Impacto das reacções de oxidação parasítica no consumo do ânodo de carbono na produção de alumínio

Abstract

In the present work, a study was done in order to make a contribution to the aluminum industry in Mozambique (Mozal), on the impact of the parasitic oxidation reactions on the anode consumption, since the factory has verified an excess consumption of the anode of carbon in relation to that expected in the production of aluminum. The study was based on the investigation of the conditions of occurrence of two main reactions that contribute to the consumption of the carbon anode, the first is the oxidation reaction with oxygen from the air, which occurs on the surface of the anode when exposed to air during the operation of the electrolytic cell. The degree of this reaction can be minimized or eliminated by protecting the anode in the electrolytic cell by covering it with a mixture of alumina and a solidified electrolytic bath. The second is the oxidation reaction with carbon dioxide that occurs just above the electrochemical separation (surface of the bath and anode), and the degree of this reaction will depend on the ease with which carbon dioxide flows through the anode pores, on the permeability of air as a measure of gas flow and hydraulic pressure generated by the bath. The methodology of the work was based on the analysis of the available literature on the subject, a review and systematization of the collected information, the realization of technological tests and the analysis and discussion of the study results. During the technological tests, the anode coverage control was performed, which plays an important role in minimizing the effect of these reactions, which contribute to the increase in the total carbon consumed per ton of aluminum “net carbon”, in the operational control parameters such as weight , thickness, under pin of worn anodes, iron content due to the exposure of the pins to the electrolytic bath contaminating the metal, and in the process control parameters (temperature of the electrolytic bath, height of the electrolytic bath). In the work, the measurement results of each parameter mentioned in certain periods in the electrolytic cells under study were obtained. Regarding the amount of carbon consumed in excess, the results obtained were satisfactory for electrolytic cells with improved coverage. The results of this work allow us to warn about the effect of the difficulty of covering the anodes on the quality of the metal and the amount of carbon consumed in order to improve the procedures for the operations of covering and producing anodes.