Removal kinetics of heavy metals and metalloids from water by polyamidoamine hydrogels

The need for innovative and specific water treatment technologies explain the present study on a family of novel polyamidoamine (PAA) hydrogels and their effectiveness on the removal from water of inorganic contaminants. Batch kinetic tests were carried out in order to define the rate of the removal process and the factors affecting the reaction rate. Two samples of hydrogels, which differ for functional groups, were tested at three different solid/liquid ratios (1/150-1/300-1/600 g/mL) and in two different forms (powder -d<1mm- and grains -1mm<d<2mm-). The removal process was found to follow a saturation kinetic model and a comparison between the results obtained for the two different particle size enabled to define the influence of layer and pore diffusion on the overall rate of the process. As a function of experimental boundary conditions, equilibrium contact time ranged from 2 to 48 hours and copper uptake from 0.27±0.01 to 1.00±0.07 mgCu/gPAA, hence highlighting a strong dependence of the removal ability of PAA hydrogels on operating factors. A physical interpretation of the particle system is proposed and results point out the need for a deeper comprehension of the mechanisms of interaction between PAA hydrogels and water constituents (pH, complexes formation).