The mineralogical characterization of dry-powder barriers in Al reduction cells

Dry-powder barrier layers have been investigated in recent years to prevent fluorine penetration and degradation of insulating refractories and cell walls. The deterioration of insulating materials and cell walls is undesirable as it results in increased thermal conductivity and, therefore, higher operating costs. The mineralogy of two dry-powder barriers was characterized by several methods. Results show that after 893 days in an aluminum reduction cell, corundum and wollastonite-based powder formed an incomplete calcium-fluoride barrier. This dry powder contained a vermiculite base. An anorthite-based powder was tested in a laboratory trial and formed a nepheline barrier with complete conversion of fluorine to stable mineralogical phases after 100 hours. Testing of this anorthite-based powder in aluminum-plant reduction cells is currently in progress. Ann M. Hagni earned her Ph.D. in geology at the University of Missouri-Rolla in 1995. She is currently manager of applied mineralogy and analytical chemistry at A.P. Green Industries. Dr. Hagni is also a member of TMS.