Today’s mines are under more scrutiny than ever before to comply with ever increasing environmental regulations. Water scarcity is also a large factor especially when many ores are being mined in remote locations or in arid climates.
Recent filtration developments from FLSmidth have enabled mining companies to increase water recovery and maximize the dryness of the cake being produced as tailings from the mining process.
After ore is sent through the crushing and grinding circuits, it is typically sent through flotation processes to recover the ore. Once the base metals, such as copper, are separated through flotation, the remaining slurry is pumped to thickeners and de-watered to produce the tailings that are typically pumped to a tailings pond.
Filters reduce the need for tailings ponds
FLSmidth’s AFPIV Minerals Filter press and the Pneumapress Filters are both pressure filters which can be installed at the end of the process line to reclaim water. Pressure filters are the best equipment for recovering the most moisture from the remaining tailings to create the driest cakes.
For many years, mining companies completed the process flowsheet with thickeners but are now seeing the environmental benefits of adding FLSmidth filtration equipment after the thickeners. The dry tailings produced from filter presses, drastically reduce the need for a tailings pond that would normally be created to help catch the remaining water which is left in the pond to evaporate or dissipate back into the soil. Tailings ponds have to be left for a while before being able to revegetate the land. Instead of a pond, pressure
filtration allows the filtered tailings to be dry stacked.
Lowering environmental impact
With dry stacking provided by FLSmidth pressure filters, mining companies can stack and compact the tailings and start the reve-
getation process much faster than just using tailings thickeners. The dry stack tailings concept is currently being incorporated into existing mines to eliminate the need for conventional tailings impoundment sites. This results in a much smaller foot print than a tailings pond, the site is much easier to reclaim, and has a lower long-term liability in terms of environmental impact.
In addition, the filtered dry tailings concept allows a plant to use much less water when compared to similar concentrator plants. AFP Filter technology can be combined with our RAHCO material handling equipment to supply complete tailings management systems. When added altogether, the filtered dry stack tailings concept exhibits the most advanced technologies and makes for a more environmentally friendly mining site.
Selecting the right filter
To choose the right filtration equipment, the factors that have to be evaluated include slurry feed concentration, the viscosity and temperature of the material being processed, the volume of slurry to be processed in a given time-frame, how quickly the cake is formed, and the particle size distribution.
Once having settled on the type of filter that will probably work best, the next hurdle is to choose the most economical and efficient design. The factors that influence this decision include overall capacity of the filter, its capability to deliver the specified moisture content in the filter cake as well as the type of washing it provides, if required, and how the cake is discharged.
A good deal of test work is often required to determine how a particular filter design will perform under real production conditions. FLSmidth has experience and know-how for all filter applications as well as the facilities to perform the necessary test work.
Current AFP filters have up to 120 chambers, with more than 19.2 m3 of volume and 1,000 m2 of filtration area per filter. Due to their size and capacity, they can be used in a variety of applications. The filters can operate up to 15 bar filtration pressure and are available with both recessed and membrane filter chambers. The large filter capacity unit becomes particularly advantageous in tailings dewatering applications where multiple filters are required to dewater large volumes of solids. With its large capacity, a dozen AFPs will achieve what would have required as many as 30 conventional filter presses.
FLSmidth is looking at even larger filtration equipment to handle more capacity while producing lower cake moistures with the quality and consistency needed for greater efficiency
CONTACT: Reuben Neumann