Contamination of Lead-Acid Electrolyte

[DenzilPenberthy]

Hi All,

 I have some friends who live off-grid in the woods. I built them a nice solar system with batteries and 230V inverter a while ago. I went to see them a while ago and noticed a problem 

Due to a mix-up they've topped the batteries up with a bottle that I left there which is Sodium Bicarbonate solution to be used in case of acid spills.

The batteries are Trojan T105RE : http://www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf

They have an interesting white paper on the subject of electrolyte contamination here : http://www.trojanbattery.com/pdf/WP_EffectOfImpurities_0612.pdf

But it does not mention the effect of Sodium or Bicarbonate ions on battery performance. Does anyone have any ideas where I might find further information about how this is likely to affect the capacity and life span of the batteries?

To complicate matters, not all of the cells received the same amount of contamination.

I have access to tame chemists at work so I thought I might ask them to find the concentration of the bicarb solution and estimate how much went into each cell then ask Trojan's technical support but I wonder if anyone here has any experience of this sort of problem or any thoughts?

[macboy]

First off, IANAC (I Am Not A Chemist), but...
The small amount of sodium bicarbonate will be completely consumed and will leave you with less sulfuric acid, plus the products of the reaction: Sodium Ions, Sulfates (S0₄), Water, Carbon dioxide. I think that carbonic acid is produced but decomposed into more water and carbon dioxide. The carbon dioxide of course bubbles off, so you are left with some sodium ions not normally present, replacing some of the hydrogen (H₂+) ions. Technically you added water and water is produced in the reaction, but I don't think you have really diluted the acid; you have the same amount of Sulfates as before. You now have a mix of two acids: H₂S0₄ and a little Na₂S0₄. I have no idea what the implication of that is.

Curiously, I have seen discussion of using pure sodium sulfate as an electrolyte in lead batteries. So maybe the contamination isn't too deadly to the battery.

[SeanB]

Measure the specific gravity of the electrolyte in the cells, at a full charge, and simply use some sulphuric acid as top up to get them all the same SG.

Otherwise you can fully charge the battery, disconnect it and drain out the electrolyte and replace with the correct concentration of fresh acid. runs a risk of contaminating the plate area with sediment and shorting out cells, so you probably want to just equalise the SG of all the cells by adding acid to those low ones.

[MagicSmoker]

The sodium bicarbonate will consume some of the sulfuric acid, producing sodium sulfate and carbon dioxide. The sodium sulfate will lower the acidity, but maybe not the specific gravity (s.g. assumes the electrolyte only contains sulfuric acid and water). The end result is a lowering of Ah capacity as sulfuric acid is consumed by the plates during discharge (forming water and lead sulfate) and regenerated by charging (also reforming the lead/lead dioxide plates).

I would dump the acid down the drain (not considered hazmat - some drain openers are conc. sulfuric acid), rinse once with distilled or deionized water, then refill with fresh "battery acid solution" (usually available at "pro" auto parts stores like NAPA in the US).

[johansen]

my guess is you don't have enough sodium in the batteries to affect the amp hours or affect the specific gravity.

that said, if you can dump the electrolyte out (cap the cells when they are empty, fill with water, or purge with nitrogen or argon to prevent oxygen in the air from reacting with the negative plates)

anyhow, if you can dump the electrolyte out, pull it down to -20C you may be able to crystallize out all the sodium sulphate crystals present.

https://upload.wikimedia.org/wikipedia/commons/3/3f/Na2SO4_solubility.png
http://www.tellusb.net/index.php/tellusb/article/download/15588/17460

or just buy new acid.

[DenzilPenberthy]

Interesting replies, thanks all. I've managed to scrounge a battery hydrometer so I'll go and see if there is any variation in the SG between cells. I'll also find a way to work out how much bicarb went into each cell. If I know how many sodium ions are in there I can see if Trojan's technical support will tell me what sort of effect they are likely to have.

Cheers.

[calexanian]

if you can get them cleaned out refilling is a relative simple matter. Battery acid is available in most auto parts stores in powder form. I would dump out the cells into a bucket and neutralize the acid with any carbonate. Baking soda works well. flush out the cells with a fresh charge of relatively weak acid to recombine the remaining bicarbonate, dump that out, then refill with new acid and you should be good. Gravity tester is a must for this, and nitrile gloves. That acid is pretty strong, but not so strong it will melt your skin off, but it burns pretty bas. Goggles are a must too. In fact i recommend a hose fed type respirator if you can borrow one.

[ChunkyPastaSauce]

Don't really know what Im talking about but:

Adding baking soda 2NaHCO3 with sulfuric acid H2SO4 creates water , carbon dioxide and sodium sulfate (Na2SO4).

2NaHCO3 + H2SO4 ->  Na2SO4 + 2 H2O + 2 CO2

Na2SO4 ha been used to renew and prolong battery life.... for sometime

From the 1887 - telegraphic journal and electrical review, the sodium sulfate likely results in:

H2 + Na2SO4   ->   H2SO4 + Na2
Na2 + 2H2O    ->    2NaOH + H2
2NaOH + PbSO4   ->    Na2SO4 + Pb(OH)2  (plate sulfate conversion)
Pb(OH)2 + H2    ->    Pb + 2H2O

https://books.google.ca/books?id=PAwAAAAAMAAJ&lpg=PA94&ots=G10R7aBYr8&pg=PA94&hl=en#v=onepage&q&f=false

