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 and separate minerals by exploiting the differences in physical properties of the different minerals that make up an ore.
Many plants also incorporate hydrometallurgical or pyrometallurgical processes as part of an extractive metallurgical operation.
Mineral processing involves four general types of operations: Comminution or particle size reduction, Sizing or separation of particle sizes by screening or classification, Concentration by taking advantage of physical and surface chemical properties, and Dewatering or solid/liquid separation.
A number of auxiliary materials handling operations are also considered a branch of mineral processing such as storage (as in bin design), conveying, sampling, weighing, slurry transport, and pneumatic transport.
Comminution
Comminution is particle size reduction of materials. Comminution may be carried out on either dry materials or slurries. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on "run-of-mine" ore, while grinding (normally carried out after crushiing) may be conducted on dry or slurried material.
Sizing
Sizing is the general term for separation of particles according to size.
The simplest of sizing processes is screening, or passing the particles to be sized through a screen or number of screens. Screening equipment can include grizzlies, bar screens, and wire mesh screens. Screens can be static (typically the case for very coarse material), or they can incorporate mechanisms to shake or vibrate the screen.
Classification refers to sizing operations that exploits the differences in settling velocities exhibited by particles of different size. Classification equipment may include ore sorters, gas cyclones, hydrocyclones, rake classifiers, rotating trommels, or fluidized classifers. When the feed material contains particles of different densities as well as particles of different size, a degree of concentration takes place during classification becuase settling velocities are also dependent on particle density.
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 seperation
- Shaking tables, such as the wilfely table
- Spirals
- Centrifugal bowl concentrators
- Jig concentrators
- Multi gravity separators
- Nelson concentrators
Electrostatic Separation
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.
