A study of processes occurring in flotation froths.
While the significant effect that the froth phase has on the performance of a flotation operation has recently been widely recognised, little work has been published which promotes an understanding of the physical processes occurring in the froth phase. A more intimate understanding of these processes and their relative importance and interactions would lead to a more rational design of froth chambers and froth removal methods, with resultant improvements in flotation plant performance. In pursuit of this understanding the following investigations were performed: (1) In a specially designed cell the variation of mineral grade with height above the froth-slurry interface - as affected by gas rate, frother concentration, the presence of froth baffles (to minimise mixing) and final product removal rate - was measured. A mathematical model was formulated to assist in the interpretation of this data. (2) The residence time distribution of a 2-phase froth (air and water without solid particles) was measured as a function of froth height, gas rate and frother concentration. Small polystyrene balls were used as a tracer. The results were interpreted using two theoretical models: (a) a streamline model which involved the solution of the 2 - dimensional Laplace equation for frictionless flow of froth in the froth chamber; (b) a semi-phenomenological model which relates the froth residence time distribution to cell dimensions, gas rate and froth stability. On the basis of insights gained in these investigations, a number of objectives which should be met by froth removal methods were formulated: (1) froth removal efficiency should be maximised, i.e. there should be no stagnant zones in the froth; (2) froth stability should be optimised; (3) the minimum residence time of froth elements in the froth phase should be maximised. One novel method of froth removal was designed, and this and a number of other methods of froth removal were compared experimentally. It was found that substantial improvement in flotation performance could be obtained by (1) sprinkling the froth with water, which removed entrained particles and improved froth stability; (2) inserting a baffle in the froth phase near the concentrate weir which increased the minimum residence time of a froth element in the froth phase, thereby improving the drainage of entrained particles from the froth; and (3) placing a froth scraper near the back of the cell, thus ensuring that no stagnant froth zones developed.