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Study of a Filter-Press Electrochemical Reactor for the Treatment of Industrial Waste

J.M. Martinez-Vazquez, P.A. Ramirez-Ortega and M. Vargas-Ramirez

Abstract This research reports the effect of hydrodynamics and the distribution of electrical potential in the electrolyte during the electro-recovery of Ag in two prototype of electrochemical reactor filter-press. The input-output smooth (RSM) and the other striated (RST). The conditions of simulation in COMSOL Multiphysics® were laminar flow and mass transfer by convection-diffusion. The concentration of silver deposited on the electrode surface after 2 h of treatment with current values of -35, -65 and -80 mA, was established based on cyclic voltammetry and kinetics using electrodeposition tertiary Nernst- Planck. It was concluded that the reactor geometry influenced the hydrodynamic properties and concentration of Ag recovered. According to the calculations, the velocity profile in the RST was 13.7 times higher with respect to RSM and the recovery of Ag increased a 4% in the RST with respect to RSM to a current value of -80 mA.

Keywords COMSOL® • Electro-recovery • Hydrodynamic • Nernst-Planck • Cyclic voltammetry

Introduction

Modeling and simulation are effective ways to predict the behavior of electrochemical system [1]. Commercially software packages have been developed; to model complex geometries, for example, Elsyca® and COMSOL Multiphysics®.

J.M. Martinez-Vazquez • M. Vargas-Ramirez

Universidad Autonoma del Estado de Hidalgo, Area Academica de Ciencias de la Tierra y Materiales. Carretera Pachuca-Tulancingo km. 4.5. Colonia Carboneras, Mineral de la Reforma, 42184 Pachuca, Hidalgo, Mexico

P.A. Ramirez-Ortega (H)

Centro de Desarrollo de Nanotecnologia, Universidad Tecnologica de Tulancingo, Area de Electromecanica Industrial, Camino a Ahuehuetitla #301 Col. Las Presas, 43642 Tulancingo, Hidalgo, Mexico

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A. Allanore et al. (eds.), Materials Processing Fundamentals 2017,

The Minerals, Metals & Materials Series, DOI 10.1007/978-3-319-51580-9_12

In this work the fluid transport modules, electroanalysis, tertiary current distribution, transport of diluted species and electrodeposition of software COMSOL 5.0 Multiphysics® were employed.

One of the most important aspects in the design of the electrochemical cells is the distribution of current density in the electrolyte and the electrodes [2]. A non-uniform current density is detrimental, resulting in a nonuniform deposition, high energy consumption [3] and possibly, undesirable side reactions; models of current density distributions are: primary, secondary and tertiary. The Nernst-Planck tertiary interface is chosen to model the electrodeposition because it incorporates transport of species through the diffusion, migration and convection and therefore is able to describe the effects of composition throughout the electrodeposition process well applies to the equations of electroneutrality what describing all the species [4]. This involve that all charged species in the electrolyte specified in the simulations, except those species that are present in very low concentrations and therefore do not contribute to the current balance. Electrodeposition is the process by which metallic ions present in the electrolyte are reduced to metal which is deposited on an electrode, to which is supplied a current or potential electrical. A basic electrochemical cell consists of an electrolyte with two immersed electrodes to which a load is applied direct current. In the negatively charged electrode, or cathode, positively charged ions reduced to form a solid (Ag0) or evolve as gas (H2). While, at the anode, negatively charged, the ions are oxidized. The main reactions occurring during the electrorecovery of silver (Ag) dissolved in nitric acid (HNO3), can be written as [5]:

At the anode:

At the cathode:

This paper presents the numerical modeling of the effect of hydrodynamics [6] on the momentum transport, cyclic voltammetry, the potential distribution, tertiary current and electrodeposition, on an electrochemical reactor prototype, filter-press [7] used to study the recovery process silver [8]. The conditions of the simulation are laminar flow [9], the mass transfer model was a combination of convection-diffusion equations, and the species concentration dependent of the kinetics.

 
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