Enhancing flotation performance of low rank coal by improving its hydrophobicity and the property of oily bubbles using 2-ethylhexanol

In this paper, the influence of 2-ethylhexanol used as a modifier/emulsifier on the surface chemical property of low rank coal and its flotation performance was investigated. According to the FTIR analysis, it showed an obvious decline in the hydrophilic groups while an increase in the hydrophobic groups on the surface of coal after pretreatment by 2-ethylhexanol solution for 12 h, resulting in the increase of contact angle from 74.9° to 95.4°. Whereas the induction time showed a significant decrease from 246.0 ms down to 85.4 ms, which meant the better hydrophobicity and floatability of coal particles after the pretreatment. As a result, a better flotation efficiency of low rank coal was attained after the pretreatment. Additionally, the oily bubble flotation combining 2-ethylhexanol was employed to enhance the flotation of coal samples. The results indicated that the mixture of diesel oil and 2-ethylhexanol improved the collecting power and selectivity of oily bubbles, with the oil contact angle for coal samples decreasing from 17.8° to 14.5° and the induction time from 50 ms down to 19.7 ms. The performance of oily bubble flotation, especially using the mixed diesel oil bubbles, was much better than that of conventional flotation, and the recovery of combustible matter and flotation efficiency index increased from 43.42% and 29.52% up to 89.27% and 59.91% respectively. Consequently, the flotation performance of low rank coal may be enhanced by the surface modification of 2-ethylhexanol as well as the novel oily bubble flotation technology.