Patent ID: 7615100

Claim:
A method of leaching zinc-bearing siliceous raw materials for the recovery of zinc, comprising: a) feeding a zinc-bearing siliceous raw material having a silica content of at least 15.5 wt %, based upon the weight of the zinc-bearing siliceous raw material, to a neutral leaching stage; b) decomposing easily soluble zinc compounds in said zinc-bearing siliceous raw material by contacting said zinc-bearing siliceous raw material with a neutral leaching solution to form a zinc-depleted precipitate and a zinc sulfate solution; c) separating said zinc sulfate solution from said zinc-depleted precipitate; d) subjecting said zinc sulfate solution to electrolysis to form elemental zinc; e) leaching said zinc-depleted precipitate with a stream of aqueous acid in an acidic leaching stage comprising a series of reactors that include a first reactor and a final reactor to convert silicates in said zinc-depleted precipitate to silica, comprising: (1) introducing a feedstock consisting essentially of said zinc-depleted precipitate to at least said first reactor in said series; (2) introducing the entire stream of aqueous acid into said first reactor to form a slurry with said zinc-depleted precipitate and transferring said slurry entirely from said first reactor to a next reactor in said series, until said slurry is entirely transferred to said final reactor; (3) gradually increasing the pH of each reactor from said first reactor through said final reactor, such that said pH in said final reactor is about 1.5-2; (4) removing an acid-leached slurry from said final reactor; (5) separating said acid-leached slurry into an underflow containing said silica and an overflow containing zinc sulfate and sulfuric acid; and (6) introducing said overflow directly to said neutral leaching stage such that said neutral leaching solution comprises said overflow.