Page 204 - Industrial Ventilation Design Guidebook

I 66 CHAPTER 4 PHYSICAL FUNDAMENTALS

insoluble. Another method depends on the fact that if the substance can be
ionized, its solubility can be suppressed. This is achieved by adding a highly
ionized second substance having one ion in common with the original dis-
solved solid.

Chemical Precipitation. If physical separation techniques do not work,
separation may be achieved by chemical conversion to a soluble precipitate.

Ion Exchange. Certain solid substances have the property of exchang-
ing one ion for another if placed in a solution containing the ions. Typical sub-
stances with this property are the zeolites and certain synthetic resins.

Electrolytic Deposition. The separation of a metal from a solution can
be achieved by electrolysis.

Adsorptive Properties. Substances such as silica gel and activated char-
coal can be used to collect (adsorb) certain solids from solution. The adsorber
bed may be discarded when depleted or recycled by washing and heating,

Separation of Solids in Suspension in Liquids. This can be achieved
using

1. Density difference
2. The difference in cross-section between the solid paniculate matter and
the liquid molecule
3. The electrostatic properties of the solid

Density Techniques. Many methods are in use, with the selection de-
pending on

• Particulate size
• Settling velocity
• Quantity of solids in suspension

In the case of gravitational settling, the unit design depends on the method
of solid removal after settling. The methods in use are

• Removal of solids from the separation unit in which they are contained
• Intermittent or continuous discharge of the solids from the base of
the unit
• Continuous discharge over the rim of the settling tank
• Separation by centrifugal force
Gravity filters used in the density removal are subdivided into

• Sand gravity
• Continuous gravity