The main focus of the current study was on the investigation of high current density (HCD) operation of silver electrorefining through empirical modelling of the process. The first part of modelling consists of the phenomena on the anode surface i.e. silver dissolution, passivation due to gold, and copper dissolution. Second part of modelling was optimization of the process by modelling of the electrolyte properties i.e. conductivity, density, viscosity and electrolyte circulation system. All of the modelling was conducted based on the experimental results of laboratory-scale measurements in synthetic electrolyte, under conditions similar to industrial operation. Kinetic modelling of silver dissolution in the current study suggests that the application of HCD is technically feasible. Based on the experimental results, the main cause for silver anode passivation is the gold content in the anode, since gold did not dissolve in the dilute nitric acid solution used in electrolysis. Meanwhile, copper present in the anode dissolved during the process and accumulated in the silver electrolyte. Though copper increased the conductivity of the electrolyte, the high copper content also resulted in copper contamination of the silver cathode. By modelling the kinetics of the dissolution of anode metals, limitations for copper and gold content could be established for optimum HCD operation. Electrolyte has two main roles in the electrorefining process; it is the medium for current transfer as well as the inventory and supplier of silver ions. Accordingly, optimization of the electrolyte composition allows the minimization of energy consumption while maintaining the purity of the deposit. In the current work, the optimal electrolyte conditions and circulation system were established as a function of a HCD operation. The optimal anode and electrolyte conditions in HCD silver electrorefining were found to be at max. Au of 6-8% in the anode and 100-150 g/dm3 [Ag+], 50-75 g/dm3 [Cu2+], 5-7 g/dm3 [HNO3] in the electrolyte.
|Translated title of the contribution||Korkean tuotantonopeuden soveltaminen hopean puhdistuselektrolyysissä|
|Publication status||Published - 2021|
|MoE publication type||G5 Doctoral dissertation (article)|
- silver electrorefining
- high current density
- empirical modelling