Heading 2522 covers the industrially calcined lime products — quicklime, slaked lime, and hydraulic lime — in their commercial grades, while heading 2825 covers chemically defined calcium oxide and hydroxide of higher purity. If the product meets the purity and specification criteria of heading 2825, it is classified there rather than here.

Quicklime is widely used in steelmaking, flue-gas desulfurization, and soil stabilization, where its high reactivity is valued. Slaked (hydrated) lime is preferred for water and wastewater treatment, paper manufacturing, and construction mortars, where a safer, pre-reacted form is required. The choice between them often determines which subheading applies at entry.