Already a well established technology in the diamonds and coal industries, Dense Media Separation (DMS) is now being applied to pre-concentration of precious and base metal ores. The technique provides a low-cost, high-rate method of separating coarse feed material based on small differences in bulk density, in some cases as little as 0.05 sg units!

At the heart of the process is a carefully controlled heavy media slurry of finely ground ferrosilicon or magnetite into which the ore particles are introduced. The media/ore suspension is fed through a cyclone to achieve a rapid and remarkably efficient separation at the desired density cut point. Indeed, the efficiency of DMS cyclone technology is critical to its widespread acceptance in the diamond industry where only 100% recovery will do.

New applications for DMS range from PGM deposits on the UG2 reef in South Africa; to salvage gold recovery from waste dumps; to low-grade sulfide deposits of nickel, lead and zinc.

Project benefits are likely to include: reduced power costs, simplified mine planning, reduced mill feed hardness, improved mill feed stability, and simplified tailings management.

For prospective projects, the amenability to upgrading by dense media separation can be evaluated by simple bench testing requiring only a few kilograms of sample.

The DRA group of companies has more than 20 years of experience in implementing successful DMS projects.

Read More about:

• Micro DMS Plants
• Micro "Plus" DMS Plants

Our team of engineers and project managers can provide support for your project from preliminary testing and economic evaluation, through to design, construction, and contract operations.

DRA’s plant is designed around a small-diameter gravity fed cyclone. To prevent contamination and to ensure recovery of mineral grains as fine as 300 microns it is machined from solid stainless steel and attached to a seamless mixing box. An automatic density controller and demagnetizing coil are essential to the plant.

Micro DMS plant

The plant is built into a six metre shipping container with a reinforced roof to serve as a work platform for sample loading and storage. It can recover heavy minerals and diamonds from prepared loam and stream sediment samples or crushed core in the –6 +1mm or –2+0.3mm size ranges. Excessive fine material and vegetation in the feed can affect performance so it is important that they are kept to a minimum.

The standard DMS plant consists of:

• feed hopper and vibrating feeder
• mixing box and cyclone
• combined product screen with woven wire screen cloths
• separate concentrate screen with removable sieves
• circulating medium pump
• dilute medium pump
• wet drum magnetic separator (Magsep)
• magsep effluent sump and pump
• medium holding tank with agitator
• demagnetizing coil
• density control system
• paperless chart recorder for data logging

All drives except the vibrating feeder, density controller and chart recorder are 3 phase (380V 50 or 60Hz). All equipment is started from a central control panel fitted with safety lockouts and emergency stop buttons.

Process description
The washed and screened sample, stored in the feed hopper, is fed into the mixing box by the vibrating feeder. It is mixed with ferrosilicon (FeSi) before gravitating to the cyclone where it is separated under pressure. The float product is drained and then washed to recover adhering FeSi. The screen washings are pumped to the wet drum magnetic separator for medium recovery and densification.

The tailings are discarded and the concentrates, which are collected in a sieve, are washed by hand to remove adhering medium before being dried and sorted to recover heavy mineral indicator grains and diamonds.

A separate concentrate screen with removable sieves is used during heavy mineral recovery, while the combined float and sink screen is used for larger samples. The plant is capable of treating twenty 50kg (-2+0.3mm) samples a day, increasing to around 300kg/h when continually processing crushed kimberlite core (–6+1mm).

Cyclone separation and recovery efficiency can be monitored by adding plastic tracers of known density and plotting a tromp curve based on the numbers recovered.

Micro ‘Plus’ DMS plant

This plant is identical to the standard one but has the following additional equipment:

• Mounted inside the DMS container
• a feed preparation screen with screen under pan
• plant undersize pump
• mixing box
• cyclone feed pump and 150mm cyclone with associated chute work
• A stand-alone skid mounted front end consisting of:
• feed bin, belt feeder with variable speed drive and a feed conveyor
• rotary scrubber with a trommel screen for oversize removal
• cat ladder and platform for access to the scrubber feed chute
• scrubber product sump and pump
• jaw crusher
• DMS tailings conveyor
• electrical control panel with plug-in leads for easy dismantling

These items are stored and transported in a second unmodified six metre shipping container. The additional equipment changes the standard Micro DMS plant from an exploration tool into a mini bulk sampling facility which can quickly be converted back to treat samples for heavy mineral recovery.

Process description
The scrubber accepts –75 mm material and depending on the amount of fines/clay can be fed at up to 5 tph. The trommel screen oversize is crushed to –10 mm in the jaw crusher and returned by wheelbarrow to the feed bin for reprocessing. The trommel screen undersize is pumped to the feed preparation screen where undersize material is removed (-1mm). The undersize is then pumped to an optional de-gritting circuit for water recovery and slimes disposal.

The –10+1mm material is mixed with ferrosilicon (FeSi) in the mixing box before being pumped to the 150 mm cyclone. Separation is under pressure and the resulting products are drained and washed to recover adhering FeSi. The screen washings are pumped to the wet drum magnetic separator for medium recovery and densification.

The larger diameter cyclone increases the effective top size of the plant from 6mm to 10mm, from which meaningful diamond size distribution can be obtained. The tailings are discarded and the concentrates collected in a secure container for hand sorting. X-ray equipment can be used for large amounts of material. The Micro ‘Plus’ DMS cyclone feed rate is limited to a maximum of 1.5tph.

Optional equipment includes the following:

• de-sliming/water treatment and recovery circuit
• jaw crusher product conveyor
• cone crusher (laboratory size)
• power generator (65 or 85kVA)
• office/workshop container

DRA also designs and builds diamond recovery plants and the circuit could include any combination of:

• gravel driers
• magnetic separators (belt or drum type)
• X-Ray machines (wet or dry)
• grease tables
• secure diamond sorting glove boxes
• access control and security monitoring equipment.

We consider expertise in the following disciplines to be essential to your project’s success:

• Health & Safety
• Process Engineering & Metallurgy
• Design (Structural, Civil & Piping)
• Electrical & Instrumentation Engineering
• Infrastructure
• Project Support
  (Planning, Cost Estimation, Procurement)
• Construction Management
• Commissioning & Process Optimization

• Chrome
• Coal
• Copper, Nickel & Cobalt
• Diamonds
• Gold
• Iron Ore
• Platinum Group Metals
• Zinc

• Metallurgical Consulting & Decision Support
• Engineering Studies
• Basic & Detail Engineering
• Project & Construction Management
• Contract Operations (Process Plant)