Operating Experience with the Alcoa 398 Process for Fluoride Recovery

Abstract

During the 1940’s, aluminum smelting installations were increased in size to provide aluminum necessary for World War II. Increased evolution of fluorides made necessary the capture and treatment of pot gases. Following the application of water scrubbers, cyclones, and electrostatic precipitators, Alcoa Research Laboratories at New Kensington, Pa., discovered that small quantities of HF gas would react at low temperature with alumina. Following a series of design efforts, the Alcoa 398 Process was developed, incorporating a fluidizedbed reactor to contact pot gases with incoming feed alumina. Bag filters are used to separate entrained solid materials from pot gases. Ninety-five percent interception of pot gases is reported with 99% recovery of fluorides from gases treated. No significant effect is observed on purity of metal produced.

Installation costs are in the range of $>28-$37 per annual ton for new installations and about 50% more for conversion of old plants. These are somewhat less than the conventional electrostatic precipitators and water scrubbers at today’s prices. Direct operating costs for the Alcoa 398 Process range from $2.90 to $4.70/ton of aluminum and recover $8 worth of fluorine, giving a net credit. This contrasts with $3.93/ton of aluminum to operate existing precipitator scrubber combinations. The Alcoa 398 Process is being rapidly extended throughout the Alcoa system.