
What is Calcined Alumina?

Chemical Properties and their Importance
Three types of alumina are produced at the Gramercy plant: calcined alumina (Al2O3) as reduction grade ore (RGO),
dried alumina trihydrate (Al2O3 • 3H2O), and wet hydrate or wet cake. The current specifications for these products follow.
- %Na2O (Precipitation Conditions and hydrate filter operation) Smelter Bath Generation and Bath Chemistry
- %SiO2 (Liquor Silica Control) Affects metal conductivity, ductility, formability (high purity Al)
- %Fe2O3 (Bauxite Dependence or press filter performance) Metal purity need for end-use
- %CaO (Liquor Causticity and press filter operation) Bath Chemistry
- %TiO2 (Liquor Causticity/Lime addition rate) Metal Conductivity
- %P2O5 (Digestion and Security Filtration Dependent) Smelter Current Efficiency, Metal Porosity and Brittleness
- %V2O5 (Calcination Fuel Dependent) Metal Conductivity
- %ZnO (Bauxite Dependent, sulfide control) Metal Grainy Surface Finish - spangling (Foil, Extrusions)
- % CuO (Bauxite Dependent) Metal Conductivity
- %Cr2O3 Metal Conductivity
- %MnO (Bauxite Dependent) Metal Conductivity
- % BeO (Bauxite Dependent) Environmental
Chemical Properties and their Importance
%Na2O (Precipitation Conditions and hydrate filter operation) Smelter Bath Generation and Bath Chemistry
%SiO2 (Liquor Silica Control) Affects metal conductivity, ductility, formability (high purity Al)
%Fe2O3 (Bauxite Dependence or press filter performance) Metal purity need for end-use
%CaO (Liquor Causticity and press filter operation) Bath Chemistry
%TiO2 (Liquor Causticity/Lime addition rate) Metal Conductivity
%P2O5 (Digestion and Security Filtration Dependent) Smelter Current Efficiency, Metal Porosity and Brittleness
%V2O5 (Calcination Fuel Dependent) Metal Conductivity
%ZnO (Bauxite Dependent, sulfide control) Metal Grainy Surface Finish - spangling (Foil, Extrusions)
% CuO (Bauxite Dependent) Metal Conductivity
%Cr2O3 Metal Conductivity
%MnO (Bauxite Dependent) Metal Conductivity
% BeO (Bauxite Dependent) Environmental
Size (Precipitation Control Dependent)
– +150 microns
- – Alumina Dissolution in Smelter Bath
– -45 Microns and -20 Microns
- – Smelter Operation
• Current Efficiency and Anode Effects
• Alumina Flowability, Particle Segregation
• Emissions and Dust Control
• Fines Generation – Attrition Index
• Attrition Index (Precipitation and Calcination Technology) – Fines Generation
• BET Surface Area, m2/gm (Calcination Operation Dependent) – Fluoride Absorption - Environmental and Safety
• LOI % (300 – 1000 oC) (Calcination Operation Dependent) – Related to Surface Area and Alpha Alumina Phase Content
Bulk Density, kg/m3 (Precipitation Control Dependent)
– Smelter Pot Feeding Rates
Alpha Phase Content, % (Calcination Operation Dependent) – Alumina Solubility in Smelter Bath, Free Heat of Reaction
Moisture Content, % (Atmospheric Condition Dependent)
– Economics of Shipping
– Bath Effects
Alumina Quality Consistency Is Important In Refineries and Smelters because of:
– Process Stability
– Process Efficiency
– Improved Economics