Here’s a report by Iowa State on lime sludge (lime from water treatment), sponsored by Iowa Dept of Transportation. It’s clearly not investigating from the perspective of what is best for agriculture. However, pg 22 eludes to what contaminants are in the lime sludge. Says, lime water treatment removes 100% of lead and cadmium, and of course many other things….

Clearly, the point of lime water treatment is to remove contaminants that aren’t good for humans. Chances are the contaminants that aren’t good for humans aren’t good for the soil either.

If the lime sludge wasn’t contaminated, they would keep using it for filtration. They wouldn’t throw out clean calcium carbonate. It says on page 22 that lime sludge is 90% calcium carbonate and 3%-5% “other”. I would be very concerned what 3-5% “other” is. Even if it were just 3% sodium chloride, the 3% could have a bigger negative impact than the 90% of calcium carbonate if you already have high sodium chloride levels. (it’s not sodium chloride, this is just a for example).