Sodium Sulfite Supplier South Africa

What Is Sodium Sulfite?

Sodium sulfite (Na₂SO₃) is an inorganic sulfite salt — the sodium salt of sulfurous acid (H₂SO₃). It is a reducing agent and the most widely used chemical oxygen scavenger in industrial boiler water treatment. Dissolved oxygen in boiler feedwater causes pitting corrosion of boiler tubes, economiser sections, and feedwater pipework — oxygen pitting is a primary cause of boiler tube failures and plant shutdowns. Sodium sulfite scavenges (chemically removes) dissolved oxygen through the reaction: 2Na₂SO₃ + O₂ → 2Na₂SO₄, converting oxygen to sulfate ion without forming corrosive by-products at low and medium boiler pressures.

Boiler Feedwater Oxygen Scavenging

Sodium sulfite is dosed into the boiler feedwater downstream of the deaerator to remove residual dissolved oxygen that passes through the mechanical deaeration step (target: reduce O₂ from ~20–50 µg/L deaerator outlet to <10 µg/L, preferably <5 µg/L). The reaction is accelerated by elevated temperature (above 60°C) and is catalysed by cobalt sulfate, which is commonly added to sodium sulfite products (catalysed sodium sulfite) to improve reaction rate in feedwater systems with low temperature or short contact time. Sodium sulfite is dosed at a 7–10× stoichiometric excess over measured dissolved oxygen (to provide a residual of 20–40 mg/L Na₂SO₃ in the boiler water, confirming oxygen-free conditions).

Application Limits and Water Treatment Use

Sodium sulfite is suitable for low- and medium-pressure boilers (typically up to ~60 bar). At higher pressures, thermal decomposition in the boiler produces SO₂ and H₂S gases that carry over into steam and cause condensate corrosion — above this pressure range, non-oxidising organic oxygen scavengers (DEHA, erythorbic acid) are preferred. Na₂SO₃ also introduces sulfate ions with each dose, and in high-cycles-of-concentration systems this can increase TDS load. Terracore Chemicals supplies sodium sulfite in 25 kg bags and 1 MT bags, in plain and cobalt-catalysed grades, for boiler water treatment across Southern Africa.