How zinc is made

Zinc boils off in a smelting furnace, so the biggest share is dissolved in acid and plated out by electricity instead.

stations: 6
things upstream: 5
raw sources: 4
steps from the ground: 2

The short version

Zinc is made from sphalerite, a zinc sulfide. The ore is concentrated by flotation, roasted into zinc oxide, and dissolved in sulfuric acid. After the solution is purified with zinc dust, an electric current plates pure zinc onto aluminum sheets, and the metal is melted and cast into ingots.

Float the zinc sulfide

Ore is crushed and floated to give a zinc concentrate. About 95 percent of new zinc comes from sulfide deposits, where sphalerite is nearly always mixed with sulfides of copper, lead and iron.

Goes in
Zinc ore
Roast it to oxide

In a roaster, hot air turns the sulfide into impure zinc oxide called calcine. About 90 percent of the zinc ends up as oxide, and roughly 10 percent reacts with iron to form zinc ferrite. The sulfur dioxide given off is captured and made into sulfuric acid.

Goes in
Air
Leach it in acid

The calcine is washed first in a weak acid solution, and then in strong sulfuric acid, to pull out all the zinc. Some of the acid comes from the roaster's own sulfur dioxide.

Goes in
Sulfuric acid
Purify the solution

Zinc dust and steam knock copper, cadmium, cobalt and nickel out of the liquid. The solution must be very pure, or the cell will make hydrogen gas rather than zinc.
Plate it out electrically

An electric current passes through the solution in a hall of cells, and zinc deposits on aluminum sheets used as cathodes, while oxygen forms at the anodes. The cells stay at 30 to 35 °C, and the sulfuric acid they make is returned to the leach tanks.

30 to 35 °C
Melt and cast ingots

Sheets of zinc are stripped from the cathodes, melted and cast into ingots, ready for galvanizing plants and brass makers.

End of the lineZinc Next it goes into sunscreen, hearing aid, aa battery and 20 more.

Worth repeating

A zinc plant partly feeds itself: roasting gives off sulfur dioxide that becomes the sulfuric acid which dissolves the roasted ore, and the plating cells make more acid to send back.
Zinc is the fourth most common metal in use, after iron, aluminum and copper.
Over 30 percent of zinc comes from recycling.