LOSS OF CURRENT EFFICIENCY IN ALUMINUM ELECTROLYSIS CELLS

Consideration of the mechanism of loss of current efficiency (CE) leads to a form of equation which is simple, likely to give reasonable extrapolation beyond the range where experimental data are available, and convenient for responding to practical questions. With coefficients generated from plant experiments (performed by others), the equation is log (pct loss of efficiency) = 0.0095 (superheat) - 0.019 (pct AlF3) - 0.060 (pct LiF) + const where superheat is the difference (in degrees-C) between cell temperature and the pseudo-binary eutectic temperature with Al2O3, and pct AlF3 is excess AlF3. The coefficient for CaF2 is zero. The constant is characteristic of the cell design. The question of reconciling the values of the coefficients with literature data on the solubility of Al in cryolite melts and current theories of loss of efficiency is discussed.