Flotation column

In mineral processing plant , The column flotation concept has been around for nearly 40 years, but it attracted attention with the lead-zinc mining and iron ore processing problems of the early 1980s. The column flotation technique uses the countercurrent principle to improve separation by reducing entrapment of particles. A schematic diagram of column flotation cells is shown in Figure 8.53. The important operating difference from mechanical flotation cells is the lack of an impeller, or any other agitation mechanism, which reduces energy and maintenance costs. The other major difference is that for most ore-processing applications, wash water is sprayed into the froth at the top of the column, which is impossible to accomplish in a mechanical cell as it can kill the froth. The amount of wash water added is a major factor in determining flotation selectivity and recovery as well as column operation stability.
In column flotation, the ore is fed into the column via a distributor located at about two-thirds of the height of the column; the tails are removed from the bottom; concentrate overflows at the top; and the air bubbles are generated at the bottom of the column by a porous sparger. Three characteristic features are the use of a sparger to generate bubbles near the base, a countercurrent slurry/bubble flow in the collection zone, and a deep froth zone (0.5–2.0 m) coupled with the use of wash water to induce a cleaning action. This design was first patented in Canada in the early 1960s and is sometimes known as the “Canadian” or “conventional” column.
Industrial column equipment has a height of 9 to 14 m and a diameter of not more than 2 m without baffling. Generally, the unit is operated with enough overhead wash water to provide a net downward flow of water, a condition known as a “positive bias.” Positive bias is the norm in column operation, because the froth layer in a column is then stabilized by the wash water. The greater the flow of water down the column, the greater the selectivity, and the thicker the froth layer. The froth depth in a stable operation is a little deeper than one meter. A negative bias eliminates the froth altogether, which is very deleterious for a process where the concentrate is the desired product.
The design of any ore-processing operation with columns must ensure that the rate-controlling flotation mechanism is always bubble capture of mineral particles that have been precoated with collectors in a prior flotation step.
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