mechanical cells use a large mixer and diffuser mechanism at the bottom of the mixing tank to introduce air and provide mixing action. flotation columns use air spargers to introduce air at the bottom of a tall column while introducing slurry above. the countercurrent motion of the slurry flowing down and the air flowing up provides mixing action. mechanical cells generally have a higher throughput rate, but produce material that is of lower quality, while flotation columns generally have a low throughput rate but produce higher quality material.