Chlorine (Cl2)

Chlorine (Cl₂) is a greenish-yellow, sharply pungent gas that is highly reactive and corrosive to the respiratory tract. Even at low concentrations it irritates the eyes, nose and lungs; at higher levels it causes chemical burns to the airways and pulmonary oedema. Indian general emission standards cap chlorine in stack gas at 15 mg/Nm³.

Chlorine is used and released in chlor-alkali (caustic soda) plants, water and effluent disinfection, bleaching, and various chemical processes. In recycling, the relevance is twofold. First, chlorine and chloride chemistry appears wherever chlorinated plastics such as PVC are processed — thermal treatment of PVC releases HCl and can generate chlorine-bearing species, and chloride is the precursor to dioxin formation. Second, chlorine gas is used in effluent and water disinfection at treatment plants, where storage and dosing of chlorine cylinders is a safety hazard.

The danger is acute: a chlorine leak from a cylinder or process line can incapacitate workers within minutes. It is also corrosive to equipment. Where PVC or chlorinated feedstock is thermally processed, the chlorine/chloride route raises both the acid-gas (HCl) and the dioxin/furan risk, which is why segregating PVC out of plastic and tyre feedstock is a core operational rule.

Control depends on the source. For gaseous chlorine handling (disinfection), use proper cylinder storage, leak detection, and emergency scrubbing/neutralisation systems. For thermal processing, the primary control is feedstock segregation — keep PVC and chlorinated material out of pyrolysis and incineration feed — backed by alkaline scrubbing of acid gases on the stack. Stack chlorine is a tested parameter against the 15 mg/Nm³ limit.