[DougC]

I work for a very small company that does some acid cleaning jobs on industrial equipment.  All of the cleaning is internal of the equipment so we use a method of chemical circulation and pumps with a containment drum.  Every now and then we run into a silica problem and need to use HF to dissolve the silica scale.  What we have been doing is converting inhibited HCl to HF by adding ammonium bifluoride.  I currently use a calculation method of 5#'s ABL per 100 tons of cooling.  See my concern.  A very vague method for determining a very dangerous acid.  I am not a chemist by any means, but have had enough in HS and College to know that I'm not comfortable with the info that I have been given.

What I am trying to figure out is a simple method of converting HCl to HF.  I need to know how many pounds of ABF per gallons of HCl to convert to HF.  I hope I have given enough info for someone to offer some helpful advice.

Thanks in advance.
Doug

[Borek]

Simple stoichiometry. You must start with balanced reaction equation. Problem is a little bit tricky, as you have mass of ammonium bifluoride and volume of (probably concentrated) HCl, so you probably need acid density as well.

[DougC]

From what is on the label of the HCl drum, it appears to be 20%.  If that is indeed the case, then (through a little internet research) the density is 1.098 kg/l.  Will that help in determining a much more accurate and dependable conversion method?  Once again, all help is very much appreciated.

[Borek]

20% is 6.0 M (mol/L) - that's the most important information here.

See below - reaction, stoichiometry and volume of HCl required per 5 pounds of ABL. Done with EBAS - looks like (stoichiometrically) you need around 10.2L of acid.

Then, I am not sure what the problem is. It doesn't matter if the mixture is stoichiometric - HF is always dangerous.

[DougC]

I can't thank you enough Borek. You have been a tremendous resource.     It is refreshing to see some solid numbers and not a vague conversion "recipe".  I now know that for every 2.75 gallons of 20% HCl that is used, I will need to add 5lbs of ABF. 

The more research I have done on HF, the more I have realized just how dangerous this product is.  I knew it was bad, just didn't know it was BBBAAADDD.

Again, thank you very much for your help.  I am so glad that I stumbled into this forum.  I did a lot of searching and reading about HF and ABL in here before posting my question.  Now, I just need to become even more educated on HF and ABL to make sure that I understand each respective chemical and their abilities.

[TheBigF]

Just to add my 2cents here - HF is indeed, potentially, very dangerous - it can give very bad burns that go down to the bone before stopping - although the real problem is the intense pain associated with HF burns - which is often delayed, even by hours.

Full HF treatment kits should be available, in addition, of course, to suitable personal protection gear, and a full safety assessment for anyone using HF (in any form)

[DougC]

That HF treatment kit is a great idea.  That is something that we should have when doing any type of acid cleaning.  I'm going to make sure that one is on the next job. 

And what is the best way to raise the pH?  Dense soda ash is used, which of course has a very aggressive release of CO₂.  It's nearly impossible to neutralize in a timely manner because of the reaction.  It's a back and forth battle with the soda ash and silicone defoamer.  Sometimes we may have 40-50 gallons of 10% acid solution to neutralize.  Any suggestions on what to use?  The same goes for the neutralization of HCl too. 

BTW...Honeywell has some great info on their hfacid.com site.  Maybe some of my questions are premature as I plan to use that site as a tool to learn as much as possible about HF.

[agrobert]

And what is the best way to raise the pH?  Dense soda ash is used, which of course has a very aggressive release of CO2.  It's nearly impossible to neutralize in a timely manner because of the reaction.  It's a back and forth battle with the soda ash and silicone defoamer.  Sometimes we may have 40-50 gallons of 10% acid solution to neutralize.  Any suggestions on what to use?  The same goes for the neutralization of HCl too.

Don't you have SOPs (Standard Operating Procedures) at your work?  You should calculate  the required amount of a basic solution needed to neutralize the acid before you do anything.

[DougC]

Don't you have SOPs (Standard Operating Procedures) at your work?  You should calculate  the required amount of a basic solution needed to neutralize the acid before you do anything.

I wish we had SOPs.  And even if we did, I would question those too.  See, I have come into the company and questioned a lot of what we do.  This is something that nobody has done because the owner doesn't like to be questioned.  He likes to rule with and iron fist because it is HIS company.  He doesn't threaten/scare me because I question everything.  It is my plan to establish SOPs for doing some of these acid jobs.  It seems I'm the only one that gives a crap about personal safety and the effects these chemicals, if done incorrectly, has on the equipment.   It is amazing to me that I have found so many things that we have been doing wrong just by common sense and internet research.

For years they had been using a hydrometer to get percent ethylene glycol and had been reading it wrong.  Nobody knew that a hydrometer measured specific gravity, only that if it floated at 30 (which was actually 1.030) that they had 30% glycol.  Wrong, wrong, wrong.  I had to point out that you need a chart to convert the sg to % glycol.  Not to mention that it reads propylene different than ethylene, plus the effects of temperature.  Luckily I have talked them into using refractometers (which can measure both glycols and compensates for temp) and doing away with the hydrometer.  So maybe you can begin to see kind of what I'm up against.

Sorry, I'll step down from my soapbox now.