# Fother Characterization Using a Novel Bubble Size Measurement Technique
## 1 Introduction
### Traditional Bubble Size Measurement Tools  
Bubble size measurement devices have been a staple of flotation analysis toolkits for well over 40 years. In their technical note on bubble size measurement, [PERSON] et al. provide an extensive list of different bubble size analysis techniques dating back to 1970 [7]. One of the most enduring and popular methods is that of bubble image capture (via either still photography or video recording), followed by image analysis and bubble segmentation.  
While the early bubble size measurement devices were developed for laboratory use, the technique gained prominence when devices capable of measurements in industrial flotation cells became available. One of the more frequently utilized devices is the Anglo Platinum Bubble Sizer (APBS). The device design was developed by the University of Cape Town in collaboration with Anglo Platinum as a modification of a device built by McGill University [7,8], and currently manufactured by Stone Three.  
Although there are many different individual bubble viewers and bubble size analyzers available, the basic design of these instruments has remained largely the same. These devices all tend to share the following features [7, 8, 9, 11, 12]:  
* Bubbles are sampled from the pulp through a bubble rise tube or column, leaving the solids behind.
* The bubbles rise through the sampling column into a measurement chamber. This chamber can be a bubble viewer window, where bubble images are captured employing a camera. Alternatively, bubbles can be captured by a bell capillary, where the volume of individual bubbles is calculated from the total volume of collected gas.
* In all cases, the measured size of the bubbles needs to be adjusted to compensate for a difference in hydrostatic pressure between the sampling point and the measurement point.
* Before measurement, the instrument needs to be filled with water that matches the chemical composition of the flotation pulp. However, an additional fother is usually added to the analyzer to prevent bubble coalescence inside the sampling tube.  
Figure 1: Electrical conductivity of the dam process water at a coal mine in Queensland, Australia.  
* During the measurement, the water contained within the instrument is displaced by the collected gas. The downward flow of water then flows counter-current to the rising bubbles.  
While these methods of bubble size measurement are undoubtedly effective, they still have disadvantages. The most obvious of these is the potential inconsistency in bubble size between the sampling point and the measurement point. The downward flow of water from the measurement chamber has the potential to bias the bubble size distribution, as the smallest bubbles will be swept out of the tube by the flow. An additional concern is the possibility of bubble coalescence within the riser tube. For this reason, extra frother reagent is typically added to the measurement chamber at a concentration that exceeds the Critical Coalescence Concentration (CCC) of the frother reagent [13,14].  
Until recently, there were no bubble size measurement tools available that could operate in situ within the flotation pulp. This also means that there was no effective way to validate the accuracy of traditional bubble size measurement devices. However, due to recent advances in in situ measurement systems, such tools are becoming increasingly available.