Studies on Biosorption of Mercury (II) from Aqueous Solution on Nitric Acid Modified Activated Carbon Prepared from Water Hyacinth

Abstract

The aim of this study was focused on using dried Water hyacinth stems and leaves (DS, DL) and nitric acid modified activated carbon stems and leaves (MACS, MACL) as effective adsorbents for removal of Hg(II) from aqueous solutions. Adsorption experiments were performed in batch technique to study the effect of various operating parameters, pH of the solution (1 to 5.5), initial concentration of lead ions (10 to 500 mg /l), contact time (2 – 250 min), and temperature(298- 323 K), ionic strength, and adsorbent dose. It is clear that the maximum adsorption capacity of mercury at pH 5 and 298K onto MACS, MACL, DL and DS was 102.6, 81.9, 57.59 and 41.70 mg. g-1, respectively. The obtained results revealed that the percentage of mercury removal increased with increased contact time till reach to the equilibrium time (60 min).When the bio sorbent dosage increased from 0.4 to 4 g/L, the percent of mercury removal by DS, DL, MACS and MACL increased from 37.43 % to 79.58 %, from 32.59% to 78.27 %, from 41.49 % to 82.33% and from 28.66 % to 87.17%, respectively. The adsorption capacity of mercury decreased with the increase in ionic strength. The equilibrium data were fitted well with the linear form of Langmuir model. Adsorption kinetic data followed a pseudo-second-order model. Thermodynamic parameters, involving ΔHº, ΔGº, and ΔSº for the adsorption process of mercury from aqueous solution onto dried water hyacinth and modified activated carbon indicated that adsorption was endothermic and spontaneous process. Desorption were also investigated using HCl as desorbing agent. The results revealed that the percent recovery of Hg (II) increased from 53% to about 88% with increase of HCl from 0.3 to 0.8 M and then remained constant.