Swelling and aggregation of Leonardite upon pH change and Pb(II) binding: an AFM study

DOS REIS COPELLO, FEDERICO; LIZARRAGA, LEONARDO; ORSETTI, SILVIA; MOLINA, FERNANDO V.

ENVIRONMENTAL CHEMISTRY

CSIRO PUBLISHING

Lugar: Collingwood; Año: 2018

1448-2517

The swelling and aggregation of Leonardite humic acid, due to acid-base and Pb(II) binding interactions, was studied through AFM tapping mode measurements and correlated with potentiometric experiments. These experiments allowed determination of parameters for the NICA-EPN model, which predicts size and electrostatic potential changes. AFM observations showed growth of agglomerates at low pH values; height distribution analysis allowed discrimination of single particles from agglomerates. The size of individual particles increased slightly with pH increase. Agglomeration was evaluated through the dispersity, which increased at pH < 5, concomitant with a decrease of the electrostatic repulsion and an increase of protonated carboxylic groups, thus the agglomeration is attributed to both factors. In the presence of Pb(II), agglomeration is observed to rise strongly with the increase in metal concentration, which is attributed to bridging of humic particles by Pb(II) ions. The AFM ex-situ results suggest consistency between NICA-EPN predictions and experimental behaviour.