Lime Slurry (Mining / Flotation) Storage & Tank Compatibility

Storing Lime Slurry (Mining / Flotation)? Start Here

Lime slurry — also called milk of lime — is an aqueous suspension of calcium hydroxide, Ca(OH)₂, produced by slaking quicklime (CaO) in water. It is a white, opaque, milky fluid carrying roughly 10–40% solids, with a strongly alkaline pH near 12.5. In mineral processing it is the workhorse pH modifier for sulphide flotation: cheap, abundant lime raises pulp pH to depress pyrite and tune collector selectivity during the selective flotation of copper, lead, zinc and other sulphides. The same slurry is dosed for acid neutralization, water treatment and tailings conditioning. Because the alkalinity is mild toward thermoplastics but the suspended solids settle into a hard, abrasive pack, material-of-construction choices hinge on managing solids, scaling and erosion rather than on chemical resistance. Tank interiors, agitation, recirculation and fitting placement matter as much as the resin grade selected for the vessel.

Polyethylene (HDPE / XLPE) Compatibility

Polyethylene is an excellent fit for lime slurry on chemical grounds. HDPE and crosslinked polyethylene (XLPE) are both rated highly resistant to strong alkaline solutions, including calcium hydroxide and sodium hydroxide across broad concentration ranges, and — unlike metals — poly does not suffer caustic stress-corrosion cracking or high-pH scale attack. The honest verdict is S (suitable): the high pH is not a threat to the resin.

The real engineering constraint is physical, not chemical. Lime slurry settles quickly and packs into a hard layer; the solids are abrasive and tend to scale on surfaces. Specify smooth-wall poly tanks, keep the slurry agitated or recirculated to prevent hard-pack, slope outlets, and use abrasion-tolerant valves and fittings. Within those handling provisions, an HDPE or XLPE tank is a standard, cost-effective choice for lime slurry storage.

Material compatibility at a glance

Lime slurry is strongly alkaline (pH ~12.5) but chemically benign toward polyethylene. HDPE and XLPE are both rated excellent against high-pH caustic media, so the dominant tank-selection driver is not chemical attack but the abrasive, settling, scale-forming nature of the suspended solids. Poly tanks are widely used; specify smooth interiors, agitation or recirculation to prevent hard-pack, and abrasion-tolerant fittings.

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

• Strongly alkaline (pH ~12.5) — causes serious eye damage (H318) and skin irritation (H315); splashes can cause chemical burns on prolonged contact.
• Dust and dried residue may cause respiratory irritation (H335); avoid breathing mist or powder from slaking and handling.
• Wear chemical-splash goggles, face shield, alkali-resistant gloves and protective clothing when sampling or maintaining tanks.
• Slaking quicklime is exothermic — control feed rate and temperature; never confine reacting lime in a sealed vessel.
• Settled hard-pack can plug outlets and overload agitators; follow confined-space and lockout procedures before entry or cleanout.
• Keep an eyewash and safety shower accessible; for eye contact, rinse cautiously with water for at least 20 minutes (P305+P351+P338) and seek medical attention.

Common questions

Can I store lime slurry in a polyethylene tank?

Yes. HDPE and XLPE are rated excellent against high-pH alkaline media, so calcium hydroxide slurry does not chemically attack the resin. Plan instead for the abrasive, fast-settling solids: smooth interior, agitation or recirculation to prevent hard-pack, and abrasion-tolerant fittings.

Why is lime slurry used in flotation?

Lime is the most common and economical pH modifier in sulphide flotation. Raising pulp pH depresses pyrite and tunes how collectors interact with target minerals, improving selectivity when separating copper, lead, zinc and other sulphides.

What is the main problem with storing lime slurry?

Settling. The suspended calcium hydroxide drops out and packs into a hard, abrasive layer, and it can scale on surfaces. Continuous agitation or recirculation, sloped outlets and routine cleanout keep the system flowing.

Does lime slurry need a special high-density tank?

Not for chemical reasons — the alkalinity is poly-friendly. Because the slurry is denser than water and abrasive, a standard chemical-grade poly tank rated for the slurry specific gravity, with abrasion allowances, is appropriate. Confirm the SG-rated capacity with your supplier.