Extractive metallurgy of iron

 

The following raw materials are involved in manufacturing iron:

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

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

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

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

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

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

The 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).

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

Oxigen containing in air reacts with the coke, producing carbon monoxide:

2C + O₂= 2CO

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

3Fe₂O₃ + CO = 2Fe₃O₄ + CO₂

Fe₃O₄ + CO = 3FeO + CO₂

FeO + CO = Fe + CO₂

Iron 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.

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

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

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

2003 EMPA POWDER METALLURGY

METAL AND METALLURGY

PHYSICAL METALLURGY

POWDER METALLURGY

Extractive Metallurgy of Copper

Beneficiation and extractive metallurgy of copper ores comprises several steps that have for objectives concentrate and extract the copper present in the ore. The methods to be used vary with the mining operation and depend on the ore characteristics and economical aspects. Thus, initially is common to have the sizing and classification stage which employs crushing, screening, grinding, and sorting operations. In a second step can be required a concentration which can be done by froth flotation, ion exchange, solvent extraction, and precipitation. The next step usually involves pyrometallurgical processes, and finally an electrolytical process that let to obtain metallic copper.

The minerals employed in the copper extraction are usually sulphides that content iron and other impurities with economical interest or not such as arsenic, antimony, lead, bismuth, gold, silver, and nickel. The gangue is usually quartz. Two fundamental methods are used: dry and wet route. The first is the most important and treats concentrates with not less than 24% copper. The second route is the hydrometallurgical option and usually treats ores with less than 2% copper.

With the first route, the copper is concentrate from 0.5 to 1 %Cu until 24 to 30% Cu. In this part is very important to eliminate no useful material. Once the concentrate is obtained, will be sent to a pyrometallurgical process where the concentrate is partially roasted in order to eliminate sulphur, and later is smelted to produce a mate that contains all the material in liquid state. In this part, there is an unproductive material called slag. The latter one is formed from the gangue and iron oxide formed during the roasting, and left a product, the mate (Cu2S, nFeS). This product needs to be oxidized in order to obtain an impure copper. For this operation is used the remanent iron and for several reaction will be obtained a copper no pure.

The copper obtained in the last step needs to be improved in grade and quality. The improving can be done in two steps, the first steps involves a pyrometallurgical process where the metal is introduced into a furnace at the temperature of 1100 ^oC, then is produced an oxidant reaction which forms cuprous oxide and some impurities are liberated by air addition. Once the impurities are eliminated as a slag, is required to reduce the copper to the called blister copper (99% Cu). The second step is to purify electrolytically the impure metal by an acid solution of copper sulphate. Thus, the final product is obtained in cathodes which has a purity of 99.999% Cu. The remanent impurities go to the electrolytic sludge.

The second route is a hydrometallurgical option that is done by acid leaching and metal precipitation. The leaching process can be done in tanks, heaps, vats, or dumps. The election depends strongly of the type of copper mineral present in the ore body. The leaching agent is usually sulfuric acid. The solution obtained is always low in copper (approximately 1 g/l). The metallic copper can be precipitated from the solution by scrap iron. Other possibility is to improve the copper content in the solution by solvent extraction. In this case, the solution is treated electrolytically in an acid bath, and the copper is recovered as cathodes of high purity which are called copper electrowon.

