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Author Topic: Replacing sulphuric acid for Epsom salts or Alum?  (Read 7524 times)
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« on: February 07, 2010, 01:50:04 PM »

Back on another forum some guy started posting on my thread about rejuvenating old flooded lead acid batteries by replacing the electrolyte with a solution of 1:10 Alum/water electrolyte.  A bunch of people have tried it and claimed varying degrees of "success" in being able to get batteries that have sometimes been been sitting in the weeds for years to hold a charge again...

A guy called Sepp Hasslberger has a blog on it and from there there are a load of comments from people trying it and links to more info on variations on the idea and general battery info.

Asides from what to do with the lead-rich toxic sludge you'd get from washing out old cells, I'm curious as to whether this really works. I have a bunch of old flooded batteries in various states of ruin in the garage.  Epsom salts and alum are easy and cheap to get hold of (although there seems to be a lot of debate as to what "Alum" actually is).  Some think it refers to pool conditioner, others reckon it's the stuff you get in food shops for making pickles crisp and so on ("Alum" just being a common name used in shops, like "salt").

Even if you don't fancy getting your hands dirty (dissolved!) it's an interesting read.

I suppose you could decant the stuff into coke bottles and leave it at the council battery recycling facility. As they recycle the acid and gunge from whole dead batteries, I guess they wouldn't be too upset about the same gunge turning up but minus the rest of the battery.  It's better to re-use than recycle the box and grids...

Apparently, it only works well on old batteries as the Alum electrolyte actually relies on there being PbSO4 (lead sulphate) crystals on the plates to make it work, so a new battery won't work as it hasn't got any hard sulphate crystals in it (yet).  They reckon the hard sulphate is a catalyst for the reactions.
3.58kWp & 800Ah LiFeYPO4 off-grid(ish). See 'Cobbled together PV in W.Sussex' (in "Show Us Yours")
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« Reply #1 on: February 07, 2010, 03:39:23 PM »

I think he's used the term alum incorrectly on his website. "Alum" as far as I know refers to a group of compounds containing a group one metal (lithium sodium or potassium), a group 3 metal ( eg alumimium) and sulphate ions. For example, potash alum is potassium aluminium sulphate, KAl(SO4)2.

He seems to be referring to a group of compounds called aluminosilicates rather than sulphates. As far as I was aware, this is added to the electrolyte with an acid to form the gel in the well known lead acid gel batteries.

I'm fairly certain you would still have to add an inorganic acid to the electrolyte in order for it to work as a battery, it reacts with the aluminosilicate forming silicic acid otherwise I can't quite see how the chemistry would add up.

In short though, I need to get to the lab and try it cos I don't believe his recipe would work.  stir

p.s nothing to do with this topic but after reading that you might think chemistry is as dull as me. Here's a link to prove otherwise!


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