Why is SPL Hazardous?
The hazardous materials in SPL are mostly cyanide and other volatile substances that can react with water and air to create flammable gases. Cyanide is the chemical combination of carbon and nitrogen.

The symbol for carbon is C
N represents nitrogen
The symbol for cyanide is CN

This symbol tells the chemist that the basic building block in cyanide is made of 1 part carbon and 1 part nitrogen. Air in the atmosphere is approximately 70 percent nitrogen. Cyanide forms in the pot lining when nitrogen (N) from the air reacts with the carbon (C) in the cathode lining to chemically combine into CN.

The reactive compounds in SPL include aluminium metal, sodium metal and various carbon compounds that react with water and air to produce dangerous gases, such as acetylene, ammonia, methane and hydrogen.

Other ingredients in the SPL are fluorides. Fluorine is an element which mixes readily with metals to produce salts called fluorides. These play an important role in aluminium production.

During smelting, most of the fluorides are given off as gases and are caught in special baghouse dust collectors called fume scrubbers. The fume scrubbers mix the gases with the alumina pouring into the pot and so recycle the fluoride back into the process. A small proportion goes into the pot lining.

Fluoride compounds can harm vegetation and animal life if they escape into the environment in enough quantity so it is vital that SPL is stored and treated properly.

Storage of SPL

The SPL is removed in two stages. The first cut yields the carbon and the second cut removes the refractory.

When the SPL is removed from the pot, it is stored in covered sheds with concrete floors.

Proper storage prevents materials in this SPL from reacting with water and air. The concrete base prevents seepage and contamination of the soil.