Sodium Bicarbonate in Flue-Gas Treatment and Water Treatment

Beyond food and feed, sodium bicarbonate (CAS 144-55-8, NaHCO₃) has two important environmental uses: as a dry sorbent for removing acid gases from flue gas, and as a pH and alkalinity adjuster in water and effluent treatment. Both exploit the same chemistry – bicarbonate neutralises acids and buffers near pH 8.

Flue-gas treatment: the dry sorbent route

Acid gases (SO₂, HCl, HF) are formed in combustion and industrial processes and must be removed before the stack. One well-established method is dry sorbent injection (DSI): a fine alkaline powder is injected into the flue gas, reacts with the acid gases, and the resulting solid is captured in a baghouse or ESP.

Sodium bicarbonate is a favoured sorbent for this duty because it is highly reactive and, on heating in the duct, it decomposes to sodium carbonate with a very porous, high-surface-area particle:

2 NaHCO₃ -> Na₂CO₃ + CO₂ + H₂O

That in-situ activation makes it react quickly and efficiently with acid gases at moderate temperatures, often allowing a lower stoichiometric ratio than some other sorbents.

Comparing sorbents for acid-gas removal

Sorbent	Chemistry	Notes
Sodium bicarbonate	NaHCO₃ -> Na₂CO₃	Highly reactive dry sorbent; porous after activation; good for HCl, SO₂, HF
Hydrated lime	Ca(OH)₂	Widely used; lower cost; often needs more sorbent
Limestone (wet)	CaCO₃	Wet scrubbing; different plant
Sodium carbonate	Na₂CO₃	Directly reactive; already the active form
Trona / sesquicarbonate	Na₂CO₃.NaHCO₃	Combined sodium sorbent option

The right choice depends on the acid-gas load, temperature, existing capture equipment and cost; bicarbonate is chosen where high removal efficiency and a reactive dry sorbent are worth the material cost.

Water and effluent treatment

In water treatment, sodium bicarbonate is used as a mild, easily dosed source of alkalinity and a gentle pH adjuster.

Use	Function
pH adjustment	Raises pH gently toward pH 8 without caustic’s overshoot risk
Alkalinity / buffering	Adds bicarbonate alkalinity; buffers against pH swings
Effluent neutralisation	Brings acidic waste streams toward neutral in a controlled way
Process water conditioning	Sets the alkalinity and pH a downstream process needs

Because bicarbonate buffers near pH 8, it is chosen where a mild, safe adjustment is wanted and where a strong base (caustic) could overshoot or present a handling hazard. It also adds sodium, so the sodium balance of the water must be considered.

Dosing notes

Duty	Starting-point guidance
Dry sorbent injection	Set on the acid-gas load and target removal; the stoichiometric ratio and excess are determined by test
Water pH / alkalinity	Dose to a target pH or alkalinity, controlled by titration or online monitoring

Because bicarbonate is a mild alkali, larger weights are needed than for caustic or soda ash to reach the same pH change; confirm the dose on your own system.

Handling

Non-hazardous, free-flowing solid; keep dry (it cakes if wet) and cool.
Keep away from acids – acid contact releases CO₂.
Use dust control where large amounts are handled; it is non-corrosive.

Frequently Asked Questions

Why is sodium bicarbonate used for flue-gas cleaning?

It is a highly reactive dry sorbent: on heating it forms porous sodium carbonate that reacts quickly with acid gases such as SO₂, HCl and HF.

How does it compare with lime?

Bicarbonate is more reactive and often needs a lower sorbent ratio, at a higher material cost; lime is cheaper but typically needs more. The choice depends on the plant and the target.

Can it be used to raise the pH of water?

Yes – it raises pH gently toward about pH 8 and adds buffering alkalinity, with less overshoot risk than caustic soda.

Does it add sodium to the water?

Yes; account for the sodium contribution in the water balance.

How is it dosed?

As a dry powder for gas treatment, or dissolved/dosed for water treatment, set by the target and confirmed by test.