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I am working on recovering some lead acid batteries that have lost some of their capacity. I drained all of the sulfuric acid out and there was an awful lot of brownish red precipitate in it. My understanding was the lead sulfate was white crystals, and so I'm curious what this contaminant was?

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Lead oxides have various colors.

Likely you have a mix of all of them.

BTW, this is not the safest project -- whole communities have been poisoned recycling lead-acid batteries.

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You did something responsible with the acid (which is usually around 35% if memory serves) such as neutralize it to pH 7, right?

The best (and cheapest) way to neutralize sulfuric acid is with ash from a wood fire. Wood fire ash is mostly potassium, calcium, magnesium, manganese, sodium, phosphorous, and carbon. So combined with sulfuric acid you get sulfates of all those elements, such as magnesium sulfate and potassium sulfate. All of which are essentially fertilizers. But whatever you do, please make sure your H2SO4 is properly neutralized when you dispose of it.

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