Copper metallurgy

The economic production of pure copper metal, suitable for fabrication and use, from copper ores containing as little as 0.5% Cu. Over 90% of the consumption of primary copper in the Western world is produced from ores containing sulfide minerals (chalcopyrite, CuFeS₂; chalcocite, Cu₂S; and bornite, Cu₅FeS₄) that can be economically treated only by pyrometallurgical processes. See also Pyrometallurgy, nonferrous.
In the main processes used in the production of copper from sulfide ores, the mined ore (0.5–2.0% Cu) is finely ground, and then concentrated by flotation to form copper concentrates containing 20–30% Cu. The concentrates are then smelted at high temperatures (about 2280°F or 1250°C) to form a molten mixture of copper and iron sulfides called matte. The molten matte is converted to blister copper (about 99% Cu) by oxidizing the remaining iron and sulfur. After removing the residual sulfur and oxygen in an anode furnace, copper anodes are cast and then refined electrolytically to produce high-purity cathode copper (99.99% Cu), which is suitable for most uses. See also Ore dressing.
Smelting and converting a typical copper concentrate generates over 0.50 ton SO₂ per ton concentrate (0.50 metric ton SO₂ per metric ton concentrate), and the resulting SO₂ emissions must be controlled to meet local environmental standards. This is generally achieved by converting the SO₂ to sulfuric acid in a contact acid plant, as long as the SO₂concentration exceeds 4% and a viable market for acid exists. See also Sulfur.
Electrorefining is used to remove the remaining impurities in the anode copper (principally As, Bi, Ni, Pb, Sb, and Se) and produce a pure cathode copper (99.99+% Cu). Also, many copper ores contain appreciable amounts of precious metals (Ag, Au, Pt, and so on), which are concentrated into the anode copper during smelting and are recovered as valuable by-products in electrorefining. The impure anodes are suspended alternately with pure copper cathodes in tanks through which an electrolyte of copper sulfate and free sulfuric acid is continuously circulated. When direct current is applied, the copper in the anodes is electrochemically dissolved and then plated as pure copper on the cathodes. Some of the anode impurities, such as arsenic and nickel, are less noble than copper and dissolve in the electrolyte, but they do not plate out at the cathode as long as their concentrations are controlled. The other impurities, such as silver, lead, and selenium, are virtually insoluble in the electrolyte and fall as slimes to the bottom of the tank. These slimes are recovered and processed for eventual recovery of selenium and the precious-metal values. See also Electrochemical process; Electrometallurgy.
Oxidized copper ores are more effectively treated by hydrometallurgical processes. The ore is crushed, ground if necessary, and leached with dilute sulfuric acid, either by percolation through heaps of ore or by agitation in tanks. Copper is recovered from the resulting solution by either cementation or solvent extraction-electrowinning. In cementation, copper is precipitated by contact with scrap iron to form an impure cement copper, which is smelted, then refined. Solvent extraction-electrowinning has become the preferred process. In solvent extraction special organic reagents are used to selectively extract copper from solution. The resulting copper-containing organic phase is then stripped to give a pure and more concentrated aqueous copper solution for electrowinning. Electrowinning is similar to electrorefining except that an inert anode is used and more energy is required. Although electrowon cathode copper is generally not as pure as electrorefined copper, it is still suitable for many applications. See also Copper; Hydrometallurgy; Solvent extraction.

The Metallurgy of Copper Wire

Introduction
Copper is the preferred and predominant choice in the electrical industry because of its
high conductivity, both electrical and thermal. In order to obtain the required
properties, unalloyed high purity copper is almost always used. This article discusses
the rationale for this choice and it pays particular attention to the underlying
metallurgical principles. It is intended to serve as a technical discussion of pertinent
developments spanning the past several decades in the copper wire industry.
Conductor Requirements
Considerable progress has been made in recent years to explain the electronic nature
of the noble metals, i.e., copper, silver, and gold. These elements exhibit high
conductivity because their conduction electrons show relatively little resistance to
movement under an electric field. Copper in particular is an excellent conductor
because outermost electrons have a large mean free path (about 100 atomic
spacings) between collisions. The electrical resistivity is inversely related to this mean
free path.
Several electrically conductive metals are lighter than copper, but since they would
require larger cross-sections to carry the same current, are unacceptable if limited
space is a major requirement (e.g., in small electron motors). Consequently, aluminum
is used mainly when excessive weight could become a problem. Copper possesses
the best characteristics from commercial applications, in as much as silver must be
dismissed because of its prohibitively high cost.
Applications
Copper is one of the few metals that finds most widespread use in the pure form, rather
than as an alloy. There are approximately four dozen different wrought alloys that
contain a minimum copper content of 99.3 weight percent (and therefore designated as
“coppers”), albeit only a handful are used industrially as electrical conductors. The
most widely used of these dilute alloys is known as electrolytic tough pitch (ETP)
copper, which consists of extremely high purity metal that has been alloyed with
oxygen in the range of 100 to 650 ppm. ETP copper is not recommended for use in
hydrogen environments due to its susceptibility to hydrogen embrittlement when
exposed to those temperatures. Under these environmental environments, either
oxygen-free electronic (OFE) grades of copper should be used. Silver bearing copper

ZINC EXTRACTION PROCESSES

ZINC EXTRACTION PROCESSES

The most important raw material for production of Zinc is Zinc Sulphide (ZnS) ore commonly known as Sphalerite. Next in the importance are Zinc Carbonates (Calamine/Smithsonite) and Zinc Silicate. Most of the zinc production worldwide originates from sulphide ores.

The principal processes by which zinc is extracted from its ores can be categorised under pyro-metallurgical processes and hydro-metallurgical processes.

