Ala Lombolo
- One of Sweden's most polluted lakes
Charged particles
Apart from the large specific surface area of colloidal clays, these particles are also negatively charged. This creates an attraction between clay particles and dissolved cations, which gives clays its large sorption capacity. The negative charge of colloidal clays derives from isomorphous substitution within the clay structure and from the negatively charged sides of the particles. (Burden & Sims, 1999)
Isomprohous substitution means that a neutral clay crystal will be charged due to the substitution of a higher charged cation, located in a central position of the tetrahedron or octahedron, to a lower charged one . For example, a silica cation (Si4+) may be substituted by an aluminium cation (Al3+) due to its similar size in ionic radius. (Burden & Sims, 1999)
In this way pollutants which commonly occur as cations in solution, such as heavy metals, easily bond to clay-rich sediments. This is one of the reasons for the high concentrations of mercury and other metals found in Ala Lombolo.
