Determining optimal conditions for lignite flotation by design of experiments and the halbich upgrading curve

In this study conditions for flotation of low rank coal (lignite of Tuncbilek, Turkey) were investigated in detail. The experiments were performed using the 3-variable 2-level (23) full factorial experimental design with four base point replicates, and the results were analyzed by the regression model, Fischer test (F-test) and Halbich’s upgrading curve for the responses of ash content (or combustible matter grade) and the combustible matter recovery. The results obtained from the analysis indicated that while every factor considerably affected the combustible matter recovery, both collector (kerosene) and frother (AF65) significantly influenced the ash contents of the carbonaceous matter products. The only effective mutual interaction influencing recovery was caused by the kerosene-aeration interaction, while the interaction of kerosene-aeration and kerosene-AF65 and interactions of all factors (kerosene-AF65-aeration) were significant for the ash content of the products. Basing on the grade–recovery Halbich upgrading curve, regression model and a criterion for optimum of flotation results, it was found that a coal product with combustible matter grade of 91.09% and 71% combustible matter recovery can be obtained provided that it is processed at the higher level of kerosene (3 kg/Mg), higher level of frother AF65 (40 ppm) and lower aeration rate level of (0.16 cm/s).