Module 1 - Extraction of Metals From Ores (2).ppt

Extraction of metals and ores

1. Lecture 1: Extracting Metal from
Ores
MFG 120

2. Lecture Outline:
–‘History of Metallurgy’
–Extraction of Iron from Iron Ore
–Methods of Creating Steel From Iron

3. ‘History of Metallurgy’
•Copper – Discovered ~4700 BC
–Allowed for manufacture of tools from metal instead of stone
–Stone age  Copper age
•Silver – Discovered ~4000 BC
–Used for currency
•Lead – Discovered ~3500 BC
–Romans used lead to line drinking utensils, pipes, and aqueducts
•Tin – Discovered ~1750 BC
–Alloyed with copper to create bronze alloys (higher strength than copper alone)
–Copper age  Bronze Age

4. ‘History of Metallurgy’
•Iron – Discovered by chance by Scandinavians discovering puddles of
metal at the bottom of fire pits Observed that wind increased the flame temperature
–Increased temperature increased the amount of metal at the bottom of the pits
–Foundation for future Iron extraction methods
•Iron - ~1500 BC. Greeks created iron based tools and weapons.
–Discovered that quenching improved cutting edge and hardness
–Bronze Age  Iron Age
•Iron – 1000 – 500 BC. Blacksmiths developed ‘fire welding’ iron, carburization,
and improved mechanical properties from repeated hammering of iron
•Steel – 300 BC – 100 AD. Steel provides superior properties over iron.
–Today we will learn different ways steel is made from iron ore

5. ‘History of Metallurgy’
•Modern metallurgy stems from the ancient desire to fully
understand the behavior of metals
–‘Old School’ : mystery and folklore, significant trial and error
•20 – 30 lbs /day
–‘New School’ : Science based processing
•150 million tons / year

6. Steel Manufacturing Processes
•Three primary processes
Process 2024 Estimated
(USA and Global similar)
Overview
Blast Furnace ~30% Traditional Ore conversion
to metal
Electric Arc Furnace~70% Mostly scrap recycling
Direct Reduced IronNegligible Conversion using hydrogen
gas. “Green Steel”

7. Traditional Ore to Steel
Extract Ore
Blast Furnace
(Pig Iron)
Steel Furnace
(Basic Oxygen
Electric Arc)

9. Iron Ore
•Globally
–Most ore is mined in Australia, Brazil, China, and India for Hematite
and Magnetite
•Domestically
–USA derives most ores from Minnesota's Mesabi Range or
Michigan.
–Most ore in the USA is taconite and requires additional processing
due to the lower iron content. Previously ores of hematite near Lake
Superior were mined to exhaustion in the 1940s.
–Due to the proximity of the ore, the majority of traditional steel
making is performed in the Great Lakes Region (heavy, expensive to
transport)

10. Iron Ore
•Iron ore is an iron-rich mineral from which iron can be
extracted.
–Magnetite (Fe
3O
4) ~72% Iron
–Hematite (Fe2O3) ~ 70% Iron. “Direct Shipping” requires less processing
Taconite (Fe
3O
3) ~ 30% Iron. Most iron ored in the USA is Taconite
•Iron is combined with Oxygen and Sulfur and mixed
together with gravel, sand, clay, etc.
•Ore is dressed (separated from the undesired materials)
before being shipped to the steel mill.
Raw Materials VideoRaw Materials Video

11. Iron Ore Processing
Ore blasted and loaded onto
trucks and rail
Large Rocks broken up by
Crushers into smaller pieces
Roll and Ball Mills break up
pieces into fine particles
Magnetic Separators collect
Iron-Ore Particles. Improves
iron content and removes
impurities
Flotation Cells Use Air to
Separate Impurities
Particles can be Glued and
Bonded to form Pellets,
Heated to make hard and
durable

12. Blast Furnace (Pig Iron Production)
•Primary Function: Convert Iron Ore into Pig Iron
•Used in Integrated Steel Mills
•Main Ingredients
–Iron-Ore
–Coke
–Limestone
Blast FurnaceBlast Furnace

13. Blast Main Furnace Ingredients
•Iron ore
•Coke
•Lime Stone
What Exactly is Coke?
•Carbon rich material made from coal.
•Coal been heated in an inert atmosphere inside a coke oven
at 3600
o
F. Black, hard, porous material.
•The effluent (flue) gases released from the production of
coke include fuel gas, ammonia, sulfur, oils, and coal tars.
All of which are captured and sold or used in production.

