Highly efficient adsorption of Hg(II) and Pb(II) onto chitosan-based granular adsorbent containing thiourea groups

A series of granular hydrogels containing carboxy group and thiourea group were prepared by a facile redox-initiated polymerization in air atmosphere at room temperature, and then were used as the adsorbents for efficient adsorption of Pb(II) and Hg(II). The variables affecting the adsorption capacity were systematically investigated, including pH, initial concentration, contact time, and desorption and reusability. The results indicate that the as-prepared adsorbent has fast adsorption kinetics and high adsorption capacity, in particular for Hg(II), with the equilibrium time of about 40 min and the maximum adsorption capacity of 1106.72 mg/g for Hg(II). Over the pH range studied, this granular hydrogel shows insignificant changes in the adsorption capacity for Hg(II), while some noticeable differences are visible for Pb(II). The adsorption process for Pb(II) and Hg(II) can be described using the pseudo-second-order kinetic model and the equilibrium isotherm matches well with the Langmuir model. The reusability demonstrates that after five adsorption–desorption cycle, a high adsorption capacity is still observed for Pb(II) and Hg(II), though a decreasing tendency is inevitable. Consequently, the as-prepared granular hydrogel can be recognized as an effective adsorbent for the removal and recovery of heavy metal ions, especially for Hg(II) from aqueous solution.

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