Kinetic, Isotherm and Thermodynamic Aspects of Zn2+ Biosorption by Spirulina platensis: Optimization of Process Variables by Response Surface Methodology

The aim of this study was to assess the efficiency of Spirulina platensis for removing Zn2+ ions from the aqueous solutions. The optimized conditions of 4.48 g/L algal dose, pH of 6.62 and initial zinc concentration of 29.72 mg/L obtained by response surface methodology were employed for Zn2+ biosorption by S. platensis and up to 97.90% Zn2+ was removed, showing that there is a favorable harmony between the experimental data and model predictions. Different kinetic and equilibrium models were used to characterize the biosorption manner of Spirulina as a biosorbent. The kinetic manner of Zn2+ biosorption was well characterized by the pseudo-second-order, implying that the adsorption process is chemical in nature. The Langmuir and Dubinin–Radushkevich isotherm models were best fit to the equilibrium data. The maximum adsorption capacity of the Langmuir monolayer was 50.7 mg/g. Furthermore, the thermodynamic analysis revealed that Zn2+ biosorption was endothermic, spontaneous and feasible. As a result of biosorption process, FTIR, SEM, and EDX investigations indicated noticeable alterations in the algal biomass’s properties. Therefore, the dried Spirulina biomass has been shown to be cost-effective and efficient for removing the heavy metals, particularly zinc ions from wastewater, and the method is practicable, and environmentally acceptable.