Extractive Metallurgy Metallurgy for the Non-Metallurgists

Learning 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 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 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

Concentration 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 Concentrate 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 Pyrometallurgy-heat Hydrometallurgy-wet chemicals Electrometallurgy-electrical energy

Cutaway view of thickener. Courtesy of Environmental Equipment Div., FMC Corp.

Cutaway view of drum filter with scraper discharge. Courtesy of Filters Vernay.

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 Reduction 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 Pyrometallurgical Reduction 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 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 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 furnace shop

Electric Arc Furnace Schematic diagram of an electric arc furnace

Electroslag Remelting (ESR) Furnace Schematic illustration of a basic electroslag remelting (ESR) furnace

Vacuum Arc Remelting (VAR) Furnace Schematic diagram of a typical vacuum arc remelting (VAR) furnace

Lead Blast Furnace Lead blast furnace, open-top type

Pierce-Smith Converter Schematic of Pierce-Smith converter

Horizontal Zinc Retort

Vertical Zinc Retort Vertical (New Jersey) continuous zinc retort

Pyrometallurgical 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 Processes Leaching—a separation process using liquids Goal of Leaching: Production of a pure compound Production of a metal from impure metal or metal compounds Direct production of a metal from an ore Methods of Leaching Situ Leaching Heap Leaching Agitation Leaching

Heap Leaching Heap leaching cyanidation

Pahuca Tank Airflow Schematic of airflow in a Pachuca tank

Purification Chemical and Physical Treatment Solvent Extraction Precipitation Results in physical change Solvent Extraction Use an aqueous and organic solution Solvent removes metal ions from the aqueous solution Ion Exchange Exchanges ions between the aqueous solution and a solid

The Leaching/Electrowinning Process Simplified block diagram showing the cyclical nature of the leaching/ electrowinning process

Hall-Heroult Aluminum Cell Hall-Héroult aluminum production cell with self-baking anodes