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  Chemical Processing of Minerals, Chemistry tutorial

Introduction:

The processing of minerals is a main division in the science of extractive metallurgy. The extractive metallurgy has been stated as the science and art of extracting metals from their ores. Within an ore body, the valuable minerals are surrounded by gangue and it is the main function of mineral processing, to release and concentrate such valuable minerals. Minerals can be extracted or processed either through physical or chemical methods. Though, we shall be treating the chemical processes or steps in the processing of minerals.

What is Mineral?

Minerals are the solid constituents of all rocks; igneous, sedimentary and metamorphic and takes place in crystals. The mineral can be stated as any substance which takes place naturally in the earth and is not made up from animal or vegetable matter. This could as well be stated as a natural inorganic compound having a specific chemical composition or a range of composition and a regular atomic structure to which the crystalline forms are associated.

The minerals are acknowledged to have the given physical properties that comprise:

  • Color
  • Form
  • Luster
  • Hardness
  • Cleavage
  • Fracture
  • Tenacity
  • Specific gravity

Chemical methods of processing minerals:

The minerals can be processed by some chemical methods. Here, we shall illustrate each of such steps and what they comprise.

Electrolytic Method:

This method is employed for the extraction of the highly electropositive metals such as potassium, sodium and calcium that take place as chlorides, carbonates and sulphates. In this process, metals are extracted via the passage of electric current via the ores in molten state.

The passages of electric current yields in the cation, M+ migrating to the cathode while the anion X-moves to the anode. Now what procedure do you think takes place at the cathode?  Well, at the cathode, reduction takes place in which the cation accepts electrons and is thus reduced to their corresponding metals.

For illustration, consider this:

CaCl2 → Ca2+ + Cl-

At cathode,

Ca2+ + 2e- → Ca

Heating and Roasting:

The concentrated mineral ore is heated in a controlled amount of air. The heating transforms the sulphides and carbonates ores to oxides, proceeding to the reduction of the oxides to the metal. Impurities are as well driven off at this phase. An illustration is Sphalerite (ZnS) in which the arsenic is driven off as impurity. 

2ZnS + 3O2 → 2ZnO + 2SO2

This heating as well transforms sulphide ore partially into its oxide that is often reduced to metal by further reaction with sulphide ore. For illustration, Galena (PbS)

2PbS + 3O2 → 2PbO + 2SO2

PbS + 2PbO → 3Pb + SO2

Sintering:

Sintering comprises heating the material unit for partial fusion to take place to make larger more simply handled materials before smelting.

Smelting:

This comprises the reduction of roasted sintered ores to the molten metal at a high temperature. Fluxes are added to join by the gangue to form liquid slag that floats on the surface of the molten metal. An illustration is the extraction of iron that is carried out in a blast furnace inside constructed by steel and lined with firebricks. The extraction method is summarized in the given equations.

2C + O2 → (at 1400oC) → 2CO

CaCO3 → (at 800oC) → CaO + CO2

CaO + SiO2 → (at 1000oC) → CaSiO3 (Slag formation)

Fe2O3 + 3CO → (at 600oC) → Fe + 3CO2

Refining:

There are many different kinds of refining namely electrolytic refining and zone refining.

=> Electrolytic Refining: In this, the metal of interest is purified electrolytically via making the impure metal the anode of an electrolytic cell. Copper for example is purified electrolytically through making the impure copper anode of an electrolytic cell that includes copper (ii) sulphate solution as electrolyte and a thin strip of pure copper as the cathode. By the suitable selection of voltage, pure copper is transferred from the anode to cathode. 

=> Zone Refining: This process is applied on an extremely small scale in producing metals and some non-metals of extremely high quality. It based on the principle that an impure molten metal deposits pure crystals on solidifying.

Alloying:

The alloy is a mixture or solid solution comprised of a metal and the other element. Alloying is a method in which the two metal elements are melted altogether in a precise combination to make a specific material or alloy.

Alloys are often favored over single element metals, specifically for solder performs, due to their dissimilar melting points, specific conductivity attributes or enhanced thermal expansion values. Alloying is completed in either an induction furnace or a casting operation, based on the alloy. Whenever an induction furnace is employed the alloy is poured into bars or ingest for future use. After refining a metal, the pure metal can be joined by one or more metals or even non-metals that often improve its properties. For illustration steel is stronger as compare iron, its primary element.

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