EXPERIMENTAL FLOTATION

EQUIPMENT: Although many different machines are currently being manufactured and many more have been developed and discarded in the past, it is fair to state that two distinct groups have arisen; pneumatic and mechanical machines. The type of machine is the great importance in designing a flotation plant and is frequently the characteristic causing most debate. Pneumatic machines either use air entrained by turbulent pulp addition (cascade cells), or more commonly air either blown in or induced, in which case the air must be dispersed either by baffles or some form of permeable base within the cell. Mechanical flotation machines are the most widely used, being characterized by a mechanically driven impeller which agitates the slurry and disperses the incoming air into small bubbles. The machines may be self aerating, the depression created by the impeller inducing the air, or supercharged where air is introduced via an external blower. In a typical flotation bank, there are a number of such machines en series, cell to cell machines being separated by weirs between each impeller, whereas open flow or free flow machines allow virtually unrestricted flow of slurry down the bank. The flotation column has been claimed to give better separations than cell-type machines, particularly when operating on fine particles. It consists of two distinct sections. In the section below the feed point, particles suspended in the descending water phase contact a rising swarm of air bubbles produced by a sparger in the column base. Floatable particles collide with and adhere to the bubbles and are transported to the washing section above the feed point. Non-floatable material is removed from the base of the column as tailing. Gangue particles that are loosely attached to the bubbles or are entrained in bubble slipstreams are washed back into the recovery section, hence reducing contamination of the concentrate.