Zinc: the roast–leach–purify–electrowin family

Zinc is recovered by the roast–leach–electrowin (RLE) route, a hybrid that starts with a pyrometallurgical roast and finishes with a hydrometallurgical tankhouse. It composes from mechanisms taught earlier, and this page assembles them — naming each and what it contributes — rather than teaching them again.

The flowsheet in one line

Roast the sulfide concentrate to an oxide calcine, leach the calcine in acid, cement the impurities out of the solution, and electrowin the zinc: roast–leach–purify–electrowin. The R-L-E acronym names the spine.

What each stage is doing

The roast is the thermal pre-treatment of topic 3.2: the zinc sulfide concentrate is roasted to a zinc oxide calcine, and the sulfur leaves as SO₂ that goes to an acid plant — the calcine-leach hybrid interface in practice. The leach is acid tank leaching, the residence-time-and-sizing mechanism of topic 4.3, dissolving the calcine in sulfuric acid (much of it recycled spent electrolyte). Purification is cementation — topic 6.3 — adding zinc dust to displace more-noble impurities such as copper, cadmium, cobalt and nickel out of the solution, because the electrolyte must be very pure before it reaches the cells. Electrowinning is topic 7.1: high-purity zinc is plated from the cleaned sulfate electrolyte.

The defining numbers

The roaster is sized by residence time on the rotary-kiln relation shared across the path — the kiln residence-time calculator below. The leach is sized by slurry residence time on the leach tank residence-time calculator. The electrowinning step reads on the zinc sulfate hub for the electrolyte property data. The cementation purification itself is read as a mechanism rather than a single committed calculation.

Where it differs from the others

Zinc shares its purification mechanism — cementation — with the Merrill-Crowe gold variant, and its electrowinning back end with copper, but it is the family that leads with a roast: the pyro-then-hydro interface is its defining feature. It uses cementation, not solvent extraction, to clean the electrolyte, which sets it apart from the SX-EW commodities.