The study of operation conditions on solvent extraction of gold in continuous process using laboratory scale mixer-settler

In this research، a video technique was developed by a digital camera (Canon، 12 MPixel)، to measure the organic drop size in the mixer-settler. For drop size determination، the recorded pictures (in the output of the mixing chamber) were analysed with Clemex software. Then the Sauter mean diameter was calculated. The effects of different parameters such as stirring speed، aqueous and organic volumetric flow rate، holdup، gold and DBC concentration on gold extraction have been reported. The Increase of stirring speed (in rang of 335 - 600 rpm) had a direct effect on drop breakage and number of smaller drops، consequently higher gold extraction by about 50 % was obtained. As it is shown in figure 3، D32 depends on the impeller speed (N) as a power function with the average exponent of -1. 43. Hence، the results verified the Hinze- Kolmogorov’s theory. The enhancement of aqueous volumetric flow rate from 16 ml/min to 50 ml/min causes short contact time in the system and resulted in decreasing the extraction about 35 %. However، when organic flow rate (Holdup) rose more than 30ml/min، phase inversion occurred and gold extraction decreased. By comparing the results، it was found that it is better to fix aqueous phase volume flow rate and change organic one to get good result in the industrial scale. The gold concentration in aqueous phase had an important effect on the physical property of system like interfacial tension. Lower interfacial area in the higher gold concentration resulted in smaller drops. Therefore، E% increased about 50 % at the same conditions. For the DBC concentration range between 60 and 100 %، drop size decreased most sharply with increasing the concentration، because the interfacial tension was diminished considerably. Furthermore، this decrease was due to the drops breakage and consequently، higher gold extraction about 4. 5 timeswas obtained.