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

F. DOS REIS COPELLO; F.V. MOLINA; S. ORSETTI; S. ORSETTI; L. LIZARRAGA; L. LIZARRAGA; F. DOS REIS COPELLO; F.V. MOLINA

ENVIRONMENTAL CHEMISTRY

CSIRO PUBLISHING

Lugar: Collingwood; Año: 2018 vol. 15 p. 162 - 170

1448-2517

The swelling and aggregation of Leonardite humic acid, due to acid?base and PbII binding interactions, was studied through atomic force microscopy (AFM) tapping mode measurements and correlated with potentiometric experiments. These experiments allowed determination of parameters for the non-ideal competitive adsorption (NICA)-elastic polyelectrolyte network (EPN) model, which predicts size and electrostatic potential changes. AFM observations showed growth of agglomerates at low pH values. Height distribution analysis allowed discrimination of10 single particles from agglomerates. The size of individual particles increased slightly with pH increase. Agglomerationwas evaluated through the dispersity, which increased at pH,5, concomitant with a decrease of the electrostatic repulsionand an increase of protonated carboxylic groups, thus the agglomeration is attributed to both factors. In the presence ofPbII, agglomeration is observed to rise strongly with the increase in metal concentration, which is attributed to bridging ofhumic particles by PbII ions. The AFM ex situ results suggest consistency between NICA-EPN predictions and15 experimental behaviour