| Description |
Unusual deposits of copper may cause short-circuits in copper electrowinning cells. The objectives of this thesis are to provide experimental and modeling data for near surface electrowinning that is pertinent to industrial electrowinning. A bench-scale electrowinning cell was set up to produce copper under the similar conditions used in industrial copper electrowinning to see the effect of various operating parameters such as Cu concentration in electrolyte, electrolyte temperature, current density, and guar concentration. A statistical analysis was performed to analyze the deposited thickness, surface roughness, and maximum feature height data. A finite element analysis-based simulation package (COMSOL Multiphysics) was used to validate the experimental data. The statistical analysis of deposits obtained from the short-term and long-term experiments shows there is a significant effect of current density and temperature on the roughness of copper deposits. These experiments were performed using a number of small coupons, and linear maximum feature height was analyzed using various statistical distribution density functions. Extrapolation from the small length of the sample to a length of 1 meter was carried out to see the effect of operating parameters on short-circuit. Extrapolation for time was also carried out and it was found that, with 475 A/m^2 current density, 175 gm of guar per tonne of copper, 35 g/l of concentration of Cu, and 55°C temperature, the cell may be short-circuited by growth of copper in 12 days. On the other hand, with 325 A/m^2 current density, 250 gm of guar per tonne of copper cathode, 45 g/l of copper concentration, and 55°C temperature, short-circuiting is predicted in 23 days. Linear maximum feature height data were compared to 3-dimensional surface feature height data using stacked 2-dimensional slices of maximum feature height with intervals of 0.05 cm per slice for 10 layers for two experiments (rough and smooth deposits). The 3-dimensional analysis of surface roughness was very similar to 2-dimensional line scan. Long-term experiments showed that short-circuit occurred after 9.5 days of experiment, which is 2.5 days less than the linear data prediction. Further validation was performed using an experiment with 475 A/m^2 current density, 175 gm guar per tonne of copper cathode, 35 g/L of Cu, and 55°C temperature. The first short-circuit in this test was observed after 8 days of experiment, as predicted by statistical analysis. These results were compared with the model predicted ratio of current density to limiting current density (i/iL) and it was noted that model prediction is in proximity to the experimentally obtained data. This study provides an industrial relevant baseline against which the new operating parameters can be compared. Results from the bench-scale copper electrowinning experiments, statistical analysis, and modeling show that operating parameters adjustments can reduce short-circuiting in copper electrowinning. |
