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SEPARATION & CLASSIFICATION the separation process . You have dewatering applications to maximise water recovery from solids – and cyclones are often used where other dewatering equipment is not practical or involves too much investment . Cyclones are also used in underground mines for backfilling applications where you have certain requirements for the mass split or underflow size distribution when can have a big influence on the backfill drainage rates once it is delivered underground . Finally , there are tailings dam applications – here again you need to ensure the correct mass split and the correct size distribution to build the outer wall with the correct densities throughout the wall .
So , which is the highest value application ? “ It depends on what is important for the customer ,” Bekker said . “ In some cases , in South America , tailings dam cyclones arguably add a greater overall value to the project than the milling cyclones . But clearly in high tonnage , particularly copper applications , milling cyclones represent a high return on investment . You are looking to minimise milling energy and cyclones do play an important role . You also have pumping requirements in the mill circuit and here cyclones can play a role in reducing cost .”
Bekker also talked about availability and the materials in terms of the construction of cyclones in the processing plant from a maintenance perspective regarding life expectancy and availability . If a unit fails unexpectedly and you don ’ t have spare capacity it can have a major negative effect . One needs to look at how many standby units you have in the application and ensure that the design has been thought through carefully , balancing CAPEX against availability .
He adds : “ There are also trade-offs in cyclone use . If you have an area of the plant where you want to minimise water usage , cyclones are important , however , you want to make sure you have the maximum efficiency . Cyclones are most efficient at lower solid concentrations but to reduce water usage , plants try to use the highest solids concentration allowable . One needs to balance how much water you are really saving against what is happening as a result of these decisions on the efficiency of the process . If there is no other equipment other than the cyclones that can recover water , then the cyclone and its operation becomes very important .”
Back to tailings dam applications , and again , you need to make sure the cyclones are performing as efficiently as possible . He said : “ One of the drawbacks of tailings dam cyclones is that they are located remotely from the main mine and plant operation and I would say they don ’ t always get the attention in terms of monitoring and maintenance they deserve . Here the materials of cyclone construction can make a difference , plus you want to ensure that the dimensions are optimal , as that can affect performance - for example the spigot diameters .
If the spigot starts to wear , the opening becomes bigger and progressively discharges more unwanted water and fines to the outside of the tailings dam . Those monitoring the cyclones may still assume the units are working as material is still coming out of the overflow and underflow but the performance has dropped . Using better materials can ensure this dimensional integrity is kept . On the flip side , using high wear resistant materials make the cyclones heavier so any manual maintenance becomes more challenging .”
Returning to backfill cyclones , there is a certain requirement for PSD and if you don ’ t maintain that then you can have problems underground . “ The greater value depends on what is important for the client but in big operations , yes , the milling circuit cyclones add the most value but as outlined , in terms of water recovery , tailings dam quality , backfill performance and slimes removal , they are also vital pieces of equipment ,” he said .
An in-depth process understanding
Multotec supplies equipment for all of these applications , and therefore places great importance on having an in-depth understanding of the limitations of the equipment but also on its experience . Bekker said : “ Often when a plant is encountering abnormal conditions , and the client is looking to improve performance through
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