14. Coke
Role in Steel Making
•Fuel source: helps produce the high
temperature for steel making
•Reducing Agent: Carbon and Iron react
Fe
2
​
O
3
​
+3CO→2Fe+3CO
2
​
•Process Support: Porous to allow gases to
rise and allow molten iron and slag to trickle
down

15. Coke Production
•Only Bituminous coal can be used for
steelmaking
•USA
–Most coal for electricity production in Wyoming
–Appalachia (West Virginia, Kentucky,
Pennsylvania) is where most steel making
(Bituminous coal) is found

16. Limestone
•Calcium Carbonate
–Common rock, mined from quarries

•Role
–Impurity removal
•limestone (CaCO
3) turns into lime (CaO) and reacts with the silica gangue to make slag, which
floats on top of the molten iron.
•Gangue is undesired material that comes with the iron ore. The slag is drawn off into a slag car.
–Product Quality
•Without the limestone, impurities would be remain making the steel brittle

17. How it works
1.Charge Furnace
–Add components (Iron Ore, Coke, Limestone) in layers
2.Hot Air Blast
–Hot (preheated) air is injected from the bottom of the
furnace and reacts with the coke to make carbon
monoxide gas.
3.Reduce to Iron
–Carbon monoxide gas reacts with the iron ore (iron
oxide) and reduces it to iron metal. This may occur in
stages
4.Form Slag
–Limestone reacts with impurities to form slag, floats on
top and can be removed
5.Collect Molten Iron (Pig Iron)
–Sinks to the bottom. Furnace is tapped (hole burned
through) and is drawn off into a “hot iron car”.
6.Hot gas effluent are routed into stoves which
heat bricks. The incoming air is heated using the
heat from the stove bricks.

18. Blast Furnace
•Depending on the global region, blast
furnaces have been around for 2,500 years
•European blast furnaces date base as early
as the 14
th
century
•But…the steel quality from blast furnaces is
poor, needed refining which was slow,
expensive, and little yield

19. Pig Iron
•Pig iron was named in colonial times. Molten iron was poured into long
troughs with openings; the casting pattern resembled a family of suckling
pigs lined along the sow
•Pig iron contains too many impurities, too much carbon (3-4%), and is
hard and brittle to be useful on its own.
•Pig Irons takes one of two paths
–Poured into long molds and cooled. Refined and sold to foundries to be melted
–Poured into ladles and directly into steel making furnaces, no cooling or
solidification
Ingots or
“pig iron”

20. Converting Pig Iron to Steel
Obsolete Processes
•Bessemer Furnace (1
st
Commercial process)
•Open Hearth Furnace
Modern Furnaces
•Basic Oxygen Furnace
•Electric Arc Furnace

21. Bessemer Converter
•Invented by Henry Bessemer around 1856.
•It’s the first commercial process for converting pig iron to
steel.
•Steel is an alloy of iron with 0.05% to 1.00% carbon.
•It separates iron from impurities and removes carbon, both of
which are necessary to make steel.
•Efficient removal of carbon and impurities was the most
difficult step in the production of steel prior to the invention
of the Bessemer converter.
•Eventually replaced by Open Hearth Furnace

22. How it works
•Molten pig iron is poured into the converter.
•Air is injected from the bottom and it reacts with carbon and
forms carbon dioxide gas, which escapes through the top
opening.
•The air also reacts with impurities and forms a slag which
floats on top of the molten iron.
•This was the first commercial process for producing steel. It
has since been superseded by more efficient processes.
•Bessemer ConverterBessemer Converter

23. Bessemer Converter
•Limitations
–Couldn’t remove phosphorus (makes steel
brittle in cold temperature) or sulfur (makes
steel difficult to process) effectively
–Eventually replaced by another process (Basic
Oxygen) which is faster and more flexible

24. Open Hearth Furnace
•Steel (pig iron and some scrap) placed in a hearth (large basin)
•Powerful flames heat the contents of the hearth until melting
•Very slow process (8+ hours) but easier to control than Bessemer
•Slag forming agents (limestone), iron oxide to remove excess carbon
from Pig Iron
•Furnace is tapped similar to a blast furnace

25. Open Hearth

26. Basic Oxygen Furnace
•The BOF is a modernized version of the Bessemer
converter.
•It uses 99% pure oxygen in place of air, which avoids
contamination from nitrogen and is more efficient.
•External heating is not required because heat is generated
when oxygen reacts with carbon and impurities in the
melt.

27. How it works
•The BOF is charged with molten pig iron (from Blast
Furnace), iron ore, steel scrap, and fluxes (such as limestone).
•The BOF process uses 99% pure oxygen flowing at supersonic speeds to apply
a pressure in excess of 100 psi to the melt surface.
•Temperature is controlled by adding scrap or iron ore, which cools off the
vessel.
•The process is completed in approximately 20 minutes and the furnace is tilted
for pouring. Alloying elements are added after the molten steel is in the ladel.
•Once the steel has been poured out, slag is poured out separately.
BOF VideoBOF Video

28. Advantages of BOF
•BOF replaced Open Hearth Furnace
–Lower Capital (start up) Cost
–Faster process (40 minutes compared to 8-10 hours)
–Uses High Purity Oxygen instead of Air (Bessemer
Furnace). Air contains Nitrogen which can cause
Steel to become brittle

