Abstract
A two-compartment lab-scale reactive electrodialysis (RED) cell with a moving particulate cathode has been used for copper electrowinning. The cathodic reaction was copper electrodeposition on a bed of copper particles forced to circulate inside a fixed cylindrical enclosure by the action of rotating paddles; the anodic reaction was ferrous to ferric ion oxidation on an anode made of static graphite bars. The anolyte (aqueous FeSO 4 + H 2 SO 4 ) and catholyte (aqueous CuSO 4 + H 2 SO 4 ) are kept separate by an anion membrane which prevents cation transport between the electrolytes. Experiments were carried out in order to characterize cell performance under various conditions. When operating with 40 g/L Cu (II), I = 6 A, T = 50°C, 40 rpm paddle rotation and 990 mL/min electrolyte recirculation flowrate, the specific energy consumption (SEC) for copper electrowinning was 2.25 kWh/kg. An optimization of cell dimensions gave an improved SEC of 1.55 kWh/kg whereas a temperature increase from 50 to 56°C (without changing cell dimensions) produced a SEC of 1.50 kWh/kg, which is 25% lower than normal values for conventional copper electrowinning cells. A comparison was drawn between the performance of this cell and a squirrel-cage cell previously developed by the authors.
Highlights
Conventional copper electrowinning cells exhibit limitations which have led to the development of several alternative designs[1] such as the fluidised bed cell[2,3,4,5,6], the spouted bed cell[7,8,9] and the squirrelcage cell[10]
Results in table II indicate that, at constant temperature, the cell voltage increased with cell current; this is to be expected from a process where both reactions take place under mixed control
Results from experiments 1 and 7 showed that a catholyte and anolyte recirculation flowrate decrease from 990 to 412 cm3/min caused a slight increase in both the cell voltage and the specific energy consumption
Summary
Conventional copper electrowinning cells exhibit limitations (limited mass transfer rates, limited specific surface area of the cathodes, high specific energy consumption, environmental issues) which have led to the development of several alternative designs[1] such as the fluidised bed cell[2,3,4,5,6], the spouted bed cell[7,8,9] and the squirrelcage cell[10] These cells have been shown to produce reductions in energy requirements. Despite the fact that membrane-based copper electrowinning cells have not yet been implemented in industrial production, they remain promising given: a) that some designs have produced considerable reductions (over 50 %) in specific energy consumption, and b) that the ferric compounds produced in the anolyte exhibit a far higher cost (6 to 10 times higher) than the ferrous compounds use as reactants It is clear, that further work is required before the new designs are used in large-scale copper production. Both cells exhibit advantages compared to conventional technology, e. g. increased mass transfer rates and increased specific surface area of the cathode, but they exhibit limitations such as heterogeneous cathodization and physical discontinuity of the particulate bed
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