[George Pumpkin]

Hi everyone 

I have been assigned to a task where I have to measure Silica in a sample of mortar. Long story short - the protocol I have received has a part (one of the last bits) where I have to add 4.0 mL of HF (40%) to a sample + a few drops of a concentrated sulphuric acid.

I have never dealt with HF and seeking advise about safety and precautions when using HF.

Additionally, I thought of - does anyone have an idea why HF is required to be used in this case? I thought maybe I can use something else or avoid this step.

I look forward to hearing your opinions 
 

[Babcock_Hall]

Hydrofluoric acid is very toxic.  I advise extreme caution.

[marquis]

HF is one of the few acids that will dissolve silicates.  That may be
why you are using it.

A side note-if it is dissolving silicates, it may dissolve your glassware.
They make special polytetraflouroethylene beakers for HF.  And,
as you were told, it is extremely dangerous to use.

Don't use the HF, if possible.

Good luck.

[Corribus]

Unfortunately sometimes it's just unavoidable. You don't have many options to digest silica.

As others have said, it's a fairly hazardous substance and you need extra precautions beyond what you'd take to work with most mineral acids. In addition to corrosive properties, it's also quite toxic and is absorbed readily through the skin. Handle it with care. I suggest having a supply of calcium gluconate gel on hand, which is can be used in the event of a dermal exposure. You should definitely have an SOP on hand as part of your safety procedures. That said, if you have experience working with dangerous chemicals, and proper procedures in place, there is no reason you can't use this reagent safely.

All your parts, including instrument parts, need to be glass free. For ICPs and digestion equipment, there are specialized HF compatibility kits that you will need to use. This is not just to protect your equipment but to prevent contamination of your samples and give you reliable results. In fact, silica is just about everywhere and can be hard to eliminate without a good clean facility. We had to give up silica work because our lab was just too dirty and environmental background was too high, despite exhaustive attempts to eliminate it.

Speaking of which, we have done some silicate digestion in our lab (clays mostly). Our safety people have been reluctant to allow us to use this reagent (ridiculous, we're chemists trained to use dangerous chemicals, but that's how it goes I guess; our safety people get nervous around regular mineral acids as well). We have had good success using mixtures of mineral acids, phosphoric acid, and hydrofluoroboric acid, which are much safer to handle. Not saying this will work in your case, but it may be worth exploring some other possible options if you are leery of using HF. If you are using a microwave to effect your digestions, most manufacturers have applications scientists available who can help you identify potential alternative digestion procedures that don't involve HF. This is actually how we arrived at our HBF4 method.

Be aware, though, that commercial HBF4 and some other potential alternatives are not always available in any kind of ultra-trace metal purity, meaning if you are also analyzing for other elements, you may have problems with these reagents. HF is available in Optima grade.

[Arkcon]

There are a number of threads on this forum regarding hydrofluoric acid, you should try a search.  Here's one of mine, referencing some policies and procedures you can follow for safety:  http://www.chemicalforums.com/index.php?topic=56444.msg203599#msg203599

[George Pumpkin]

Guys, thank you so much for your attention and useful feed back! I will definitely look into your suggestions and now I know what options I can research. Thanks heaps!