Further googling seems to indicate Na2SO4 is a fairly common additive for deep cycle batteries, but  usually combined with others additives (otherwise the plate connections corrode faster as well as faster self discharging of the battery)

https://books.google.com/books?id=TAi_QBsTz5UC&pg=RA3-PA617&lpg=RA3-PA617&dq=Na2SO4+lead+acid+battery+additive&source=bl&ots=1_RPSBMnqG&sig=IdU_TTXU8YJZMnAkC3j6e55p2Gs&hl=en&sa=X&ved=0CEYQ6AEwB2oVChMI-o2sjqePyQIVCOsmCh27ugQz#v=onepage&q=Na2SO4%20lead%20acid%20battery%20additive&f=false

https://books.google.com/books?id=8bMoshJhC-wC&pg=PA141&lpg=PA141&dq=Na2SO4+battery+lug+lead+acid+additive+deep+cycle+conductivity&source=bl&ots=IhcJe7b0s8&sig=J6pWIlnXO-tS6qRe5NeCa0Y9wnk&hl=en&sa=X&ved=0CCMQ6AEwAWoVChMI_IelyKmPyQIVBuImCh3UzwqR#v=onepage&q=Na2SO4%20battery%20lug%20lead%20acid%20additive%20deep%20cycle%20conductivity&f=false

Also searching Na2SO4 and "trojan battery" results in several patents, the battery maybe already designed to handle some of it already, but not a ton

So it sounds like to me that the batteries wont be immediately harmed but probably should charge, drained, and then add new electrolyte

[sarepairman2]

so thats how vitamin water is made

[BradC]

Battery acid is available in most auto parts stores in powder form.

Have you got a link for that? I can't quite get my head around how you dehydrate sulphuric acid down to a powder or what else you would use for a lead acid battery electrolyte that could be made up from powder.

[Fraser]

Interesting comments in this thread. As a side note, I tried to buy sulphuric acid from motor factors here in the UK. All refused to supply such to me. If I bought a battery, they would fill it, but they declined to sell just acid. This is apparently due to attacks on people using concentrated sulphuric acid. What is the world coming to eh ?

[BradC]

I can go to any number of chemical suppliers here and get it with no questions asked. Having a large number of pools, it's even available in pool stores as an alternative to hydrochloric acid (I have 25L in the garage of sufficient purity to use in lead acid batteries).

You know the sad thing is in the UK I can go to B&Q and by 95% sulfuric acid drain cleaner off the shelf (did it in Scotland last Christmas). The only hassle is it may not be pure enough to dilute and use for battery acid, but a damn sight stronger than battery acid and available everywhere to anyone over the age of 18.

[calexanian]

Battery acid is available in most auto parts stores in powder form.

Have you got a link for that? I can't quite get my head around how you dehydrate sulphuric acid down to a powder or what else you would use for a lead acid battery electrolyte that could be made up from powder.

I actually went looking for the stuff and could not find it. All I could find was liquid stuff. Napa used to sell a powdered battery electrolyte rejuvenator and it evidently is not on the market anymore. http://www.walmart.com/ip/PHCC-PRO-SERIES-N002209-Battery-Acid-6-Qt/40722804

[rs20]

...but a damn sight stronger than battery acid and available everywhere to anyone over the age of 18.

What state are you from, and when did you last try? Maybe I'm suspicious-looking, but I could only get battery acid from the second battery store I went to here in Sydney after quite the inquisition. Despite sulphuric acid being literally the most abundantly manufactured chemical in the world; the Australian government seems to have decided that it's useful for drug manufacture (because, you know, it's useful for all chemistry) and therefore a smart idea to crack down on it. 

[BradC]

...but a damn sight stronger than battery acid and available everywhere to anyone over the age of 18.

What state are you from, and when did you last try?

WA and a couple of weeks ago. My local "City Farmers" store has 20L tubs of sulfuric acid on the shelf, as does my local pool store. My local chemical supplier has about 40 different preparations (concentrations, volumes, so on..) on the shelf. Look up "Rowe Scientific". They are in every state and I guarantee every branch will have anything you need in the way of sulfuric acid on the shelf. You generally need an account, but if you talk nicely to the girl behind the counter you will probably get what you want on a cash sale basis. Buy some concentrated sulfuric and dilute it down yourself, or you'll probably find they have the right concentration on the shelf. I bought plenty of stuff from them before I opened an account (and I did that just so I could order on-line).

Many places won't sell you chemicals on the basis that "they can be used for drug or explosive manufacture". They are lying to you. There is a very limited number of chemicals you will have "difficulty" getting because they are on the "precursors list", but that difficulty is limited to filling in a document (and end user declaration) and giving them a copy of your license. Sulfuric acid is not on that list. They are simply not selling it to you because they can't be bothered dealing with an individual. They might not sell you HF however, but you don't really want to play with something like that anyway.

Now, having said that. Please be careful. Concentrated acids really are not to be trifled with, and "Add acid to water, just as you aught to".

(Edit). Just checked quickly. First hit on pre-mixed Battery acid is part number CB1700, 5L less than $60 and lead time of 5 days.

[calexanian]

Available here from Walmart online. Even in pansy California!

[DenzilPenberthy]

More excellent replies especially ChunkyPastaSauce's information that sodum sulphate is often deliberately added to lead acid batteries. Some very interesting links and I quite fancy having a bit more of a read about this - the benefit of having access to a university library. (I won't be buying the ebook of the Encyclopedia of Electrochemical Power Sources though - £1284.60 is a bit steep for a bloody pdf!!!)

I've sent an email to Trojan's tech support so we'll see what they say but I'm feeling a lot more optimistic about this now.