Not many are there who have not heard of alumina but may not be aware of how it is produced and used in the metal world. So, to begin with, alumina, also popularly known as aluminium oxide, is a chemical amalgamation of aluminium and oxygen with the chemical formula Al₂O₃. It is a white crystalline substance produced through the Bayer Process, the principal industrial means of refining bauxite into alumina, and used in the production of aluminium as an abrasive owing to its hardness and as a refractory material due to its high melting point. As of 2020, there were around 75 operational alumina refineries across the world, producing 133.07 million tonnes of the mineral, including 125.52 million tonnes of metallurgical grade. Having mentioned alumina refineries, let us now learn what an alumina refinery is.
What is Alumina refinery?
The process of extracting alumina from bauxite is commonly known as refining, and the industrial facility where it is carried out is called a refinery. Alumina refining produces alumina from the bauxite ore, leveraging the reversible reaction of the Bayer process. Bauxite is first washed, ground, and then dissolved in caustic soda (sodium hydroxide) at high pressure and temperature at an alumina refinery. Approximately four tonnes of bauxite are required to produce one tonne of alumina, and about two tonnes of alumina are needed to churn out one tonne of aluminium. Now, let us delve into the details of the Bayer process that involves four steps for refining alumina.
Fours steps of the Bayer process:
Digestion, wherein bauxite is finely ground in mills and mixed with recycled caustic soda solution. The output is then put on steam in digester vessels at a very high temperature and pressure to dissolve the alumina of the bauxite. Post that, the solution is cooled in a series of flash tanks.
Then follows the step Precipitation, wherein alumina crystals are recovered from the caustic solution by mechanically stirring the solution in open tanks.
The final step involves Calcination, which allows precipitated material to be washed and dried at temperatures more than 1000 degrees Celsius. This process forms the dry white anhydrous aluminium oxide powder (alumina), which is then cooled and conveyed to storage.
What are the salient features of an Alumina refinery?
An Alumina refinery should ideally be capable of-
- Resisting atmospheric pressure during the process.
- Producing maximum volume of alumina and maintaining inter-stage cooling.
- Holding an energy-efficient, fluidized, heating throughout.
- If it’s a system-generated plant then it should have a co-power generation back-up system powered by at least 5×18.5 MW turbine.
How does an Alumina refinery function?
A Bayer process gives a customized solution, curtailing the overall operational cost and capping the capital expenditure. The two key objectives of an integrated refinery are fastening project implementation and optimizing the overall output. But as any chemical refining process has a physical impact on our mother nature, companies are in constant search of enhanced physical safety management systems to achieve utmost employee protection. The Bayer process through which alumina is produced requires high-end machinery to perform the task to reduce the chance of physical and environmental hazards. No production can cost bigger than workers’ health, so operational moves such as space entry, dropping of heavy-weight objects, heat management system, vibration regulation, and noise controlling system need to be regularly checked by the authority. Alongside, a critical safety management system should be present to monitor the process and scrutinize risk-controlling measures. Many of the leading players have included an expert team of IT professionals to critically observe and update the entire processing system. The professionals are also liable to keep a close watch on the machinery to ensure seamless performance during the production. They are also responsible for maintaining a spreadsheet registering problems daily to avoid hazards. Behind any successful industry, there should be a structured methodology, and the aluminium industry is no exception. Here the key is how well they keep up the coordination between the operations and maintenance departments.
