How does gravity concentration equipment work?

Gravity concentration equipment separates minerals based on differences in gravity, with minimal energy requirements. Gravity concentration products are quick and easy to install and because they have no moving parts, they are a set-it-and-forget-it processing solution for mineral classification. Gravity concentration is used in coal, copper, iron ore, chrome, mineral sand and gold processing. 

Spiral separators for gravity concentration 

Spiral separators separate/concentrate particles either by density or by shape.

Gravity concentration relies on the behaviour and reaction of different particle densities and sizes to gravity and centrifugal force. As a stream runs through the gravity concentration spiral, 2 or 3 mineral grades can be accumulated. This means more accurate and efficient downstream processing from your gravity concentration system.

Spiral separators use centrifugal force to segment mineral streams as they are fed down the spiral trough. In wet spiral separators, the particles within a slurry will begin to cluster according to their density. Lower-density particles are forced towards the outer edge of the path, while higher-density particles remain in the centre. Dry spiral separators sort by shape. Rounder particles travel faster and are forced towards the outer edge of the spiral, where they are collected separately.  

Types of mineral plants in which gravity concentration can be used 

Gravity concentration is mostly used for coal, gold, iron ore, platinum, chrome and mineral sand beneficiation.

Coal
Gravity concentration is used for processing coal fines downstream of a cyclone, following desliming and sizing. After gravity concentration, coal streams are fed into dewatering screens, then into a Siebtechnik centrifuge. Siebtechnik centrifuges include filtration, sedimentation and hybrid centrifuge types. They cover the widest range of solid-liquid separation applications in many industries, including mining, chemical, pharmaceutical and food and beverage processing.

Gold
Gravity concentration spirals are optional in gold processing, used for carbon degritting.

Iron ore
Gravity concentration is used in iron ore processing. Following a range of screening processes, large assemblies of spiral concentrators are located downstream of a cyclone cluster and are used in classifying iron ore fines from waste. 

(Read more about the steps involved in iron ore processing, here). 

Platinum beneficiation
Multotec gravity concentration solutions can be found in platinum beneficiation plants. Gravity concentration is used to separate chrome from a stream that has already been classified from the main platinum streams by a desliming screen.

Chrome
You will see gravity concentration spirals at 2 points in typical chrome processing plants. Following classification from a sizing screen upstream, gravity concentration spirals are used for fine- and medium-density streams, both following cyclone classification.

Mineral sands
Spiral concentrators play an important role in the typical mineral sand processing plant. Gravity concentration is used early in the separation process downstream of a trommel screen and cyclone. It is also used considerably further downstream after magnetic separation and sizing. You can also use gravity concentration after hot-acid leaching to separate tails from streams still containing zircon. 

Downtime and maintenance advice 

To reduce downtime, spirals must be kept clean and free of build-up at all times. It is a good idea to clean the spirals with a water hose daily. Regular inspection for plugging and proper water dissolution are also good to perform on a daily basis. Spirals are maintenance-free and can be left alone, since they have no moving parts. However, regular walk-around inspections will ensure a proper and efficient operation.

(Read more about our maintenance field services, here).  

How to choose the right spiral for your application

Spirals are selected according to the mineral type and ore characteristics. Design variations include spiral width, pitch angle, number of turns, repulping device used, and whether wash water is added to dilute and help the separation process.

(Learn more about how spirals work, here).

Your Multotec specialist will help you make the right selection for your application. Contact us to find out more.