Investigating the effect of operational and geometric parameters on the performance of an axial spiral series mixer in the solvent extraction process

Abstract The performance of an axial spiral stirrer in mixing two aqueous and organic phases in a tank at different test conditions has been studied, and its effect on copper ion extraction was determined. The influence of speed, O/A, pH, and tank baffle parameters were investigated. Experiments were also done without a baffle, requiring a smaller tank diameter to study the effect of radial tip clearance without baffles. Mass transfer has been assessed by measuring the overall mass transfer coefficient and Sherwood number. Examination of the samples collected from nine locations on the stirring tank wall with the larger baffled tube diameter showed that apart from the speed of the stirrer, the extraction of Cu ions was influenced by the presence of baffle, liquid O/A ratio, and pH in that order. Cu ion extraction at optimal conditions (600 rpm, O/A = 1.2, pH = 2.5, and with baffle) at the end of the stirring time (180 s) was already at 99.5%. Moreover, the stirred flow axial concentration was uniform. The results of tests with a smaller diameter tank (i.e., without baffle) showed that the radial distance between this stirrer and the tank wall without the baffle after 360 s had only a 6.5% negative impact on Cu ion extraction effectiveness with the same optimal test conditions (600 rpm, O/A = 1.2, pH = 2.5), and an axially non‐uniform fluid concentration was observed. Also, the large value of Sherwood numbers acquired from all the experiments (in the 300 s) gave insight into the improved performance of this stirrer design compared to pure diffusion.