Minimizing entrainment recovery of ultrafine silicate minerals in pentlandite flotation using carboxymethyl cellulose

• Quartz was used as an entrainment monitor in the flotation of pentlandite. • Quartz entrainment recovery increased with a decrease in particle size. • CMC enhanced the formation of plateau borders that facilitate particle drainage. • Determination of optimum CMC concentration is crucial to limit the negative effect on pentlandite flotation. The presence of silicate minerals is a common occurrence in various ore types, including nickel sulphide ores. These silicate minerals dilute the grade of flotation concentrates through recovery by entrainment which leads to poor flotation performance and subsequently loss of values. Flotation by entrainment is further enhanced as the particle size of the feed becomes finer. The present work investigates the entrainment characteristics of silicate minerals in the flotation of pentlandite. Within the context of the selective flotation of pentlandite from silicate gangue minerals, the influence of different particle sizes on entrainment flotation was also carried out. PAX was used as a collector for recovering pentlandite, whereas carboxymethyl cellulose (CMC) was employed as a dispersant for the silicate gangue mineral. Microflotation experiment was conducted on a pentlandite-quartz mixture of different particle sizes including − 106 + 75 µm, − 75 + 38 µm, − 38 + 20 µm, and − 20 µm. Electroacoustic zeta potential measurements, Fourier-Transform Infrared (FTIR) Spectroscopy, and Ultraviolet–Visible (UV–Vis) spectroscopy were used to characterise the interaction between pentlandite and quartz and in the presence of PAX and CMC. It was observed during the mixed minerals flotation tests that flotation by entrainment increased with a decrease in feed particle size irrespective of the dosage of CMC. Notwithstanding, the addition of CMC led to notable reduction in entrained silica flotation from 58 % to 38 % in the −20 µm size fraction attributed to improved particle drainage from the froth layer in the presence of CMC. Furthermore, UV–Vis spectroscopy and FTIR results gave further evidence that PAX adsorbed onto pentlandite and quartz minerals surfaces in the presence of CMC, which is consistent with the flotation response observed. Overall, this study confirms entrainment of gangue species is dominant within fine or ultra-fine mineral particles and proposes the use of CMC as a dispersant to limit gangue flotation by entrainment.