Process measurement specialist Endress Hauser supplies a wide range of instrumentation to the mining industry. One of the many mining processes for which Endress+Hauser’s products is ideal for is flotation cell optimisation.
The process of flotation in gold, copper, lead, zinc and coal mining is used to recover fine mineral particles. The flotation technique uses the surface tension of the mineral particles to separate them from the ore slurry. The mineral particles to be floated are made hydrophobic in each flotation cell with the addition of flocculant chemicals.
Air is then pumped through the slurry mixture and the desired mineral particles attach themselves to the bubbles, rise to the surface and high concentration mineral 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 flotation cell process makes the mining of mixed ore bodies efficient and economically viable.
In a typical flotation cell, various parameters need to be controlled. These include surface level and interface measurement, slurry pH, flowmeters for flocculant agent dosing, slurry flow, compressed air flow and valve control using electromagnetic flowmeters.
Accurate and reliable measurement is crucial during the process as there needs to be a balance between the amount of base slurry and the amount of froth produced. Too much slurry and too little froth leads to an under recovery of minerals, thus affecting the efficiency of the process. Too much injected flocculant costs money, but is also expensive to remove from the process later down the line.
The common way to optimise the process is to measure the relative thickness of the froth in relation to the level of the slurry in each flotation cell. Since the density of the froth is high enough to reflect ultrasonic pulses from a continuous ultrasonic level sensor, this is an ideal technology for monitoring the level of the foam floating on the slurry.
By using Endress+Hauser’s new two-channel, four-wire device Prosonic S system, one ultrasonic sensor measures the distance to the froth, while the other ultrasonic sensor – complete with float, rod and reflecting disk – measures the distance to the interface since the float drifts on the slurry interface with the disk protruding through the foam.
When the Prosonic S measures the distance to the disk, it is in fact measuring the actual interface level. The Prosonic S measures can therefore be determined if operating conditions are optimised or if further adjustments to the chemical dosing, slurry, or bubbles need to be made.