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National Pollutant Release Inventory (NPRI) Emission Estimate Guide for Primary Aluminum Producers

5. Description of operations (raw materials, products, releases vs. reporting criteria)

The following figure illustrates the many operations that take place in a primary aluminium production plant.

Figure 2: Industrial procedure for primary aluminium production

Figure 2: Industrial procedure for primary aluminium production

Source: Environment Canada, 2011

Once the raw materials are received and stored, the calcined petroleum coke and pitch are shipped to the anode manufacturing plant.

In the prebaked anode process, the anodes are baked in ovens to produce blocks of solid carbon. The anode rods are then attached to these carbon anodes by pouring grey iron over them. The sealed anodes are sent to the electrolysis area. During the electrolytic phase, the alumina is reduced to aluminium in a bath of molten cryolite and other salts. Finally, a vacuum pump is used to remove the resulting aluminium from the pot. The spent anodes (butts) as well as the adhering bath are cooled, treated and reused in the process.

In the Söderberg process, green anode paste produced by the anode manufacturing process (paste tower) is sent directly to the electrolysis area, where it is baked in situ.

The liquid aluminium produced by either process is sent to the casting centre to be processed into aluminium ingots, pigs, billets, etc.

The main air pollutants, which are released during these operations and listed as NPRI substances, are as follows: polycyclic aromatic hydrocarbons (PAHs), hydrogen fluoride (HF), volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen oxide (NOx), sulphur dioxide (SO2) and particulate matter (TPM, PM10 and PM2.5).

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