Effect of Carbon Dust on the Electrical Resistivity of Cryolite Bath

For many years anode dusting has been an issue for aluminum producers. Suspended carbon particles enhance the electrical resistivity of the cryolite bath, setting off a chain reaction of adverse effects for the pot. Many studies have documented the negative influence of carbon dust on current efficiency or bath temperature which are indirect effects of contaminated bath. The dependence of bath resistivity on the amount and on the size of carbon particles is poorly understood though. Tube-type cell experiments were performed to determine the electrical resistivity at 980 °C of standard bath mixtures added with carbon dust. The carbon content ranged from 0.06 to 1.01% in weight with mean particle size of 2 μm. A bath resistivity increase of 70% was measured when comparing the bath with the lowest carbon concentration with the one with the highest. From a bath with a carbon content of 0.06% to a one with 0.16%, the change in resistivity was equal to 13%. Thus the difference in bath resistivity between a benchmark bath with 0.03% carbon content and a bath from a dusty pot will be even larger. These results agree with variations of voltage measured during the ACD squeeze of groups of clean and dusty pots.