Results and Discussion
Figure 2 shows the velocity profiles of reactor filter-press without applying a potential for a) RSM and b) RST respectively. In both models, the high velocity zones are located in the inlet and outlet of the reactor, the velocity values (VRSM = 0.309 m s-1 and Vrst = 0.307 ms-1) and pressure (pRSM = pRST = 1.61 kPa) were similar in both reactors. However, when a change in the cell potential of 1.8 V is applied, the velocity profile changes for both models, as shown in Fig. 2c and d. The RSM exhibits a decrease in velocity (VRSM = 0.0254 m s-1) and the velocity profile is similar to showed without application of the potential. The RST exhibits an increase in speed (VRST = 0.342 m s-1) in the order of 13.7 with respect to the RSM in the same conditions.
For reducing potentials, the oxidation reaction is not taking place and the generated current is negligible, as shown in Fig. 3. When the potential, move toward the reduction potential of the redox couple, the reaction of oxidation is accelerated and the current increases. Once the oxidation reaction has consumed the reagent on the electrode surface, the current is limited by the rate of transport of Ag+ to the working electrode. Therefore, a current peak is observed, and at higher potentials, the voltammetric current drops to a potential independent of the speed; this region is called “diffusion controlled” or “controlled transport”. In the sweep back toward more reducing potential, conversion of the product, Ag0, in the original reagent (Ag+) gave a negative current value (cathode, reductive). The depletion of the reacting species causes a negative peak current and conversion takes place, then, controlled by the diffusion rate. In Fig. 4, the concentration profile of RST reactor, shows a uniform distribution of silver on electrode; whereas in the RSM, the concentration profile focuses on the inputs and outputs of the reactor. The uniform distribution in the RST reactor could likely lead is a purger recovery of silver with respect to the RSM reactor, as seen below.
Fig. 2 Velocity profiles without applying a potential a RSM and b RST. Velocity profile of the reactor when a potential of cell of 1.8 V was applied
Fig. 3 Cyclic voltammetry of reactor filter-press when to was applied a potential -0.4 to 1.8 V in a RSM b RST
Fig. 4 Concentration profile in the reactor a RSM and b RST, after applied the study of cyclic voltammetry
In Fig. 5, the effect of reactor model and current distribution in the potential of the electrolyte for the time interval from 0 to 7200 s, indicates that the geometry and current does not significantly affect the distribution of potential in the electrolyte.
Fig. 5 Profile potential distribution in the electrolyte in reactors RSM and RST for the time interval from 0 to 7200 s to the values of current of -35, -60 and -80 mA
Fig. 6 Concentration profile of the silver electro-recovered for the work of current of -35, -65 and -80 mA in the reactors RSM and RST
The concentration profiles in the RSM and RST reactors, shown a behavior similar in relation to Fig. 6, showing a higher concentration of Ag at a current of -80 mA in the RST reactor at an approximate time of 1080 s.