Almost all the metals are so unpretentious that they are not elementary in nature but in the form of their ores, For example, as oxides or sulfides. By using certain methods, the metals can be recovered from their ores. For example, lead is obtained from the sulphide ore leadiness in a roasting reduction process.

Sulfidic ores are also important as a raw material for sulfuric acid synthesis. Sulfur compounds, such as metal sulfates or sulfur dioxide, which can be processed very well, are also obtained from them - also by roasting processes.

Only very noble metals such as gold or silver occur in nature in metallic form. Most metals are often contained as oxides, carbonates or sulphides in the ores. Especially the heavy metals are often found as sulphide ores.

Importance

In metallurgy, the sulphide ores are roasted to obtain from them sulfur dioxide and the metal, usually as metal oxide. Sulfur dioxide is used for the synthesis of sulfuric acid and the resulting metal oxides are then reduced to the corresponding metals. Roasting is a necessary step in the production of metals, since the metals can not be obtained directly from sulphides, but from their oxides.

Roasting processes

The roasting is a preparation process of ores, where they are heated in kilns of air. The metal sulphides of less noble metals are converted into their oxides. Since many sulphide derivatives also contain traces of other elements, (As), antimony (Sb), selenium (Se) and tellurium (Te), as well as sulfur dioxide. These are also used to produce the corresponding elements from them. If precious metal salts such as, For example, silver sulfide, the pure metal (in this case, elementary silver) can be obtained directly.

Base metals can only be converted into their metal oxides. The temperature and oxygen concentration can be used to determine whether the metal sulfide is converted into sulfur dioxide and metal oxide or into the metal sulfate. If the metal sulfates are obtained in the roasting furnace, this is referred to as sulphating roasting in metallurgy . Metal sulfates have the advantage that they are almost all readily soluble in water.

Reaction course

Conversion of the sulfide of a base metal into sulfur dioxide and metal oxide:

4 FeS2 + 11 O2 ----> 2 Fe2 O3 + 8 SO2

Conversion of a noble metal sulfide into sulfur dioxide and the pure metal:

Ag2S + O2 ----> 2 Ag + SO2

Formation of a metal sulfate from the metal sulfide:

CuS + 2 O2 ----> CuSO4

Reduction processes

The metal oxides obtained can be reduced in various ways. For the large scale reduction, it is necessary that the reducing agent is readily and inexpensively available, which is why coke (carbon) or carbon monoxide formed from coke is most commonly used.
For instance, the resulting carbon monoxide serves as a reducing agent in the production of iron in the blast furnace:

2 C + O2 → 2 CO

Fe3O4 + 4 CO ----> 3 Fe + 4 CO2

Some metals, Tungsten (W) or chromium, but with carbon alloys, which is why they have to be reduced in other ways. One way to reduce such metal oxides is to use hydrogen as a reducing agent.

WO3 + 3 H2 ----> W + 3 H2O

A further possibility is the use of metallothermic processes in which base metals are used as reducing agents. These include, for example, aluminothermia:

Cr2 O3 + 2 Al ----> 2 Cr + Al2O3

Some metals are also obtained electrolytically from solutions of suitable metal salts. For example, zinc is obtained from a zinc sulfate solution by cathodic reduction.

References:

1. Extraction of Metals by Molten Salt Electrolysis: Chemical Fundamentals and Design Factors

2. Extreme extraction

3. The extraction of iron

4. Extraction of Metal Ions from Aqueous Solutions Using Imidazolium Based Ionic Liquids

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