The impact of rising Ni and V impurity levels in smelter grade aluminium and potential control strategies

The technology for controlling smelter metal impurities post reduction has steadily improved. For example, control of sodium has seen the reduction and, in some plants, the elimination of chlorine gas from the casthouse. However, changes in the purity of cell feed materials such as anodes are giving rise to new challenges in impurity control; vanadium and nickel levels are an emerging problem. This paper briefly reviews the important impurities and their effects on downstream casting, forming and final application properties. Particular emphasis is given to nickel and vanadium. Strategies for controlling these impurities are also discussed and areas where new technology is needed are also highlighted. In some cases it is not known what the tolerable limits of impurities are. There are a plethora of metal refining techniques used in the extraction of other metals which could be investigated for the control of impurities in smelter grade aluminium