What is Calcined Alumina?

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