Ramachandran, P. (1988) Studies on anodes for electrochemical cells in electro winning of metals. PhD thesis, Madurai-Kamaraj University.

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Abstract

Although lead and its alloys have been used as conventional anode materials since the inception of the electro winning process, the problems of high over potential for oxygen solution and the corrosion of lead to lead sulphate and oxides still remain providing large scope for exploring improvements in these areas. Some contributions have been made in the present work to the anodic behaviour of some lead and non-lead systems under electro winning conditions. Electrochemical techniques like steady state measurements and linear sweep voltammetry have been used to obtain data on the corrosion and oxygen evolution characteristics of anodes under different conditions. The anodic behaviour of Pb and Pb-1% Ag has been investigated in sulphuric acid and chromic acid electrolytes with additives and impurities commonly encountered in electro winning operations. The electrode processes have been characterized by cyclic voltammetry. An analysis on the peak parameters providing information with regard to dissolution characteristics of the anode materials. The chloride present in the H2SO4 electrolyte restricts the formation of PbO2 and aggravates anode corrosion in the form of divalent lead. Mn2+ in the electrolyte retards the corrosion of lead anodes under oxygen evolution conditions. Anions like phosphate and arsenate in ppm level tend to inhibit PbO2 formation in their preferential adsorption on the electrode surface. The dramatic effects of CO2+, added to the electrolyte, in reducing the corrosion of lead anodes and facilitating oxygen evolution have been made clear through cyclic voltammetry. Cyclic voltammetry for Pb and Pb-1% Ag in chromic acid has identified in anodic formation of PbCrO4, PbO and PbO2 phases. Addition of small amounts of CO2+ is found to depolarize the anode in the same way as in H2SO4. Another significant contribution, made in the present work, relates to preconditioning of Pb-1% Ag anodes in fluoride solution, prior to electro winning operations. This pretreatment involves the anodic treatment of lead electrodes in fluoride solution, where a compact adherent layer of PbO2 is built up in a shorter time. Studies have been designed to understand the anodic films formed under different conditions of pretreatment. Oxide growth, compactness of the anodic films and oxygen evolution characteristics have been examined both in sulphate and fluoride media. Potentiodynamic studies and steady state measurements carried out throw much light on the electrode processes in the preconditioning step. One of the energy saving measures, investigated in the present work for electro winning of metals, particularly zinc, relates to anodic decomposition of methanol and similar alcohols at lead substrates. Steady state measurements indicate an anode potential saving of heavily 200 mv when methanol is added in 2-3% to the sulphuric acid electrolyte. The reductions in anode potential are more prominent only at lower anodic current densities where the oxidation of methanol is essentially under activation control. At higher current densities, the electrode process becomes diffusion controlled and simultaneously oxygen evolution starts. Catalytic anodes based on noble metal oxides like RuO2, IrO2 have been examined for the potential reduction in electro winning cells. A different type of catalytic anodes, which is known as the activated lead electrode (ALE), has been investigated under anodic polarization conditions where a reduction of nearly 500 mv in anode potential has been observed. The effect of manganese ion present in the electrolyte, on the catalytic activity, has been examined in this context

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Anodes for electrochemical cells
Subjects:	Electrohydrometallurgy
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	13 Jun 2012 05:29
Last Modified:	13 Jun 2012 05:29
URI:	http://cecri.csircentral.net/id/eprint/2838

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