Biosorption is an effective way of extracting heavy metal ions from aqueous solutions of various compositions. The brown algae, Cystoseria indica, when treated with sodium chloride, demonstrates significant capacity to extract cadmium and nickel, simultaneously, from aqueous solutions. The batch system was running over wide ranges of initial metal ion concentrations (5–150 mg/L), pH (2–6), adsorbent mass (1–4 g/L), and contact times (20–300 min), at a temperature of 25 °C. The results obtained when applying the system in these conditions exhibit higher removal capacities for cadmium than nickel. The optimal conditions of the biosorption process were found as the adsorbent mass of 1 g/L, initial concentration of adsorbates of 100 mg/L and pH of 6. The equilibrium data obtained are better described by the extended-Freundlich isotherm for nickel and cadmium. The maximum biosorption of nickel and cadmium in binary-metal-component system were 18.17 and 55.34 mg/g, respectively. The kinetic data derived from these experiments were evaluated with pseudo-first-order, pseudo-second-order and intra-particle-diffusion kinetic models. Kinetic examination of the equilibrium data derived from these models suggest that the adsorption of nickel and cadmium both follow the intra-particle-diffusion kinetic model.
