Hexafluorosilicic acid

Hexafluorosilicic acid (CAS 16961-83-4), also known as fluorosilicic acid, is a strong inorganic acid supplied primarily as an aqueous solution. It is produced as a byproduct of phosphate fertilizer manufacturing. This chemical serves as a cost-effective source of fluoride and silicon across several industrial sectors. In municipal water treatment, it is the most commonly used chemical for drinking water fluoridation.

The acid is dosed to regulated concentration targets to ensure safety and efficacy. The construction and concrete industry uses it to harden and densify cementitious surfaces by reacting with calcium compounds. This reaction forms insoluble silicates that reduce porosity and improve wear resistance. In metal surface treatment, it functions as an etchant and adhesion promoter for preparing various substrates.

It is frequently used prior to coating or plating operations to ensure quality. Mining operations use it in ore processing and as a pH-regulating agent in leaching circuits for mineral extraction. Fluorosilicic acid is supplied as an aqueous solution, with 20–25% and 23% w/w concentrations being the most commercially standard. These concentrations are ideal for water treatment applications.

Higher-concentration solutions up to approximately 35% are available for industrial uses. Technical grade is the predominant market specification for most large-scale manufacturing and processing needs. Product quality is typically referenced against water treatment authority standards or regional regulatory requirements. This ensures the material meets the necessary safety profiles for public infrastructure.