Patent ID: 7247282

Claim:
A method for the removal of metals from their aqueous solution as metallic hydroxides and gypsum using lime precipitation, comprising introducing a lime compound and a majority of a feed solution containing nickel, iron and chrome into a first neutralization stage to form a metallic hydroxide-gypsum slurry having a pH at least 10.5, feeding the balance of the feed solution and the slurry from the first neutralization stage in its entirety to a second neutralization stage where the pH of the slurry is adjusted to at least 9.5 and a precipitate forms; after the final neutralization stage setting the precipitate in a settling stage, and recirculating the metallic hydroxide-gypsum slurry to the first neutralization stage, wherein the pH of the second neutralization stage is less than the pH of the first neutralization stage, and wherein all of the lime compound or neutralizing agent is fed to the first neutralization stage.