7.2 Ore identification and processing

Ore identification and processing are crucial steps in extracting valuable metals from the earth. Prospectors use geological surveys, geophysical tools, and chemical analysis to find promising deposits. Once located, ores undergo crushing, grinding, and separation to concentrate the valuable minerals.

After initial processing, ores may be roasted or treated chemically to make extraction easier. Techniques like flotation, leaching, and smelting then separate and purify the target metals. These methods allow miners to efficiently recover valuable resources from complex mineral deposits.

Ore Identification

Prospecting and Exploration Techniques

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• Prospecting involves searching for mineral deposits through geological, geophysical, and geochemical methods
• Geological surveys examine rock formations, structures, and surface features to identify potential ore-bearing areas
• Geophysical methods utilize instruments to measure physical properties of rocks (magnetic susceptibility, electrical conductivity)
• Geochemical prospecting analyzes soil and water samples for trace elements indicative of nearby ore deposits
• Remote sensing technologies (satellite imagery, aerial photography) aid in identifying large-scale geological features
• Exploratory drilling confirms the presence and extent of ore deposits discovered through prospecting

Assaying and Mineral Analysis

• Assaying determines the quantity and quality of valuable minerals in an ore sample
• Fire assay method heats ore samples with fluxes to separate precious metals (gold, silver)
• Wet chemical analysis dissolves ore samples in acids to quantify metal content
• Instrumental methods (atomic absorption spectroscopy, X-ray fluorescence) provide rapid and precise elemental analysis
• Mineralogical studies examine ore samples under microscopes to identify mineral species and textures
• Bulk sampling collects large quantities of ore for pilot-scale testing of processing methods

Ore Preparation

Size Reduction and Classification

• Crushing reduces large ore pieces to smaller fragments using jaw crushers, gyratory crushers, or cone crushers
• Grinding further reduces crushed ore to fine particles in ball mills, rod mills, or autogenous mills
• Particle size distribution affects subsequent processing efficiency and recovery rates
• Sieving separates crushed and ground ore into different size fractions using vibrating screens or trommels
• Classifiers (hydrocyclones, spiral classifiers) separate particles based on size and density in wet processing

Washing and Concentration Methods

• Washing removes clay, silt, and other impurities from ore using water sprays or log washers
• Gravity concentration separates minerals based on differences in specific gravity (jigs, sluices, shaking tables)
• Dense medium separation uses heavy liquids or suspensions to float lighter particles and sink heavier ones
• Magnetic separation removes magnetic minerals (magnetite) from non-magnetic gangue using electromagnets
• Electrostatic separation utilizes differences in electrical conductivity to separate minerals (rutile from zircon)

Ore Processing

Thermal and Chemical Pretreatment

• Roasting heats ore in the presence of air to remove volatile components and alter mineral structures
• Oxidizing roast converts sulfide minerals to oxides, facilitating subsequent leaching or smelting
• Chloridizing roast adds salt to convert metal oxides to chlorides for easier extraction
• Reduction roast uses carbon monoxide or hydrogen to convert metal oxides to more easily processed forms
• Calcination heats carbonate ores to drive off carbon dioxide and produce reactive metal oxides

Concentration and Separation Techniques

• Flotation separates valuable minerals from gangue using differences in surface properties
• Collectors adsorb onto mineral surfaces, making them hydrophobic and allowing attachment to air bubbles
• Frothers create stable bubbles to carry mineral particles to the surface of flotation cells
• Beneficiation increases the concentration of valuable minerals through physical or chemical means
• Leaching dissolves target metals from ores using acids, bases, or other chemical solutions
• Solvent extraction transfers dissolved metals from aqueous solutions to organic solvents for purification

Smelting and Refining Processes

• Smelting uses high temperatures to extract metals from their ores through chemical reduction
• Blast furnaces reduce iron ores to pig iron using coke as a reducing agent and limestone as a flux
• Reverberatory furnaces melt and refine copper concentrates in the presence of silica flux
• Flash smelting injects fine ore particles and oxygen into a hot furnace for rapid reaction and metal recovery
• Electrolytic refining purifies crude metals by dissolving them at the anode and depositing pure metal at the cathode
• Zone refining moves a molten zone along an ingot to concentrate impurities at one end, producing ultra-pure metals