Preparation of an environmentally friendly lead adsorbent. A contribution to the rational design of heavy metal adsorbents

"This work described the preparation and characterization of water insoluble chitosan derivatives as lead adsorbents. In highly regioselective reactions, N-substituted crosslinked chitosan derivatives were obtained by crosslinking native chitosan with mucic and adipic acid (a polyhydroxylated and a non-functionalized diacid of the same length chains). The crosslinking degree of the chitosan modified with adipic acid was significantly higher than that crosslinked with mucic acid (0.446 and 0.316, respectively), while the degree of substitution was almost the same (approximately 80 %). Lead adsorption isotherms were constructed at different temperatures and adjusted to well-known models, obtaining the best fit to the experimental data with Langmuir model. The lead adsorption capacity of new materials was greater than many of the adsorbents described in literature (76.3 and 69.7 mg g−1 for chitosan modified with mucic and adipic acid, respectively). Moreover, thermodynamic parameters were calculated, and results showed that the lead adsorption on the derivatives was spontaneous, exothermic, and governed by chemical interaction. Besides, kinetic studies were performed and adjusted to well-known models. The pseudo-second order kinetic equation was the one that most appropriately described the lead adsorption on the new materials. Results were consistent with the strong electrostatic attraction established between the lead cations and the free carboxylate groups of the derivatives."