Alternative use of cross-linked polyallylamine (known as Sevelamer pharmaceutical compound) as biosorbent

• Sevelamer pharmaceutical compound as biosorbent.
• Simultaneous removal of Cr(VI) and reactive dye from binary aqueous mixtures.
• Characterization with swelling tests, FTIR, SEM, and XRD.
• Effect of pH, kinetics, isotherms, thermodynamics and reuse cycles.
• Theoretical calculations and adsorption mechanism.

In this study, an alternative use of Sevelamer carbonate (SEV, a cross-linked polyallylamine which is a widely known pharmaceutical compound) was suggested. The existence of primary and secondary amino groups (with different ratios) in its molecule increases its adsorption potential and use as biosorbent material. SEV was tested as biosorbent material aiming the removal of heavy metals and dyes from simulated effluents. As heavy metals and dyes, hexavalent chromium (Cr(VI)) and Remazol Brilliant Blue RN (RB) were used, respectively. A full adsorption study was done confirming the strong adsorption capability of SEV. The maximum theoretical adsorption capacity (Qm) was 772 and 485 mg/g for single-component solutions of RB and Cr(VI), respectively; the respective values for binary mixtures of the same concentration (200 mg/L) were 445 and 309 mg/g respectively (calculated after fitting to Langmuir–Freundlich isotherm model at 25 °C). The same experiments were also done at increasing temperatures (45 and 65 °C) concluding thermodynamic remarks (ΔH0 > 0; ΔG0 < 0; ΔS0 > 0). The effect of contact time was analyzed running kinetic adsorption experiments and fitting them to pseudo-second order kinetic equation. The reusability was evaluated completing successfully 20 cycles of reuse (adsorption/desorption). The adsorption mechanism among SEV molecules and Cr(VI) or/and RB was clarified using FTIR spectroscopy before and after adsorption in line with a detailed theoretical modeling which provided important calculations. SEV was also characterized using swelling experiments, BET, SEM, XRD, TGA techniques.

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