With a well established presence in the mining industry, instrumentation specialist Endress+Hauser has a comprehensive product range to suit a variety of applications. One of the many processes for which the company's products are ideal is flotation, in which measurement, and thus instrumentation, plays a key role in controlling the quality of the process.
The process of flotation in gold, copper, lead, zinc and coal mining is used to recover fine mineral particles. The technique uses the surface properties of the particles to separate them. The particles to be floated are made hydrophobic with the addition of chemicals. Air is then pumped through the mixture and the desired particles attach themselves to the bubbles and froth is formed. This froth is extracted and the concentrated mineral is further refined. Waste rock particles do not adhere to the bubbles and drop to the bottom of the tank. The waste material that exits at the bottom of the tanks, at the tail end of the process, is known as tailings. The process makes the mining of mixed ore bodies economically viable.
In a typical flotation cell, various parameters need to be controlled. These include level and interface measurement, slurry pH, flowmeters for frothing agent dosing, slurry flow and valve control using electromagnetic flowmeters.
Measurement is crucial at this stage as there needs to be a balance between the amount of slurry and the amount of bubbles produced. Too much slurry and too few bubbles lead to under recovery of minerals, thus affecting the efficiency of the process. Maintaining the correct level of slurry is accomplished using ultrasonic measurement.
This method is used to measure the slurry and bubble interface, which is of the utmost importance in order to control the quality of the process. The density of the foam bubbles is high enough to reflect ultrasonic pulses from a continuous ultrasonic level sensor, such as the Loop Powered Prosonic M from Endress+Hauser.
By using a two-channel, four-wire device, such as the new Prosonic S, one sensor measures the distance to the bubble surface, while the other sensor, complete with float, rod and disk, measures the distance to the disk. The float drifts on the interface foam with the disk in the slurry below. When the ultrasonic device measures the distance to the disk, it is in fact measuring the actual interface. In this way it can be determined whether operating conditions are optimised or whether further adjustments to the chemical dosing, slurry, or bubbles need to be made.
For more information contact Hennie Blignaut, Endress+Hauser, +27 (0) 11 262 8000, [email protected]
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