General Principles & Isolation of Metals

## Common Terms

Free State

Combined State

Ore

Minerals

Gangue

Metallurgy

General Process of Metallurgy

## Metallurgy

Pyrologymetallurgy

Hydrologymetallurgy

Electrometallurgy

## Concentration

The process of removal of gangue from the ore is called concentration of ore , also known as dressing or benefaction .

### **Gravity Separation**

**Hydraulic Washing using Wilfey Table**

The powdered ore is kept on top of a slating floor of Wilfey's table . A running stream of water is placed across the table . The lighter gangue particles are carried away by the water and heavier particles settle in the wooden cleats on the table .

**Hydraulic Classifier**

A hydraulic classifier is an inverted conical vessel , filled with water . There is a tube at the top of water level . The powdered ore is then poured into the water . The gangue floats on the surface , while the mineral sinks down . The floating gangue is removed from the tube attached at the top . The or is collected at the bottom of the vessel .

### **Magnetic Separation**

The ore is placed on a magnetic roller . The mineral gets attracted to the magnet , while the gangue remains unattracted . The minerals are then directed to a vessel , and the gangue is directed to another vessel . The gangue and the minerals have different velocities due to attraction of minerals . This property is used to separate them .

### **Leaching**

Leaching is the process of extracting a soluble material from an insoluble solid by dissolving out in a suitable solvent .

## Oxidation

**Roasting**

Roasting is a process of heating ores to a high temperature in excess of air to convert the metal into volatile metal oxides from their Sulphate forms .

**Calcination**

Calcination is the process of heating of ores to a high temperature in limited air to convert the metal to volatile oxides from their carbonate forms .

## Reduction

**Pyrometallurgy**

It is a process in which the concentrated ores are reduced to form crude metals at high temperature .

Smelting is the process of extracting the impure molten metal from it's ore at a high temperature using a suitable flux and a reducing agent .

Flux is a chemical substance added to the concentrated ore during in order to remove the gangue to form easily fusible slag .

A slag is a waste product formed by concentration of a flux and gangue during the extraction of metals by smelting process

**Hydrometallurgy**

It is a process of extraction of metals by converting their ores into aqueous solutions of metal compounds and reduction of these solutions using suitable reducing agents . Mac Arthur Forest Cyanide Process , for extraction of gold and silver is an example of Hydrometallurgy .

**Elctrometallurgy**

Electrometallurgy is a process of reduction used for highly electropositive elements like Sodium , Potassium . In this method , the metal oxides are fused and electrolyzed . The metal ions are discharged at the cathode .

**Alumina Thermite process**

## Ellingham Diagram

The Ellingham Diagram is a Graph of Gibb's Energy v/s Temperature , which shows the feasibility of a reduction reaction . The Ellingham Diagram is plotted for formation of oxides , thus the reverse is applicable for removal of oxygen .

For a reaction to be spontaneous , the ΔG value should be negative . The ΔG value would become negative at a certain value . If a reaction is spontaneous at low temperature , the reverse reaction is spontaneous at high temperature . Thus , reactions at lower end of the graph (Al,Mg) need low temperatures for oxidation but high temperatures for reduction . The reactions at top of the Graph (Hg,Ag) need a low temperature for reduction .

## Refining

**Liquation** : This method is used when the Metal has a low melting point . The crude metal is heated and the molten metal is collected separately .

**Polling** : Polling is used for metals with oxide impurities . The crude metal is stirred with Green logs of wood . The heat of molten metals makes the green logs to liberate hydrocarbons which reduces the metal oxide into metal .

**Electrolytic refining** : This method is used exclusively for highly electropositive metals . The Anode is made up of rods of impure metal and the cathode is made up of pure metal . The pure metal is collected at cathode .

**Zone Refining** : In Zone refining , a single section of solid metal is heated . Thus, the impurities float on the molten metal . When the next section is heated , the previous section solidifies and the impurities try to migrate to the molten section of the metal . In this way , the impurities are collected in the last section of the metal .

**Vapour Phase Refining** : Metal is converted into its volatile an easily decomposable form .

Mond Process

**van Arkel method** : This method is used to remove oxygen and nitrogen completely . The crude metal is heated in a vessel with little iodine to foem iodide of the metal . The metal iodide is volatile .

**Chromatography** :

## Extraction of Zinc

**Ore :** Zinc Blende (ZnS)

**Concentration :**  1) gravity separation 2) magnetic separation 3) Froth Floatation

**Roasting :**

 Heating in excess air at **1200 K**

2ZnS + 3O2 ----------→ 2ZnO + 2SO2

If any ZnSO4 is formed then

2ZnSO4 ----------→ 2ZnO + 2SO2 + O2