Trace Element Concentration in Particulates from Pot Exhaust and Depositions in Fume Treatment Facilities

In dry cleaning of pot exhaust, expensive fluorides are captured and returned to production. At the same time impurities are accumulated in the finer fractions of the secondary alumina fed to the cells. While in secondary alumina the impurity content increased in the finer fractions, raw gas revealed a significant increase in impurities for particles with D i > 1 µm. Fume particles were sampled using a cyclone with varying cut-sizes and analyzed with help of HD ICP-MS. A statistical approach is used to identify correlations between element concentrations and particle diameters. Maximum impurity concentrations were recorded for fume fractions with particle size D i > 10 µm. It is expected that an economically feasible way of removing coarse particles from pot exhaust will lead to improved metal quality and increased current efficiency while keeping fluoride losses at a minimum.