Modelling the Effect of Solution Composition and Temperature on the Conductivity of Zinc Electrowinning Electrolytes

Zulin Wang,Mari Lundström,Steinar Jørstad,Arif Tirto Aji,Benjamin Paul Wilson,Maria Møll

doi:10.3390/met11111824

Abstract

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.

Highlights

Zinc is widely used in the production of a number of key materials and applications, including brass, galvanized steel, sacrificial anodes, and batteries
Zinc electrowinning is normally conducted at a temperature between 30 and 40 ◦C in a zinc sulfate electrolyte that is composed of H2SO4 (150–200 g/dm3), Zn (50–70 g/dm3), Mn (4–8 g/dm3), and other impurities such as Mg and Ca
The main objective of this study is to develop an improved zinc electrolyte conductivity model, increasing prediction accuracy by taking into account the independent effects of metal impurities—such as Mn and Mg—along with the typical process parameters of zinc concentration, acidity, and temperature

Summary

Introduction

Zinc is widely used in the production of a number of key materials and applications, including brass, galvanized steel, sacrificial anodes, and batteries. More than 80% of the world’s primary zinc is produced through hydrometallurgical processes that typically incorporate electrowinning as the final step. Zinc electrowinning is normally conducted at a temperature between 30 and 40 ◦C in a zinc sulfate electrolyte that is composed of H2SO4 (150–200 g/dm3), Zn (50–70 g/dm3), Mn (4–8 g/dm3), and other impurities such as Mg and Ca. The main reactions during the electrowinning process are zinc deposition on the cathode (Equation (1)) and oxygen evolution on the anode (Equation (2)), hydrogen evolution as an additional side reaction may decrease the current efficiency at the cathode (Equation (3)). Hydrogen evolution is reduced to a minimum rate in order to avoid excessive current usage; the overall reaction that occurs in the electrowinning cell and thermodynamical cell voltage (ET) can be outlined as in Equation (4): Zn2+

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Conclusion