Pumping Hydrofluoric Acid

Hydrofluoric acid is a colourless fluid with a strong acrid or pungent odour. 

It is perhaps best known as an acid which can dissolve glass and certainly many metals, organic and inorganic polymers. 

Hydrofluoric acid sits as one of the most dangerous acids due its unique poisoning effect affecting the body calcium balance. Direct contact to the skin of just a palm-sized area can be fatal.

In the fracking and mining industry, hydrofluoric acid is highly controversial due to the residual effects on the land and introduction to ecosystems.

• The predominant use of hydrofluoric acid is as a precursor to flourine-based compounds used in products such as ptfe coatings, refrigerants and pharmaceuticals.
• In the petrochemical industry, hydrofluoric acid is used as an alkylation catalyst in the production of fuel additives and to increase extraction yields by injecting solutions by dissolving rock to improve conduit flow and access deeper deposits.
• Hydrofluoric acid is used to etch and prepare semiconductors, silicon wafers, metals and glass.
• Found in rust and stain removal products.
• Used in uranium and mineral refining both industrial and in laboratory environments. 

The key pumping considerations for hydrofluoric acid is its toxicity and chemical compatibility.

Hydrofluoric acid is extremely dangerous and any direct contact with skin or eyes can be catastrophic. The acid quickly penetrates the skin and affects the nervous system so onset of any pain or even knowing the specific fluid has made contact is delayed. 

As the acid affects the calcium metabolism and system toxicity as it circulates throughout the body, it can quickly cause cardiac arrest, organ failure and eventually death in hours.

Should a release to atmosphere event occur, the acid can fume and cause a hazardous background vapour which can attack human tissue and the respiratory system.

It is quite clear that the containment of the acid should be first and foremost in the minds any plant manager.

A suitable recommendation for a leak-free solution is to install a mag drive centrifugal pump. A mag drive pump eliminates the risk of leakage as there are no wearable mechanical seals around the pump shaft which are at inherent risk of failing. The mag drive pump instead uses an o-ring sealing system for a hermetically sealed unit which is 100% leak-free. 

Fitted with a lining of ETFE, a Verdermag U series mag drive pump combines this sealing system and is chemically resistant. A metallic pump may be used such as Hastelloy C-2000/G-30 however many metals are subject to severe corrosion and even more advanced alloys will suffer minor corrosion. Providing the pump is chemically resistant, it will 100% contain the fluid.

An alternative leak-free pumping solution is to use an air operated double diaphragm pump (AODD) fitted with a fluid barrier and diaphragm rupture detection. 

A double diaphragm pump also uses an o-ring sealing system to contain the fluid. The double diaphragm pump does feature a wearable part in contact with the flow path; the diaphragms themselves. All diaphragms will eventually fail and must therefore be checked in regular servicing. 

It is recommended fitting the pump with a barrier protection fluid - A thin chamber of fluid which sits between an extra diaphragm so in the event of a rupture the fluid sends a signal to the operator indicating there is the danger of a leak, however the fluid is contained in the first instant. A spill-pot can also be installed on the exhaust system of the AODD pumps. For absolute piece of mind, the AODD pump can be fitted inside a fuming cabinet.

It is strongly recommended to avoid silicon-based materials, aluminium, titanium, glass linings, and natural rubber.

Suitable materials include pure virgin polypropylene, PVDF, PTFE, Kalrez and where the acid is of mild concentrated certain grades of stainless steel may be acceptable, however these may be subject to corrosion which will affect the tolerances of a pump.

Using an AODD pump allows the handling of abrasive particles such as those found in etching and pickling. The pump can also run dry and self-prime making it a very robust solution when transferring from containers.

The AODD pump may also be used a simple dosing pump when fitted with a stroke counter. AODD pumps are available as a complete non-metallic build for chemical resistance.