As Australia’s water supplies continue to plummet, mining companies are searching for new ways to process minerals without using a tailings dam. Alfa Laval offers an answer to this need with advanced dewatering solutions.
Hamid Foroush is a technical support engineer at Alfa Laval and is one of the many brains behind the company’s solid bowl centrifuge technology.
The machines provide a new way to dewater tailings, allowing mineral processing plants to reuse tailings water. Solid bowl centrifuges provide an economically and environmentally friendly solution to dewatering tailings dams.
Alfa Laval has a significant installed base for its solid bowl centrifuges with large machines currently being used by mining companies across Australia and in other large mining regions around the world.
“We’ve got several machines installed and commissioned in Queensland and New South Wales, for coal tailings application as well as a number of units in WA for mineral processing,” says Foroush, who has just finished trialling the technology’s next generation.
“A solid bowl centrifuge is a type of equipment used for dewatering tailings. We normally get the slurry from one point of the machine. The slurry contains suspended solids with water. Alfa Laval’s unique technology separates the solids from water using centrifugal force. As a result, the solids come out from solid discharge and the liquid from liquid discharge.”
Larger solid bowl centrifuge machines can spin slurry at up to 1600 revolutions per minute (RPM) when processing coal tailings. The speed allows the solids to separate from water – removing the need to wait for water to evaporate in a tailings dam.
“The water which is recovered could be used for processing – it can just be pumped back to the plant for reuse,” Foroush says.
Not only is the technology effective in reducing how much water is wasted, but it also has the potential to save costs during the rehabilitation process of a mine.
“With the current practice of pumping slurries into a tailings storage facility (TSF), the rehabilitation costs are huge at the end of mine life for mining companies,” Foroush says.
“If the customers already have some other technologies for dewatering, it still pays to compare. Our technology usually consumes less polymer, has smaller footprints, and operates with an enclosed process that is fully automatic. Also, solid bowl centrifuge technology works better for finer particles where filters struggle.”
Foroush says the speed and efficiency of solid bowl centrifuge technology makes it a better choice for tailings dewatering.
“The dewatering stations within solid bowl centrifuges have a very small footprint compared to belt filter press, and belt and frame press, and can make tailings dams completely redundant or add critical capacity as new TSF licences are harder to come by. Normally the life expectancy for our machines is between 25 to 30 years,” Foroush says.
“If you use tailings dam you will lose water through evaporation because it might take several weeks for the solids to settle.
“But if you use solid bowl centrifuge technology, you will recover the water instantly and you can use it straight away in the plant. We’re seeing customers in Australia that are able to re-use 80–90 percent of their process water in the plant, thanks to Alfa Laval solid bowl centrifuges.”
Foroush says Alfa Laval Australia has a design for full scale skid mounted solid bowl centrifuge which could be used for trials as well as an interim solution for sites where tailing dams are reaching its capacity.
“Our trial unit allows customers to see the operational benefits and results firsthand before committing to a full-scale deployment,” he says.
Safety is another important factor when processing minerals. As pressure to improve safety and operational performance increases, major mining companies are looking to eliminate tailings dams and move towards what they call “dry stacking” or “dry disposal” of tailings.
Foroush explains that Alfa Laval’s solid bowl centrifuges discharge solids as a cake with a low moisture content that can be dry-stacked, and used for mine rehabilitation in a similar fashion to overburden and coarse rejects.
“Depending on the mineral being processed and other parameters such as solids density and particle size distribution, the cake moisture ranges from 15-40 percent,” he says.
With solid bowl centrifuge technology, mining companies have the opportunity to move away from storing slurries in dams and lower the risks associated with TSF.
This article also appears in the April edition of Australian Mining.