Magnesium Hydroxide Pulping Slurry Storage & Tank Compatibility

Storing Magnesium Hydroxide Pulping Slurry? Start Here

Magnesium hydroxide pulping slurry is a milky white aqueous suspension of magnesium hydroxide solids, Mg(OH)₂, used across the pulp and paper industry as a mild mineral alkali. In magnesium-based (“magnefite”) mills the magnesium and sulfur values are recovered separately, and magnesium oxide is slaked into a hydroxide slurry that is then used to scrub sulfur dioxide into fresh cooking liquor or to neutralize digester liquor. The same slurry is widely dosed as the alkali source in hydrogen-peroxide bleaching of mechanical and chemical pulps, where its buffering action and gentler initial pH protect cellulose, raise pulp viscosity and brightness, and lower effluent COD/BOD versus caustic soda. Because Mg(OH)₂ is only slightly soluble, the product is shipped and handled as a pourable slurry. Material of construction matters because the medium is alkaline (pH roughly 9-11) and laden with settling abrasive solids — so storage must resist high pH, handle solids, and keep the slurry homogeneous.

Is Polyethylene (HDPE / XLPE) Safe for Magnesium Hydroxide Pulping Slurry?

Yes — polyethylene is a recommended choice. Published polyethylene chemical-resistance data rate saturated magnesium hydroxide and its slurries as Satisfactory (“S”) on HDPE and crosslinked polyethylene at both ambient (~70°F) and elevated (~140°F) service temperatures. The slurry is only mildly alkaline and contains no oxidizers, solvents, or hydrocarbons that would degrade polyethylene, so chemical attack is not the limiting factor. The practical considerations for a poly tank are physical, not chemical: suspended solids settle and can pack, so size the agitation/recirculation to keep the slurry moving, and choose a tank with adequate specific-gravity (fluid weight) rating for the as-shipped solids loading. For these reasons a properly rated HDPE or XLPE tank is a durable, cost-effective option for storing magnesium hydroxide pulping slurry. Always confirm against the slurry supplier’s SDS and the tank manufacturer’s chemical-resistance and fluid-weight ratings for your concentration and temperature.

Material compatibility at a glance

Magnesium hydroxide pulping slurry is a mild, mineral alkaline suspension, so the dominant design drivers are high-pH compatibility and abrasion from suspended/settling solids rather than chemical attack. HDPE and XLPE polyethylene are a sound, economical fit; aluminum is the notable material to avoid because high pH attacks it.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Causes skin irritation (H315) and serious eye irritation (H319) — wear chemical splash goggles and gloves; alkaline mineral solids are abrasive and drying to skin.
• May cause respiratory irritation (H335) from mists or dried dust — provide ventilation and avoid generating aerosols.
• Non-flammable, non-reactive aqueous slurry (NFPA Flammability 0, Instability 0) — no fire or explosion hazard under normal handling.
• Settled solids form hard, slippery deposits — manage spills promptly and keep tanks agitated to prevent packing.
• High-pH liquid — do not store or transfer in bare aluminum; protect carbon steel from abrasion and water-line corrosion.
• Follow the specific product SDS for exposure limits, first aid, and disposal; impurity content can vary by source.

Common questions

What is magnesium hydroxide pulping slurry made of?

It is an aqueous suspension of magnesium hydroxide solids, Mg(OH)₂, in water — typically on the order of 30-60% solids by weight (representative, formulation-dependent) with small amounts of dispersant/suspension aids. Because magnesium hydroxide is only slightly soluble, it is handled as a slurry rather than a clear solution.

Can I store magnesium hydroxide pulping slurry in a polyethylene tank?

Yes. HDPE and XLPE are rated Satisfactory for saturated magnesium hydroxide and its slurries on polyethylene resistance charts at normal and elevated temperatures. The main design factors are keeping the solids suspended (agitation/recirculation) and selecting a tank with an adequate fluid-weight (specific-gravity) rating, not chemical attack.

What is the pH and is it corrosive?

The slurry is mildly alkaline, roughly pH 9-11 depending on solids and source. It is irritating to skin, eyes, and the respiratory tract but is a weak, buffered alkali — far less aggressive than caustic soda. High pH does attack amphoteric metals such as aluminum, which should be avoided.

Why is magnesium hydroxide used instead of sodium hydroxide in pulp bleaching?

Magnesium hydroxide acts as a buffered, gentler alkali source in peroxide bleaching. Its lower initial pH protects cellulose (preserving pulp viscosity and brightness) and reduces dissolution of organics, which lowers effluent COD, BOD, and TOC compared with sodium hydroxide, often at competitive cost.