AY Honors/Rocks & Minerals - Advanced/Answer Key

Mineral processing, otherwise known as mineral dressing, is the practice of beneficiating valuable minerals from their ores. Industrial mineral treatment processes usually combine a number of unit operations in order to liberate, concentrate and classify minerals using physical properties and processes.

Many plants will also incorporate hydrometallurgical or pyrometallurgical processes as part of an extractive metallurgical operation. Mineral processing involves manipulating particle size by crushing and grinding the ore. Combined with particle size classification unit operations, this area is often termed comminution.

Comminution

Comminution is the science of the size reduction of rock particles. Crushing and grinding processes are used in combination with classification processes.

Classification

Fine and coarse particles are separated using shaking or static screens, gas cyclones, hydrocyclones, rotating trommels or fluidized classifers.

Froth Flotation

Froth flotation is achieved when particles are separated based on their surface potential. Hydrophobic particles are recovered to the froth, whereas hydrophilic particles are discharged with the tailings stream. Some mineral particles are naturally hydrophobic, whereas others require specific reagent additions to change their surface potentials.Oxide ores, such as spodumene and tantalite can be treated using oxalic acid based collectors. Sulfide ores can be recovered using xanthate or dithiophosphate type collectors.

Solvent Extraction - Electrowinning

Solvent extraction-electrowinning (SXEW) is a process by which ore is treated with a leachant (generally acid) to dissolve ore components. The ore is generally piled on heaps, and this process is part of the heap leaching processing method. Generally, carbonate minerals such as malachite are most amenable to SX-EW heap leaching.
The leachate is collected and passed through a solvent extraction circuit where metal ions in solution are exposed to organic solvents such as turpentine or other petrochemicals, where the metal ions bind to the solvent via chelation. The solvent is then stripped of the metal via manipulation of pH, into a second acid circuit. The metal in this second circuit is sent to an electrolytic cell where metal is stripped via electrolysis onto the anode.

Gravity Concentration

Particles can be classified based on their specific gravity. Gravity concentration processes include:

• Heavy media or dense media separation
• Shaking tables, such as the wilfely table
• Spirals
• Centrifugal bowl concentrators
• Jig concentrators

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Electrostatic Separation

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Non-conducting particles maintain an electrostatic charge induced electrically, and so remain pinned to a charged drum. Conducting particles do not maintain the electrostatic charge and so fall off the drum, thus minerals such as ilmenite and rutile can be separated.

Magnetic Separation

Minerals such as magnetite and pyrrhotite are naturally magnetic, and so can be separated from non-magnetic particles using strong magnets.