479 Korean J. Chem. Eng., 35(2), 479-488 (2018) DOI: 10.1007/s11814-017-0311-y INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: ramavandi_b@yahoo.com, b.ramavandi@bpums.ac.ir Copyright by The Korean Institute of Chemical Engineers. Adsorptive performance of calcined Cardita bicolor for attenuating Hg(II) and As(III) from synthetic and real wastewaters Abolfazl Teimouri * , Hossein Esmaeili ** , Rauf Foroutan ** , and Bahman Ramavandi *** ,† *Department of Chemical Engineering, School of Chemical Engineering, Kherad Institute of Higher Education, Bushehr, Iran **Department of Chemical Engineering, Bushehr Branch, Islamic Azad University, Bushehr, Iran ***Department of Environmental Health Engineering, Bushehr University of Medical Sciences, 7518759577 Bushehr, Iran (Received 13 September 2017 • accepted 5 November 2017) Abstract-The first application of calcined Cardita bicolor oyster shell (CCBS) for Hg(II) and As(III) adsorption from synthetic and real wastewaters was tested. The main elements in CCBS structure were carbon, oxygen, magnesium, phosphor, and calcium. Effects of different parameters like initial pH, contact time, temperature, and CCBS dosage were assessed. The results showed that the maximum recovery of Hg(II) and As(III) adsorption was determined as C 0 =10 mg/L, t=80 min, T=25 o C, CCBS dosage=5 g/L, and pH=6 (for mercury ion) and 7 (for arsenic ion). In these conditions, 95.72% Hg(II) and 96.88% As(III) were removed from aqueous solution. The correlation coefficient (R 2 ) values for both adsorbates were obtained >0.98 and >0.96 for Langmuir and Freundlich isotherm models, respectively. Pseudo-second-order kinetic model was more capable to describe kinetic behavior of adsorption process of both metal ions in comparison with pseudo-first-order model. The half life (t 1/2 ) value for Hg(II) and As(III) with initial concen- tration of 10 mg/L was 4.032 and 4.957 min, respectively. Moreover, thermodynamic parameters of enthalpy (ΔH o ), entropy (ΔS o ), and Gibbs free energy (ΔG o ) were investigated. Two real wastewaters obtained from a leather factory and a landfill leachate were successfully treated using CCBS. The results confirmed that adsorption process of metals ions was exothermic and spontaneous. Keywords: Cardita bicolor , Adsorption Isotherm, Hg(II), As(III), Kinetic Behavior, Real Wastewater INTRODUCTION Industrial wastewaters contain high amount of organic and inor- ganic toxic contaminants like heavy metals. These toxic metals are discharged into the water bodies and have serious effects on the quality of water bodies [1]. Toxic heavy metals are carcinogenic, and if the metals are not removed from wastewater, they can deterio- rate the environmental quality and contaminate the food chain [2,3]. Among toxic and hazardous heavy metals, mercury can cause water and air pollution [4,5]. It is non-biodegradable and consid- erably toxic and can be released into the environment through dif- ferent processes such as mining and metals purification, cement production plants and natural gas processing [6,7]. Allowable amount of mercury ion in the drinking water based on World Health Organization (WHO) recommendation is 0.001 mg/L [8]. Increas- ing the mercury ion in the human body can damage the cells and central nervous system and inhibit the activity of enzymes [2]. Arsenic ion is another toxic and hazardous metal in the envi- ronment. It is produced during natural process of slate and sedi- ment washing and human activities including mining, burning fossil fuels, and the use of pesticides and insecticides and enters into the environment [9]. Arsenic can be transferred into human bodies or other creatures through drinking water and/or food chain. It causes various diseases such as skin, lung, and kidney cancer and nervous disorders, weakening of muscles, anorexia and nausea [10]. Maxi- mum allowable amount of As(III) in the drinking water was set as 10 μg/L based on WHO, European Union (EU), and United States Environmental Protection Agency (US EPA) [11]. In recent years, various methods such as chemical precipitation, solvent extraction, membrane processes, filtration, reverse osmosis, oxidation, ion exchange, and adsorption have been applied to re- move heavy metal ions from wastewater [12-15]. However, some of these methods are not widely used due to high cost and low feasibility in the industrial scale [16]. Recently, adsorption method was frequently used as it is economically feasible, versatile, efficient, simple, and bio-compatible [17,18]. Besides, the adsorbate (here, heavy metals) and adsorbent could be recycled if desired [19], which makes the adsorption process more cost-effective. In the adsorp- tion method, the utilization of low- or no-cost agricultural and bio- logical waste materials has been highly considered. Aspergillus flavus biomass [20], Rhizopus oryzae biomass [14], Malva sylvestris [2], and Sargassum oligocystum [21] are instances of low-cost materi- als applied for heavy meals removal. Although horticultural and agricultural wastes have been widely used to produce adsorbents, marine resources (except algae whose research on their adsorption characteristics is going to be com- pleted) such as bivalves, crayfish, shrimp, and oyster are rarely used to produce adsorbents. Literature review showed that the marine resources, especially oysters shell wastes, have suitable properties