Abstract
Conventional ion flotation is hydrodynamically constrained by coupling of the gas flux and liquid flux that report to the concentrate. This constraint has greatly limited the industrial application of ion flotation, despite its remarkable effectiveness in extracting ionic species down to very low concentrations, of order 1 ppm. Previous work demonstrated that these hydrodynamic constraints could be significantly relaxed using the reflux flotation cell (RFC), a system incorporating parallel inclined channels to improve bubble-liquid segregation. However, it was found that bubble coalescence placed an additional limit on performance. In this study the impact of coalescence was minimized by reducing the volume reduction from 20 to 5, ensuring sufficient liquid reported to the concentrate with the bubbles. Under these conditions, an equivalent adsorptive recovery was achieved using the RFC at feed fluxes up to four times those in the conventional system. The maximum adsorptive extraction rate achieved with the RFC was three times that for the conventional system. A refined experimental methodology was used to quantify much more accurately the relative hydrodynamic limits of conventional and RFC operation. The previously neglected issue of split-zone segregation, resulting in smaller bubbles in the lower part of the cell, was also investigated.
Highlights
Ion flotation involves the separation and concentration of ions from solution, through the promotion of surfactant adsorption onto rising air bubbles, forming a foam, and capturing the foam via an overflow launder
The model predicts a significant increase in achievable adsorptive recovery, and the flow rate at which this can be achieved, as a result of the inclined channels (IC) being used
Bubble surface flux is increased by increasing the gas flux and decreasing the bubble size, but results in bubbles being entrained into the tails at lower feed fluxes, reducing recovery
Summary
Ion flotation involves the separation and concentration of ions from solution, through the promotion of surfactant adsorption onto rising air bubbles, forming a foam, and capturing the foam via an overflow launder. This powerful technique has been used in laboratories for over half a century [1,2,3], its effectiveness in industry has been far more limited due to the limited volumetric fluxes that can be applied. It is noted that the present work excludes particulate flotation, which involves very different mechanisms, including irreversible adhesion. Ion flotation by contrast involves reversible adsorption
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