A comprehensive literature survey was conducted to obtain the available information on the manganese electrodeposition process.Using this information and measurments obtained from an industrial electrowinning plant,a modal was developed where the Interrelations between the most important parameters ware taken into account.Fundamental concepts were used wherever possible,except in a small section where no theoretical data was available. In this case empirical fitting of parameters was resorted to. The trends experienced in practice were all confirmed by the mode1,namely$ (i) the increase of cathodic currant efficiency with increased pH,which la limited by the precipitation of manganese hydroxide t (li) the increased current efficiency with decreased ammonium sulphate concentration; (ill) the existence of an optimum operating temperature for a given current density; (iv) the existence of an optimum current density for a given temperature; (v) the effect of total impurity level on current efficiency, the latter decreasing with increasing impurity level (vi) the steep increase of current efficiency with inorease of feed flow rata,to an upper limit condition at which point manganese hydroxide starts precipitating.

No description available.

The thermal characteristics of the electroslag remelting process have been investigated on a laboratory scale unit. The heat generation and distribution in the slag bed is discussed. The voltage gradients in the slag bed are predicted using a resistance network analogue and tested against experimental results. A self-consistent model for electrode temperature gradients in the electroslag remelting process has been tested against experimental results. An unsteady-state method has been used to determine the electrical resistance and the overall heat transfer coefficient of the interface region, liquid slag/slag skin/copper wall in the electroslag furnace. An accurate heat balance of the process is carried out on laboratory scale ingots. Attention has been devoted to the influence of various melt parameters i.e. polarity, power input, geometry, atmosphere etc. on the melt rate. The power requirements and the melt rate for industrial ingots are predicted and compared with the data collected from the literature. The liquid metal pool volumes in ESR ingots are predicted from the operational data. The pool profiles are computed using a finite difference technique and compared with the experimentally obtained profiles. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Thesis (Ph. D.)--Columbia University, 1939. / Vita.

Several aspects of the production of cerium by electrolytic reduction were investigated to determine more efficient operation. The solubility of cerium oxide in a molten fluoride salt bath(CeF₃, BaF₂, LiF) was determined by measuring the change in electrical conductivity of the bath as a function of added cerium oxide. The saturation solubility was found to be 2.9 wt% at 900 °C. The solubility was found to increase with temperature. Increasing the cerium fluoride content of the electrolyte also showed a small increase in the solubility. There was no difference found between the solubility of cerous oxide and eerie oxide. A heat balance model of a pilot plant scale cerium electrowinning cell was developed to improve cell design. The results of the model showed that most of the heat is lost through the anodes. The model showed that reducing the number of anodes and increasing their size would reduce heat losses, and thus improve cell operation. Increasing the-amount of insulation would reduce heat losses and make maintenance of the cell easier. It was also found that the production of lanthanum, praseodymium, and neodymium by electrolytic reduction of their respective oxides would be feasible. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

No description available.

No description available.

No description available.

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

No description available.