Alkaline pulping, cleaner bleaching and lighter effluent

Magnesium hydroxide lets a mill run its alkaline processes with less caustic, less scaling and a lighter effluent load. It is a drop-in change at the wet end that shows up on three line items at once: fibre yield, chemical cost, and COD.

01Alkaline pulping and pH buffering

In alkaline sizing and pulping, Mg(OH)₂ works as a pH buffer, replacing alum and part of the caustic soda. Because it is a weak, sparingly soluble base, it holds the system at a stable, mildly alkaline pH instead of swinging it — which protects the cellulose from alkaline degradation and improves brightness stability over the life of the sheet.

The practical effect is better fibre yield and a sheet that resists yellowing, with less risk of the scaling and deposit problems that come with high-soluble-alkali operation.

02Bleaching with less caustic

In hydrogen peroxide bleaching, sodium hydroxide provides the alkalinity — but too much of it destroys peroxide and dissolves carbohydrates, which then leave the mill as COD in the effluent. Replacing part of the caustic with Mg(OH)₂ gives a gentler, self-buffering alkalinity:

• Higher brightness at equal or lower peroxide charge.

• Lower COD in the bleach effluent — a direct reduction in treatment cost.

• Better peroxide stability, because the pH never spikes.

03Effluent treatment

The same chemistry helps at the end of the line: Mg(OH)₂ neutralises acidic wastewater and precipitates dissolved heavy metals as hydroxides. Compared with lime or caustic, it is safer to handle, feeds more evenly, and produces a denser, easier-to-dewater sludge — which lowers the volume going to disposal.

04Recommended grades