Mineral Processing Separation

• Separation


  The word conveys different meanings in different situations
• Types of separation operations in Mineral Beneficiation Plants


  • Separation of ore particles according to their size
  • Separation of ore particles according to a property where valuable mineral particles are different from gangue mineral particles in that property
  • Separation of ore particles from the mixture of solids and fluids
• Separation of ore particles according to their size

  1. Screening

  2. Sizing Classification

  3. Centrifugal Sizing
• Separation of ore particles according to a property where valuable mineral particles are different from gangue mineral particles in that property

  1. Ore Sorting by hand and by mechanical means

  2. Sorting Classification

  3. Gravity Separation or Concentration

  4. Heavy Liquid Separation

  5. Heavy Medium Separation

  6. Jigging

  7. Spiraling

  8. Tabling

  9. Centrifugal Separation

  10. Flotation

  11. Magnetic Separation

  12. Electrical Separation
• Separation of ore particles from the mixture of solids and fluids

  1. Dewatering by screening

  2. Thickening

  3. Filtration

  4. Drying
• The ore particles separated by the first type of operations are fed to the second type of operations which are the actual beneficiation operations
• Separation of ore particles according to their size by the first type of operations is needed because each beneficiation operation in the second type is suitable for a particular size range of particles
• Pneumatic or dry beneficiation


  Beneficiation done by the medium of air, the products are directly sent for further processing
• Wet beneficiation


  Beneficiation done by the medium of water, the products contain water and are sent to the third type of operations to remove the water and to make them suitable for further processing
• Classification, Gravity separation and Thickening are based on the settling of solid particles in a fluid medium
• The basic principles of settling are the same in Classification, Gravity separation and Thickening even though the conditions maintained in each operation are different
• Density


  The mass of the particle per unit volume
• Specific gravity


  The ratio of the density of the particle to the density of water
• Density, together with the size and the shape of the particles, has an important role in all beneficiation operations, particularly in Gravity Concentration operations
• Determination of density of an ore

  1. Wash, dry and weigh the density bottle with stopper

  2. Thoroughly dry the ore sample

  3. Add 5–10 grams of ore sample to the bottle and reweigh

  4. Fill the bottle with a liquid of known density

  5. Insert the stopper, allow the liquid to fall out of the bottle, wipe off excess liquid and weigh the bottle

  6. Remove ore and liquid from the bottle and fill the bottle with liquid alone and repeat the previous step
• Pulp


  The mixture of water and solid particles
• Suspension


  When the solid particles are held up in the water, the pulp is called suspension
• Slurry


  A mixture of fine solids (slimes) and water
• Sludge


  Thick pulp i.e., pulp with less quantity of water
• Pulp or slurry density

  The weight of the slurry per unit volume
• Fraction of solids by weight (Cw)


  The ratio of the weight of the particles to the weight of the slurry
• Fraction of solids by volume (Cv)

  The ratio of the volume of the particles to the volume of the slurry
• Dilution ratio


  The ratio of the weight of the water to the weight of the solids in the slurry
• Sedimentation is the act of the settling of solid particles in a fluid medium under the force of gravity
• Gravity force, buoyant force, and drag force are the three forces acting on a particle falling under gravity in a viscous fluid
• When the acceleration is zero, the particle attains the terminal velocity
• The expression for terminal velocity is applicable for fine particles of less than 50 microns in size, and is also applicable, with small deviations, up to 100 microns
• As the size of the particle increases, settling velocity increases
• At high velocities, the main resistance is due to the displacement of fluid by the particle and is known as form resistance
• Viscous resistance


  1. Fluid in contact with body moves with it

  2. Fluid short distance away is motionless

  3. Zone of intense shear in fluid around descending particle
• Viscous resistance


  Resistance to motion due to shear forces or viscosity of the fluid
• Stokes assumed resistance is due to viscous resistance and deduced equation 12.1.4
• Equation 12.1.5 is applicable for fine particles less than 50 microns, and up to 100 microns with small deviations
• As particle size increases, settling velocity increases
• Turbulent resistance


  Main resistance due to displacement of fluid by particle at high velocities
• Newton assumed resistance is entirely due to turbulent resistance and deduced equation 12.1.6
• Equation 12.1.7 is applicable for particles more than 2 mm (2000 microns)
• Terminal velocity is quickly reached as acceleration decreases rapidly
• Terminal velocity


  • Function of size and specific gravity (density) of particle
  • Larger diameter particle has higher terminal velocity
  • Heavier particle has higher terminal velocity
  • Irregular shaped particle depends on shape
• Coarser, heavier and rounder particles settle faster than finer, lighter and more angular particles