BACKGROUND: In the present work, Hg (II) is considered as one of the most dangerous elements being released excessively into the environment from various sources. Therefore, the aim of this study is the removal of Hg (II) from wastewater effluent by synthesizing a magnetic chitosan modified with glutaraldehyde (MCS-GA) as an adsorbent. The composite structure was characterized using SEM/EDAX, FTIR, and XRD techniques. The adsorbent was tested by a batch system to determine the optimum conditions for removing Hg (II) under real conditions. RESULTS: The results showed that 0.5% GA effectively enhanced the removal efficiency. The maximum adsorption capacity of MCS-GA was 96 mg g(-1) at pH 5.0 and 25 degrees C. The adsorption isotherm data obeyed the Langmuir model (R-2>0.981) and pseudo -second -order (R-2>0.996) kinetic models. It was also found that Hg (II) adsorption on MCS-GA is inherently exothermic and occurs spontaneously. The reusability of MCS-GA was approved over 12 sequential cycles of adsorption -desorption. ANOVA analysis showed that the contact time has a synergistic effect on Hg (II) removal, whereas pH and initial concentration have antagonistic effects. CONCLUSION: Overall, the synthesized adsorbent was able to remove Hg (II) efficiently under both experimental and real conditions. (C) 2016 Society of Chemical Industry