A study on biosorption of heavy metals using seaweed eucheuma denticulatu

The ability of seaweed species Eucheuma denticulatum to remove Cr(VI) and Pb(II) from aqueous solutions was investigated in a batch system by using AAS. The influence of pH, contact time and initial concentration of the metals on the uptake byE. denticulatum were investigated. The study revealed that the optimum pH for Pb(II) and Cr(VI) uptake were 4.0 and 3.0, respectively, whereas the optimum contact time for the metals adsorption was about 120 min. Pb(II) and Cr(VI) uptakes of 4.7 and 0.91 mg/g, respectively, were attained at optimum pHs, 28 ℃ and 3 hrs contact time. Cr(VI) uptake increased with the increase in initial Cr(VI) concentration and reached saturation at 200 mg/l. Pb(II) uptake also increased with the increase in initial Pb(II) ions concentration. However, beyond 1000 mg/l the rate of increase in Pb(II) uptake slowed down. Pb(II) uptake was found to decrease by 4.37% and 3.48% on addition of Na+ and Mg2+ ions in concentration range of 10 to 25 mg/l to the test solutions, respectively. Na+ and Mg2+ ions in Cr(VI) test solutions caused a decrease in Cr(VI) uptake by the biomass by 31.5% and 25.6% respectively. Desorption experiments indicated that 0.1 M CaCl2 was an effective elluant for the] recovery of Pb(II) from the biomass but not for Cr(VI). Regeneration of the metal loaded E. denticulatum by using 0.1 M HCl caused dissolution of the biomass. The biosorption of Pb(II) onto E. denticulatum fitted well to Langmuir isotherm with maximum adsorption capacity (qmax) of 416.67 mg/g while that of Cr(VI) fitted well to Freundlich isotherm with constants K and n values of 0.652 and 5.95, respectively. It can be concluded that E. denticulatum is an effective biosorbent for the removal of Pb(II) from aqueous solution but not for Cr(VI).