Recent work at University of Manchester Institute of Science and Technology indicates that coal may be able to be beneficiated by ultrafine grinding to below 45 mum followed by froth flotation. This was achieved under laboratory-scale test conditions. In order to develop a basis for an economic analysis of this process it is necessary to have a relationship between the extent of grinding and the degree of mineral liberation. A heavy liquid separation at 1.4xspecific gravity carried out in a centrifuge was used to characterise the liberation. This publication reports an experimental investigation of the effect of grinding on the liberation of mineral from a low-rank semibituminous UK coal and develops a mathematical model based on this data, which could be used for scale-up. It was found that the ash content could be predicted approximately by the solution of the batch grinding equation with a breakage distribution for ash different from that for total mass.