A comparative study of batch and continuous column flotation of fine coal

Semi-batch and continuous flotation experiments were carried out in 0.063 m x 1.5 m and 0.076 m x 3.55 m columns, respectively. Semi-batch studies used Lower Kittaning and Upper Freeport coals, while only Lower Kittaning for the continuous experiments. In semi-batch experiments, frother concentration, coal aging, air flow rate and initial feed solid concentration were studied. Continuous column tests evaluated the effects of recovery zone height, airflow rate, feed solid concentration and gas sparger type (Mott porous and Vortactor turbulent contactor).; Average and axial gas hold-ups were estimated for the continuous column for two-(gas-liquid) and three-phase (gas-liquid-solid) systems. Average gas hold-up increased with gas velocity for both spargers in two- and three-phase systems. Axial gas hold-up profiles decreased with height for the Mott sparger in both two- and three-phase systems, while remaining fairly constant with the Vortactor. For the Mott, gas hold-up increased substantially in the froth phase.; A correlation was found between loss of the pulp/froth interface and the existence of free flotation conditions. High product grades were observed with increasing froth phase gas hold-up.; Freshly ground coal, aging under argon for two weeks resulted in lower a yield and grade. Air flow rate had no significant effect on the product yield and grade under bubbly flow conditions. Under churn turbulent conditions, yield and product ash increased. Yield remained fairly constant with increasing initial solid concentration, but product ash increased.; Change in the recovery zone height had little effect on the product yield and grade for the continuous column. Clean coal yield and ash content increased with air flow rates. Under bubble surface limiting conditions, yield decreased with increasing feed solid concentration, but gave the highest product grades.; Results for batch and continuous tests revealed that the two processes are fundamentally different. Batch tests can provide information on sample floatability, optimum ash rejection and yield, but not of concentrate grade and column carrying capacity.; A correlation for the column carrying capacity correlation developed, predicted the experimental data under both flotation conditions.