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Author Topic: Responsible battery acid disposal  (Read 7907 times)
profp
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« on: October 25, 2010, 02:02:37 PM »

I want to refresh the acid in my forklift cells. Is it remotely feasible to dispose of the acid on a DIY basis, perhaps by neutralising it first? If not, are there recycling centres that handle it? (Our local 'tip' isn't geared up for it). If neither of these routes is feasible, I will contact a battery specialist direct, but thought it worth asking here first...
Cheers
P.
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dhaslam
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« Reply #1 on: October 25, 2010, 02:55:33 PM »

It seems that adding it to a big quantity  of  water  isn't  sufficient, I suppose it would  become concentrated again with evaporation.   

I found this with a Google search

http://www.newton.dep.anl.gov/askasci/chem00/chem00693.htm

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« Reply #2 on: October 25, 2010, 05:40:27 PM »

I guess you could decant the acid into some plastic containers and leave it at the council battery recyclers.  They do re-use the acid from dead batteries so I don't see why they wouldn't accept it in a container that just coincidentlally didn't also have the lead in it too.  Just mark it up clearly as sulphuric acid (in case you're using old milk bottles to hold it)  whistlie

Diluting the acid with more water doesn't neutralise it.  You could add an equal strength / quantity of alkalii (like common "caustic soda" crystals dissolved in water) you'd be left with a neutral salt solution.

From what I've seen of the local battery recycling bin at the tip they're pretty lax about acid safety anyhow.  I saw a bin full of lead acid batteries, most at all sorts of angles that would have meant the acid had leaked out of them and into the bin (more like the ground)  Roll Eyes

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« Reply #3 on: October 25, 2010, 08:18:01 PM »

Hmmmm,

acid + base -> 'salt' + water + energy

The amount of energy is dependent upon the nature of the acid and base,
the stronger or more concentrated the more energy released,
to the point where the 'neutralising' mixture can boil.

Battery acid is pretty concentrated,
so,
is best neutralised with a weak base/alkali,
so,
probably best to avoid caustic soda pearls.

Weak bases/alkalis likely to be found around the house:

common chalk, (even Rennies antacid tablets), (calcium carbonate CaCO3
baking soda, (sodium bicarbonate NaHCO3,
washing soda, (sodium carbonate, Na2CO3

each of these will release carbon dioxide on contact with the battery acid,
and,
this will be your indicator.

Add your chosen base/alkali slowly allowing any bubbles frothing to die down.

When further addition of base/alkali does not cause any further bubbling
you have neutralised your acid.

The resulting neutral liquid is probably best disposed of down the toilet.
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profp
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« Reply #4 on: October 26, 2010, 01:39:26 PM »

Great, just the advice I was after mespilus, will post back on the experience in due course.

P.
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knighty
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« Reply #5 on: October 26, 2010, 02:19:52 PM »

profp.... where do you plan to get the new acid from ?   is it easily available ?
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KenB
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« Reply #6 on: October 26, 2010, 02:50:12 PM »

I thought it was normal practice to "top up" fork lift cells with either distilled water, or with acid solution of the correct pH rather than disposing of the existing acid and starting again.

All flooded batteries will end up with a sludge in the base of the cell, consisting primarily of compounds of lead, antimony etc. Basically its small particles that have fallen off the plates and sunk to the bottom.

Large capacity cells often have a sludge trap in the bottom of the contained to stop this stuff circulating around the cell with the acid.

Inverting the cell to remove the existing acid is only going to disturb this sludge, as well as possibly knock off some more of the active plate material.

Unless you are going to pump the acid out of each cell, with a tube that won't disturb the sludge or the plates, I would advise against trying to replace the acid - it will probably do more harm than its worth.

Acid is not the active material in the battery, its merely a convenient way of allowing ions to move between plates.  Provided that the acid is the right pH, there's very little else that can go wrong with it.

Loss of battery capacity over time, is normally because the active lead material is being converted to lead sulphate. If the plates have started to sulphate, fresh acid is not going to make much difference. There are certain pulse charging devices which claim to reduce/reverse the effects of plate sulphation, and return the battery to it's original capacity. Some swear by these devices, but generally if a battery has knackered plates - it's knackered.

The pH will increase as the battery loses water, and this is why you top up with distilled water to restore the pH balance.


Ken

« Last Edit: October 26, 2010, 02:55:50 PM by KenB » Logged
profp
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« Reply #7 on: October 26, 2010, 03:53:31 PM »

profp.... where do you plan to get the new acid from ?   is it easily available ?

http://www.countybatteryservices.co.uk/battery-acid-electrolyte-128sg-25-litre-p-201.html  -- swift and efficient, ordered over the weekend and arrived at the quayside today.
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profp
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« Reply #8 on: October 26, 2010, 04:08:25 PM »

I thought it was normal practice to "top up" fork lift cells with either distilled water, or with acid solution of the correct pH rather than disposing of the existing acid and starting again.

