Polyaniline sorption of ruthenium

Abstract

The goal of this project was to determine if polyaniline would be an adequate matrix to sequester ruthenium from aqueous solutions. Ruthenium is a component of radioactive hazardous waste, and therefore developing a sorption method could provide an opportunity to lower costs and be more efficient. The sorption process of RuCl3 in phosphate buffer by PANI powder chemically synthesized from phosphoric acid was spectrophotometrically monitored as function of time. It was determined that the sorption process follows the Langmuir and Freundlich isotherm models and their equation constants were evaluated. The rate constant averaged within the tested ruthenium concentration range (7.9x10-5 to 1.2x10-3M) was experimentally determined to be 1.3x10-2 g*mg-1*min-1. The high R2 value (0.99+) of the rate constant supports the pseudo-second order kinetics and is in agreement with chemisorption being the rate-controlling step. By conducting detailed studies we assigned the chemisorption to Lewis acid based interactions of the sorbent electron pair localized at the benzenoid amine (–NH2) and quinoid imine (=NH) groups, with the sorbate, RuCl3 in solution, as the electron acceptor. The stability of the interaction over a period of approximately a week showed that the presence of the Ru(III) in the PANI matrix reverses its state from emeraldine base to emeraldine salt resulting in a change of conductivity. The partial electron-donor based charge transfer is a slow process when compared to the sorption process involving Brønsted acid doping.