Advanced gravity separation of a high-ash (36%) semi-coking coal in a Floatex density separator (FDS) is investigated. The influence of the operating variables on the separation features has been identified. It is established that a higher bed pressure and a higher teeter water flow rate enhance the mass yield of the clean coal albeit with a poorer grade. A higher bed pressure reduces the bed voidage leading to a higher cut point density. Although bed voidage is reduced due to higher teeter water rate, the hydraulic transport increases significantly. A higher pulp density and a higher feed rate introduce severe hindered settling conditions leading to an increase in the cut point density. This results in a poorer product grade with a higher yield. The optimum condition for 23% product ash in a single-stage operation is identified. The yield at the optimum condition is found to be 64.3% which is close to the theoretical maximum for this coal. The dependence of the cut point density as well as Ecart probable (Ep) value on the operating variables is quantified. A specific gravity of separation of below 1.8 and an Ep value of around 0.15 is achievable under controlled operation of the FDS.