The batteries were in need of significant topping up when I got them, and although I do not have a pH meter or other means of measuring the pH, I'm pretty sure that the acid is weak - small spills that I would have normally expected to have burnt holes in a cloth when mopping up, don't, for example.

Quote
Large capacity cells often have a sludge trap in the bottom of the contained to stop this stuff circulating around the cell with the acid.

Inverting the cell to remove the existing acid is only going to disturb this sludge, as well as possibly knock off some more of the active plate material.

Unless you are going to pump the acid out of each cell, with a tube that won't disturb the sludge or the plates, I would advise against trying to replace the acid - it will probably do more harm than its worth.

Acid is not the active material in the battery, its merely a convenient way of allowing ions to move between plates.  Provided that the acid is the right pH, there's very little else that can go wrong with it.

I'd thought to pump out the top 1/3 to 1/2 of the electrolyte in each cell, and then top up with fresh, and see if that improves the overall capacity. They charge nicely (bubbling quietly), and have a consistent voltage across the cells (2v-2.1v), and seem fine under light loads (2A-5A@24W), but discharge very quickly (in minutes) under heavy loads (50A+@24V). I'm happy to experiment with reconditioning the cells: they cost me very little, but it has been a major logistical exercise to transport them to the island, so it would nice to revitalise them if at all possible.

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Philip R
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« Reply #9 on: October 26, 2010, 04:38:37 PM »

I am replying as I question the logic of replacing the acid in the batteries.  
If you replace the acid in the cells because it is contaminated, then the cells themselves will probably be shot. Or if the acid electrolyte has lost specific gravity due to it combining with the lead to form lead sulphate ( during the discharge cycle), again batteries will possibly be shot.

If the cells can be recharged, the SG of the electrolyte will increase as the sulphate ions return to solution in the electrolyte. By adding premixed 1280 gravity acid to you cells you may need to adjust with demin water to get the desired SG at full charge.

When you empty your cells of electrolyte, the spongy lead negative plate will start to oxidise. The reaction is exothermic, giving out heat. Also known as negative plate burnout. Once this has occurred, recharging with a fresh acid electrolyte will probably be a bit futile.

In the past, I have dealt with several large Plante battery disposals & replacements. The acid was removed using a specialist waste disposal company using a vacuum tanker, neutralised with alkali and the salt solution disposed of at a licensed facility, very expensive. The lead was reprocessed at a lead smelter and returned to the supply chain.

Electrolyte loss by evaporation or gassing does not change the pH by very much as it is a logarithmic scale. Stronger acid, lower pH. If the acid is not contaminated or neutralised with an alkali, then its strength is meassured using its specific gravity or relative density.(In a laboratory situation, its strength or concentration would be defined as its molarity). In industry, you would purchase the stuff from the former ICI as a minimum percentage. Ours came by tanker at I believe 98%, i.e. very concentrated.(At that concentration it did not eat through metal)

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profp
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« Reply #10 on: October 26, 2010, 04:58:50 PM »

I am replying as I question the logic of replacing the acid in the batteries.  
If you replace the acid in the cells because it is contaminated, then the cells themselves will probably be shot. Or if the acid electrolyte has lost specific gravity due to it combining with the lead to form lead sulphate ( during the discharge cycle), again batteries will possibly be shot.
8< --- snip --- 8<
Quote
Electrolyte loss by evaporation or gassing does not change the pH by very much as it is a logarithmic scale. Stronger acid, lower pH. If the acid is not contaminated or neutralised with an alkali, then its strength is meassured using its specific gravity or relative density.(In a laboratory situation, its strength or concentration would be defined as its molarity). In industry, you would purchase the stuff from the former ICI as a minimum percentage. Ours came by tanker at I believe 98%, i.e. very concentrated.(At that concentration it did not eat through metal)

I was inspired by this
http://www.navitron.org.uk/forum/index.php/topic,6478.msg67370.html#msg67370

and also by another post, which I now can't find, in which someone said they had successfully revitalised a set of forklift-type batteries by flushing and refilling with acid normally used for pool treatment.

I appreciate the input about exothermic plate oxidation - if I go ahead with this, I guess I should try and keep the plates wet throughout?

The SG's of the cells are very low, so is this indicative of weak acid, just knackered cells or possibly both?

P.

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Philip R
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« Reply #11 on: October 26, 2010, 05:24:09 PM »

Give it a go, but minimise the time the plates are exposed to the atmosphere, no longer than 20 minutes. After draining out the old electrolyte, refill promptly. (We emptied our old battery cells because the cases were made of glass and they did not like being moved. A few cracked while lifting them onto the lorry). After draining the electrolyte, vapour was observed venting from the cells top up port and the -ve plates were hot to touch.

The acid you bought was not too expensive, so again give it a go. Please tell us your experience as to its success

I have read that seawater is a good buffer for dilute acid. ( In not too large quantities)!!!
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