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Dynamic process simulation of zinc electrowinning

University of British Columbia

Zinc electrowinning is the final aqueous processing step in the production of metallic zinc. It is a complex process that is difficult to control and monitor. This thesis seeks to develop a time transient process simulation of zinc electrowinning to aid in controlling and monitoring. Based on reported models of zinc electrowinning, and other electrowinning processes, a dynamic simulation of a zinc electrowinning cell capable of representing time-based effects was developed. The new model incorporates more sophisticated estimations of electrolyte activity using Pitzer parameters. Further, recently determined empirical relations for solution conductivity, density and viscosity were included. The effect of gas evolution on the conductivity of solution was also included. First, the simulation was validated using a reported data set, and the kinetic constants of the primary cathodic reactions were determined using a simplex optimization algorithm. A model of a counter-flow cooling tower was also developed in order to simulate a full cell house. The simulation was then successfully validated against data collected from three industrial cell houses in Canada. Once validated, the simulation was used to investigate its possible applications. The benefits of optimizing a single electrowinning cell in comparison to optimizing the cell house was examined. Due to the inability to directly control both the acid and zinc concentrations in the electrowinning cell without major process changes, it was established that the optimal single cell conditions favoured zinc concentrations of approximately 70 g L‐¹, while the cell house optimization favoured lower zinc concentrations by comparison (approximately 50 g L‐¹). The simulation was used to track the consumption of manganese ions in the cell house when using variable concentrations of manganese in the purified electrolyte fed to the cell house. The experimental rates reported for Mn consumption overestimated the Mn consumption in a cell house. The simulation was also used to investigate process control strategies. With the use of a basic process control scheme, the production could increase by 4 % and decrease the variability in the spent electrolyte concentration.

Text

2016-01-12

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/56366

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/