Obiettivo
POTENTIAL BENEFITS - EUROPE PRODUCES ABOUT 20% (10 6 TONNES/YEAR) OF THE WORLD'S ELECTROWON ZINC. COMPARED TO CONVENTIONAL ANODES, PTFE (TEFLON) BONDED PBO2 SHOULD SAVE 0.2-0.3V ANODE POTENTIAL/CELL VOLTAGE, EQUIVALENT TO 200-300 KWH/TONNE ZN, WITH ADDITIONAL SAVINGS POSSIBLE BY USING NEW ELECTROCATALYSTS.
THE OBJECTIVE OF THIS STUDY IS TO DEVELOP IMPROVED OXYGEN EVOLVING ANODES WHICH OPERATE AT LOWER OXYGEN OVER POTENTIALS AND HAVE A LOWER WEAR/CORROSION RATE THAN THE EXISTING PB/PBO2 PLANAR ELECTRODES. THIS WOULD LOWER THE CELL VOLTAGE/ENERGY REQUIREMENT FOR A RANGE OF ELECTROLYTIC PROCESSES SUCH AS ELECTROWINNING OF METALS FROM LEACH SOLUTIONS AND OTHER ELECTROLYTIC SYSTEMS WHERE ACID ELECTROLYTES ARE USED. THE PROJECT INVOLVES TWO NOVEL APPROACHES :
A) DEVELOPMENT OF TEFLON BONDED OXYGEN EVOLUTION ELECTRODES.
B) EVALUATION OF NOVEL OXYGEN ELECTROCATALYSTS BASED ON THE LOWER OXIDE/HIGHER OXIDE CONCEPT DEVELOPED AT THE CITY UNIVERSITY.
Roast leach electrowin processes are used in the production of about 80% of the World's zinc and about 20% of copper from their respective sulphide minerals. The total production of each metal being of the order of 10E7 tonnes per year.
The anode overpotential for oxygen evolution using traditional lead silver alloys is about 0.6 V. This constitutes a major component of the energy requirement for the electrolytic process (about 600 kWh/tonne metal). A reduction of 0.25 V in the oxygen evolution potential would result in savings of 250 kWh/tonne of zinc or copper. The potential monetary saving, for the European zinc electrowinning industry alone, would be in the region of 10 million pounds sterling per year less the additional cost of introducing improved anodes.
AT PRESENT, LEAD ALLOY ANODES (PB-SB, PB-AG, OR PB-CA) ARE USED FOR OXYGEN EVOLUTION IN ACIDIC METAL WINNING PLANTS. THESE ELECTRODES HAVE HIGH OVERVOLTAGES AND ARE GRADUALLY CORRODED IN USE.CONTAMINATING THE CATHODICALLY DEPOSITED METAL. THE USE OF PRECIOUS METAL BASED ANODES IS NOT PRACTICAL BECAUSE OF HIGH COST AND THEIR SENSITIVITY TO POISONING BY IMPURITIES. RECENT WORK ON ALKALINE ELECTROLYSER AT THE CITY UNIVERSITY SPONSORED BY THE EEC HAS SHOWN THAT TEFLON BONDED ELECTRODES ALLOW MORE OF THE AVAILABLE CATALYSTS SURFACE TO BE USED AND ARE LESS PRONE TO POISONING BY IMPURITIES.
THEREFORE, IT IS TIMELY TO EVALUATE WHETHER SIMILAR CONSIDERATIONS ARE APPLICABLE IN THE ELECTROWINNING INDUSTRY. THE PROJECT INVOLVES THE EVALUATION OF TWO NOVEL APPROACHES TO THE IMPROVEMENT OF OXYGEN EVOLVING ELECTRODES IN ACIDIC MEDIA. THE FIRST APPROACH IS TO EVALUATE THE FEASIBILITY OF USING TEFLON BONDING OF THE PRESENTLY USED ELECTROCATALYST TO IMPROVE THEIR UTILIZATION AND IMPART GREATER RESISTANCE TO POISONING. THE SECOND APPROACH IS TO USE THE ' LOWER OXIDE/HIGHER OXIDE ' MECHANISM PROPOSED BY TSEUNG ET AL TO SEARCH FOR NOVEL ACID RESISTANT OXYGEN EVOLUTION ELECTROCATALYST WHICH HAVE LOWER OXYGEN EVOLUTION POTENTIAL THAN THE TRADITIONAL MATERIALS.
INITIALLY, THE FEASIBILITY OF USING TEFLON BONDED LEAD/LEAD OXIDE ELECTRODES FOR OXYGEN EVOLUTION WILL BE STUDIED IN ELECTROCHEMICAL HALF CELLS IN ACIDIC MEDIA WILL BE INVESTIGATED IN A TEMPERATURE RANGE (20 - 60 CELSIUS DEGREES) AND CURRENT DENSITIES UP TO 100 MA/CM. THE WORK WILL THEN BE EXTENDED TO OTHER NOVEL ELECTROCATALYST SYSTEMS BASED ON THE LOWER/HIGHER OXIDE CRITERIA DESCRIBED EARLIER. PROMISING CANDIDATE MATERIALS WILL THEN BE SUBJECTED TO LIFE TESTING AND SCALE UP TO 100 SQ CM2 PROTOTYPE ELECTRODES FOR EVALUATION BY COLLABORATING INDUSTRIAL PARTNERS.
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LONDON
Regno Unito