Simulations of Turbulent Flow, Mass Transport, and Tertiary Current Distribution on the Cathode of a Rotating Cylinder Electrode Reactor in Continuous Operation Mode during Silver Deposition

Abstract

This work presents numerical simulations of turbulent flow, mass transport and tertiary current distribution on the cathode of a rotating cylinder electrode reactor (RCE) in a continuous operation mode. A configuration of a RCE with electrolyte inlet at the bottom and the electrolyte exit at the top was employed. Silver electrodeposition (12.15 mol m −3 (1300 ppm) Ag(I), 883.5 mol m −3 (23000 ppm) CN − , pH 13 and 150 mS cm −1 conductivity) was used as a test system. Bulk electrolysis in the RCE was performed at a constant potential of −1.2 V vs. SCE, which ensured complete mass transport control. A constant volumetric inflow rate of 0.1 L min −1 at the RCE inlet was employed. CFD simulations were obtained solving the RANS equations with the standard k −ε turbulence model. For mass transport simulations, the averaged diffusion-convection equation was solved. For the simulations of tertiary current distribution, wall functions were employed. The tertiary current distribution on the RCE interface along the z-coordinate presented one border effect close to the electrolyte inlet, afterwards, even current distribution was obtained. The border effect is created by the abruptly silver concentration depletion at the electrolyte inlet. Good agreement between mass transport correlation and current distribution simulations with experimental data were attained. The rotating cylinder electrode electrochemical reactor (RCE) is a geometry widely used in the following studies: metal ion recovery, [1][2][3][4][5][6] alloy formation, 1,2 corrosion, 1,2,7 effluent treatment, 5,[8][9][10][11][12][13] and Hull cell studies.14 The RCE is employed for metal ion removal because this cell allows metal removal from 10,000 to 10 ppm, 15 i.e. this reactor has been used to recover cadmium, 9,16 copper, 11,13 nickel, 17 silver, 18 tin, 19 and zinc. 20The RCE generates turbulent convection at Re > 100, where peripheral velocity, u, normally lies in the range 0.6-20 m s −1 . 1 In previous studies carried out by our group the influence of using fourplate, six-plate, and a concentric cylinder as counter electrode on the turbulent flow in batch 21 and continuous 22 operation mode have been deeply discussed. In the former paper, the formation of three turbulent Taylor vortex flow for the four-plate and six-plate arrangements was developed, however, these vortexes did not appear in the concentric arrangement. The presence of the Taylor vortex flow was attributed to the turbulence promoted by the plates. Whereas in continuous mode, for the six plate arrangement, only one turbulent Taylor vortex appeared, owing to the electrolyte inflow and outflow modifying the flow pattern in the RCE.On the other hand, the turbulent mass transport is imposed by the angular rate of the inner cylinder and the applied limiting current density. 2,3,23,24 When the flow pattern is developed entirely in the RCE, the parameters of mass transport can be determined by a dimensionless group correlation of the form: Many papers have showed that mass transport correlation, desc...

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