Leaching

Question 1

Name the three parts in which a process of leaching can be divided

Answer 1

• The change of phase of the solute as it dissolves in the solvent
• Diffusion of the solute through the solvent in the pores of the solid to the outside of the particles
• The transfer of the solute from the solution in contact with the particles to the main bulk of the solution

Question 2

What factors influence the rate of extraction

Answer 2

• Particle size: the smaller the size the higher the rate of transfer of material
• Solvent: the liquid chosen should be a selective solvent with a low viscosity so that it circulates freely
• Temperature: in most cases, the solubility will increase with temperature to give a higher rate of extraction
• Agitation of the fluid: increases the eddy diffusion and therefore increases the transfer of material from the surface of the particles to the bulk of the solution. It also prevents sedimentation

Question 3

What three processes are involved in leaching operations

Answer 3

• Dissolving the soluble component
• Separating the solution formed, from the insoluble solid residue
• Washing the solid residue to free it of unwanted soluble material

Question 4

The type of equipment employed depends on…?

Answer 4

…the nature of the solid - whether it is granular or cellular and whether it is coarse or fine

Question 5

Name the quantities that must be defined for a countercurrent washing system

Answer 5

• The composition of the solvent fed to the system (concentration of soluble material already present)
• The quantity of solvent used or the concentration of the solution to be produced
• The composition of the solid to be leached
• The amount of solid fed to the system
• The amount of liquid discharged with the solid in the underflow
• The number and arrangement of units

Question 6

Define leaching

Answer 6

Leaching refers the the extraction of a soluble constituent from a solid by means of a solvent