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Title: Characterisation of electrochemically activated solutions for use in environmental remediation
Author: Cai, Zhuo.
Awarding Body: University of the West of England, Bristol,
Current Institution: University of the West of England, Bristol
Date of Award: 2005
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This thesis aims to investigate the production of electrochemically activated solution via electrolysis of diluted NaCI solution using a commercial electrochemical system (STEL device), characterise the activated solution, and evaluate the potential application of this solution in the treatment of water containing organic compounds. The research shows that the electrolytic cell in the STEL device consists of a titanium based metal oxide (Ir02, Sn02, and Ti02) coated anode, a tubular titanium cathode, and a tubular ceramic diaphragm that separates the anode and cathode. A model electrolytic cell using STEL anode material was designed and constructed for investigating reaction mechanisms occurring at the electrode and identifying the oxidising species generated at the anode during the electrolysis of NaCI solution. Experimental results show that chlorine and oxygen were two main oxidants contained in the anolyte, indicating that the generation of chlorine and oxygen are involved in the electrode reactions. The evolutions of chlorine and oxygen were found to be achieved via the formation of a series of adsorbed intermediates such as OHad, Oad on the anode surface during electrolysis. Evidences for the occurrence of the intermediates were obtained by several electrochemical observations. It is suggested that the evolution reaction of chlorine involves a mechanism in which an intermediate of OClad is formed instead of Clad. The adsorbed intermediates may also be released from the anode surface to form chlorine free radicals and hydroxyl radicals when the electrolysis is carried out at higher potentials. This was investigated using the electro-oxidation of salicylic acid (SA). It was found that in a buffer solution containing chloride ions, the oxidation processes of SA were dependent on the potential applied on the anode. At + l.5V, the reaction product was 2,4,6-trichlorophenol, indicating that chlorine free radicals were generated. At +2.5V, the obtained products included 2,5-dichloro-l,4-benzoquinone, indicating that a hydroxyl group is introduced to the benzene ring of SA. These results suggest chlorine free radicals were generated at + l.5 V while hydroxyl radicals were generated at +2.5V. The operating conditions of the STEL device were optimised with respect to the redox potential, pH, and chlorine concentration of the generated ECAS. Anolyte produced from the STEL system, using a 100/0 NaCI solution under optimised electrolysis conditions, is an acidic solution (PH 2.2) containing a mixture of oxidants with a redox potential of 1190 m V and an available free chlorine concentration of 280 mgIL. The catholyte solution is a reductive basic solution with a pH of 12.6 and a redox potential of -950m V. The anolyte solution can maintain the oxidation ability up to 6 days when it is stored in an air tight container. However, it will lose its oxidation ability in 30 min if is purged by nitrogen or in 60 min if is stirred in the atmosphere. The anolyte solution can degrade trace amounts of aromatic compounds in aqueous solution. The degradation products are dependent on the concentration and chemical nature of the reagents. Usually, 10-4M SA can be converted to ring opened compounds, while 10·3M SA can only be converted to quinonic compounds. A subsequent dechlorination step is required when using anolyte for treating aqueous solution containing organic compounds as the by products include chlorinated compounds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available