Which tailings solution is best for your conditions?

In wet climates, for instance, the cost of water is low and the availability of water for a mine is high, which makes filtration of tailings potentially not an attractive option. Minerology of the deposits, specifically the type and amount of clays, greatly impacts the dewatering rates of tailings. High amounts of clays mean low dewatering rates and expensive large equipment.

Meanwhile, flat ground means expensive dams surrounding the full perimeter of the tailings, while tailings in a valley can use the valley walls as part of the tailings containment with only a dam at the end of the valley. All tailings facilities are, of course, directly dependant on the amount of water contained in the tailings.


Maximising water efficiency, lowers costs and risk

Water losses at wet tailings dams are unavoidable. This can be through seepage, evaporative transportation and the residual water encapsulated in the tailings are due to seepage and evaporative transpiration. Thickening tailings slurries prior to deposition in the tailings dam can reduce water losses, while filtering tailings can further improve water recovery.  It must be noted however, that thickening is always required prior to any type of filtration equipment and maximising the performance of the thickener is critical to getting the most out of the filtration equipment.

In arid climates these additional water savings can offset the costs of the filtration process. Major increases in cost and availability of water is leading to mine operators starting to examine dry tailing solutions more closely.


Potential water recovery potentials for copper flotation tailings are shown in the below table. In Chile, current estimates for the cost of desalinated water pumped to the mine are as high as $5 per cubic meter or higher.

Table 2: Potential Water Recovery for Dewatering Copper Flotation Tailings [1]

Tailings Consistency

Potential Total Water Recovery





Filter Cake



Filtration and centrifuge options

There are four main filtration options for dewatering tailings after thickening but prior to disposal: vacuum filters, centrifuges, belt presses, and filter presses. For every solution, it is recommended the filter feed slurry be thickened prior to filtration as this can substantially reduce capital and operating costs of the filtration operation.

Option 1: Vacuum Filters

Used for tailings dewatering since the 1970s, vacuum filters are continuous in their operation, which leads to a less complicated material handling interface. This filter produces a non-saturated filter cake, meaning that the void spaces inside the filter cake are not saturated with filtrate and contain some air.

The driving force for filtration is generated by vacuum source, meaning the difference between atmospheric pressure and absolute 0 pressure is the maximum driving force available for filtration. At sea level a vacuum filter can only achieve 0.8 bar driving force and at high altitude, such as in the Atacama Desert it is less than 0.4 bar of pressure. As the driving force for filtration is reduced the performance of the filter is reduced, meaning vacuum filters are not usually recommended for use above 2,500 meters above sea level.

Vacuum filters have many different configurations with disc and horizontal belt being the most common in minerals applications. Disc filters are commonly used for smaller tonnage underground paste backfill operations. For large tonnage surface tailings disposal horizontal belt filters are the most common type of vacuum filter used. A vacuum type filter works best on large particles with limited clays and fine particles present such as iron tailings in Brazil.

Option 2: Belt Presses

Belt filter presses have been used extensively for small tonnage tailings dewatering since the 1980s, and are extensively used in the coal industry for dewatering the fine tailings. This pressure filter also has the advantage of being a continuous operation. The disadvantage of a belt press is that it is limited in size and therefore only suitable for small tonnage operations. Belt filter presses produce higher moisture, saturated, filter cake and require pre-treatment of the tailings slurry with expensive flocculating agents.

The typical maximum driving forces are around 5 bar which are produced by tensioning a filter cloth around rolls. Machines are supplied in widths of up to 4 meters, with capacities of between 5 and 15 tons per hour (tph) of dry solids per meter of width producing a cake with a moisture content between 25-35 wt%.

The saturated filter cakes will also have poor geotechnical properties. However, this filtration method does work well for dewatering phosphate washing slimes and coal refuse, for instance.

Option 3: Centrifuge

Centrifuges again have the advantage of being a continuous operation. The disadvantage is that they are limited in size and therefore only suitable for small tonnage operations. Centrifuges produce a saturated cake and typically require pre-treatment of the tailings slurry with flocculating agents. While centrifuges require lower amounts of flocculant than belt presses they do require large motors to drive the spinning bowl and scroll.

Centrifuges are limited in size due to fabrication and machining limitations of their designs. The largest sizes have a ~ 350 kw drive motor and a capacity of between 5 and 25 TPH of dry solids per machine. Centrifuges will produce a saturated cake with a moisture content between 20-35 wt%. This type of dewatering equipment is applicable for low tonnage coal refuse may be applicable for gold paste backfill operations but pilot testing would be needed to verify this potential.

Option 4: Filter Press

The advantage of a filter press is that it can achieve much higher driving forces compared to a vacuum filter or a belt press. The higher driving force is of great benefit on clay type materials and most pressure filters today will reach a driving force of 15 bar or greater. The disadvantage of a filter press is the batch type process which it uses. The batch discharge of filter cakes can lead to complications in the design of the downstream material handling equipment in installation with multiple filters.

The pumping of the feed slurry under pressure, into the chambers/cloths, provides the force to build a cake within the chamber. As the cakes form, the pressure to produce a properly compacted cake rises steadily. Most filter presses on tailings applications operate with up to a 15-bar driving force. This driving force can easily be reached using just the feed pumps to the filter or alternatively, through the use of expandable membranes.

The moisture of the discharged filter press cake is in the range of 10 to 25 wt% and can be either saturated or unsaturated depending on the filter design and geotechnical requirements. Filter presses are an applicable technology for all types of tailings.

Comparing the technologies

Table 2 compares the performance of each of these types of equipment.  Depending on the type of equipment, mineralogy and particle size distribution, the discharged cakes can be sticky in nature or crumbly depending on the final moisture of the cake.  Higher moistures mean a stickier type of cake. The nature of the discharged cake will significantly impact the operation of the downstream material handling equipment. Sticky cakes will plug transfer chutes and stick to the conveyors. These problems can be mitigated by proper design of the entire system.


Table 2: Comparison of Horizontal Belt Filters, Belt Presses, Centrifuge, and Filter Presses

Filter Type

Largest Size

Highest production capacity per filter (MTPD)

Applicable for Clays

Flocculant needed

Typical Filter Cake Moisture Concentration, (wt%)

Vaccum Filter

300 m2






350 kw





Belt Press

4 m wide





Filter Press

4,000 m2



Not usually



As can be seen in the table above, filter presses have the largest single machine capacity and have the lowest possible cake moisture concentration. This allows them to have the smallest installed footprint and lowest installed costs along with the greatest operational flexibility. Operational flexibility is needed as the tailings filtration characteristics change over the life of the mine. For these reasons, large modern filter presses are becoming the equipment of choice for high tonnage tailings dewatering applications.

As the need for dry stack tailings has increased, so has the need for larger and larger dewatering equipment to accommodate the potentially huge volumes of tailings slurry. Some large mining operations process over 100,000 dry tonnes of flotation tailings per day. It is widely held that fewer / larger pieces of equipment reduce both operational costs (OPEX) and total installed costs (CAPEX). To meet this demand and allow customers to benefit from lower costs, we developed a 5m x 3m filter press capable of dewatering 30,000 tons per day of tailings. The new design is shown in Figure 10.

A new high capacity filter press has been developed, suitable for high tonnage flotation tailings dewatering. The filter was developed as part of the EcoTails® project and can dewater up to 30,000 tons per day per filter.

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