Fundamental Chemistry and Hydraulics - Mathematics and Statistics for the Environment - page 350

TABLE 14.3
Types of Colloids

Name Dispersing Medium Dispersed Phase

Solid sol Solid Solid

Gel Solid Liquid

Solid form Solid Gas

Sol Liquid Solid

Emulsion Liquid Liquid

Foam Liquid Gas

Solid aerosol Gas Solid

Aerosol Liquid Aerosol

Source: Adapted from Davies, P., Types of Colloids ,
University of Bristol, 2013, http://www.chm.bris.
ac.uk/webprojects2002/pdavies/types.html.

In dilute solutions, the osmotic pressure is directly proportional to the solute concentration
and is independent of its identity. The properties of electrolyte solutions follow the same
trends as nonelectrolyte solutions but are also dependent on both the nature of the electro-
lyte as well as its concentration .

14.1.2.6 Colloids/Emulsions
A solution (e.g., seawater) is a homogeneous mixture of two or more substances. A suspension (e.g.,
sand and water) is a brief commingling of solvent and undissolved particles. A colloidal suspension
is a commingling of particles not visible to the naked eye but larger than individual molecules.

Note: Colloidal particles do not settle out by gravity alone.

Colloidal suspensions can consist of

• Hydrophilic solutions of macromolecules (proteins, for example) that spontaneously form
in water
• Hydrophobic suspensions, which gain stability from their repulsive electrical charges
• Micelles, special colloids having charged hydrophilic heads and long hydrophobic tails

Colloids are usually classified according to the original states of their constituent parts (see Table
14.3). The stability of colloids can be primarily attributed to hydration and surface charge , both of
which help to prevent contact and subsequent coagulation.

Note: In many cases, water-based emulsions have been used to replace organic solvents (e.g., paints,
inks), even though the compounds are not readily soluble in water.

In wastewater treatment, the elimination of colloidal species and emulsions is achieved by vari-
ous means:

• Agitation
• Heat
• Acidiication
• Coagulation (adding ions)
• Flocculation (adding bridging groups)