M. Tech. Chemical Engineering Tshwane University of Technology 2013. / The effects on cobalt electrowinning at low concentrations, varied temperature range, presence of impurities and the change in flow rate of the electrolyte on current efficiency and cathode deposition quality was investigated. The investigation was conducted in a three-electrode cell configuration, however a SEC-CCS (Symmetric Electrolysis Current-Continuous Circulating System) type was used, and forced circulation of the electrolyte as a means of agitation to help in increasing the diffusion limit current density. A 20g/L cobaltous sulphate electrolyte was prepared and electrowon using a SEC-CCS cell, 20g/L boric acid was used as a buffer for hydrogen evolution, the electrolyte was introduced from the bottom of the cell at regulated investigated flow rates of 30, 60 and 90 L/h and discharged into the pump suction end establishing a continuous circulation of the electrolyte. The temperature was regulated between investigated range 35, 55 and 75oC using immiscible heating probe. A pH meter was used to measure the pH value of the solution and pH was manipulated using 120g/L of sulphuric acid and 2M sodium hydroxide to maintain pH 4. Investigations to apprehend the effects of impurities were carried out at standard cobalt electrowinning conditions with only cobalt concentration maintained at low values to support the effort of the study. A 20 g/L cobaltous sulphate was prepared together with 120 g/L sulphuric acid, 20 g/L boric acid, and operation conditions were maintained at 450 A/m² current density, temperature of 50°C and a pH of 4. Investigated impurities considered in this study were zinc (Zn) and iron (Fe) respectively; both impurities were introduced into the cell at concentrations of 50ppm and 100ppm each. Though impurities have an effect on cobalt electrowinning, more of their effects were evident in the cobalt deposition morphology, quality and current efficiency. This rather suggests that there's opposition for the available potential, the SEC-CCS set-up proved to be optimistic. The perpetual fluid flow pattern and electrochemical reaction surface requires steady flow of fluid at moderate pressure. This will continuously supply fresh feed and consequently the rate of mass transport adequate, adversely increasing fluid flow results in decrease in current efficiency, and rather cause high energy consumption. This statement is supported by insignificant effects of the flow rate on imperative cobalt electrowinning parameters such as cathodic overpotential, cell potential, energy consumption and current efficiency. The effects of temperature changes are observed to have significant effect on current efficiency and energy consumption. The cathodic overpotentials of cobalt electrowinning decreases with an increase in temperature and the transfer coefficients rather favors high temperature operation for cobalt electrowinning, however this conditions influences reductions in the current efficiency and adversely lowers the cathode deposition quality. The positive attribute of the SEC-CCS system in the cobalt electrowinning is that it minimized pitting and peeling as hydrogen bubbles of the plate surface and this somewhat increases the quality of the metal deposit morphology, and rather has insignificant attributes to electrowinning parameters
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:tut/oai:encore.tut.ac.za:d1000605 |
| Date | January 2013 |
| Creators | Malatsi, Robert. |
| Contributors | Mbaya, Richard Kady Kadiambuji, Mukongo, T. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | |
| Rights | © 2013 Tshwane University of Technology |
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