HYDROFLUOROSILICIC ACID

CAS No.: 16961-83-4
EC No.: 241-034-8

Synonyms:
HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Fluorosilicic acid; fluosilic acid; hydrofluorosilicic acid; silicofluoride; silicofluoric acid; oxonium hexafluorosilanediuide; oxonium hexafluoridosilicate(2−); Hexafluorosilicic acid; Dihydrogen hexafluorosilicate; hexafluorosilicic acid; hexafluorosilicic acid; Flurosilicic acid; Hexafluorosilicic acid; HFS acid agreed in SIEF; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; hexafluorosilicic acid; Hexafluorosilic acid; Hexafluorosilicic acid; hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; hexafluorosilicic acid, own case; Hexafluorosilicic acid; Composition 12; Composition 13; hexafluorosilicic acid; hexafluorosilicic acid; ACTH; ACTH 1-39; ACTH (1-39), HUMAN; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; ADRENOCORTICOTROPIC HORMONE (1-39) (HUMAN); ADRENOCORTICOTROPIC HORMONE HUMAN; CORTICOTROPHIN; CORTICOTROPIN; CORTICOTROPIN A; CORTICOTROPIN (HUMAN); DIHYDROGEN HEXAFLUOROSILICATE; FLUOROSILIC ACID; FLUOROSILICIC ACID; FLUOSILICIC ACID; HEXAFLUOROSILICIC ACID; HEXAFLUOSILICIC ACID;  HYDROFLUOROSILICIC ACID; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOSILICIC ACID; HYDROGEN HEXAFLUOROSILICATE; HYDROSILICOFLUORIC ACID; ACTH; ACTH 1-39; Sand acid ; CORTICOTROPHIN; CORTICOTROPIN A; FLUOSILICIC ACID; FLUOROSILIC ACID; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Fluorsilicic acid; SILICOFLUORIC ACID; ACTH (1-39), HUMAN; Hexafluorosilicic acid; Fluorosilicic acid; 16961-83-4; Dihydrogen hexafluorosilicate; Silicate(2-), hexafluoro-, dihydrogen; Fluosilicic acid, 25 wt.% aqueous solution; UNII-53V4OQG6U1; hexafluorosilicon(2-); hydron; Hexafluorosilic acid; MFCD00036289; Kieselfluorwasserstoffsaure; 53V4OQG6U1; DTXSID2029741; hexakis(fluoranyl)silicon(2-); hydron; SC-47078; DB-064742; FT-0626488; A811126; Q411250; J-521443; Fluosilicic acid; Hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Acide fluorosilicique; Acide fluorosilicique [French]; Acide fluosilicique; Acide fluosilicique [French]; Acido fluosilicico; Acido fluosilicico [Italian]; Caswell No. 463; CCRIS 2296; Dihydrogen hexafluorosilicate; Dihydrogen hexafluorosilicate (2-); EC 241-034-8; EINECS 241-034-8; EPA Pesticide Chemical Code 075305; FKS; Fluorosilicic acid; Fluorosilicic acid (H2SiF6); Fluosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaeure; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaeure [German]; Hexafluorokieselsaiure; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaiure [German]; Hexafluorokiezelzuur; Hexafluorokiezelzuur [Dutch]; Hexafluorosilicic acid; Hexafluosilicic acid; HSDB 2018; Hydrofluorosilicic acid; Hydrofluosilicic acid; Hydrogen hexafluorosilicate; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hydrosilicofluoric acid; Kiezelfluorwaterstofzuur; Kiezelfluorwaterstofzuur [Dutch]; NSC 16894; Sand acid; Silicate (2-), hexafluoro-, dihydrogen; Silicofluoric acid; Silicofluoride; Silicon hexafluoride dihydride; UNII-53V4OQG6U1; Hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Silicate(2-), hexafluoro-, dihydrogen; Silicate(2-), hexafluoro-, hydrogen (1:2); Fluorosilicic acid; Fluorosilicic acid (30% or less); Fluorosilicic acid [UN1778] [Corrosive]; Hydrofluosilicic acid; UN1778; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Fluorosilicic