Investigations of flotation charateristics of Lumwana and Kansanshi Ores using formulated frothers
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The initial work of this project involved determining the optimum mesh of grind and frother dosage for Lumwana and Kansanshi ores. This work was conducted at the University of Zambia mineral dressing laboratories based at School of Mines. Further work involved carrying out surface tension, bubble size and froth stability measurements at University of Cape Town’s Centre for Minerals Research (CMR) laboratories based at the Department of Chemical Engineering. Finally, water recovery tests were conducted at Lumwana andKansanshi mine sites.The optimal mesh of grind for Lumwana and Kansanshi ores were established as 65% and 80% passing 150μm, while frother dosages were established at 60g/t and 80g/t respectively.On flotation kinetics, aliphatic alcohol frother MIBC and higher molecular weight glycolbased formulated frother Betafroth 245 achieved the optimal grade-recovery curves on Lumwana and Kansanshi ores respectively. There was a general decrease of surface tension as the frother concentration increased.However, all the frothers showed a sudden drop in the surface tension at lower concentration of around 20ppm, indicating that the surfactants tested were more surface active at lower concentrations. Beyond this concentration (20ppm) the surface tension started to level off suggesting that the interface was saturated and the critical micelle concentration (c.m.c) had been reached. Frothers Betafroth 245, Dowfroth 200 and MIBC seemed to give lower critical micelle concentrations. A lower critical micelle concentration is an indication that there is increased adsorption of surfactant at the water-air interface and therefore, such a surfactant had a higher hydrophobicity effect on the flotation performance of the ore, resulting in better flotation results. Bubble size measurements showed that bubble size decreased as the concentration of frothers increased and that the critical coalescence concentration (CCC) was reached around 25ppm,after which there seemed to be a gradual decrease to the maximum of 100ppm. Beyond the critical coalescence concentration, frothers Betafroth 20, Dowfroth 200, Betafroth 245 and MIBC produced the smallest bubble size distribution. Smaller bubble distribution enhances flotation kinetics (recoveries) and mineral selectivity (concentrate grades). This seemed to support the better performance of the three frothers, on Lumwana and Kansanshi ores,except Betafroth 20 for explained reasons.Results from froth stability and water recovery tests showed Dowfroth 250 was the most stable frother, and that froth formed was too stable that it recovered high quantities of water and consequently higher entrained gangue (fines) on both ores. The frother Betafroth 245 gave the optimal stability, since its froth was much “drier” and recovered the least quantities of water and therefore less entrained gangue.These results imply that; Though the chalcopyrite mineral in Lumwana ore is liberated at coarser grind (65% passing 150μm), compared to the chalcopyrite in Kansanshi sulphide ore that is liberated at 80% passing 150μm, the ore (Lumwana) responded well (grades and recoveries) to lower molecular weight frothers such as MIBC and Dowfroth 200, because it contained higher levels of fine gangue (micas). ii On one hand higher molecular weight frothers like Betafroth 245 and Betafroth 20 performed well on Kansanshi sulphide ore and yet not as good on Lumwana ore, because on the other hand the higher molecular weight frothers were forming froths that were to stable due the stabilisation effect of fine gangue. The response of ores to higher molecular weight frother Dowfroth 250 has showed that in spite giving higher recoveries, the frother gave poor grades on both ores. The poor grades given by Dowfroth 250 can be attributed to formation of highly stable froth enhanced by fine gangue (mica) and gangue entrainment caused by higher water recoveries. The work has shown that it possible to investigate and establish frothing properties and characteristics of a frother by looking at following properties; (i) surface tension properties, (ii) coalescence (ii) water recovery and lastly (iii) froth stability tests.Further work to establish the role pH plays in the hydrophobic effect a frother has on a mineral particle and bubble at one end, and the interfacial surface carrying opposite charge on the other is being recommended.
- Mines