Insight into the low-rank coal flotation using amino acid surfactant as a promoter

• Sodium Cocoyl Glycinate (SCG) serves as the flotation promoter. • SCG enhanced coal surface hydrophobicity. • Kerosene were emulsified into smaller droplets in presence of SCG. • SCG helped with stable forth layer during low-rank coal flotation. Low-rank coal flotation faces challenges due to its poor surface hydrophobicity. Massive oily collector, e.g. kerosene and diesel, are needed to improve its flotation performance, causing huge cost input. This study experimentally demonstrated that Sodium Cocoyl Glycinate (SCG), an amino acid surfactant, could help with obtaining higher efficiency when adopted in low-rank coal flotation. Results showed that compared with the condition using kerosene (5000 g/t) alone, a tiny amount of SCG (50 g/t) increased the concentrate yield by about 12%, while its ash content roughly remained the same. Effects of SCG on low-rank coal flotation was established from coal surface hydrophobicity, solution surface tension and the forth layer. The amphipathic groups of Sodium Cocoyl Glycinate would bond both with the hydrophilic and hydrophobic sites on the coal surface through hydrogen bonding, leaving the hydrophobic end exposed, which shorten the bubble-particle attachment time to about 100 ms. The decrease of solution’s surface tension was conducive to the emulsification of kerosene, making droplets diameter distribution into a smaller range of 0.26 to 10 μm. Meanwhile, lower surface tension offset the negative impact of oily collector, providing a more stable froth layer. Considering its hypotoxicity, biodegradability, environmental friendliness, Sodium Cocoyl Glycinate could be a green flotation promoter assisting with the conventional oily collectors.