Material Insights · Understanding the Material World

Hydrofluoric acid and Sulphuric acid

Hydrogen fluoride is made by heating acid-grade fluorspar with sulphuric acid, about 2.45 t of acid per tonne of HF in theory, leaving about 3.6 t of anhydrite. Fluorspar, 60% of it mined in China in 2025, is the scarce and dearer input; sulphuric acid is the bulk reagent, whose cost rose with the 2025 to 2026 sulphur spike.

Hydrofluoric acid (chemical) and Sulphuric acid (chemical): 4 relationships.

How they are linked

1. Reagent: acid digests fluorspar

Physical flow · Strong · Sulphuric acid to HF

In a heated rotary kiln, calcium fluoride in fluorspar reacts with sulphuric acid, releasing hydrogen fluoride gas and leaving calcium sulphate.

  • about 2.45 t sulphuric acid per tonne of HF, theoretical, from CaF2 + H2SO4 to CaSO4 + 2HF
  • 200 to 250°C kiln temperature, 30 to 60 minutes reaction

Plants feed the acid in slight excess, so real use is a little above the theoretical figure, and the acid is 93 to 99% pure. Because HF is the starting point for almost all fluorine chemicals, every refrigerant or fluoropolymer plant carries a sulphuric acid need behind it.

Sources: US Environmental Protection Agency; US Environmental Protection Agency; USGS

2. Anhydrite by-product

Joint production · Medium · HF output leaves calcium sulphate

The sulphate from the acid ends up as a solid residue, calcium sulphate anhydrite (fluorogypsum), in fixed proportion to HF output.

  • about 3.6 t anhydrite per tonne of HF
  • about 894,000 t fluorogypsum produced a year in the US, EPA data from the early 1990s

Each tonne of acid fed leaves its sulphate behind, so HF plants carry a disposal or sales task that scales with acid use. Some producers process the anhydrite into building materials, turning part of the waste into a saleable product.

Sources: US Environmental Protection Agency; Buss ChemTech

3. Price link: derived product

Cost and price · Strong · Both ways

Sulphuric acid is a direct reagent for HF, and both proxies sit in broad US inorganic acid price indices.

  • 0.84 monthly change correlation
  • 0.85 12-month change correlation
  • 1.33 fitted elasticity

Monthly moves correlate at 0.84 and, in the last five years, at 0.97. Much of this is likely overlapping index coverage rather than a pure cost link, so the figure overstates how closely HF contract prices follow acid.

Sources: Material Insights (World Bank, FRED, IMF data)

4. Sulphur cost into HF

Cost and price · Weak · Sulphur and acid costs raise HF cost

HF makers buy or make sulphuric acid from sulphur, so sulphur price spikes raise HF costs, though fluorspar is the dearer input per tonne of HF.

  • about $470/t acid-grade fluorspar import value, US, 2025
  • $46 to $180/t US elemental sulphur unit value, 2024 to 2025

The US sulphur unit value rose almost fourfold from 2024 to 2025, and OCP reported sulphur prices roughly tripled again in the first half of 2026. Even so, a tonne of HF needs about 1.95 t of fluorspar in theory, roughly $900 at 2025 US import values, against about $150 for the 0.8 t of sulphur behind its acid, so fluorspar supply, 60% of it mined in China in 2025, remains the main cost and risk.

Sources: US Environmental Protection Agency; USGS; USGS; Fertilizer Daily

For investors

Key learnings

  1. Fluorspar, 6.0 of 10.0 Mt mined in China in 2025, is the scarce input for HF; sulphuric acid is the bulk reagent at about 2.45 t per tonne in theory.
  2. The 2025 to 2026 sulphur spike raised acid costs for HF makers, but fluorspar, at about $470/t into the US in 2025, still costs several times more per tonne of HF.
  3. The high index correlation (0.84 monthly) partly reflects overlapping index coverage, so it is a weak trading signal.

What to track

  • Acid-grade fluorspar price: Main HF cost driver (Monthly · Argus, Fastmarkets; annual · USGS)
  • Sulphur price, Middle East FOB and Tampa: Acid cost for sulphur-burning HF plants (Monthly · Argus, CRU)
  • China fluorspar output and exports: Supply of the scarce input (Annual · USGS; monthly · China customs)

For policymakers

Key learnings

  1. A fluorochemical cluster needs a secure sulphuric acid supply as well as fluorspar, so siting near acid plants or smelters lowers risk.
  2. Anhydrite volume scales with acid use, about 3.6 t per tonne of HF; reuse in building materials reduces waste.
  3. The United States has been 100% import reliant for fluorspar since at least 2021, a reminder that countries building HF capacity, India included, face concentrated raw material supply.

What to track

  • Fluorspar import sources and volumes: Concentration risk for HF (Annual · USGS, DGCI&S)
  • Sulphuric acid availability and price: Reagent risk shared with fertiliser users (Monthly · Argus, CRU)

Sources

  1. AP-42 Section 8.7: Hydrofluoric Acid, US Environmental Protection Agency
  2. Hydrofluoric acid production: special wastes report, US Environmental Protection Agency
  3. Profitable uses for anhydrite from the production of hydrofluoric acid, Buss ChemTech
  4. Mineral Commodity Summaries 2026: Fluorspar, USGS (2026)
  5. Mineral Commodity Summaries 2026: Sulfur, USGS (2026)
  6. Price correlation, Material Insights, Material Insights (World Bank, FRED, IMF data)
  7. OCP H1 2026: sulfur costs triple as EBITDA falls 28.5%, Fertilizer Daily (2026)