Browsing by Author "Aji, Arif Tirto"

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    Application of High-Speed Silver Electrorefining
    (Aalto University, 2021) Aji, Arif Tirto; Aromaa, Jari, Dr., Aalto University, Finland; Kemian tekniikan ja metallurgian laitos; Department of Chemical and Metallurgical Engineering; Hydrometallurgy and Corrosion; Kemian tekniikan korkeakoulu; School of Chemical Technology; Lundström, Mari, Asst. Prof., Aalto University, Department of Chemical and Metallurgical Engineering, Finland
    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.
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    Finite Modeling and Simulation of the Effects of Neutral Electrolytic Pickling Process Parameters on EN 1.4404 Steel Strips
    (MDPI AG, 2023-12-12) Aji, Arif Tirto; Aromaa, Jari; Tuovinen, Teemu; Riekki, Elina; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Hydrometallurgy and Corrosion; University of Oulu; Outokumpu Stainless Oy
    Surface treatment via neutral electrolytic pickling (NEP) aims to remove oxide layers and scaling from stainless steel. The objective of this study was to investigate the factors that affect the energy efficiency of the process. This study developed a COMSOL Multiphysics model for the distribution of current across a bipolar steel strip by controlling the following parameters: Na2SO4 concentration, temperature, electrode-to-strip distance, and inter-electrode distance. Full factorial measurements of the electrolyte’s conductivity as well as the steel strip’s and the electrode’s polarization were conducted to provide data for the NEP model. Galvanostatic pulse measurements were performed to calculate transient times during pickling. According to the model, an applied voltage of less than 11 V was insufficient to polarize the steel strip to the potentials needed on both the anodic and cathodic sides. A higher voltage of 11–15 V resulted in anodic current densities of 600–1600 A m−2 and cathodic current densities of 700–2000 A m−2 on the steel strip. These current densities are within the range of previous experimental studies and industrial practices. The model showed that when a steel strip acts as a bipolar electrode, the current’s efficiency decreases, as only a fraction of the strip facing the anodes or cathodes is polarized sufficiently. The galvanostatic tests showed that anodic polarization of the steel strip is easier than cathodic polarization. The slow polarization in the cathodic direction can be improved by using a higher current density. The time needed to polarize stainless steel indicates that the strip’s velocity should be less than 1 m s−1 to give enough time for polarizing the steel strip.
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    Modelling the effect of solution composition and temperature on the conductivity of zinc electrowinning electrolytes
    (Multidisciplinary Digital Publishing Institute (MDPI), 2021-11-13) Wang, Zulin; Aji, Arif Tirto; Wilson, Benjamin Paul; Jørstad, Steinar; Møll, Maria; Lundström, Mari; Hydrometallurgy and Corrosion; Department of Chemical and Metallurgical Engineering; Boliden Odda Zinc Smelter
    Zinc electrowinning is an energy-intensive step of hydrometallurgical zinc production in which ohmic drop contributes the second highest overpotential in the process. As the ohmic drop is a result of electrolyte conductivity, three conductivity models (Aalto-I, Aalto-II and Aalto-III) were formulated in this study based on the synthetic industrial electrolyte conditions of Zn (50–70 g/dm3), H2SO4 (150–200 g/dm3), Mn (0–8 g/dm3), Mg (0–4 g/dm3), and temperature, T (30–40◦C). These studies indicate that electrolyte conductivity increases with temperature and H2SO4 concentration, whereas metal ions have negative effects on conductivity. In addition, the interaction effects of temperature and the concentrations of metal ions on solution conductivity were tested by comparing the performance of the linear model (Aalto-I) and interrelated models (Aalto-II and Aalto-III) to determine their significance in the electrowinning process. Statistical analysis shows that Aalto-I has the highest accuracy of all the models developed and investigated in this study. From the industrial validation, Aalto-I also demonstrates a high level of correlation in comparison to the other models presented in this study. Further comparison of model Aalto-I with the existing published models from previous studies shows that model Aalto-I substantially improves the accuracy of the zinc conductivity empirical model.