Papermaking Alum (Paper-Grade Aluminum Sulfate) Storage & Tank Compatibility

Storing Papermaking Alum (Paper-Grade Aluminum Sulfate)? Start Here

Paper-grade alum is liquid aluminum sulfate — Al₂(SO₄)₃ dissolved in water — refined to a low iron content (typically under 100 ppm as Fe₂O₃) so it will not discolor the sheet. In the wet end of a paper machine it is the workhorse acid that drops pulp pH into the rosin-sizing window, sets rosin size onto fibers, fixes cationic charge, and helps retain fillers and fines. The same low-iron liquid also serves potable-water and effluent coagulation. Because it is a strongly acidic aqueous salt solution — dense (around 1.3 specific gravity) but containing no fuel, solvent, or oxidizer — the dominant materials-of-construction concern is corrosion of metals by the acidic sulfate liquor, not chemical attack on plastics. That is why polyethylene tanks are the default for storing and dosing liquid alum, while any steel in contact with it must be lined.

Is Polyethylene Safe for Paper-Grade Liquid Alum? (Yes)

Yes. Aluminum sulfate solution is one of the classic poly-tank chemicals. Industry resistance data rate aluminum sulfate at storage concentrations as recommended for HDPE and crosslinked polyethylene (XLPE), and polypropylene is likewise resistant. Polyethylene shrugs off the acidic, salt-laden liquor that corrodes bare steel.

The one design point that is not chemical is weight: liquid alum is dense (about 1.30–1.36 specific gravity), so specify a tank rated for at least 1.5 specific gravity to carry the load with margin. Confirm the resin rating, gaskets (EPDM is a good default), and fitting materials against your supplier's data for the exact grade, concentration, and service temperature before finalizing a tank.

Material compatibility at a glance

Paper-grade liquid alum is a dense, strongly acidic aqueous salt solution — not a fuel, solvent, or oxidizer — so polyethylene is the standard, economical tank material. Crosslinked or high-density polyethylene (specify the 1.5 specific-gravity rating to carry the heavy liquid), polypropylene, and acid-grade FRP all serve well. Bare carbon steel and ordinary stainless are corroded by the acidic sulfate liquor and must be lined (rubber or acid brick) if used at all.

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

• Eye damage (H318): The acidic solution can cause serious eye damage — wear chemical splash goggles and have eyewash within reach.
• Skin irritation (H315): Causes skin irritation; use chemical-resistant gloves and avoid prolonged contact.
• Strongly acidic: Representative pH of roughly 2–4 means it attacks bare carbon steel and concrete — provide acid-resistant containment and dosing equipment.
• Incompatibilities: Reacts with strong bases (exothermic neutralization) and can liberate heat; keep separated from caustics and limestone/cement in spill areas.
• Not flammable: The aqueous solution does not burn (Flammability 0), but spilled liquid is slippery and corrosive to floors.
• SDS governs: Hazard codes, pH, and NFPA values vary by grade and concentration — always defer to the supplier Safety Data Sheet.

Common questions

Can I store paper-grade liquid alum in a polyethylene tank?

Yes. Aluminum sulfate solution is rated as recommended for HDPE and XLPE polyethylene. The acidic sulfate liquor does not attack polyethylene the way it corrodes bare steel, which is why poly tanks are the standard choice for alum storage and dosing.

What tank specific gravity rating do I need?

Liquid alum is dense — roughly 1.30–1.36 specific gravity at typical concentrations. Choose a polyethylene tank rated for at least 1.5 specific gravity so the wall thickness carries the heavy liquid with a safety margin.

Why not just use a steel tank?

Paper-grade alum is strongly acidic (representative pH around 2–4) and corrodes bare carbon steel and ordinary stainless. Steel can only be used if it is rubber- or acid-brick lined. Polyethylene and acid-grade FRP avoid that lining cost entirely.

Is liquid alum flammable or an oxidizer?

No. It is a non-combustible aqueous salt solution (Flammability 0) and is not an oxidizer. The handling hazards are corrosivity and eye/skin contact, not fire, so no special fire-rated tank construction is required.