EXTRACTION OF IRON

            The following raw materials are involved in manufacturing of iron:

ØIron ores (magnetite, hematite) – iron oxides with earth impurities;

ØCoke, which is both reducing agent and fuel, providing heat for melting the metal and slag.

ØCoke is produced from coking coals by heating them away from air.

ØLimestone – calcium silicate fluxes, forming a fluid slag for removal gangue from the ore.

ØIron is produced in a blast furnace, schematically shown in the picture. 

Blast furnace:-

ØIt the shaft-type furnace consisting of a steel shell lined with refractory bricks.

ØThe top of the furnace is equipped with the bell-like or other        system, providing correct charging and distribution of the raw   materials (ore, coke, limestone). 

ØAir heated to 2200°F (1200°C) is blown through the tuyeres at the bottom.

ØOxigencontaining in air reacts with the coke, producing carbon monoxide:

Ø2C + O2= 2CO

ØHot gases pass up through the descending materials, causing reduction of the iron oxides to iron according to the follwing reactions:

Ø3Fe2O3 + CO = 2Fe3O4 + CO2

ØFe3O4 + CO = 3FeO + CO2

ØFeO + CO = Fe + CO2

ØIron in form of a spongy mass moves down and its temperature reaches the melting point at the bottom regions of the furnace where it melts and accumulates.

ØThe gangue, ash and other fractions of ore and coke are mixed by fluxes, formig slag which is capable to absorb sulphure and other impurities.

ØThe furnace is periodically tapped andthe melt (pig iron) is poured into ladles, which are transferred to steel making furnaces.

ØPig iron usually contains 3-4% of carbon, 2-4% of silicon, 1-2% of manganese and 1-1.2% of phosphorous.

METALLURGY

                                                                  IRON MAKING
INTRODUCTION:-
          1. metallurgy:-
                          •The science that deals with procedures used in       extracting metals from their ores, purifying, alloying and fabrication   of metals, and creating useful objects from metals.

                      •The field of metallurgy may be divided into process metallurgy (production metallurgy, extractive metallurgy) and physical metallurgy. In this system metal processing is considered to be a part of process metallurgy and the mechanical behavior of metals a part of physical metallurgy.

Process metallurgy,

ØThe science and technology used in the production of metals, employs some of the same unit operations and unit processes as chemical engineering. 

ØThese operations and processes are carried out with ores, concentrates, scrap metals, fuels, fluxes, slags, solvents, and electrolytes.

ØDifferent metals require different combinations of operations and processes, but typically the production of a metal involves two major steps.The first is the production of an impure metal from ore minerals, commonly oxides or sulfides, and the second is the refining of the reduced impure metal, for example, by selective oxidation of impurities or by electrolysis.

•Extractive metallurgy

Øis the study of the processes used in the separation and concentration (benefaction) of raw materials.

ØIn extractive metallurgy, benefication is any process which removes the gangue minerals from ore to produce a higher grade product (concentrate), and a waste stream (tailings).

ØThe field is an applied science, covering all aspects of the physical and chemical processes used to produce mineral-containing and metallic materials, sometimes for direct use as a finished product, but more often in a form that requires further physical processing which is generally the subject of physical metallurgy, ceramics, and other disciplines within the broad field of materials science.

•Physical metallurgy

 investigates the effects of composition and treatment on the structure of metals and the relations of the structure to the properties of metals.

•Physical metallurgy is also concerned with the engineering applications of scientific principles to the fabrication, mechanical treatment, heat treatment, and service behavior of metals.

ELECTROMETALLURGY

                         •Electrometallurgy involves metallurgical processes that take place in some form of electrolytic cell.

•The most common types of electrometallurgical processes are electrowinning and electro-refining.

•Electrowinning is an electrolysis process used to recover metals in aqueous solution, usually as the result of an ore having undergone one or more hydrometallurgical processes.

•The metal of interest is plated onto the cathode, while the anode is an inert electrical conductor. Electro-refining is used to dissolve an impure metallic anode (typically from a smelting process) and produce a high purity cathode.

•Fused salt electrolysis is another electrometallurgical process whereby the valuable metal has been dissolved into a molten salt which acts as the electrolyte, and the valuable metal collects on the cathode of the cell.

•The fused salt electrolysis process is conducted at temperatures sufficient to keep both the electrolyte and the metal being produced in the molten state. The scope of electrometallurgy has significant overlap with the areas of hydrometallurgy and (in the case of fused salt electrolysis) pyrometallurgy. Additionally, electrochemical phenomena play a considerable role in many mineral processing and hydrometallurgical processes.

Annealing

Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the critical temperature, maintaining a suitable temperature, and then cooling. Annealing is used to induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by substantially heating the material (generally until glowing) for a while and allowing it to cool. Unlike ferrous metals—which must be cooled slowly to anneal—copper, silver and brass can be cooled slowly in air or quickly by quenching in water. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming.

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