LED-induced fluorescence monitoring of multiphase behaviour in a reflux flotation cell

This study presents the first application of LED-induced fluorescence (LED-IF) as a non-intrusive diagnostic method for monitoring local multiphase conditions in a small-scale Reflux Flotation Cell (RFC). Rhodamine B was evaluated as the fluorescent tracer through surface-tension and hydrodynamic measurements, and 0.1 µM was selected as the operating concentration because it provided sufficient fluorescence contrast with minimal disturbance to silica yield and cell behaviour. The effect of feed solids concentration, wash water flux, and downcomer position on the optical response was examined alongside gas holdup, bubble size, bed length, and silica yield, using silica as a model hydrophilic particle. The recorded signal was highly sensitive to changes in the local multiphase environment. Increasing feed solids concentration from 0 to 12 wt% reduced the average normalised intensity from 0.093 to 0.032, consistent with stronger optical attenuation and concurrent changes in bubble size. Increasing wash water flux increased the measured intensity, while changing the downcomer position altered both the mean response and its spatial variability through changes in solids loading and bubble structure. Under the conditions examined, the LED-IF signal reflected the combined effects of tracer concentration and optical attenuation caused by bubbles, liquid and solids. It therefore provides a qualitative indicator of changes in the local multiphase state of the flotation cell. With improved calibration to account for these coupled effects, LED-IF could be further developed for quantitative monitoring of RFCs and related multiphase systems.