Supersonic testwork to optimise your flotation performance

Particles smaller than 20µm pose unique challenges in flotation due to their high specific surface area, low momentum, small mass, and high surface energy. These characteristics lead to issues such as:

• Higher Reagent Consumption: Fine and ultrafine particles require increased reagent dosages due to their high surface energy, leading to higher operational costs and environmental concerns.
• Low Energy for Bubble Attachment: The small mass and low momentum of these particles reduce their likelihood to attach to bubbles, affecting flotation efficiency and recovery.

Current research involving traditional flotation technologies, including mechanical and column flotation, show these technologies struggle to effectively recover fine and ultrafine particles. The Concorde Cell™ was developed originally by Professor Jameson and further developed by Metso to address these challenges. Concorde Cell™ enhances the flotation rate and recovery by optimising bubble-particle interactions by reducing bubble size. Creating smaller bubbles with the same overall volume greatly increases the available surface area boosting both collision and attachment efficiencies—crucial for fine particle flotation.

The Concorde Cell™ launched in 2021 and Concorde Blast Tube™ Upgrade, launched by Metso in 2022, represents a significant evolution in flotation technology. This advanced pneumatic flotation cell utilises a supersonic shockwave for fine bubble generation and a high-shear environment, designed specifically to improve the recovery of fine and ultrafine particles. The Concorde Cell™ has been successfully installed in various mining operations globally, including  copper, gold, and metallurgical coal.

Understanding the Concorde Cell Technology

The key differentiation between the self-aspirated downcomer and the Concorde Blast Tube are listed below. 

The recovery process can be described in two stages. In the first stage, small bubbles are formed in the Blast Tube under pressure. The feed enters as a plunging jet and mixes with the air under pressure. In the second stage, the aerated mixture then passes through a choke, where it reaches the speed of sound appropriate to the local conditions.

Downstream of the choke, the flow conditions become supersonic, and a sonic shockwave is created. On passing through the choke, there is a significant change in pressure over a small distance and the bubbles reduce markedly in size. The function of the impingement bowl is crucial in proving efficient dispersion of small bubbles back into the tank and reduce any turbulences for increased bubble-particle collision. At the same time the impingement bowl prevents the bubbly air-slurry mixture from bypassing straight to the tails.

Supporting client demand with Concorde testwork options

Metso has a number of Concorde testwork options in Australia, including a labcell and a containerised pilot test rig, both of which can be easily mobilised for onsite testing, if necessary. Recently Metso conducted a laboratory scale testwork programme, to assess the performance of the Concorde Technology with a client’s ultrafine spodumene tailings sample.

The testing sought to determine the achievable spodumene recovery, grade and enrichment ratio by conducting a series of batch tests with varying testwork parameters. Typical flotation parameters such as flotation time, froth washing, reagent types (collector, frother, dispersant etc..), dosages and conditioning time can all be tested along with some Concorde Technology specific parameters such as air flow rates, slurry flow rates and top and bottom nozzle sizes and parings. The air and slurry flow rates combine to create the Concorde Technology specific term of air to pulp ratio (ARP).

Each batch test consumes 30-40 litres of slurry at the desired slurry density of the flotation process stream. With only one parameter changed per test, the total slurry requirement can become quite large, especially for greenfields projects. In these instances, Metso can still conduct testwork with a more targeted approach dependent on customer requirements.

In the case of the recently conducted spodumene testwork, limited sample was available, so the testing was targeted towards varying the collector dosage and testing the effectiveness of froth washing on improving the concentrate grade. Two spodumene samples were tested, one being -50µm with the other having a large portion of the -8µm material removed via cyclones. 

Testing was conducted by conditioning the spodumene sample, within the Concorde labcell’s inbuilt mixing tank, with the desired dosage of collector for ten minutes. The conditioned slurry was then pumped into the Concorde Cell shown in figure 5. The cell is only filled to 300-400 mm below the lip. At this point the feed pump is manually locked to the desired slurry flowrate whilst a second pump draws the tails from the bottom of the Concorde Cell, regulating the froth depth and mass pull rate. This second pump recycles the tails from the Concorde Cell back into the mixing tank.

With the cell filled with the conditioned slurry the air is turned on and is injected into the blast tube, where it meets the conditioned slurry. Once the froth is established the recycle pumps output can be manually adjusted to control the concentrate pull rate. Froth washing is also turned on.

Timed concentrates are taken on an intuitive basis to produce a grade vs recovery curve. Once the concentrate becomes visually barren of any valuable minerals or the sample can no longer maintain a stable froth depth, the test can be finalised.

The Concorde Technology achieved on average an enrichment ratio of 2.9 for the uncycloned sample and 2.8 for the sample with majority of the -8µm material removed.

With a head grade of 0.48% for the uncycloned sample, the Concorde Technology achieved a cumulative concentrate grade of 2.5% spodumene with a recovery of 37%, with froth washing. These positive results will be used to present a case for further, more in depth onsite testwork. This testwork will provide confidence in the Concorde Cell Technology sizing and process performance guarantees.