Comparative Evaluation of the Adsorption of Chromium (VI) by Modified and Unmodified Mangrove Leaf Sorbents

The adsorption capacity of modified (MML) and unmodified (UML) mangrove leaves sorbents on chromium (VI) was analyzed in terms of pH, adsorbent doze, chromium (VI) concentration and contact time using batch adsorption technique. Results obtained showed greater chromium (VI) adsorption on MML than UML. Adsorption capacity diagrams described for MML were higher than those of UML. The adsorption was influenced by low medium pH, low adsorbent dosage, high chromium (VI) concentration and long contact time. Adsorptive capacity decreased from 15.9 - 14.19mgg^-1, for MML and 13.59 - 12.19mgg^-1, for UML and from 74.99 - 9.59mgg^-1, for MML and 44.89 - 5.79mgg^-1, for UML as pH and adsorbent dosage were increased from (2 to 8) and (0.25 to 2g); but increased from 5.09 - 46.19mgg^-1, for MML and 1.89 - 25.59mgg^-1, for UML and from 26609.0 - 38719.0mgg^-1, for MML and 28869.0 - 35089.0mgg^-1, for UML as concentration of chromium (VI) and time of contact increased from (10 to 100ppm) and (30 to 240minutes), respectively. Isotherm studies reveal that experimental data for MML and UML fitted on Freundlich adsorption (R² ≥ 0.93). Kinetic data analyses, with (R² ≥ 0.962) on pseudo-second order model, suggest chemisorption process for both sorbents. These results suggest the extract of mangrove leaves material after acid modification can be used as biosorbent for chromium (VI) removal in aqueous solution.