Transformation of Al Species on Carbon Surfaces: Effects of Al Species and Carbon Surface Oxygen Groups

Control of residual Al is critical, owing to its high tendency to accumulate in drinking water distribution systems and its potential risks to human health. Herein, the effects of surface properties of activated carbon (AC) on intercepting different Al species (including monomeric Al and polymeric Al species-Al₁₃) are evaluated. The results showed that Al in the form of monomers was considerably adsorbed by AC; whereas Al in the form of polymeric Al₁₃ was held to a much lower degree by AC, and the effluent Al concentration was even higher than that without AC. By comparing virgin AC and hydrogen thermal treated AC, the surface oxygen functional groups on the AC were proposed to play a critical role in the transformation of Al species. The oxygen functional groups on the AC surface can directly form complexes with monomeric Al, thereby inducing the binding of monomeric Al on the AC surface. However, the AC surface oxygen groups could not bind to polymeric Al₁₃, and the interaction between AC surface oxygen groups and polymeric Al₁₃ partially transforms Al₁₃ into monomeric Al species, which inhibited the self-aggregation of Al₁₃. This study aims to provide new insights into the control of residual Al in water treatment plants to ensure drinking water safety.