A kinetic study of simultaneous removal of EDDS and cupric ions from acidic aqueous solutions by TiO2-based photocatalysis under artificial solar light irradiation and deaerated batch conditions

The removal of cupric ions from aqueous solutions containing N,N′-ethylenediamine-disuccinic acid (EDDS) is carried out in batch conditions to simulate a possible treatment of water streams coming from soil washing treatment units for heavy metal decontamination. The reduction of cupric ions to zero-valent copper and the oxidation of EDDS species is observed with the achievement of low degrees of mineralization. A mathematical model has been developed to simulate and predict the concentration profiles of both total EDDS and cupric ions under specified experimental conditions. A series of experimental investigations have been carried out and the results have been used to build a reaction network. Kinetic models have been developed to describe the system behavior in a variety of operating starting conditions (such as different photocatalyst load, cupric ions and EDDS starting concentrations, pH). One of the mathematical models proposed has allowed to estimate the best numerical values of the unknown kinetic constants through an optimization process. A good alignment with the values reported in literature for similar reactions has also emerged for some kinetic constants. Model validation has been carried out successfully. The mathematical model proposed could be useful for the design of a photo-reactor, capable of purifying the solutions coming from soil washing procedure.