CHEE2945 – Lecture 9
Particle size reduction importance:
- We need particles of a certain size for processing.
- It is also important when considering surface area per unit volume, for
situations such as chemical reactions.
- It is also used to liberate valuable particles from larger raw rocks.
- Particle size reduction is extremely energy intensive and extremely inefficient.
Only around 1% of input energy goes into particle fracturing.
Particle fracture mechanics:
- Fracture mechanics refer to the forces that affect the way something breaks.
- The mechanism used to reduce particle size must be tailored to the fracture
mechanics of the material.
- Fracture mechanics relate to ductility.
- Most mineral processing involves brittle fractures, which occur along grain
boundaries.
Size reduction theory:
- The three main theories that predict how much energy is required to reduce a
given particle to a desired size are:
o Surface theory (1867, Rittinger),
o Volume theory (1883, Kick),
o Transitional theory (1952, Bond).
Surface theory:
- Rittinger’s theory is:
‘The required energy for particle size reduction is proportional to the particle
surface area, S’.
- For input energy per unit mass:
dS
dE=
ρV
- Surface area is proportional to a dimension squared. Therefore:
2
S=k s x
Particle size reduction importance:
- We need particles of a certain size for processing.
- It is also important when considering surface area per unit volume, for
situations such as chemical reactions.
- It is also used to liberate valuable particles from larger raw rocks.
- Particle size reduction is extremely energy intensive and extremely inefficient.
Only around 1% of input energy goes into particle fracturing.
Particle fracture mechanics:
- Fracture mechanics refer to the forces that affect the way something breaks.
- The mechanism used to reduce particle size must be tailored to the fracture
mechanics of the material.
- Fracture mechanics relate to ductility.
- Most mineral processing involves brittle fractures, which occur along grain
boundaries.
Size reduction theory:
- The three main theories that predict how much energy is required to reduce a
given particle to a desired size are:
o Surface theory (1867, Rittinger),
o Volume theory (1883, Kick),
o Transitional theory (1952, Bond).
Surface theory:
- Rittinger’s theory is:
‘The required energy for particle size reduction is proportional to the particle
surface area, S’.
- For input energy per unit mass:
dS
dE=
ρV
- Surface area is proportional to a dimension squared. Therefore:
2
S=k s x
