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The rising global demand for ore and the depletion of high-purity mineral deposits has made it necessary to recover finer-size fractions of ore in feed material.

Conventional flotation technology is not geared to recover ultrafine material; however, pneumatic flotation technology Pneuflot, designed by engineering and manufacturing company McNally Bharat Engineering (MBE) Minerals South Africa, is set to be the driving force for flotation technology in the future, says MBE MD Johannes Kottmann.

“There are a number of drivers for the choice of flotation equipment. The key drivers are normally cell efficiency and cost, both capital and operating. Agitator flotation cells have been used in coal processing owing to their ease of operation and robust nature. Pneuflot is surpassing this conventional technology for a number of reasons.”

The principle introduces flotation feed to the cell from the top using a ‘T-piece’. The feed flows through the self-aspirating aerator that generates a maximum bubble particle contact. The mixture of bubble and feed material leaves the contact area through the distributor, which is placed at the bottom of the cell. The distributed slurry sorts its concentrate and gangues in the separation vessel.

The unit does not need compressed air. Slurry is pressed through small wearproof ceramic nozzles arranged in circles that point towards a large venturi, which reduces fluid pressure that results when a fluid flows through a constricted section of pipe.

“When the pulp is pumped through the venturi, a vacuum is created, aerating the pulp,” explains Kottmann.

The circular arrangement of the nozzles distributes the pulp flow, creating the necessary turbulence for intensive bubble-mineral particle contact. Aerators come in different sizes to suit various flow rates and mineral throughputs, which enables high performance with only one aerator unit for each flotation cell.

To compare Pneuflot’s performance to that of conventional agitator cells, a pilot cell was installed at an existing coal opera- tion in the US. An incoming stream was split so that part of it passed through the pilot cell, while the rest of the stream entered the main plant, for processing by the current circuit. The flotation reagents were kept consistent with current plant operations.

The plant’s capacity is 240 t/h of bituminous coal feed and its existing flotation circuit consists of two agitator cells with a combined volume of about 300 m3. The plant had a 94% recovery rate of combustibles at less than 7.5% ash, using its two- stage process. A particle size analysis showed that 80% of the feed material was less than 240 µm.

The pilot project increased the plant’s recovery rate by 2%, with the ash content remaining at 7.5%. This means that the existing two cells could be replaced with two 6-m-wide cells, with a total volume of 160 m3.

Kottmann explains that the test results reveal that Pneuflot can reduce the plant’s carbon footprint and the amount of reagents used, as well as decrease maintenance and the number of pumps and sumps needed, which results in an increased recovery of saleable product.

“The reduction in process complexity makes Pneuflot much easier to manage. This technology offers an economic solution for all plants,” he states.

The technology can be used in any flotation application, such as sulphide nonferrous metal ore, oxide ore, industrial minerals, salt minerals, paper and plastic waste recycling, disposal of fly ash and gypsum from flue gas desulphurisation and wastewater treatment.

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