acid; fluosilic acid; hydrofluorosilicic acid; silicofluoride; silicofluoric acid; oxonium hexafluorosilanediuide; oxonium hexafluoridosilicate(2−); Hexafluorosilicic acid; Dihydrogen hexafluorosilicate; hexafluorosilicic acid; hexafluorosilicic acid; Flurosilicic acid; Hexafluorosilicic acid; HFS acid agreed in SIEF; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; hexafluorosilicic acid; Hexafluorosilic acid; Hexafluorosilicic acid; hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; hexafluorosilicic acid, own case; Hexafluorosilicic acid; Composition 12; Composition 13; hexafluorosilicic acid; hexafluorosilicic acid; ACTH; ACTH 1-39; ACTH (1-39), HUMAN; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; ADRENOCORTICOTROPIC HORMONE (1-39) (HUMAN); ADRENOCORTICOTROPIC HORMONE HUMAN; CORTICOTROPHIN; CORTICOTROPIN; CORTICOTROPIN A; CORTICOTROPIN (HUMAN); DIHYDROGEN HEXAFLUOROSILICATE; FLUOROSILIC ACID; FLUOROSILICIC ACID; FLUOSILICIC ACID; HEXAFLUOROSILICIC ACID; HEXAFLUOSILICIC ACID;  HYDROFLUOROSILICIC ACID; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOSILICIC ACID; HYDROGEN HEXAFLUOROSILICATE; HYDROSILICOFLUORIC ACID; ACTH; ACTH 1-39; Sand acid ; CORTICOTROPHIN; CORTICOTROPIN A; FLUOSILICIC ACID; FLUOROSILIC ACID; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Fluorsilicic acid; SILICOFLUORIC ACID; ACTH (1-39), HUMAN; Hexafluorosilicic acid; Fluorosilicic acid; 16961-83-4; Dihydrogen hexafluorosilicate; Silicate(2-), hexafluoro-, dihydrogen; Fluosilicic acid, 25 wt.% aqueous solution; UNII-53V4OQG6U1; hexafluorosilicon(2-); hydron; Hexafluorosilic acid; MFCD00036289; Kieselfluorwasserstoffsaure; 53V4OQG6U1; DTXSID2029741; hexakis(fluoranyl)silicon(2-); hydron; SC-47078; DB-064742; FT-0626488; A811126; Q411250; J-521443; Fluosilicic acid; Hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Acide fluorosilicique; Acide fluorosilicique [French]; Acide fluosilicique; Acide fluosilicique [French]; Acido fluosilicico; Acido fluosilicico [Italian]; Caswell No. 463; CCRIS 2296; Dihydrogen hexafluorosilicate; Dihydrogen hexafluorosilicate (2-); EC 241-034-8; EINECS 241-034-8; EPA Pesticide Chemical Code 075305; FKS; Fluorosilicic acid; Fluorosilicic acid (H2SiF6); Fluosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaeure; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaeure [German]; Hexafluorokieselsaiure; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hexafluorokieselsaiure [German]; Hexafluorokiezelzuur; Hexafluorokiezelzuur [Dutch]; Hexafluorosilicic acid; Hexafluosilicic acid; HSDB 2018; Hydrofluorosilicic acid; Hydrofluosilicic acid; Hydrogen hexafluorosilicate; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Hydrosilicofluoric acid; Kiezelfluorwaterstofzuur; Kiezelfluorwaterstofzuur [Dutch]; NSC 16894; Sand acid; Silicate (2-), hexafluoro-, dihydrogen; Silicofluoric acid; Silicofluoride; Silicon hexafluoride dihydride; UNII-53V4OQG6U1; Hexafluorosilicic acid; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit; Silicate(2-), hexafluoro-, dihydrogen; Silicate(2-), hexafluoro-, hydrogen (1:2); Fluorosilicic acid; Fluorosilicic acid (30% or less); Fluorosilicic acid [UN1778] [Corrosive]; Hydrofluosilicic acid; UN1778; HYDROFLUOROSILICIC ACID; hydrofluorosilicic acid; HİDROFLOROSİLİK ASİT; hidroflorosilik asit