29. Electric Arc Furnace (EAF)
•The EAF is the most versatile furnace. Electricity is used to heat the melt so
unlike the BOF, it can be loaded with 100% recycled steel.
•The EAF can be charged with scrap, pig iron, iron ore (or any combination).
•Primarily used for specialties steels (Tool, Stainless, etc) as the process can
better control the quality of the steel
–Electricity used for heating, easier control versus gas or liquid fuel
–Little to no oxygen is used leading to better control over oxygen content
•More expensive than BOF, but lower capital cost (easier to start up and shut
down) and continued improvements in size are leading to a more competitive
process

30. Electric Arc Furnace (EAF)
1.Load scrap steel (can use 100% scrap), pig iron, or
other iron and alloying elements if needed.
2.Graphite electrodes are lowered into the “shell” and
heat the melt.
3.Cycle time is determined by how much cold steel
has to be melted. Can be 15 – 45 minutes.
4.Tap: Pour molten steel into ladles
5.Refine (next slides)
The top of the furnace is removable to permit easy
loading

31. Electric Arc Furnace (EAF)
Advantages
•100% scrap (sustainable)
•Flexible production batches
•Faster start up
•Lower capital cost
Primarily used for
•Specialties steels (tool. Stainless, etc) as the process can better
Secondary heating systems are sometimes installed to either
preheat the charge or eliminate cold spots within the furnace.
•Recycling
•Limited access to iron ore or blast furnace
.
•EAF VideoEAF Video

32. Refining (Secondary Metallurgy)
Key Operations
1.Ladle Metallurgy
–Alloying elements added
–Different powders are injected into the molten steel to control chemistry, add
alloying elements, and control inclusion geometry.
2.Gas Injection
–Argon bubbled through to remove dissolved gases or homogenize composition
3.Deoxidation
–Chemicals added (similar to limestone) to form slag and remove impurities
4.Vacuum Treatment
–Degas using vacuum to remove dissolved gases such as hydrogen, oxygen, and
nitrogen

33. Steel Product Making
•Two primary methods for molten steel  production
Feature Ingot Casting Continuous Casting
Process
Molten steel poured into
individual molds
Molten steel poured into a
continuous mold and solidified as
a long strand
Output Shape Individual blocks (ingots) Long slabs, blooms, or billets
Efficiency Low – one ingot at a time, slower
High – continuous, faster
production
Cooling Slower, uneven Faster, more uniform
Material Waste Higher – more trimming required
Lower – near-net shape reduces
waste
Modern Use
Mostly specialty steels, small
batches
Standard in most modern steel
plants
Cost Higher per ton Lower per ton
Steel Quality Can have more internal defectsCleaner, more uniform properties

34. Traditional Steelmaking
(Ingots)
•After refinement, material is poured (cast) into large Ingots
of steel
•Ingot processing is expensive, time-consuming, and may
require re-heating for further processing to make them into
a desired shape (i.e. rolled to a desired thickness) 
•Because of how metal solidifies (discussed in detail next
module), multiple quality issues can arise from ingot making
•Today, ingots are mostly phased out in favor of another
process: Continuous Casting

35. Continuous Casting
•After refinement, liquid metal is poured into a basin called a
tundish
•Metal is distributed and fed into a flowing mold. 
•More ladles replenish the molten steel
•The outside of the metal is cooled for solidification and
rolled into a desired shape
•Further processing (cutting slabs or moving to rolling mills
for thickness reduction) may occur immediately
•Many benefits including considerable energy savings,
improved yield, and shorter cycle times

37. Billets, Blooms, & Slabs
•After refining, the ladle is moved to the continuous caster and the
melt is poured into the tundish to make semi-finished material.”
•After a secondary process, all commercial shapes (sheet, strip,
bar, plate, pipe, tube, I-beam, etc) can be made.
–PLAY VIDEO #2PLAY VIDEO #2
Bloom
6” or more per
side
Billet
Less than 6”
per side
Slab
Rectangular

38. The end of an era in the US…
•The U.S. steel industry was slow to adopt new
technology, such as replacing open hearth
furnaces with BOF.
•Legislation originally aimed at protecting
domestic steel producers ultimately caused them
to be not competitive and trailing behind foreign
sources in both quality and cost.
•This forced the domestic steel industry to change
drastically, including the bankruptcy of Bethlehem
steel, which was an American icon.

39. Mini Mills in the US
•The affordability of the EAF and its versatility gave rise to the “mini mill”.
•Mini mills use electric arc furnaces (EAFs) exclusively, which allows them
to start and stop production at the turn of a switch and have better control of
their process.
•The advantages of mini mills over integrated mills are:
–They can switch production easily to follow market trends
–They have better control of quality
–They have significantly lower startup costs than an integrated mill
–They can be located closer to their customers
•The initial cost to start up a mini mill is significantly less than an integrated
mill of the same production capacity.
•PLAY VIDEO #1PLAY VIDEO #1
•PLAY VIDEO #2PLAY VIDEO #2

41. Map of Steel Making

42. Steel Consumption by Industry