Evaluation of flotation results using rubidium ion exchange

Coal particles contain oxygen functional groups such as hydroxyl, carbonyl, and carboxyl, and mineral matters that contribute surface hydrophilicity. The occurrence of them varies considerably from coal to coal, hence the characteristics of column flotation changes from coal to coal. We expected that the characteristics of column flotation could be simply evaluated by using the area fraction of oxygen functional group sites on the exterior surface of the coal particles. In this work, we conducted column flotation for Shanxi (anthracite), Tyanfu (bituminous), Blair Athol (bituminous), Datong (bituminous), and Illinois (brown coal). The order of carbonaceous materials recovery was found to be Tyanfu > Shanxi > Blair Athol > Datong > Illinois. We also evaluated the area fraction of hydroxyl group on the exterior surface of the coal particles, α_ex-OH, and that in the coal particles, α_in-OH. For Datong coal, the value of α_ex-OH was larger than that of α_ex-OH. It means that Datong coal was slightly oxidized. The order of carbonaceous materials recovery was inconsistent with that of α_ex-OH for the three kinds of bituminous coal. For Shanxi anthracite coal, the notability is evaluated by considering the wettability of the hydrophobic sites as well as the hydrophilic sites.