Heavy metal removal by composite alginate beads composed of nanomaterials

Together with population increase and urbanization, water pollution is an important environmental problem. Heavy metals are one of the pollutant interests in water resources. These metals are toxic and carcinogenic that affect livings by accumulating in the food chain. For these reasons, it is a necessity of treating heavy metals. Adsorption, one of the treatment methods, is a cheap, easy to apply and effective alternative for heavy metal removal. Alginate is a natural adsorbent obtained from brown algae which can capture heavy metals by carboxyl groups in the polymer chain. Since alginate can make gels with cations, mostly utilized in bead form and combined with various materials in order to increase its efficiency. For this purpose, nanometal oxides (aluminum oxides, zinc oxides and zirconium oxides) known with their high surface area were preferred within the context of the study. Alginate – nanometal oxide composite beads were tested for the removal of multiple heavy metals (Pb2+, Cu2+ and Cd2+) from synthetic wastewaters by using batch and continuous reactors. The best heavy metal removal efficiencies were obtained by alginate – nano zinc oxide beads at the ratio of 1:0.5, value of pH 5.5 (in the range of 3 – 5.5). Pb2+ had the highest affinity among the metal ions towards this adsorbent that was followed by Cu2+ and Cd2+. For effective multiple heavy metal uptake, adsorption equilibrium time was determined as 24 hours and the data were found compatible with pseudo second order model. In addition, the metals adsorption was suitable for Langmuir isotherm that the maximum adsorption capacity of Pb2+ was calculated as 76.3 mg/g. On the other hand, the highest heavy metal removal efficiencies were obtained by 10 g alginate – nano zinc oxide beads at 0.25 mL/min flow rate in the continuous reactor. KEYWORDS: Adsorption, Copper, Biopolmer, Lead, Nanometal oxide