Clay mineral products for improving environmental quality

Abstract

Although clay minerals play fundamental roles in many environmental processes, especially in controlling the movement of various ions and molecules in soils, they are also useful precursors for a wide range of products that can be used to address other problems of environmental importance. This paper briefly reviews methods for activation and surface modification along with the preparation of pillared clays and clay complexes with organic molecules and polymers. After describing the application of natural clays to environmental problems, the remainder of the review is devoted to products that can improve environmental quality. These include adsorbents for the removal of various types of pollutant from waters, including heavy metals, organic and inorganic molecules. Clay-derived products also have roles in the destruction of organic waste, the production of environmental sensors, and combating various other environmental problems. Important roles exist for clay minerals in clean energy production, including light harvesting by hybrid materials based on complexes between porphyrins and clay minerals, and biofuel production where pillared clays have a role in the cracking of vegetable oils, and clay-based composites could act as storage media for H₂. The swelling properties of smectite clays form the basis for their use as environmental barriers, and these can be improved by composite materials based on clay-polymer complexes. Clays also have a role as lubricants in drilling fluids, and strategies for improving the efficiency of drilling muds are described. In addition, clay-derived products could have important uses in the control of atmospheric emissions, and the collection of CO₂ for use in the food and drinks industry. Finally, some other uses of clay-derived products are mentioned briefly, including complexes of clays with natural fibers as biodegradable food packaging materials, and as media for the slow release of fertilizers, pesticides and preservatives. Overall, clay minerals have several important roles in the production of cleaner sustainable environments, and these can be expected to increase in the future.