Metallurgy - Practice Questions & MCQ

Have you ever wondered how do we get various metals like iron, gold, silver, and aluminum, etc, and use them for a variety of purposes? Well in this chapter (General Principle and process of Isolation of metals) you will be introduced to how do we extract metals from their ores and how do we process them for final use - Metals gave us weapons, tools, ornaments, utensils, etc. The ‘Seven metals of antiquity, are gold, copper, silver, lead, tin, iron and mercury.

To obtain a particular metal, we look for minerals. Minerals are basically naturally occurring chemical substances in the earth's crust that are obtained through mining. Out of many minerals in which a metal may be found, only a few are viable to be used as a source of that metal. Such minerals are known as ores.

Rarely, an ore contains only a desired substance. It is usually contaminated with earthly or undesired materials known as gangue.

Metallurgy is a process of extracting metals from their ores and modifying the metals as per their needs. Metallurgy usually refers to the commercial method of extracting metals as opposed to laboratory methods. It also deals with the chemical, physical, and atomic properties and structures of metals and alloys (mixture of metals).

Elements are found in mainly two states in nature, mainly Native state, and Combined State.

Native State - Elements which have low chemical reactivity generally occur in native or metallic state. E.g. - Au, Pt, noble gases, etc.

Combined State - Elements that are chemically reactive generally occurs in a combined state. E.g. - Halogen,Chalcogen etc.

Let's understand about minerals again:

The various compounds of metals that occur in the earth's crust and are obtained by mining are called minerals. In the earth crust order of abundance of elements is OSiAlFe

Ores - Minerals that are viable to be used as a source of that metal. Such minerals are known as ores. All the ores are minerals but all minerals can not be ores. 

The mineral from which a metal can be profitably and easily extracted is called an ore.

There are different types of ores present in nature. Below is the list of a few type of ores.

1. Oxide Ores - They exist in a combined state with oxygen. Examples - Bauxite (Al₂O₃.2H₂O),Hematite (Fe₂O₃), Cassiterite (SnO₂) and Cuprites (Cu₂O)
2. Carbonate Ores - They exist in a combined state with carbonates. Examples - Limestone (CaCO₃), Calamine (ZnCO₃), Siderite (FeCO₃)
3. Sulphide Ores -  They exist in a combined state with sulphides. Examples - Zinc blende (ZnS), Copper glance (Cu₂S), Galena (PbS), and Cinnabar (HgS)
4. Halide Ores - They exist in a combined state with halides. Examples - Rock Salt (NaCl), Fluorspar (CaF₂), Horn silver (AgCl)

Let's have a look at the mineral from Hematite ore

Principal Ores of Some Important Metals:

Now Let's discuss what is the principle of extractive metallurgy and what factors are looked before extracting any element.

The process of metallurgy depends upon the nature of metal to be extracted. But an ore is usually contaminated with earthly or undesired materials known as gangue. So it is required to purify metals to use them.

So let's discuss the different types of metals:

Highly Reactive metals: K, Na, Mg and Ca are few examples of highly reactive metals and they are found in the combined state in nature. These elements are extracted by electrolysis of their molten salts and the process is known as Electrometallurgy.

Moderately Reactive metals:  Cu, Fe, Al and Zn are few examples of moderately reactive metals and they are found in the combined state with oxygen or sulfide. These elements are extracted by the reduction of oxide or sulfide into metals by providing enormous heat and the process is known as Pyrometallurgy.

Low Reactive metals:  Ag and Au are examples of low reactive metals. These elements are extracted by their displacement of a more reactive metal from the aqueous solution of their salt and the process is known as Hydrometallurgy.

There are various stages of metals before it comes into pure form. Hence we need to perform certain steps to extract a particular metal. We will discuss the different processes which are required for extracting these metals.

1. Crushing and grinding: The first process in metallurgy is the crushing of ores into a fine powder. This process is known as pulverization.
2. The concentration of ores: The process of removing impurities from ore is known as a concentration of minerals or ore dressing. The concentration of ores can be done by the following methods
   • Hydraulic Washing
   • Magnetic Separation 
   • Froth Floatation Method
   • Leaching
3.  Roasting: In metallurgy, the process of heating a concentrated ore in the presence of oxygen is known as roasting. This process is applied in the case of sulfide ores.
4. Calcination: For ores containing carbonate or hydrated oxides, heating is done in the absence of air to melt the ores, and this process is known as calcination.
5. Refining: The impurities contained in the metal product of the roasting/reduction process are removed.