Lime (calcium oxide or hydroxide) is produced by calcining limestone and is used in steelmaking, water treatment, and flue-gas desulfurization, among other applications. Gypsum (calcium sulfate dihydrate) is either mined or recovered as a byproduct of flue-gas desulfurization and is primarily used to manufacture wallboard. Each has distinct purity specifications, packaging requirements, and end-use markets, so sourcing strategies and HTS classifications differ substantially between the two.

Calcining limestone into lime requires significant fuel input, so regions with low energy costs can produce lime more competitively. For gypsum, synthetic gypsum recovered from power-plant scrubbers has expanded domestic supply, reducing import dependence in some regions. Importers should monitor domestic production capacity and energy price trends when evaluating the long-term competitiveness of imported lime or gypsum.