Froth flotation relies on the differential hydrophobicity of valuable minerals and gangue to separate them. In this method, the chemically treated slurry of ore is subjected to aeration in a flotation cell, which makes the hydrophobic minerals adhere to air bubbles and float upwards in the form of a mineral-enriched froth. One of the major problems in today’s processing facilities is the froth instability due to bursting of the air bubble layer prematurely, particularly when there is blending of the ores.
The variability in the mineralogy and size distribution of the particles should be mentioned as the real cause of froth instability during the ore blending process. In case ores of different mineralogy and physical characteristics are being added, it causes great disturbance to the system’s equilibrium. The point is that the variability in mineral liberation caused by the variability in mineral dissemination while blending ores leads to changes in particle sizes.
Variations in gangue mineralogy, especially the addition of clay minerals as a result of changing blend, serve as harsh destabilizers. Being high in specific surface area and surface charge, clay particles form a coating on valuable minerals as well as air bubbles, and cause what is called slime coating. It prevents the adhesion of hydrophobic minerals and causes too much water to be entrained in the froth. The formed froth fluctuates from becoming too brittle and releasing the valuable minerals instantly to being too viscous to allow proper gangue drainage.
Moreover, changes in ore blends strongly affect the formation of ultrafine particles that are associated with froth destabilization. Processing of complex ores or flotation tailings results in the need to perform intensive grinding due to the presence of fine dispersed structures in gangue minerals (Zhang et al., 2021). The obtained ultrafine particles settle within the interstitial liquid passages between the bubbles. Their presence reduces the thickness of the water film between the bubbles and results in rapid bubble coalescence.
However, there are several methods used by metallurgists to overcome the negative impact of these forces when the cells undergo the transition process. The first method is the use of froth washing, where the addition of the wash water helps to wash out the gangue particles in the entrained liquid in the bubble (Jera & Bhondayi, 2022). However, froth washing helps in removing the entrained hydrophilic fines without harming the structure of the froth. Another strategy applied is that of adjusting the cut sizes of the hydrocyclones.
In conclusion, it can be seen that the primary reason behind froth instability in a flotation circuit when changing ore blend is the varying mineralization and gradation of the feed. Due to the random introduction of ultrafine minerals, gangue materials, and clay components, the mechanism of bubble coalescence and particle adsorption undergoes dramatic changes. Understanding the root cause helps state-of-the-art processing plants go beyond mere adjustments to take corrective measures.
References
Jera, T. M., & Bhondayi, C. (2022). A Review on Froth Washing in Flotation. Minerals, 12, 1462. https://doi.org/10.3390/min12111462
Zhang, X., Kou, J., Sun, C., et al. (2021). Mineralogical characterization of copper sulfide tailings using automated mineral liberation analysis: A case study of the Chambishi Copper Mine tailings. International Journal of Minerals, Metallurgy and Materials, 28, 944–955. https://doi.org/10.1007/s12613-020-2093-1
