Removing toxic metals from wastewater with ion exchange treatment Some historians believe that heavy metal poisoning played a part in the fall of the Roman Empire. Several thousand years later, man is trying to better protect himself against heavy metal contamination. Climate Change and Environment © PhotoDisc Broadly speaking, metallurgy is the science of metallic elements and their mixtures, alloys. Great benefits for mankind have been reaped from this field, though hand in hand with environmental threats. Wastewater effluent from activities like metal plating is rich in heavy metals that are potentially toxic to all forms of life. Today the most common method of cleansing the wastewater is hydroxide precipitation. The pH of the wastewater is artificially increased past the point of solubility and the resulting metal hydroxide precipitate is removed from the flow by filtration. However, environmental legislation is raising the bar regarding allowable levels of heavy metals, therefore improved methods of purification must be identified. Researchers took the initiative to explore the technique of ion exchange, specifically the discovery of new adsorbing materials. With ion exchange, heavy metal ions are attracted to a special resin. A significant advantage of the process is that once the resin is fully saturated, it can be removed, cleansed and reused. The trick is in the materials used to create the resin. The scientists tested both organic and inorganic materials. New resins were developed in the laboratory using raw materials like seaweed extracts. Ion exchange characteristics and decontamination performance were assessed with real wastewater as well as on the computer through modelling exercises. In addition to seaweed, activated carbons also proved to be very effective. The work also led to the development of resin preparation methods that helped improve their efficiency. Finally, a new technique to extract metals using a pH parametric pump was realised. These results will help the metallurgical industry meet the increasingly stringent standards, extending beyond the current limitations of hydroxide precipitation. Furthermore, increasing the amount of heavy metal recovery will lead to additional recycling, increasing the sustainability of many manufacturing processes. While we no longer use lead-lined pots and jugs like the ancient Romans, we still strive to protect ourselves against the potential dangers of heavy metal poisoning.
