The effect of surfactant concentration on batch flotation mineral flux and froth structure

It is known that the froth structure plays an important role in the potation separation achieved. The appearance of the upper bubble surface is indicative of the internal froth structure, and is used qualitatively as a basis for control in industrial flotation cells. A quantitative kinetic model based on the flux of loaded bubble surface overflowing the concentrate weir in a free-flowing froth is described. The froth is divided into two distinct phases; the bubble shells which contain hydrophobic solids selectively attached, and the inter-bubble lamellae, which contain non-selectively entrained solids. The flux of coal, mineral and water for three surfactant concentrations was measured. Neither the solids concentration nor the thickness of the bubble shells varied significantly during the tests. The flux of bubble surface overflowing the weir decreases to zero during the course of a test. The result of this is that selectively collected solids and water that were present in the bubble shells fall back into the froth and enter the lamellae. This is confirmed by estimates of the lamella thickness, which increases significantly during the test, and are thicker for higher surfactant concentrations. The concentration of coal in the lamellae increases sharply towards the end of the test. In contrast, the transport of mineral in the lamellae decreases during the test. By developing quantitative relationships between the froth structure and flotation performance, the froth structure can be optimised and flotation control based on froth appearance automated. (C) 1998 Elsevier Science Ltd. All rights reserved.