Milk of Lime

Milk of lime is made by mixing calcium oxide (CaO) with water in an exothermic reaction known as lime slaking:

CaO calcium oxide + H₂O water →Ca(OH)₂ milk of lime

This reaction initially produces a fine dry calcium hydroxide powder solution (hydrated lime or slaked lime). Continuing to add water allows for the liquid solution known as milk of lime to be produced.

The exothermic heat of the slaking reaction of milk of lime requires a specialized piece of equipment, known as a lime slaker, to safely control and contain the slaking reaction.

Users of milk of lime may choose to slake quicklime on site, or source pre-slaked dry calcium hydroxide. This latter material can simply be added to water in a mix tank (i.e. no slaker is required). Alternatively, ready-made milk of lime can be sourced from suppliers such as Carmeuse.

Milk of lime storage is important. The milk of lime is usually consumed before any degradation in quality occurs. That said, over time the calcium hydroxide particles will react with carbon dioxide (CO₂) in the atmosphere to produce calcium carbonate lime (CaCO₃). This adversely impacts the effectiveness of the slurry in whatever process or application it is being added to.

As mentioned above, milk of lime has a broad range of industrial uses:

• Milk of lime is used in water and wastewater treatment processes for pH adjustment, contaminant removal, disinfection and water softening.
• Milk of lime is used to help separate non-ferrous metals from their parent rocks, either in flotation processes or as part of metathesis (double displacement) reactions.
• Milk of lime is used as a base (alkali) for pH adjustment, as a desiccant or, again, in metathesis reactions in the manufacturing of chemicals.
• Milk of lime is used to modify and stabilize soils, particularly clay soils, in civil engineering and construction applications.
• Milk of lime is used for biosolid treatment and soil improvement in agriculture.
• Milk of lime is used to help purify raw sugar juice in sugar refining.

More niche applications for milk of lime include as a primary supplement of calcium and alkalinity for reef aquariums, fresh plaster, in buon fresco painting as color solvent, and for making maize-based foodstuffs, such as corn tortillas (nixtamalization).