Effect of the presence of lignin or peat in IPN hydrogels on the sorption of heavy metals

The adsorption of metal ions Cu²⁺ and Ni²⁺ from contaminated simulated water was studied using new starch/acryl amide-based hydrogels in the presence of lignin or peat to create an interpenetrating polymer network (IPN). The chemical structure of the materials was studied using infrared spectroscopy and their morphology was observed by scanning electron microscopy (SEM). The behavior of hydrogels in water and the water transport mechanisms were characterized using Fick’s law. Metal ion sorption was analyzed using inductively coupled plasma spectrometry. Hydrogels showed maximum water absorption values at about 100 h and all of them showed a Fickean water transport mechanism. On one hand, SEM confirmed that the new material is in fact an IPN and, on the other, that the internal porosity shown is responsible for the water absorption. On the other hand, the hydrophobic nature of the dispersed phase and its concentration in the hydrogel formulation seem to influence this process, which could also influence or facilitate the diffusion/sorption of metal ions. Peat-containing hydrogels showed a slightly lower absorption capacity of these ions than lignin-containing formulations. These hydrogels have a high potential to obtain metal ion-collector membranes.