HYDROFLUOROSILICIC ACID

Abstract
Water fluoridation programs in the United States and other countries which have them use either sodium fluoride (NaF), hydrofluorosilicic acid (HFSA) or the sodium salt of that acid (NaSF), all technical grade chemicals to adjust the fluoride level in drinking water to about 0.7–1 mg/L. In this paper we estimate the comparative overall cost for U.S. society between using cheaper industrial grade HFSA as the principal fluoridating agent versus using more costly pharmaceutical grade (U.S. Pharmacopeia – USP) NaF. USP NaF is used in toothpaste. HFSA, a liquid, contains significant amounts of arsenic (As). HFSA and NaSF have been shown to leach lead (Pb) from water delivery plumbing, while NaF has been shown not to do so. The U.S. Environmental Protection Agency's (EPA) health-based drinking water standards for As and Pb are zero. Our focus was on comparing the social costs associated with the difference in numbers of cancer cases arising from As during use of HFSA as fluoridating agent versus substitution of USP grade NaF. We calculated the amount of As delivered to fluoridated water systems using each agent, and used EPA Unit Risk values for As to estimate the number of lung and bladder cancer cases associated with each. We used cost of cancer cases published by EPA to estimate cost of treating lung and bladder cancer cases. Commercial prices of HFSA and USP NaF were used to compare costs of using each to fluoridate. We then compared the total cost to our society for the use of HFSA versus USP NaF as fluoridating agent. The U.S. could save $1 billion to more than $5 billion/year by using USP NaF in place of HFSA while simultaneously mitigating the pain and suffering of citizens that result from use of the technical grade fluoridating agents. Other countries, such as Ireland, New Zealand, Canada and Australia that use technical grade fluoridating agents may realize similar benefits by making this change. Policy makers would have to confront the uneven distribution of costs and benefits across societies if this change were made.

Hexafluorosilicic acid
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"Fluorosilicate" redirects here. For Fluorosilicate glass and glass-ceramics, see Fluorosilicate glass.
Hexafluorosilicic acid
Hexafluorosilicic acid molecular structure.png
Hexafluorosilicic-acid-3D.png
Names
Preferred IUPAC name
Hexafluorosilicic acid
Systematic IUPAC name
Dihydrogen hexafluorosilicate
Other names
Fluorosilicic acid, fluosilic acid, hydrofluorosilicic acid, silicofluoride, silicofluoric acid, oxonium hexafluorosilanediuide, oxonium hexafluoridosilicate(2−)
Identifiers
CAS Number    
16961-83-4 check
3D model (JSmol)    
Interactive image
Interactive image
ChemSpider    
17215660 check
ECHA InfoCard    100.037.289 Edit this at Wikidata
EC Number    
241-034-8
PubChem CID    
21863527
RTECS number    
VV8225000
UNII    
53V4OQG6U1 check
UN number    1778
CompTox Dashboard (EPA)    
DTXSID2029741 Edit this at Wikidata
InChI[show]
SMILES[show]
Properties
Chemical formula    F6H2Si
Molar mass    144.091 g·mol−1
Appearance    transparent, colorless, fuming liquid
Odor    sour, pungent
Density    1.22 g/cm3 (25% soln.)
1.38 g/cm3 (35% soln.)
1.46 g/cm3 (61% soln.)
Melting point    ca. 19 °C (66 °F; 292 K) (60–70% solution)
< −30 °C (−22 °F; 243 K) (35% solution) 
Boiling point    108.5 °C (227.3 °F; 381.6 K) (decomposes)
Solubility in water    miscible
Refractive index (nD)    1.3465
Structure
Molecular shape    Octahedral SiF62−
Hazards
Safety data sheet    External MSDS
GHS pictograms    GHS05: Corrosive
GHS Signal word    Danger
GHS hazard statements    H314
GHS precautionary statements    P260, P264, P280, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)    
NFPA 704 four-colored diamond
030
Flash point    Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)    430 mg/kg (oral, rat)
Related compounds
Other cations    Ammonium hexafluorosilicate
Sodium fluorosilicate

Related compounds    Hexafluorophosphoric acid
Fluoroboric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Hexafluorosilicic acid is an inorganic compound with the chemical formula H
2SiF
6 also written as (H
3O)
2[SiF
6]. It is a colorless liquid mostly encountered as diluted aqueous solution, from there, the second chemical notation also proposed. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is produced naturally on a large scale in volcanoes.[1][2] It is manufactured as a coproduct in the production of phosphate fertilizers. The resulting hexafluorosilicic acid is almost exclusively consumed as a precursor to aluminum trifluoride and synthetic cryolite, which are used in aluminium processing. Salts derived from hexafluorosilicic acid are called hexafluorosilicates.

