MATERIALS ENGINEERING 10: ENGINEERING MATERIALS

Lecture 5: Metallic Materials I: Basic Concepts, Mineral Processing, & Metal Extraction

OBJECTIVES

Describe important properties of metals

Explain the process used for extracting metals from ores

THE BASIC MATERIAL CLASSIFICATIONS

COMPOSITES ELECTRONIC

MATERIALS

METALS

METALS

METALS Good thermal and electrical

conductors

Strong yet deformable

Not transparent

Lustrous

Do not easily break

Malleable

Ductile

High-density

Ductility of Metals

Deformation under tensile stress

cup and cone failure

Malleability of Metals Deformation under compressive stress

A gold nugget of 5 mm in diameter can be expanded through hammering into a gold foil of about 0.5 square meter.

Toughness

Electrical Conductivity of Metals

Thermal Conductivity of Metals

So where do metals come from?

Short answer: from the EARTH.

Long answer: by mining raw ore from the earth and converting this to raw metal, which is then processed to refined metal.

Metal Sources

NATURAL RECYCLED

VALUABLE

MINERAL

GANGUE

• Valuable minerals – mixture of minerals , one or more of which can be economically exploited to become a source or supply of a particular metal • Gangue – minerals of no economic value

MAGNETITE

(Fe3O4) HEMATITE

(Fe2O3)

LIMONITE

(Fe2O3•H2

O)

CHALCOPYRITE

(CuFeS2)

BORNITE

(FeS•2CU2S•

CuS)

BAUXITE

(Al2O3•H2

O)

GALENA

(PbS)

ARGENTITE

(Ag2S)

IRON COPPER

ALUMINUM LEAD SILVER

Thinking Part

Think of some advantages of using recycled metal over raw ore in metal production.

For all these advantages, why do you think recycled metal is secondary to raw ore?

Thinking Part

Advantages:

involves fewer and simpler processing operations

requires less total energy during recovery

produces less pollution during the process

Disadvantage: difficulty in collection as well as sorting of scrap

Metal

Energy Expended

on Production

from Ore (primary)

Energy Expended

on Recovery from Scrap (secondary)

Net Energy Savings on Recycling

Magnesium 372 10 362

Aluminum 253 13 340

Nickel 150 16 134

Copper 116 19 97

Zinc 68 19 49

Steel 33 14 19

Lead 28 10 18

Of course, we cannot use this ore in its raw form.

They have to undergo the process of MINERAL PROCESSING.

MINERAL PROCESSING

COMMINUTION

SIZING

CONCENTRATION

DEWATERING

• liberation of valuable minerals from the ores by crushing and grinding, and their separation by physical methods

1. Comminution Crushing of ore to smaller sizes necessary for mechanical

separation and metallurgical treatment

Why?

to increase the surface area available for chemical reaction

CRUSHING GRINDING

Crushing – blocks to coarse (Jaw Crushers) Grinding – coarse to fine (Roll Crushers)

2. Sizing Separation of fractions into component sizes

SCREENING/SIEVING CLASSIFICATION

usually done in between comminution steps to ensure particle size

Separation of materials which depends on the settling velocity of

particles in a fluid (1mm to 50 microns)

3. Concentration Separation and collection of valuable minerals

in bulk. GRAVITY SEPARATOR

FLOTATION

ELECTROSTATIC

MAGNETIC

3. Concentration Gravity Concentration

Collection of valuable minerals wherein specific gravity and in some cases, sizes are the basis for effecting concentration (concentrate, fine particles, gangue tailings)

Electrostatic Concentration

Separation carried out by utilizing forces acting on charged or polarized particles in an electric field

Flotation

Separation is accomplished as the mineral-laden bubbles rise to the surface and leave behind minerals or ore particles which have not responded to the treatment

Magnetic Separation

Magnetic materials are separated from the gangue due to the action of the applied magnetic field on the drum

4. Dewatering

Removal of water from solids

Objectives:

• Decrease pulp weight to reduce handling and shipping cost • Adjust the characteristics of the process streams so that they are suitable for subsequent treatments • Necessary to be able to recover and recycle water within the plant and prevent contamination of freshwater resources

4. Dewatering

THICKENING FILTERING

Thickening Allows a dilute suspension of fine

solids in a liquid to settle in a

tank, until a clear liquid layer is at

the top of thicker mud layer

Filtering Done by removing solid particles

from the liquid by passing the

fluid through a filtering medium

on which the solids build up

Once we have our ore refined to the highest possible purity, we will now extract the metal from the ore.

Most of the time, ore = chemical compound.

Therefore, we NEED a CHEMICAL process to extract our metal!

METAL EXTRACTION

PYROMETALLURGY

HYDROMETALLURGY

ELECTROMETALLURGY

• chemical processing of a concentrate

Pyrometallurgy

High-temperature, non-aqueous reactions

Uses thermodynamic data to predict whether a reaction proceeds

Same data is used to predict effect of changing temperature

Pyrometallurgy

separation melting smelting

reducing a metallic ore to a crude metal

Matte solutions of various sulfides (usually of copper, iron and nickel)

Slag less dense (non-valuable constituent)

Hydrometallurgy

Production of metallic materials/ compounds from ores/scrap at a specific temperature range: (T < 300°C, P< 300 psi)

Desired metals are dissolved into aqueous medium (leachant), purified then recovered.

Leaching

Solution Purification

and Concentration

Metal Recovery/ Winning

1. Leaching

Use of an aqueous solvent/ lixiviant in ore dissolution

a. Concentration Leaching – desired metal is dissolved (e.g. dissolution of gold)

4Au + 8KCN + O2 + 2H2O 4KAu(CN)2 + 4KOH

b. Separation Leaching – undesirable mineral constituent is removed or dissolved; residue is the valuable product (e.g. leaching of ilmenite)

FeTiO3 + 2HCl TiO2 + FeCl2(aq) + H2O

2. Solution Purification and Concentration removal of undesirable constituents in the

leach liquor (pregnant solution) and pre-concentration of the metal in the solution

Methods:

1. Ion Exchange – uses synthetic polymer resins designed to exchange ions for ions in solution

2. Solvent Extraction – a distributive process wherein the valuable metal is allowed to partition itself between two immiscible phases

3. Metal Winning Final recovery of metal

i. Precipitation – the formation from the solution of a solid product as the result of dilution or addition of a reagent to the solution

ii. Electrolytic Deposition – uses electrons for the reduction of metal ions

Electrometallurgy Utilizes electrons for reduction of metal ions

Uses reactivity series for:

Metal recovery from solution – ELECTROWINNING

Metal purification – ELECTROREFINING

Application of metallic coating - ELECTROPLATING

Electrowinning electrolytic process in which cathodic

reduction is used to recover the sought metal from the electrolyte derived from a leaching process.

Electrorefining involves dissolution of the impure metal

(anode) producing metal ions in solution. Metal ions in solution are conducted through an electrolyte and recombine with electrons in the cathode to produce a purified metal.

Electroplating process that uses

electric current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode.

Thank you for listening!