Development of seaweed biomass as a biosorbent for metal ions

Three seaweed species collected from Hong Kong waters were screened for their adsorption abilities for Cu²⁺, Ni²⁺ and Zn²⁺; and Ulva lactuca having the highest metal ion removal capacity (RC) was chosen for further study. Effects of algal biomass and medium pH on the metal ions RC of Ulva lactuca were determined and optimized. Under the optimal conditions of the corresponding metal ions, the algal Cu²⁺, Ni²⁺ and Zn²⁺ RCs were 65.54, 21.00 and 49.54 mg/g, respectively. The presence of other cations and anions affected the metal ions adsorption by the seaweed. The effect was dependent on the combination between the target metal ions and other cations/anions. The kinetic study revealed that the adsorption of Cu²⁺, Ni²⁺ and Zn²⁺ by Ulva lactuca fitted the Langmuir isotherm. Comparing with 0.1 M HCl, citric acid, thiourea, EDTA and HNO₃, 0.1 M H₂SO₄ efficiently recovered close to 100% adsorbed metal ions from Ulva lactuca. In three successive adsorption-desorption cycles, reduction in metal ion RCs was found in the second and third cycles, but almost all adsorbed metal ion could be recovered.