The stability and mechanism of cerium complexation with humic substances from poultry manure – A combined experimental/theoretical approach

The complexation between humic substances (HS) extracted from manure poultry and the rare earth element (REEs) cerium (Ce) was investigated. The coordination of Ce with humic and fulvic acids occurs mainly by the carboxylate groups, increasing the thermal stability of the HS due to the reorganization of its chemical structure. The leaching of Ce3+ in phosphate buffer solution indicates Ce-phosphate precipitation over time. The complexation between Ce and benzenedicarboxylic acids used as model molecule of the HS were investigated by means of density functional calculations (DFT). The coordination of [Ce(H2O)9]3+ and [Ce(OH)(H2O)8]2+ species with the benzenedicarboxylic groups occurs preferentially in the meta position that is less electrodefficient. These results are an important step towards understanding the interactions of soil elements with natural organic matter and aqueous systems.