Surface Reactions at the Aluminum-Water Treatment Residual/Solution Interface as Determined by Flow Calorimetry and Phosphorus Modeling.

Flow calorimetry was used to investigate the energetics of phosphorus (P) sorption reactions occurring at surfaces on amorphous aluminum water treatment residual (Al-WTR) and the effects on surface charge and ion exchange. Heats of exchange were determined using Cl/NO₃ exchange. Exothermic reactions were observed when NO₃ replaced Cl from anion exchange sites. At pH 5.8, Cl/NO₃ heats of exchange were about 3.0-4.0 kJ/mol.  P sorption reduced the surface charge on Al-WTR as measured by Cl/NO₃ exchange. Surface area analyses together with energetics suggest possible limited sites for adsorption. The use of flow calorimetry may clarify the mechanisms of P sorption at the Al-WTR surface.  The magnitude and energetics of phosphorus sorption were modeled and simulated using mathematical numerical methods. The time required for Al-WTR to reach full sorption capacity can be predicted from the simulation, which are however limited to traditional batch techniques. Further, time for all P to be immobilized from the system can also be predicted.