Effect of Anode Quality on Composition of Gases in Aluminum Electrolysis

摘要

The effect of anode quality as well as operational parameters of aluminum electrolysis on the composition of anode gases, i.e. the content of fluorine, carbon monoxide and carbon dioxide, were studied in laboratory under controlled conditions. It was found that the extend of Boudouard equilibrium is approx. 20 times higher using anodes made of spectral graphite compared to the ones made of pyrolitic graphite. The reason is the much higher specific surface of spectral graphite compared to that of pyrolitic graphite. The composition of anode gas is affected by the anode material, its porosity, volume density, and temperature. The concentration of CO in anode gasses increases with increasing temperature. For anodes made of pyrolitic graphite the primary product is practically (>99%) CO_2 and CO is formed secondary only by the reaction between CO_2 and anode. The CO concentration in anode gases increases with decreasing content of Al_2O_3. In electrolytes saturated with Al_2O_3 the concentration of CO in anode gases increases with increasing concentration of AlF_3. At constant temperature the current efficiency decreases with increasing content of AlF_3. The dusting index of anodes at constant temperature increases with increasing content of AlF_3.