Technology Type

The synthesis of sodium hexafluoroaluminate (Na₃AlF₆), the IUPAC name for synthetic cryolite, is an inorganic double-replacement (metathesis) reaction in which fluoride ions progressively substitute hydroxide or oxide ligands around aluminium, while sodium cations combine with the resulting [AlF₆]^3- complex to precipitate the final crystalline product. All industrial routes share the same three essential inputs: a fluorine source (hydrofluoric acid or fluorosilicic acid), an aluminium source (aluminium hydroxide, sodium aluminate, or aluminium fluoride), and a sodium source (soda ash, sodium hydroxide, or sodium chloride).

Industrial Production Routes

Route 1 — HF / Sodium Aluminate Process (Dominant — ~55–65%)

The primary commercial process combines hydrofluoric acid with aluminium hydroxide to form fluoroaluminic acid, which is then neutralised with sodium chloride or soda ash to precipitate cryolite:

Step 1 — Complex formation:

Step 2 — Ion exchange / precipitation:

Or alternatively using sodium aluminate directly:

After precipitation, the cryolite slurry undergoes solid-liquid separation, washing, and calcination in a rotary kiln to produce the final granular or milled product.

Route 2 — Fluorite (Fluorspar) / Soda Ash Process (Industrial — ~5–10%)

An alternative route—starting from fluorite (CaF₂)—involves three sequential steps:

Step 1 — Fluorite conversion to HF via sulphuric acid digestion:

Step 2 — HF reaction with Al(OH)₃ to form AlF₃:

Step 3 — Aluminium fluoride precipitated as cryolite using soda ash:

Route 3 — Aluminium Fluoride / Sodium Sulphate Process (Regional / Declining)

Aluminium fluoride reacts directly with sodium sulphate in a double-replacement reaction, used where both are available as chemical by-products:

Route 4 — Phosphate Fertiliser By-Product  / Fluorosilicic Acid Process (Growing — ~25–35%)

Fluorosilicic acid (H₂SiF₆), a waste gas scrubbing product from phosphate fertiliser plants, is converted to sodium fluorosilicate and reacted with sodium aluminate to precipitate cryolite.

Step 1 — Fluorosilicic acid reaction with sodium hydroxide:

Step 2 — Sodium fluorosilicate reaction with sodium aluminate:

Route 5 — Secondary Aluminium Dross Recovery (Emerging)

A novel eco-friendly route synthesises cryolite from secondary aluminium dross (SAD) — the oxidised waste from aluminium melting and casting operations — via alkaline leaching to recover sodium aluminate, followed by fluorination and precipitation:?

Process Summary

References

1. Wikipedia. Sodium hexafluoroaluminate (Page version: Oct 13, 2025)
2. Fluorsid (Nov 5, 2019). Synthetic Cryolite
3. Wan B., Li W., Sun W., Liu F., Chen B., Xu S., Chen W., Yi A. Synthesis of Cryolite (Na₃AlF₆) from Secondary Aluminum Dross Generated in the Aluminum Recycling Process. Materials (Basel). 2020 Sep 2;13(17):3871. DOI: 10.3390/ma13173871. PMID: 32887240; PMCID: PMC7503661
4. PMC/MDPI. Synthesis of Cryolite from Secondary Aluminum Dross
5. Ataman Chemicals. Synthetic Cryolite (Accessed Mar 5, 2026)
6. Jiaozuo Jinshengwei Fluoride Chemical Industry Company. Summary of Common Melting Point Methods for Cryolite Production at Home and Abroad (Accessed Mar 5, 2026)
7. Lavanga M., Di Lena S., Sullivan S., & Ingram A. (2000). Recovery of fluosilicic acid and fluoride bearing waters for the production of a mixture of silica and precipitated calcium fluoride usable for the production of cement. Paper presented at the IFA Technical Conference, New Orleans, Louisiana, USA, 1-4 October 2000
8. Indian Bureau of Mines (Aug 2021). Indian Minerals Yearbook 2019 (Part-III: Mineral Reviews) - Cryolite (Final Release). 58^th Edition. Government of India, Ministry of Mines. Retrieved via the Web Archive