Contents
1    Structure
2    Production and principal reactions
3    Uses
3.1    Niche applications
4    Natural salts
5    Safety
6    See also
7    References
Structure
Hexafluorosilicic acid is generally assumed to consist of oxonium ions charge balanced by hexafluorosilicate dianions as well as water. In aqueous solution, the hydronium cation (H3O+) is traditionally equated with a solvated proton, and as such, the formula for this compound is often written as H
2SiF
6. Extending that metaphor, the isolated compound is then written as H
2SiF
6·2H
2O, or (H
3O)
2SiF
6.The situation is similar to that for chloroplatinic acid, fluoroboric acid, and hexafluorophosphoric acid. Hexafluorosilicate is an octahedral anion; the Si–F bond distances are 1.71 Å.[3] Hexafluorosilicic acid is only available commercially as solution.[4]

Production and principal reactions
The commodity chemical hydrogen fluoride is produced from fluorite by treatment with sulfuric acid.[5] As a by-product, approximately 50 kg of (H3O)2SiF6 is produced per tonne of HF owing to reactions involving silica-containing mineral impurities. (H3O)2SiF6 is also produced as a by-product from the production of phosphoric acid from apatite and fluorapatite. Again, some of the HF in turn reacts with silicate minerals, which are an unavoidable constituent of the mineral feedstock, to give silicon tetrafluoride. Thus formed, the silicon tetrafluoride reacts further with HF. The net process can be described as:[6]

SiO
2 + 6 HF → SiF2−
6 + 2 H
3O+
Hexafluorosilicic acid can also be produced by treating silicon tetrafluoride with hydrofluoric acid.

In water, hexafluorosilicic acid readily hydrolyzes to hydrofluoric acid and various forms of amorphous and hydrated silica ("SiO2"). At the concentration usually used for water fluoridation, 99% hydrolysis occurs and the pH drops. The rate of hydrolysis increases with pH. At the pH of drinking water, the degree of hydrolysis is essentially 100%.[7]

H2SiF6 + 2 H2O → 6 HF + "SiO2"
Neutralization of solutions of hexafluorosilicic acid with alkali metal bases produces the corresponding alkali metal fluorosilicate salts:

(H3O)2SiF6 + 2 NaOH → Na2SiF6 + 4 H2O
The resulting salt Na2SiF6 is mainly used in water fluoridation. Related ammonium and barium salts are produced similarly for other applications.

Near neutral pH, hexafluorosilicate salts hydrolyze rapidly according to this equation:[8]

SiF2−
6 + 2 H2O → 6 F− + SiO2 + 4 H+
Uses
The majority of the hexafluorosilicic acid is converted to aluminium fluoride and synthetic cryolite.[6] These materials are central to the conversion of aluminium ore into aluminium metal. The conversion to aluminium trifluoride is described as:

H2SiF6 + Al2O3 → 2 AlF3 + SiO2 + H2O
Hexafluorosilicic acid is also converted to a variety of useful hexafluorosilicate salts. The potassium salt, Potassium fluorosilicate, is used in the production of porcelains, the magnesium salt for hardened concretes and as an insecticide, and the barium salts for phosphors.

Hexafluorosilicic acid is also used as an electrolyte in the Betts electrolytic process for refining lead.

Hexafluorosilicic acid (identified as hydrofluorosilicic acid on the label) along with oxalic acid are the active ingredients used in Iron Out rust-removing cleaning products, which are essentially varieties of laundry sour.

Niche applications
H2SiF6 is a specialized reagent in organic synthesis for cleaving Si–O bonds of silyl ethers. It is more reactive for this purpose than HF. It reacts faster with t-butyldimethysilyl (TBDMS) ethers than triisopropylsilyl (TIPS) ethers.[9]

Hexafluorosilicic acid and the salts are used as wood preservation agents.[10]

Natural salts
Some rare minerals, encountered either within volcanic or coal-fire fumaroles, are salts of the hexafluorosilicic acid. Examples include ammonium hexafluorosilicate that naturally occurs as two polymorphs: cryptohalite and bararite.[11][12][13]

Safety
Hexafluorosilicic acid can release hydrogen fluoride when evaporated, so it has similar risks. Inhalation of the vapors may cause lung edema. Like hydrogen fluoride, it attacks glass and stoneware.[14] The LD50 value of hexafluorosilicic acid is 430 mg/kg.[15]

Hydrofluorosilicic acid, or H2SiF6, is a challenging chemical because it has properties that pose danger and specific storage concerns. With its common use in water treatment, it’s important that you’re aware of the risks that storing this chemical improperly carries.
Let’s take a closer look at the nature of hydrofluorosilicic acid, its applications, the specific storage concerns and solutions available, and safety considerations when working with this complicated chemical.

