CLAYS, WATER AND ENVIRONMENT: AN INTERESTING TRIANGLE WITH MUTUAL INTERACTIONS

Mineralogical definition of "Clay" is "a naturally occurring material composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden with dried or fired” (Guggenheim & Martin, 1995).

In water most clays behave as colloids due to their small size and their surface charge. Both characteristics lead to a series of unique effects that amplifies the environmental influence of those minerals even when present in soils and rocks in relatively low amounts.

This lecture will discuss some of those interesting effects, for example: (a) adsorption desorption processes of organic and inorganic pollutants, (b) degradation and stabilization of chemicals, (c) flocculation and dispersion of colloidal suspensions and (d) influence on water content. Such interactions were exploited by men for thousands of years: for example- the use of clays to remove oils and greases from wool or clothes, the hardening-upon-drying applications in construction, the impermeability applied in containers and aqueducts, and the medicinal properties as sorbents of toxic materials had been established tens of centuries ago.

By all those processes and many others, clays and clay minerals are one of the leading factors when it comes to understand, explain, or even try to solve and remediate issues related to the interactions of environmentally affecting compounds, soil or rocks, and water.

Better understanding of the reactions and processes that occur in the interface between water, clay and chemicals might yield to very interesting additional new applications that might improve technological, industrial or commercial process, minimizing their environmental hazard. Some examples of such "clean-tech" applications of naturals and modified clay minerals in wastewater and industrial polluted effluents will be presented.