Extractive Extractive Metallurgy Metallurgy

Metallurgy for the Non-Metallurgists

Learning ObjectivesLearning Objectives• Upon Completion of this lesson, you will be able to:• List several methods for concentration of ores and

the methods and techniques for mineral processing • Define hydro-, pyro-, and electrometallurgy the

techniques to provide the energy necessary for extraction of metals from metallic ores

• Describe the processes of oxidation and reduction and understand that oxidation of metals is a naturally occurring process

• Outline the steps in production of pig iron and steel

Mineral ProcessingMineral Processing• Earth’s crust contains oxygen containing minerals

and sulfur containing minerals• An ore general is part of the crust that contains

valuable minerals and metals• Mineral Processing extracts the valuable minerals

from the rocks without changing them

Processing TechniquesProcessing Techniques• Crushing—breaks down the ore rock to 4-6 inch

pieces• Grinding—breaks up the crushed ore• Comminution—the process of crushing and

grinding the ore• Classification—the separation of particles

according to their settling rates in a fluid

The major types of crushers

Three basic types of crushing and grinding circuits: (a) conventional,(b) autogenous, and (c) autogenous with separate fine grinding

ConcentrationConcentration• Gravity Devices—minerals are usually denser

than the waste rock of the ore• Magnetic Devices—Iron minerals are magnetic• Electrostatic Devices—crushed ore is exposed to

an ionizing electrode• Flotation—separates wettable from non-wettable

particals

Spiral (mechanical) classifier. Courtesy of Mine and Smelter Corp.,division of Kennedy Van Saun Corp.

Denver flotation cell mechanism. Courtesy of Joy Manufacturing Co.

Dewatering of Dewatering of ConcentrateConcentrate

• First the concentrate is thickened• Thickened concentrate is sent to vacuum filter to

reduce moisture• The ‘cake’ then goes to a smelter• Concentrated ore goes through a chemical

process to extract the metal• Energy is used to extract the metal

o Pyrometallurgy-heato Hydrometallurgy-wet chemicalso Electrometallurgy-electrical energy

Cutaway view of thickener. Courtesy of Environmental EquipmentDiv., FMC Corp.

Cutaway view of drum filter with scraper discharge. Courtesy of FiltersVernay.

Extraction of copper from a low-grade ore

Extraction of aluminum from bauxite ore

Flow diagram for production of 900 kg (one ton, 2000 lb) of pig iron (when molten, “hot metal”) and further processing to steel

Oxidation and Oxidation and ReductionReduction

• Chemical processes involve reactions between mineral constituents and the environment that surrounds the mineral

• Oxidation involves the reaction between the metallic elements and oxygen (ex. Rusting of steel)

• Oxidation reactions release heat• Oxidation refers to a loss of electrons from the

metal• Oxidation is an increase in valence because of the

loss of electrons• Metal oxide is reduced to a metal when it regains

its electrons

Oxidizing and reducing processes

Preparation for Preparation for Pyrometallurgical Pyrometallurgical

ReductionReduction• Drying—heating or vacuum system• Calcination—high temperature operation• Roasting—heating to just below the melting point

of the ores• Sintering—variations of roasting

Pyrometallurgical Pyrometallurgical Reduction Reduction

• Pyrometallurgical equation: MX + R + heat = M + Rx

• Reverberatory Furnaces—rectangular with an arched roof (figure 11)

• Blast Furnaces—good for oxides that are not highly reactive

• Iron Blast Furnace (figure 12)

Schematic views of copper matte smelting reverberatory furnace

Schematic illustration of an iron blast furnace, showing temperatures and chemical reactions

Iron and SteelmakingIron and Steelmaking• Concentrated ore, coke, limestone and other solid

materials are loaded in the top of the furnace• These materials are called the “burden”• Burden meets air as it moved down furnace• Carbon burns, producing heat and CO• Burden becomes molten as it reaches the hearth• Slag is removed and the metal hardens• Steel is Iron combined with less than 2% carbon• Pig iron is normally the product of the blast furnace—

pig iron is iron with greater than 2% carbon• An Electric Arc furnace is also used to make steel

(figure 14)

Basic oxygen furnaceBasic oxygen furnace

Basic oxygen furnace shop

Electric Arc FurnaceElectric Arc Furnace

Schematic diagram of an electric arc furnace

Electroslag Remelting (ESR) Electroslag Remelting (ESR)

Furnace Furnace

Schematic illustration of a basic electroslag remelting (ESR) furnace

Vacuum Arc Remelting (VAR) Vacuum Arc Remelting (VAR)

FurnaceFurnace

Schematic diagram of a typical vacuum arc remelting (VAR) furnace

Lead Blast FurnaceLead Blast Furnace

Lead blast furnace, open-top type

Pierce-Smith ConverterPierce-Smith Converter

Schematic of Pierce-Smith converter

Horizontal Zinc RetortHorizontal Zinc Retort

Horizontal zinc retort

Vertical Zinc RetortVertical Zinc Retort

Vertical (New Jersey) continuous zinc retort

Pyrometallurgical RefiningPyrometallurgical Refining• Trying to remove impurities• Refining with Gaseous Reagents (oxygen is an

example of a gaseous reagent)• Passing oxygen through molten pig iron removes

some of the carbon• Chlorine is a gaseous reagent for refining

Hydrometallurgical Hydrometallurgical ProcessesProcesses

• Leaching—a separation process using liquids• Goal of Leaching:

o Production of a pure compound o Production of a metal from impure metal or metal

compounds o Direct production of a metal from an ore

• Methods of Leachingo Situ Leachingo Heap Leachingo Agitation Leaching

Heap LeachingHeap Leaching

Heap leaching cyanidation

Pahuca Tank AirflowPahuca Tank Airflow

Schematic of airflow in a Pachuca tank

PurificationPurification• Chemical and Physical Treatment

o Precipitationo Results in physical change

• Solvent Extractiono Use an aqueous and organic solutiono Solvent removes metal ions from the aqueous solution

• Ion Exchangeo Exchanges ions between the aqueous solution and a

solid

The Leaching/Electrowinning The Leaching/Electrowinning

ProcessProcess

Simplified block diagram showing the cyclical nature of the leaching/electrowinning process

Hall-Heroult Aluminum CellHall-Heroult Aluminum Cell

Hall-Héroult aluminum production cell with self-baking anodes