A new insight into the inhibition mechanism of calcium ion on low-rank coal flotation

The presence of large amounts of Ca2+ in the flotation water can cause a poor flotation index of low-rank coal (LRC), and its influence mechanism has not been reported. In this paper, the mechanism of the Ca2+ effect on LRC flotation was analyzed for the first time from the perspective of the interaction between Ca2+ and the LRC surface oxygen-containing functional groups using flotation tests, solution chemistry calculations, ICP, Contact angle, Zeta potential, Fourier transforms infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) detection. The results of solution chemistry calculations and flotation tests show that the calcium in flotation water with pH = 6-8 is mainly in the form of Ca2+, and it has a certain inhibitory effect on the LRC flotation. The results of Contact angle, Zeta potential, FTIR, and XPS show that Ca2+ can adsorb on the LRC surface and chemically react with phenolic hydroxyl and carboxyl groups of the LRC surface, leading to an increase in the hydrophilicity of the LRC particles, weakening the adsorption effect of collectors on the LRC surface. These will further deteriorate the LRC flotation index.