Comparative study of natural and modified biomass of Sargassum sp. for removal of Cd2+ and Zn2+ from wastewater

Natural as well as acid modified dead biomass of brown marine alga Sargassum sp. was employed for the elimination of cadmium and zinc ions from synthetic wastewater; batch mode experiments were carried out to optimize various factors like adsorbent dosage, contact time, pH, agitation speed and primary metal ions concentration at room temperature (298.15 K) for both types of adsorbents i.e. natural and acid treated. Application of Langmuir and Freundlich isotherms suggested that the modified biomass adsorbed better as compared to the natural one; though sorption on the natural biomass was a physical process while that on the modified one was a physico-chemical process and thus was relatively difficult. The quantity of cadmium ions adsorbed was greater than that of zinc ions. Adsorption equilibrium for the metal ions sorption on treated Sargassum sp. biomass was established within 60 min for both cadmium and zinc ions with 95.3 and 90.1% removal efficiencies, respectively, but it was greatly influenced by the pH of the solution. The optimal conditions in the batch experiments were as follows: cadmium ions were removed effectively using 0.5 g of adsorbent and 5 mg/L initial metal ions concentration at pH 4 and 150 rpm agitation speed whereas the best results for zinc ions were obtained with 1 g of adsorbent and 5 mg/L initial metal ions concentration at pH 3 and 200 rpm agitation speed. The experimental data fitted well to the pseudo first order model as the values of metal uptake capacities were in good agreement with the experimental values. Thermodynamic studies show that the process is spontaneous and endothermic in nature. Desorption and regeneration studies reveal that recovery of biosorbent is low.