Coal flotation washability: An evaluation of the traditional procedures

The characteristic separation performance achievable from the treatment of fine coal using a froth flotation process is commonly estimated using either the release or tree analysis procedure. The two flotation characterization procedures differ substantially in the method of achieving selectivity between particles having varying degrees of hydrophobicity. From the treatment of -180 μm coal, the separation performance curves generated using the release analysis method were superior to those produced by tree analysis on the basis of both product ash and total sulfur contents. However, after grinding to reduce the amount of middling particles, the separation performance achieved by the tree procedure on the basis of product ash content was nearly equal, and in some cases, exceeded the performance provided by release analysis. In terms of product total sulfur content, the results obtained from release analysis remained superior. The differences in the separation performances achieved from the two flotation characterization methods are a result of the presence of middling and coal pyrite particles, which degrade the froth product upon flotation. Improvements in the two traditional procedures, such as the use of high feed solid concentrations to ensure a significant amount of selective reflux between the froth and collection zones, are presented in this publication.