A. Pyrometallurgical Processes:

i) Horizontal Retort Process

ii) Vertical Retort Process

iii) Electro Thermal Process

iv) Imperial Smelting Process

B. Hydrometallurgical Processes:

i) Roast Leach Electrowin Process

ii) Pressure Leaching Process

USES OF ZINC METAL

ZINC METALLURGY

Zinc Consumption: 
First-use and End-use( World Scenario)

Firstuse

Items	Percentage
Galvanizing	48
Brass	18
Zinc base Alloy	15
Chemicals	8
Semi-Manufacturers	7
Others	4

Enduse

Items	Percentage
Construction	48
Transport	23
Machinery	10
Consumer-Durables	10
Infrastucture	9

Zinc Consumption: 
First-use ( Indian Scenario)

Items	Percentage
Galvanizing	70
Brass & Alloys	10
Dry cell	10
Diecasting	5
Chemicals	5

METAL OF ZINC BASIC DATA

ATOMIC NUMBER 30 ATOMIC WEIGHT 65.37 DENSITY(AT 25°C) 7140 kg/m3 MELTING POINT 419.5°C (692.7 K) BOILING POINT(760 mm Hg 907°C(1180 K) MODULUS OF ELASTICITY 7x104 MN/m2 SPECIFIC HEAT (20°C) 0.382 kJ/kg.K LATENT HEAT OF FUSION(419.5°C) 100.9 kJ/kg LATENT HEAT OF VAPORIZATION(906°C) 1.782MJ/kg HEAT CAPACITY   Solid Cp = 22.40 + 10.5 x 10-3 TJmol-1(298 - 692.7 K) Liquid Cp = 31.40 Jmol-1 Gas Cp = 20.80 Jmol-1 LINEAR COEFFICIENT OF THERMAL EXPANSION (polycrystalline 20-250°C) 39.7 µm/m.K VOLUME COEFFICIENT OF THERMAL EXPANSION(20-400°C) 0.89 x 10 -6/K THERMAL CONDUCTIVITY : solid (18°C) 113W/m.K ELECTRICAL RESISTIVITY(polycrystalline at 20° C) 5.9mVm STANDARD ELECTRODE POTENTIAL(against H2 electrode) - 0.762 V

PROPERTIES OF ZINC

ATOMIC NUMBER	30
ATOMIC WEIGHT	65.37
DENSITY(AT 25°C)	7140 kg/m3
MELTING POINT	419.5°C (692.7 K)
BOILING POINT(760 mm Hg	907°C(1180 K)
MODULUS OF ELASTICITY	7x104 MN/m2
SPECIFIC HEAT (20°C)	0.382 kJ/kg.K
LATENT HEAT OF FUSION(419.5°C)	100.9 kJ/kg
LATENT HEAT OF VAPORIZATION(906°C)	1.782MJ/kg
HEAT CAPACITY
Solid	Cp = 22.40 + 10.5 x 10-3 TJmol-1(298 - 692.7 K)
Liquid	Cp = 31.40 Jmol-1
Gas	Cp = 20.80 Jmol-1
LINEAR COEFFICIENT OF THERMAL EXPANSION (polycrystalline 20-250°C)	39.7 µm/m.K
VOLUME COEFFICIENT OF THERMAL EXPANSION(20-400°C)	0.89 x 10 -6/K
THERMAL CONDUCTIVITY : solid (18°C)	113W/m.K
ELECTRICAL RESISTIVITY(polycrystalline at 20° C)	5.9mVm
STANDARD ELECTRODE POTENTIAL(against H2 electrode)	- 0.762 V

Zinc Metallurgy

INTRODUCTION

Zinc is one of the strategic non-ferrous metal next only to Aluminium and Copper. It plays a very important role in country's economy and develoment. Modern life is inconceivable without zinc. It provides the most cost-effective and environmentally efficient method of protecting iron & steel from corrosion. By protecting iron and steel against corrosion , zinc extends its life, helps saving natural resources and energy .

Besides, its use in galvanizing of iron and steel, it finds applications in :

• Die casting alloys, for automotive equipment and house hold appliances, fitting, toys, tools ,
• Brasses, 
• Dry cells, 
• Agriculture, 
• Chemicals, for tyre and rubber goods,
• Pharmaceuticals, fertilizers and cosmetics etc. 

With industrial development in India , use of zinc has increased considerably, however, specific consumption is much lower as compared to other developing countries. 
The most important raw material for the production of zinc is sulphide ore from which zinc is extracted either through pyro-metallurgical route or through hydro-metallurgical-electrowin route. At present nearly 80% of the worlds production of primary zinc is through hydrometallurgical route the balance is through pyro-metalurgical route.