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 o Pyrometallurgy-heat o Hydrometallurgy-wet chemicals o 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

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

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: 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 Leaching o Situ Leaching o Heap Leaching o Agitation Leaching Heap Leaching

Heap leaching cyanidation Pahuca Tank Airflow

Schematic of airflow in a Pachuca tank Purification • Chemical and Physical Treatment o Precipitation o Results in physical change • Solvent Extraction o Use an aqueous and organic solution o Solvent removes metal ions from the aqueous solution • Ion Exchange o 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