TAILINGS slurries can have a major impact on the community living in the vicinity of mining activity, and also carry significant environmental risk.
Calls for greater transparency are mounting from all stakeholders including the mining industry, investors and governments in mining countries around the world.
Small miners to large mining conglomerates are conducting trials to characterise their tailings and assess which dewatering technologies are the most effective and efficient.
Alfa Laval offers a cost-effective solution to dewatering tailings using mechanical separation by solid bowl decanter centrifuges, which enable mines to dispose of tailings solids as a solid cake and remove the risk of storing slurries in a tailings dam.
Conventional methods like pressure filtration have limitations, particularly when processing fines, high clay content, silt or slimes which can bind up the filter cloth.
Solid bowl decanter centrifuges are not a form of filtration, rather relying on G forces and the difference in density between the solids and liquids, to extract a dry cake that has a shear strength which is transportable and suitable for downstream dry stacking or other forms of disposal.
Alfa Laval mining technology engineer Paul Tuckwell said technology had advanced a lot in the past 20 years.
“Before you would have needed 10 centrifuges to achieve what one could do right now,” he said.
“There’s also a number of advances within the centrifuge; the G force that can be achieved, the wear protection within the centrifuge can handle more erosive solids, and also the way the internals are designed achieves a higher capacity and drier cake.”
The cost and time saving benefits are notable. Solid bowl decanter centrifuges require a much lower labour component as automation, which means there’s no need for an operator to man it round the clock, and staff can instead focus on other parts of the plant.
“With a filter press the cake is generally discharged intermittently and for continuous feed flow a big slurry buffer tank is required plus the way cake is collected is quite complex due to the catch discharge,” Mr Tuckwell said.
“Whereas a centrifuge discharges cake continuously. So that makes the operation and the installation complexity a lot simpler – saving both time and money.”
Maintenance and downtime is also minimal, as centrifuges are physically smaller and easier (and cheaper) to transport and enable recycling of water and process chemicals.
“Instead of getting all your fresh water from a bore, which can be quite expensive, mines can re-use the water for processing purposes from the solid bowl decanter centrifuge which is recovered from the tailings,” Mr Tuckwell said.
“Our aim is for water to be reused in the plant, not dumped into a tailings pond.”
