Effects of particle size on lignite reverse flotation kinetics in the presence of sodium chloride

The purpose of this study was to investigate the effect of particle size on lignite reverse flotation with a focus on reverse flotation kinetics in the presence of sodium chloride. Six flotation kinetic models were applied to data from the tests using the 1stOpt statistical analysis software package to estimate the relationship between the flotation rate constant, the maximum ash flotation recovery and the particle size. Within the range studied, the best reverse flotation performance was obtained at a grinding fines (− 74-μm size fraction) content of 42.34% with a concentrate ash content of 11.30% at 65.29% combustible recovery after 20 min of flotation time. The results show that all kinetic models except the classical first-order flotation kinetic model gave excellent fits to the experimental data under various grinding fines contents and various size fractions. The high flotation rate constant was limited to a narrow particle size range. The maximum flotation rate constant was obtained at a grinding fines content of 42.34% and with the − 250 + 150 μm fraction. We concluded that the reverse flotation of lignite in the presence of sodium chloride can be described with the first-order and second-order models. Furthermore, the reverse flotation performance as a function of particle size was further evaluated using the reverse flotation efficiency index. We found that the − 425-μm size fraction with a grinding fines content of 42.34% resulted in the greatest index value compared with the investigated narrow size fractions at any given flotation time.