Bubble load measurements in flotation - a critical review of current practice

In the flotation process, the valuable material is recovered selectively in the pulp phase and is carried by the bubble fl ux into the froth phase and, along with material unselectively recovered by entrainment, reports to the concentrate. This is termed the ‘bubble load’ and can be assessed relative to various operating parameters such as volume of air recovered, surface area of the flux, fl ow rate relative to the concentrate etc. The measurement of ‘bubble load’ is being developed for various purposes, including the evaluation of froth recovery, characterising ore differences and changes to mineral floatability, all of which are aimed at getting a better understanding of the role of the froth and pulp phases. This paper assesses the current published techniques used to measure the bubble load in industrial cells from two perspectives: i) sampling efficiency and ii) sample representativeness. Sampling efficiency refers to understanding the loss of information when sampling a certain volume out of a complex population such as a stirred pulp. Changes in the physical and chemical conditions of the sample may lead to measurement biases particularly in the sealed devices; the physical mechanisms occurring during sampling are also evaluated. The sample representativeness refers to how well a sample can represent the turbulent three-phase system. In this case, the relationship of the bubble load measurements to operational conditions such as cell feed grade and the concentrate or tail samples are assessed. This paper compares the measurement techniques and the data that have been published to evaluate their value and limitations in flotation operations, and recommends a strategy to improve them