SELECTED PAPERS FROM THE 2ND CONTAMINATED LAND, ECOLOGICAL ASSESSMENT AND REMEDIATION (CLEAR 2014) CONFERENCE: ENVIRONMENTAL POLLUTION AND REMEDIATION Biosorption of Cu(II) by immobilized microalgae using silica: kinetic, equilibrium, and thermodynamic study Hongkyun Lee 1 & Eunjung Shim 1 & Hyun-Shik Yun 1,2 & Young-Tae Park 1 & Dohyeong Kim 1 & Min-Kyu Ji 1 & Chi-Kyung Kim 3 & Won-Sik Shin 4 & Jaeyoung Choi 1 Received: 30 November 2014 /Accepted: 26 April 2015 # Springer-Verlag Berlin Heidelberg 2015 Abstract Immobilized microalgae using silica (IMS) from Micractinium reisseri KGE33 was synthesized through a sol-gel reaction. Green algal waste biomass, the residue of M. reisseri KGE33 after oil extraction, was used as the bio- material. The adsorption of Cu(II) on IMS was tested in batch experiments with varying algal doses, pH, contact times, ini- tial Cu(II) concentrations, and temperatures. Three types of IMSs (IMS 14, 70, and 100) were synthesized according to different algal doses. The removal efficiency of Cu(II) in the aqueous phase was in the following order: IMS 14 (77.0 %)< IMS 70 (83.3 %)<IMS 100 (87.1 %) at pH 5. The point of zero charge (PZC) value of IMS100 was 4.5, and the optimum pH for Cu(II) adsorption was 5. Equilibrium data were de- scribed using a Langmuir isotherm model. The Langmuir model maximum Cu(II) adsorption capacity (q m ) increased with the algal dose in the following order: IMS 100 (1.710 mg g - 1 )>IMS 70 (1.548 mg g - 1 )>IMS 14 (1.282 mg g -1 ). The pseudo-second-order equation fitted the kinetics data well, and the value of the second-order rate con- stant increased with increasing algal dose. Gibbs free energies (ΔG°) were negative within the temperature range studied, which indicates that the adsorption process was spontaneous. The negative value of enthalpy (ΔH°) again indicates the exothermic nature of the adsorption process. In addition, SEM-energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectros- copy (XPS) analyses of the IMS surface reveal that the algal biomass on IMS is the main site for Cu(II) binding. This study shows that immobilized microalgae using silica, a synthesized biosorbent, can be used as a cost-effective sorbent for Cu(II) removal from the aqueous phase. Keywords Adsorption . Silica . Microalgae . Copper . Biosorbent . Micractinium reisseri KGE33 Introduction Copper contamination of wastewater is a significant universal problem, but some industries still dispose of copper-rich ef- fluents. These effluents can have serious implications not only for the environment but also for human populations via the food chain because excess Cu(II) can cause several diseases and disorders that can be fatal (Sağ and Aktay 2002; Gotoh et al. 2004; Justi et al. 2005). In the past decades, several traditional methods for the removal of heavy metal ions such as chemical precipitation, lime coagulation, solvent extrac- tion, ion exchange, and adsorption have been widely used, but these methods are expensive and not effective (Karthikeyan et al. 2007). Biosorption uses biomaterials with sufficiently high metal- binding capacity and selectivity for heavy metals and is be- coming an economical, efficient, sustainable, and potential alternative method (Volesky and Holan 1995; Harry 1999; Miretzhy et al. 2006; Sheng et al. 2007). The performances of biomaterials such as bacteria, fungi, algae, and higher Responsible editor: Philippe Garrigues * Jaeyoung Choi jchoi@kist.re.kr 1 Green City Technology Institute, Korea Institute of Science and Technology, Seoul 136-791, South Korea 2 Department of Environmental Engineering, Yonsei University, Wonju 220-710, South Korea 3 Soil and Groundwater Division, Hyorim Industries Inc., Seoungnam 463-839, South Korea 4 Department of Environmental Engineering, Kyungpook National University, Daegu 702-701, South Korea Environ Sci Pollut Res DOI 10.1007/s11356-015-4609-1