Monitoring Froth Density and Froth Flow

Mineral Recovery, Flotation Cells

With metallurgical variability in the ore being processed, coupled with variability in the particle size from the Grinding Circuit, caused by changes in Ore hardness, Flotation Cells, Concentrate Grade and  Recovery can constantly change. Concentrators still rely on trained operators to manually observe changes to the mineral recovery efficiency, backed up by some technologies, as well as taking Froth samples from common launders on a time basis to analyze in the laboratory.

Changes to the metallurgical/hardness characteristics in the Ore are random and therefore reduced mineral recovery may occur before the next Froth sample is analyzed or before the operator manually observes changes taking place in the Flotation Cell. Some banks of Flotation Cells may not be recovering mineral at their most efficient levels because of mechanical, hydraulic, feed, airflow, reagent imbalances.

FloLevel Technologies introduced the Analyzer Array in conjunction with the Pulp/Slurry, Froth height Array Level Transmitters to provide continuous feedback on Froth Density Measurement and  Froth Flow Rate Measurement to provide instantaneous reporting back to the control system on major changes occurring in mineral recovery from the Flotation Cell.

Ultrasonic Cleaning: Mineral Recovery, Flotation Cells

Self-Cleaning

Flotation Cells have a history of scale and soluble buildup issues on any device that are installed in the Pulp/Slurry, Froth areas. This degree of buildup and scaling, largely depends on the makeup of the ore body and for that reason is site specific.


Displacement Floats (used with level transmitters), Pressure transmitters and Conductivity probes that are immersed in the Pulp/Slurry and Froth are “passive” technologies that do not prevent these forms of soluble and insoluble buildup and so they will be adversely affected over time.


The FloLevel Array transducers, use “active” Ultrasonic Cleaning to remove soluble and insoluble scaling and buildup.


The Ultrasonic Cleaning power produced from the Array transducers, when compared to typical sonar ultrasonics, is 20 - 50 times more powerful and has been designed to create a phenomenon called RAREFACTION in front of the transducer diaphragm.


When a sound wave is produced, half of the sound wave is a pressure compression component and the other half is a reduced decompression component, which is referred to as a Rarefaction effect.


Rarefaction, causes the liquid to fracture in front of the diaphragm, which creates microscopic bubbles called cavitation. These bubbles form and collapse, which cause high powered implosions, commonly associated with Ultrasonic Cleaning. The cleaning power for the low frequency transducers used, are sufficient to remove scale, grease which are both insoluble and soil, calcium, salts, etc which are soluble in nature.


If the FloLevel Array was turned off and buildup was to occur on the diaphragms of the transducers, the system would self-clean and remove the buildup, without the necessity of removing the Array hardware from the Flotation Cell.


Sizing the transducer frequency for the mining environment is critical. Cavitation implosion intensity, for the cleaning affect in Flotation Cells needs to take into consideration, scaling and other soluble buildup issues. The cavitation intensity (bubble size) increases as the transducer operating frequency decreases. The larger the cavitation implosion intensity, the greater the power cleaning capability.


Inversely, the higher the transducer operating frequency, the smaller the cavitation intensity and therefore can only be considered for service applications that are less arduous.

Optimize Flotation Cells and Significantly Increase the Mineral Recovery

How a flotation cell work


Flotation Cells (Froth Flotation) were developed to separate and recover high value Sulphide ores from low grade ore bodies. The ore is crushed and milled at the concentrator in a process known as comminution, where the mineral is in suspension in slurry. The particle size for mineral being recovered is generally less than <0.1mm. This slurry (pulp) is dosed with a collector (Surfactant chemical) where necessary and then pumped into the Flotation Cell. The Flotation Cell is aerated to produce bubbles and agitated to keep the solids particles in suspension in the pulp. The hydrophobic particles (mineral particles being recovered) attach to the bubbles and rise to the surface where they form a blanket of froth which contains the mineral in concentrate. The Froth concentrate overflows the launders in the Flotation Cell and is then pumped to the Concentrate Thickener. The residue solids left in suspension in the Flotation Cell slurry are referred to as Tailings and either flow into further stages of Flotation to increase residence time, thereby maximizing recovery of the mineral, or are pumped to the Tailings Dam. 

How do the FloLevel products improve the flotation cell process?
The FloLevel Array provides the first level measuring technology that can survive the environmental conditions of the Flotation Cell, because of its unique rarefaction self-cleaning capability. By providing Real Time Process Control, greater automation is now possible for optimizing the Flotation Cell area. The Acoustic transducers are not affected by the density changes and conductivity changes to the Pulp/Slurry providing repeatable accurate readings. The FloLevel system also provides additional process feedback on Froth Height, Froth Density (contained mineral) and Froth Flow Rate to improve each Flotation Cells efficiency. No moving parts mean less maintenance and less downtime. 

How accurate is the FloLevel analyzer?
The FloLevel system can provide an accuracy of +-2mm or better with a similar small 2mm resolution capability. However, the surface modulation (surface agitation) of each Flotation Cell can vary from small millimetre change increments to much greater surface modulation depending on the process conditions of the Flotation Cell at the time. Another advantage of the Acoustic Array system is that you have no moving parts and even under high agitation the Array system will remain stable and provide an averaging affect for the Pulp/Slurry level interface. This will ensure the control system to stay stable under all operating conditions.

How much can be saved - ROI (Return On Investment) The FloLevel system, because of its repeatable level accuracy measuring Pulp/Slurry height and Froth height, as well as having the capability to measure Froth Density and Froth Flow Rate, will increase the mineral recovery efficiency of each Flotation Cell by providing instantaneous feedback on ore characteristic changes which affect the mineral recovery. This will also decrease the amount of time and cost required for routine sampling and laboratory testing. ROI (return on investment) for the purchase price of the FloLevel system, plus installation is measured in weeks because of its ability to provide reliable process feedback, for a minerals process application that has been around for over 100 years, but has lacked the technology to allow stable feedback on process changes in the Flotation Cell, caused by different ore body characteristics. The FloLevel system utilized with a DCS or PLC control system will now allow for a greater automation capability and be less reliant on operators manually observing each Cell for changes in mineral recovery. Individual Flotation Cells can now be tuned to produce for the optimal mineral recovery and profit return whatever the ore body grade being processed.