Extraction of Metals and Purification

Vocabulary flashcards for the lecture notes on metal extraction and purification.

Metallurgy

The history of metallurgy in the Indian subcontinent dates back to 1700 BC, with mentions in early Vedic age texts and the use of the Sanskrit term Ayas (metal) in the Rig-Veda.

Iron Pillar of Delhi Composition

The Iron Pillar of Delhi is composed of [Fe(O)(OH)] and contains elements like C, Si, S, P, Mn, and Fe.

Mechanical Separation

A method of separating metals in their free elemental form, particularly unreactive elements like coinage and platinum metals. An example is separating gold (19.3 g/cm³) by panning.

Thermal Decomposition

A method involving unstable compounds breaking down into constituent elements. For example, Ag2O decomposes into 2Ag + ½O2.

Displacement

Involves displacing one element by another with a more negative Eo in the electrochemical series, such as Cu2+ + Fe -> Fe2+ + Cu.

High Temperature Chemical Reduction

Many metals are found as their oxides or sulfides and require reduction using agents like C, Al, Si, and H2. Sulfide ores are first roasted to convert them to oxides before reduction.

Mond's Process

A chemical process used for the purification of nickel, involving the formation and decomposition of nickel carbonyl [Ni(CO)4].

Kroll's Process

A chemical process used for the production of metallic titanium.

Van Arkel-deBoer's Process

Used for metallic Zr / Ti, involves thermal decomposition of metal iodides on a hot filament in vacuum to yield pure metal.

Electrolytic Reduction

A method employing electron as the strongest reducing agent on ionic materials (salts), offering pure metal but at a higher cost.

Thermodynamic Considerations in High –T Chemical Reduction

Uses Gibbs free energy change (ΔGo = − RT ln K) to determine reaction spontaneity, favoring negative ΔGo and high temperatures. Kinetics is not important as reductions are done at high temperature.

Ellingham Diagram

A graph plotting the free energy changes that occur when one gram molecule of a common reactant (O2) is used against temperature, useful for predicting the feasibility of reducing metal oxides.

Thermit Process

Also known as Sacrificial Method. Uses aluminum to reduce metal oxides. 4/3 Al + 2/3 Cr2O3 -> 4/3 Cr + 2/3 Al2O3

Oxidative refining

When impurities have more affinity to oxygen than the metal. Impurities such as C, Si, P, and Mn, can be purified by blowing air through the molten metal in Bessimer Convertor

Blast Furnace

A high-temperature furnace used for smelting ores and refining metals.

Roasting

A process of heating a metal ore or concentrate to bring about its decomposition, oxidation, or volatilization.

Flux

A substance added to the charge in a furnace to promote fluidity and to remove impurities in the form of slag.

Slag

Molten rock or other material ejected from a volcano or fissure. In metallurgy, it refers to the mass of waste material that floats on top of molten metal.

Refining

The process of purifying a metal.

Bessemer Converter

A device for converting pig iron into steel by passing a blast of air through the molten metal to oxidize the impurities.

Zone Refining

A method of refining metals based on differences in their melting points. Impurities concentrate in the first part to freeze, leaving purer metal.

Oxidation

Heating in the presence of oxygen.

Reduction

Removal of oxygen.

Ore

A chemical compound from which a metal can be economically extracted.

Alloy

A mixture of two or more metals or a metal and a nonmetal.

What is an Ore?

An ore is a naturally occurring mineral or rock from which a metal or valuable substance can be extracted economically. Ores often contain a mix of desired metals and unwanted materials known as gangue.

Define Smelting?

Smelting is a process of extracting a metal from its ore by heating beyond the melting point in the presence of a reducing agent, such as carbon or coke. This process separates the pure metal from the unwanted materials in the ore, allowing it to be collected.

What is Gangue?

Gangue refers to the valueless rock and mineral materials present in an ore deposit, which must be separated from the desired metal during extraction. Common gangue minerals include quartz, calcite, and various silicates.

Describe the Role of a Reducing Agent in Metallurgy?

In metallurgy, a reducing agent is a substance that removes oxygen from a metal oxide to yield the free metal. Common reducing agents include carbon (coke), carbon monoxide, and hydrogen.

Elaborate on the Process of Calcination?

Calcination involves heating an ore to a high temperature in