چكيده به لاتين
The separation of metals by conventional methods, such as solvent extraction encounters defects, for example, long operating time, large required space, and high energy consumption. Therefore, it is important to apply a new technology that can address some of these defects and improve solvent extraction. Microfluidics due to having features, including high and fast heat and mass transfer, low consumption of materials, proper control of process conditions, small volume and integration capability can be used for this purpose. Thus, in this research, Microfluidic solvent extraction of cadmium ion using a cationic extractant (MDEHPA) in the parallel flow pattern in Y-Y microchannels was studied. At first, the effect of the operating parameters on the extraction efficiency utilizing response surface methodology was investigated. Extractant concentration 6% (vol/vol), feed phase pH 6.3 and residence time 20 s were obtained as the optimum conditions for the extraction. Furthermore, the stoichiometry of Cd(II)-MDEHPA using the logarithmic model of extractant concentration-distribution coefficient was determined to be 1:1.5. Also, the influence of microchannel dimensions on the extraction efficiency was examined. The increase in the microchannel length and the decrease in the microchannel width enhanced the extraction efficiency. Using the microchannel with the longest length and the shortest width, the extraction efficiency 99.3% at the residence time 8 s was acquired. Moreover, for the evaluation of mass transfer performance, the values of the overall volumetric mass transfer coefficients (K_L a) under different conditions were calculated. The K_L a values decreased non-linearly with the increase in the residence time at all of the lengths and widths of the microchannel. The rise in the microchannel length from 6 cm to 12 cm at the residence time 2 s, increased the K_L a from 0.473 1/s to 0.571 1/s but at the volumetric flow rate 8 mL/h, decreased the K_L a from 0.318 1/s to 0.192 1/s. The K_L a increased with the decrease in the microchannel width from 800 μm to 400 μm at the residence time 2 s, from 0.382 1/s to 0.91 1/s and also at the volumetric flow rate 10 mL/h, from 0.141 1/s to 0.626 1/s. The K_L a of the microfluidic system was obtained much higher than the batch mode which indicates the better mass transfer performance of the microfluidic device. Additionally, a new correlation for the estimation of the aqueous phase Sherwood number in the microchannels with liquid-liquid parallel flow was developed. The average error of this model was 9.91%, which demonstrates its accuracy for the prediction of the aqueous phase Sherwood number.
