Comparison of axial-flow impellers with inclined-blade turbines in a baffled mixer
This study was aimed at a comparison of the effectiveness of a new axial-flow type of mixer impeller (the Prochem design) with the traditional inclined-blade turbine. The intended application of the mixers was in carbon-in-pulp plants for the extraction of gold from cyanide-leached pulps. The first part of the project involved water and ion-exchange resin, and measurement of the power drawn by the various sizes of impeller to fully suspend the resin. The rate of reaction between the resin and the solution was measured as a function of the power input to the mixer. In the second part of the project, use was made of activated carbon, silver cyanide solutions, and ore pulps. The rate of absorption of silver from the solutions and pulps was determined, as well as the rate of attrition of the activated carbon caused by the various impellers in clear water. The Prochem design of axial-flow impeller was shown to fully suspend solids at only one-quarter of the power required by an inclined-blade turbine of similar size. These measurements verified the observations of other researchers that the rate of reaction is not affected by the design of impeller provided that all the solids are fully suspended. The Prochem design of impeller therefore achieved the same reaction rate as the conventional turbine at a quarter of the power input. The attrition rates of activated carbon could be correlated, in terms of the energy absorbed, by the same equation for all the impellers. Higher concentrations of activated carbon increased the amount of carbon fines produced.