Zinc ores (zinc blende) and oxide, carbonate or silicate concentrates, sometimes added with zinc secondary material (such as Waeltz oxide) are usually roasted and calcined as a first step prior to leaching. The starting material for the leaching process in most instances is thus typically a calcine (oxidic material); however, this steps can be sometimes skipped, and ores/concentrates are directly leached. (See blue triangle in the process scheme).

Leaching is a traditional hydrometallurgical extraction processes used to recover metals. Leaching of the calcine is carried out in a number of successive stages using a gradually increasing strength of hot sulphuric acid (acid leaching).  The initial stages (neutral leaching) are operated at low acidity and temperature (typically pH 4–4.5 and 50 ºC) and do not yet dissolve significant amounts of iron. The leaching process is carried out in a variety of reactors using open tanks, sealed vessels and pressure vessels or a combination of them. Depending on whether zinc ferrites are present in the calcine or not, and after the first leaching stages (neutral leach coupled with a weak acid leach), the extraction yield of zinc from the feed into the leaching liquor can vary between ~ 70 % and 95 %.
Next to Zn, other metals like Cu, Cd, Co and Ni are also partly extracted. Therefore, the leaching liquor needs to pass purification steps before being fed to the cell house. The remaining ~ 5–30 % of the zinc is trapped in the leaching residue, together with insoluble iron , lead compounds and other gangue materials. In addition to the stirred tank, leaching also involves solid-liquid separation which entails the use of thickeners/clarifiers and in some instances also filters and centrifuges. Normally, vacuum or membrane filters are used for the separation of leaching products and/or iron residues for final disposal.

After-process: Several options for further treatment of this residue are available. Direct leaching: it is a process in which ZnS ores are leached without prior oxidation in a roasting furnace. To obtain a high recovery yield of zinc, the leaching is done at higher temperatures and with injection of oxygen. There are variants that are run under atmospheric pressure, as well as others under pressurised operation in autoclaves. After process steps facilitate the further use of the susbtance in metals exctraction. 

Solutions from leaching tanks or gas-cleaning washing towers may contain unleached material, steriles and insoluble sulphates, i.e. Lead- and calcium-sulphate. Separation of those solids occurs in semi-closed settlers and, further if needed, the leachate may be filtered on adapted filters. The Leaching residues zinc ore, lead contg is the intermediate used for furtehr extraction of Zn and Pb. 

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Acute toxicity - oral

Acute toxicity - inhalation

Skin corrosion / irritation

Serious eye damage / eye irritation

Germ cell mutagenicity

Carcinogenicity

Reproductive toxicity

Specific target organ toxicity - repeated (STOT-RE)

Hazardous to the aquatic environment (acute / short-term)

Hazardous to the aquatic environment (long-term)