Colloids Properties, Types, Sources, and Formation

The size of particles in water determines to a large extent their different physical states large particles precipitate, small particles tend to dissolve. However, this differentiation is far from clear-cut, and as a result there are particles between these two extremes that remain suspended in water. Because these suspended colloidal particles (called 

A colloid is a small particle separated from others by a dispersion medium (in aqueous systems this medium is obviously water). The size of colloidal particles ranges from one nanometer (nm) to one micrometer (pm). They are formed either by aggregates of small molecules or by large molecules of high molecular weight. Dispersions created with coarser materials ( 10 pm) are sometimes considered colloidal dispersions as well. 

The most common types of colloidal dispersions in aqueous systems are 

In natural systems, solid-liquid dispersions are the most common colloidal dispersions. 

A typical example of colloid formation involves acidic streams containing dissolved Al3+ that encounter neutralizing streams, whereby aluminum hydroxide colloids form. Other cases include the formation of solid oxides and hydroxides of Fe3+ and Mn4+ through natural oxidation processes. When dissolved, the reduced species may encounter high oxygen levels in water that favor their oxidation processes, as represented in reaction 6.20 which 

---