry can influence froth flotation and equipment corrosion later in the circuit. Suspended solids, dissolved salts and dissolved oxygen should be monitored rather than treated as secondary issues; research on the role of dissolved oxygen provides useful context for understanding how water quality can affect treatment performance.

Ferrosilicon losses increase operating cost and can contaminate products if drain-and-rinse screens are undersized or poorly operated. Magnetic separators need suitable feed presentation, reliable spray systems and routine inspection. Medium recovery should be measured through mass balance so that unexplained losses are identified quickly.

Float material may be sent to a waste facility, used in construction applications if approved, or processed for additional value recovery. Tailings and waste-rock designs must account for geochemistry, dust, seepage, closure obligations and consultation with Traditional Owners and state regulators.

Australian Design And Operating Realities

Australian lithium developments often operate in remote regions with high freight costs, extreme temperatures and limited access to trades. A plant near Kalgoorlie, Karratha or Port Hedland may need larger critical spares, duplicated pumps and stronger maintenance planning than a comparable facility close to a major industrial city.

Water management is particularly important in Western Australia. Cyclones and intense rainfall can challenge ponds, sumps and access roads, while dry periods increase competition for process water. Covered conveyors, dust suppression and sealed transfer points may be needed to satisfy environmental conditions and protect nearby communities.

Power supply also shapes the flowsheet. Grid access may be limited, so diesel generation, gas engines, renewables or hybrid systems can affect the choice of drives, pumps and automation. Energy-intensive re-crushing should be justified by a measurable improvement in lithium recovery or product quality.

Approvals, Aboriginal heritage obligations, road access and port scheduling influence the whole project rather than just the mine. Concentrate may travel by road and rail to ports such as Port Hedland or Bunbury, so product moisture, stockpile capacity and loadout reliability need to be considered during design.

Testwork, Engineering And Plant Delivery

A reliable DMS flowsheet begins with geological domaining and representative sample selection. Laboratory sink-float work should be followed by continuous pilot testing where possible, covering the expected feed size range and density-control window. The test programme should measure mass yield, lithium recovery, contaminant deportment, medium consumption and water demand.

Engineering then converts those results into equipment specifications, control philosophy, piping layouts, civil requirements and operating procedures. Ore testing, mine design, procurement, construction, commissioning and operator training need to remain connected. A change in crusher setting can alter screen loading, cyclone feed density and downstream flotation performance.

For owners seeking a single delivery pathway, integrated EPC services can coordinate process engineering, equipment supply, construction management and commissioning. This approach can be useful for overseas stakeholders developing an Australian project, where interfaces between mining contractors, infrastructure providers and concentrator suppliers require disciplined control.

Commissioning should begin with water runs, screen checks, pump testing and medium calibration before ore is introduced. Ramp-up data should then be compared with the mass balance and design criteria. Plant management and operational support can help establish sampling routines, maintenance schedules and control limits during the first production campaigns.

A well-designed DMS circuit gives an Australian lithium project a practical method of rejecting waste early while preserving downstream recovery potential. Its value comes from the complete system: suitable ore characterisation, controlled crushing, stable medium separation, efficient water and ferrosilicon recovery, and a downstream circuit matched to the sink product.

Lozova.org can support lithium processing developments through ore testing, mineral processing design, equipment selection and turnkey plant delivery. Contact the engineering team to assess your pegmatite sample, define the appropriate DMS configuration and develop a flowsheet suited to your mine, infrastructure and production objectives.