preparation of alumina powders
PREPARATION OF ALUMINA POWDERS
1. BAYERS PROCESS
INTRODUCTION
The Bayer Process was invented and patented in 1887 by Austrian scientist Karl Josef Bayer.
Two to three tonnes of bauxite are required to produce one tonne of alumina.
90% of the global alumina supply of around 90 million tonnes is used in aluminium production.
DEFINITION
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide). The aluminium oxide must be purified before it can be refined to aluminium metal.
Important Ore: BAUXITE.
CONTENTS:
Al2O3 - 30 -54%
Rest -Silica, Iron Oxides and Titanium Oxides.
ADVANTAGES
Most economic means of obtaining alumina from bauxite.
APPLICATIONS
industrial and medical ceramics sandpapers pigments cosmetics Pharmaceuticals.
FLOW CHART:
THE PROCESS STAGES ARE:
1. Milling
The bauxite is washed and crushed, reducing the particle size and increasing the available surface area for the digestion stage. Lime and "spent liquor" (caustic soda returned from the precipitation stage) are added at the mills to make pumpable slurry.
2. Desilication
Bauxites that have high levels of silica (SiO2) go through a process to remove this impurity. Silica can cause problems with scale formation and quality of the final product.
3. Digestion
A hot caustic soda (NaOH) solution is used to dissolve the aluminium-bearing minerals in the bauxite (gibbsite, böhmite and diaspore) to form a sodium aluminate supersaturated solution or “pregnant liquor”.
Gibbsite:
Al (OH)3 + Na+ + OH- → Al (OH)4- + Na+
Böhmite and Diaspore:
AlO(OH) + Na+ + OH- + H2O → Al(OH)4- + Na+
Conditions within the digester (caustic concentration, temperature and pressure) are set according to the properties of the bauxite ore. Ores with a high gibbsite content can be processed at 140°C, while böhmitic bauxites require temperatures between 200 and 280°C. The pressure is not important for the process as such, but is
1. BAYERS PROCESS
INTRODUCTION
The Bayer Process was invented and patented in 1887 by Austrian scientist Karl Josef Bayer.
Two to three tonnes of bauxite are required to produce one tonne of alumina.
90% of the global alumina supply of around 90 million tonnes is used in aluminium production.
DEFINITION
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide). The aluminium oxide must be purified before it can be refined to aluminium metal.
Important Ore: BAUXITE.
CONTENTS:
Al2O3 - 30 -54%
Rest -Silica, Iron Oxides and Titanium Oxides.
ADVANTAGES
Most economic means of obtaining alumina from bauxite.
APPLICATIONS
industrial and medical ceramics sandpapers pigments cosmetics Pharmaceuticals.
FLOW CHART:
THE PROCESS STAGES ARE:
1. Milling
The bauxite is washed and crushed, reducing the particle size and increasing the available surface area for the digestion stage. Lime and "spent liquor" (caustic soda returned from the precipitation stage) are added at the mills to make pumpable slurry.
2. Desilication
Bauxites that have high levels of silica (SiO2) go through a process to remove this impurity. Silica can cause problems with scale formation and quality of the final product.
3. Digestion
A hot caustic soda (NaOH) solution is used to dissolve the aluminium-bearing minerals in the bauxite (gibbsite, böhmite and diaspore) to form a sodium aluminate supersaturated solution or “pregnant liquor”.
Gibbsite:
Al (OH)3 + Na+ + OH- → Al (OH)4- + Na+
Böhmite and Diaspore:
AlO(OH) + Na+ + OH- + H2O → Al(OH)4- + Na+
Conditions within the digester (caustic concentration, temperature and pressure) are set according to the properties of the bauxite ore. Ores with a high gibbsite content can be processed at 140°C, while böhmitic bauxites require temperatures between 200 and 280°C. The pressure is not important for the process as such, but is