The "Hidden Saboteur" in Phosphate Rock: How Chlorine Silently Damages Yellow Phosphorus Production

Phosphate rock contains not only phosphorus but also a small amount of chlorine. Although its content is low, this "hidden saboteur" triggers a chain of reactions throughout the yellow phosphorus smelting process – from the high‑temperature zone inside the furnace, to the condensation system, and even to the tail‑gas treatment stage.

What happens to chlorine inside the furnace?

Under the strong reducing atmosphere and high temperature of the electric furnace, chlorine shows high chemical activity. Chlorides in the phosphate rock begin to volatilise in the preheating zone and enter the furnace gas. Chlorapatite reacts with water vapour at high temperatures to produce hydrogen chloride (HCl). HCl then reacts with metal oxides in the furnace charge, generating various volatile metal chlorides that accelerate the migration of iron.

Corrosion of equipment: a double blow

Chlorine attacks equipment in two ways. In the high‑temperature zone, HCl causes severe gas‑phase corrosion of carbon steel and stainless steel, continuously eroding the metal surface. In the low‑temperature section of the condensation system, HCl dissolves in condensed water to form hydrochloric acid, which, together with phosphoric acid and sulphuric acid also present, creates a mixed acid system that is far more corrosive than any single acid. Even more dangerously, chloride ions can trigger stress corrosion cracking in stainless steel – a failure mode that often gives no warning.

Impact on product quality and the environment

Some chlorine in the furnace forms phosphorus chlorides that enter the condensation system with phosphorus vapour and eventually dissolve in yellow phosphorus, affecting product purity. In downstream fine chemical production, chlorine is a contaminant that must be strictly controlled. Moreover, treating chlorine‑containing wastewater adds to the environmental burden.

Solution: chlorine removal by sintering

All these problems stem from chlorine entering the production system. Sintering‑based chlorine removal addresses the issue at its source – during the sintering process, over 90% of chlorine can be eliminated, greatly mitigating equipment corrosion, product contamination, and environmental emissions.

Though present in trace amounts, chlorine can cause significant trouble in yellow phosphorus production. Sintering‑based chlorine removal is not an optional extra but a crucial step for ensuring long‑term, safe, and stable plant operation.