ABSTRACT
The adsorption, ion exchange, and reversible chemical processes discussed in this chapter are based on reversible selective interactions of gases or liquids with solids. They are very important to hazardous waste minimization. This is because of their effectiveness at recovering hazardous materials when they are present at low concentrations in the feed stream. The hazardous materials may be recovered and recycled because of their value, or may be recovered to remove them from either a process stream to be recycled or a waste stream to be discarded. Typical feed streams are industrial process streams, wastewater streams, or gas streams destined for venting to the atmosphere. The material to be removed and/or recovered from the feed stream is captured by the solids and then removed from the feed stream along with the solids. The feed stream may be either liquid or gaseous. The solids may be amorphous or crystalline materials chosen for their selectivity for either non-polar, polar, or ionic molecules. Typical amorphous materials are activated carbons, activated aluminas and clays, silica gels, and polymer-based ion exchange resins. Typical crystalline materials are natural and synthetic zeolites and molecular sieves.
