Festo, has helped improve the platinum recovery rate from flotation cells at a mine in North West Province. The mine uses the cells to extract platinum from the crude ore by agitating a mixture of ore, water and frothing and collecting reagents. The mineral particles rise to form froth on the surface and the waste material settles to the bottom. The froth is skimmed off and the water and chemicals are distilled or otherwise removed to leave the clean concentrate.
When the fluid levels within the flotation cell are not accurately controlled, the mineral-rich foam does not form or the concentrations are not optimal. The original design had all actuators controlled via external positioners with feedback through a series of linkages. This system was inherently weak and needed regular maintenance and recalibration – a time-consuming process that was happening too often. In addition to this, the system needed to operate in a potentially corrosive environment with exposure to sulphuric acid.
The Festo engineered solution
Based on experience gained with Festo installations at mines around the world, Festo sales engineer, Koot Viljoen, offered the Festo DFPI cylinder: “The design of the DFPI is compact so the positioner and valves are situated inside the actuator barrel and are therefore protected from the environment.”
The specific model DFPI that Festo supplied also has an integrated position controller and a self-initialisation feature. The DFPI’s integrated position controller checks the position of the piston rod within the available stroke range in a self-regulating closed loop system. The actuator therefore requires no calibration and is effectively maintenance free. Control of the DFPI actuator is through the positioner via a 4-20 mA analog signal, either from a master PLC/IPC, or manually on-site via an external set-point generator. The integrated positioner and the removal of the linkages ensure accurate control of the flotation cell levels, allowing for improved platinum recovery.
The Festo DFPI has a factory-defined safety position that is assumed if the operating voltage or the analog set-point value fails. In this case, a fail to extend action closes the Dart control valve in the flotation cell to minimise loss of valuable material.
The resulting improvement in control accuracy from the Festo solution has meant better platinum recovery and improved reliability. The self-calibrating and easy installation provided a speedy commissioning phase for the customer, minimising impact on productivity.
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