Gallium Enhances Water Purification

By substituting a single gallium atom into an aluminum cluster coagulating agent, a research team led by Tom A. Stewart and May Nyman of Sandia National Laboratories has created an improved material for water purification (Environ. Sci. Technol., DOI: 10.1021/es803683t). Cationic coagulants such as ferric chloride, aluminum sulfate, or polyaluminum chloride (PACl) are used at the front end of water treatment processes to clarify water by neutralizing and trapping anionic natural organic matter, clay particles, and a host of microbes. PACl's major component is the polycationic cluster Al₁₃O₄(OH)₂₄(H₂O)₁₂⁷⁺, and as part of an effort to optimize the material, the researchers found that replacing the central aluminum atom with a gallium atom makes a big difference. One reason for the enhancement is that the gallium analog is less prone to deprotonation and maintains its charge better than the aluminum cluster. The gallium material also resists transforming into larger clusters, which is a problem that reduces PACl's shelf life. Nyman says the team has filed for a patent on the gallium-based cluster and is working with Kemira, a major producer of water treatment chemicals, to explore the commercial potential of the new coagulant.