Optimization and Characterization of Cladophora sp. Alga Immobilized in Alginate Beads and Silica Gel for the Biosorption of Mercury from Aqueous Solutions

Biosorption has gained much ground as a wastewater treatment technology. In this work, modified algal biosorbents were synthesized by immobilizing Cladophora sp. alga in alginate beads and silica gel. The resultant biosorbents were evaluated for the retrieval of mercury from aqueous solutions using batch scale experiments. Optimal metal removal was achieved at pH 5, agitation time 60 min, initial metal concentration 100 mg L⁻¹, and temperature 16 °C. Moreover, the experimental data fitted the Langmuir isotherm, pseudo-second-order kinetic model and Dubinin-Radushkevich isotherm thus showing that biosorption occurred on a homogeneous layer and ion exchange was the dominant mechanism. Both biosorbents also had high selectivity for Hg²⁺ in multi-elemental solutions. This work showed the potential of Cladophora sp. immobilized in alginate beads and silica gel in removing mercury from industrial wastewaters.