What is Hydrofluorosilicic Acid?
Hydrofluorosilicic acid is a chemical often known by other names like fluorosilicic acid, fluosilicic acid, silicofluoride, and silicofluoric acid and is often abbreviated to HSA or FSA. It is a colorless chemical that is created when you take phosphoric rock from the ground and convert it to soluble fertilizer. In this process, two very toxic fluoride gases are released with hydrogen fluoride being one of them; the other is silicon tetrafluoride. The condensation from this hydrogen fluoride is collected, then scrubbed with water. In the past, the phosphate industry used to let these two gases vent freely into the atmosphere. This, however, caused severe environmental damage to downwind communities, including widespread cattle poisonings, scorched vegetation, and various human health complaints. 

Eventually, as a result of both litigation and regulation, the phosphate industry installed “wet scrubbers” to trap the fluoride gases. The liquid collected in these scrubbers (hydrofluorosilicic acid) is entered into storage tanks and shipped to water departments throughout the country. Depending on the manufacturer, impurities (arsenic, lead) can exist and are often not removed. While safeguards exist for regulating water safety, the contaminants can be a factor over time for your storage container which we will address below. The acceptable levels of contaminants are governed by NSF International – ANSI/NSF 60-2002, and American Water Works Association- AWWA B703-00.

How is Hydrofluorosilicic Acid Used
The most commonly discussed application for this chemical is water fluoridation at water treatment plants. This process helps prevent periodontal problems and is added to drinking water. Another common chemical added to drinking water for the same purpose is sodium fluoride, but it can be five times as expensive. Hydrofluorosilicic acid can, however, be more dangerous to store, so it’s important to have a reliable and safe storage solution.

Another use of FSA is to etch glass; the extremely corrosive nature of the chemical is effective for this desired application. We’ll get into storage options in the next section but for this reason, glass or fiberglass tanks are not good storage solutions when eating glass is “not” the intent. 

Hydrofluorosilicic acid is also used in the production of the salts that can contain porcelains

Storage Concerns and Solutions
Hydrofluorosilicic acid is easily the most dangerous chemical at your local water treatment plant. It can release hydrogen fluoride when it evaporates, is corrosive, and can damage the lungs if breathed in, making it especially dangerous for plant employees if stored incorrectly.

FSA also interacts negatively with metals to produce a flammable hydrogen gas, meaning a stainless steel chemical storage tank is not a viable option. It attacks glass, eats through concrete, and poses a serious storage concern. Before rotomolded plastic became a viable storage option, fiberglass tanks, constructed with a resin-rich veil, was often used for storage. The resin-rich veil, however, is often only ⅛” of chemical barrier protection from the incompatible fiberglass (chopped glass) structure itself. Since FSA eats glass, it’s actually incredibly dangerous to store FSA in something that only provides a minimal barrier of safety from a glass-made structural support container.

In these cases, a high-density cross-linked polyethylene (XLPE) storage tank is the safest option, and it’s best to choose one with secondary containment in the event of an issue. With linear polyethylene (HDPE), unzipping (or a catastrophic tear down the side of the tank) is possible, but with XLPE, the structural integrity of the tank will endure even if compromised. An XLPE tank with secondary containment, like Poly Processing’s SAFE-Tank®, can contain the chemical as well as the outlet to the pump transition from the primary tank. Not containing your fitting, the most vulnerable part of an otherwise robust system, is like having no containment in the first place. Another option is to place the pump fitting on top of the tank where chemical can not escape if a fitting fails. This, however, requires special design in the pumping system.

With the popularity of fluoridation occurring in most American water treatment plants, a tank with NSF-61 certification (and specifically for hydrofluorosilicic acid and not just potable water) should be included from the tank manufacturer. XLPE tanks are available with this certification. Always be sure NSF61 designations are for the specific chemical tested (not just water), as NSF offers certification by exact chemical according to Maximum Allowable Levels (MAL).