Adsorption of Pb2+ and Cd2+ onto Spirulina platensis harvested by polyacrylamide in single and binary solution systems

This study examined the feasibility and characteristics of microalgae waste treatment using a mixture of Spirulina platensis and polyacrylamide (SP-PAM) as an adsorbent system for removing Pb2+ and Cd2+ from simulated wastewater in single and binary solution systems. Multiple techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX) and the nitrogen-based Brunauer-Emmett-Teller (N-2-BET) method, were used to understand the adsorption mechanism of cations in this adsorbent system. Batch sorption studies were conducted to investigate the effects of the initial pH, adsorbent dosage, initial metal ion concentrations and contact time on the adsorption process in single and binary solution systems. The adsorption kinetics of SP-PAM for Pb(2+ )and Cd2+ followed a pseudo-second-order model for both the single and binary systems. The adsorption isotherm fit the Langmuir model for Pb2+ and the Freundlich isotherm for Cd2+ well, with maximum adsorption capacities of 337 and 232 mg/g, respectively, for Pb2+ and Cd2+. The results for the adsorption of SP-PAM in binary solution systems showed Pb2+ and Cd2+ exhibited antagonistic and concentration-dependent selectivity, and the decrease in the adsorption of Cd2+ in the presence of Pb2+ was larger than that of Pb2+ adsorption in the presence of Cd2+ when the initial concentration was higher than 30 mg/L. SP-PAM also had good ability to remove heavy metals in simulated industrial wastewater. In summary, SP-PAM exhibited great potential for use as an alternative adsorbent in the treatment of wastewater containing heavy metal ions.