Screening and Liberation (sa book) Flashcards
an operation used for the separation of particles according to their sizes.
Screening
a batch process used
almost exclusively for test purposes
Sieving
a continuous process and
is used mainly on an industrial scale.
Screening
The material passing through the screen
aperture is called
Underflow
material retained on the
screen surface is called
Overflow
generally used for dry treatment of coarse material.
Screening
the medium containing the apertures for the passage of the undersize
material.
Screen Surface
Rod/Bar Cross sections
used for lumpy and coarser size particles
parallel rods or profile bars
OPENINGS
- Circular, In-line and Staggered
openings - Square, In-line and Staggered
openings
used for coarser and small sizes
Punched or perforated plates
Slot-like, In-line and Staggered
openings
- Slot-like, In-line and Staggered
openings - slotted openings are
sometimes used
for fine particles
Punched or perforated plates
OPENINGS
- square
- used for fairly coarse particles
woven wires
OPENINGS
- rectangle
- used for fine particles
Woven wires
The material is fed at ____ of the screen.
One end
Openings
- Triple shute elongated
- used for fine particles
Woven wires
The screen surface can be ____ or ____
Fixed or Moveable
STATIONARY SCREENS
Equally spaced parallel rods or bars running in flow direction. Sloped to allow gravity transport.
Grizzly
Parallel rods running in flow direction. Fixed at one end. Gap increases from fixed to free end.
Divergator
Stationary curved screen with horizontal wedge bars at right angles to slurry flow. Feed slurry enters tangentially. Imparts centrifugal action.
Sieve Bend
REVOLVING SCREEN
Rotating, punched or woven wire. Slightly inclined cylindrical shell
Trommel
VIBRATING SCREEN
Similar to stationary grizzly. Mechanical or electrical vibrations.
Vibrating Grizzly
High speed motion to lift particles. Mechanical or electrical vibrations. Both horizontal and inclined types.
Vibrating Screen
mounted either horizontally or with a gentle slope, has a slow linear motion essentially in the plane of the screen.
Shaking Screen
The screen having one screening surface is called
Single-deck screen
screen has two or more screen surfaces, it is called
Multi-deck Screen
used to prepare the feed to any unit operation.
Feed Screen
used to remove the trash material.
Trash Screen
used to remove small amounts of either oversize or undersize.
Scalping Screen
used to remove water from mixture of solids and water.
Dewatering Screen
used to remove slimes from the coarse material.
Desliming Screen
used to remove medium solids from coarse material
Medium Recovery Screen
(often called the effectiveness of a screen) is a measure of the success of a screen in closely separating oversize and undersize materials. There is no standard method for defining the screen efficiency.
Screen Efficiency
The ____ is defined as the product of the recovery of oversize mate rial into the screen overflow and the recovery of undersize material into the screen underflow.
Overall Efficiency
The ____ is defined as the quantity of material screened per unit time per unit surface area of the screen and is expressed as tons/hr/m2.
Capacity of an Industrial Screen
the first and the most important step in Mineral Beneficiation.
Liberation
The second step,____, is impracticable if the first step, liberation, is not accomplished successfully
Separation
It can be defined as the freeing or detachment of dissimilar mineral grains.
Liberation
The operation employed to liberate the dissimilar mineral grains is ____ or ____
Size Reduction or Comminution
If the particles of ore consist of a single mineral, they are termed as ____.
Free Particles
If the particles of ore consist of two or more minerals, they are termed as ____
Locked Particles
If the locked particles contain valuable minerals at considerable quantity, they are termed as ____
Middling Particles
double D na yot
It is the size of a mineral as it occurs in the ore.
Grain Size
It is the size of any particle whether free or locked particle.
Particle Size
It is the size of a mineral particle at which that mineral is completely liberated. It is the size of a free particle of required (valuable) mineral.
Liberation Size
results in true freeing or detachment of minerals
Comminution
When the run-of-mine ore is reduced in size to grain size of valuable mineral, all the valuable mineral particles exist as ____, no matter whether remaining particles are free or locked particles of gangue minerals.
Free Particles
This type of liberation is known as Liberation by size reduction or Transgranular liberation. Liberation of most of the ores comes under this category.
Equivalent to Freeing
quantitatively referred to as percent liberation, of a certain mineral, is defined as the percent of that mineral liberated and occurring as free particles in relation to the total amount of the same mineral present in the ore
Degree of Liberation
In these ores, reasonable amount of crushing makes the valuables liberated.
Massive Ores
In these ores, valuables can be freed only partially by crushing and require certain amount of grinding to complete the liberation
Intergrown Ores
In these ores, valuables are sparely distributed through a waste rock matrix and require fine grinding to liberate the valuables.
Example: Gold ore
Disseminated ores
