SMELTER GRADE ALUMINA QUALITY IN 40+ YEAR PERSPECTIVE – WHERE TO FROM HERE?

Raahauge, B.E.

All commercial Smelter Grade Alumina (SGA) is produced by Calcination of Aluminium Hydroxide in Alumina Refineries. The Aluminium Hydroxide, or Hydrate, is precipitated from a super saturated solution and classified into fine seed and coarse product for Calcination in rotary kilns or stationary calciners.

Over the past 40+ years significant technology changes/shifts have taken place in Refineries and Aluminium Smelters, the only customer for SGA. The drivers for these changes were and still are Economy of Scale, Energy Efficiency and/or improved Environmental performance.

Following an introductory review of the major technology changes/shifts that have taken place, the associated challenges in SGA quality is reviewed. Emphasis will be on Alumina properties from Calcination in Rotary Kilns and Gas Suspension Calciners (GSC) at low or high temperature onwards into Smelting, such as: Particle Size, Strength and Dust Generation & Management, HF Generation and Capture, Alumina Feeding and Dissolution. Finally the impact of major chemical impurities will be discussed. The current SGA quality requirements beyond consistency are summarized with a view to optimization of the available Hydrate Precipitation and Calcination technology. Future SGA quality requirements are discussed from a Calcination point of view as the intermediate processing step between the Refiner and the Smelter, including its potential constraints or drawbacks.