© by PSP Volume 23 – No 2a. 2014 Fresenius Environmental Bulletin 613 STUDIES ON REMOVAL OF CYANIDE FROM AQUEOUS ENVIRONMENTS USING ALUMINUM ELECTRODES Mohammad Reza Samarghandi 1 , Mohammad Ahmadian 2 , Jamal Mehralipur 1 , Amir Shabanlo 1 and Ali Poormohammadi 3, * 1 Hamadan University of Medical Sciences and Health Services, Department of Environmental Health and Health Sciences Research Center, Hamadan, Iran 2 School of Public Health, Kermanshah University of Medical Sciences, Kermanshah, Iran 3 Social Development & Health Promotion Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran ABSTRACT One of the most toxic compounds, cyanide, threatens human health and can enter environment in different forms. Owing to its high ability to remove various contaminants from aqueous environments, electrocoagulation process (ECP) is now considered to be an effective process. The aim of this study was to determine magnesium oxide nanoparti- cles (MgO) as a coagulant aid in ECP on removal of cya- nide from aqueous environments using aluminum elec- trodes. In this study, a reaction chamber was used with 4 Al electrodes (with dimensions 2x20x250 mm and volume 1 L) equipped with an electricity generating device to remove cyanide. The effects of pH, current density, initial cyanide concentration in the reactor inlet, and different doses of MgO nanoparticles as a coagulant aid were studied in this process. Results showed that process efficiency under pH=5, current density=15 mA/cm 2 , initial concentration= 100 mg/L and time=40 min was equal to 80%. Moreover, as coagulant aid increased, process efficiency increased too. In optimum levels of MgO coagulant aid (0.1 mg/L in ECP) and reaction time=45 min, cyanide removal effi- ciency was equal to 90%. Results obtained from kinetic studies showed that cyanide removal is most consistent with second-order model (higher R 2 ). According to results of this study, ECP is a suitable process for removing cya- nide-toxic contaminants. Moreover, MgO nanoparticles act as suitable coagulant aid in ECP along with Al elec- trode, increase process efficiency and, subsequently, in- crease cyanide removal from aqueous environments. KEYWORDS: Cyanide, electrocoagulation process, magnesium oxide, coagulant aid 1. INTRODUCTION Cyanide is a carbon-nitrogen radical which is one of the most toxic substances threatening quality of drinking * Corresponding author water used by humans. It is usually found in different forms (e.g. salt, ion, metal complex and molecular cyanide) in aqueous environments [1, 2]. Presence of cyanide and its compounds in environment, especially water resources, has become a major concern because it has adverse effects on aqueous ecosystem and is toxic for humans, even in very low concentrations, and results in some complications like nausea, vomiting, increased heart rate, pulmonary edema, lack of consciousness and death [3]. Cyanide compounds are widely used in different industries whose effluents are considered to be big sources of cyanide. Despite its highly toxic properties, cyanide is one of the necessary substances widely used in metal mining and recycling industries, metal plating, manufacturing insecticides etc. In addition, indus- trial wastewater usually contains high levels of heavy metals, such as copper, nickel, zinc, silver and aluminum; due to their high reactivity, cyanide reacts with them and produces metallic compounds with different toxicity and stability. Cyanide used in industries enters the environ- ment, especially surface waters, through industrial waste- water discharge. It has been reported that over 14 million kg of cyanide is discharged annually from industries worldwide [4-6]. According to laws passed in the Euro- pean Union, maximum annual allowable concentration of cyanide in aqueous resources is less than 40 µg/L. WHO has determined that maximum permissible concentration of cyanide must be 0.07 mg/L in drinking water [4, 7, 8]. Simi- larly, Iranian Institute of Standard and Industrial Research has considered this level as a national standard [9]. Nowa- days, various physical, chemical and biological processes have been used to remove cyanide from aqueous environ- ments. Each method has its own advantages and disadvan- tages [5, 10]. For example, although biological processes are considered as environmentally friendly processes, high concentration of cyanide in aqueous environments may be toxic for microorganisms, may reduce biodegradation level and may reduce process efficiency. In addition, these tech- nologies have not been widely used yet and need integra- tion of metallurgy, biology and process engineering, each of which requires special evaluation and examination [10]. Other methods include chemical oxidation and adsorp- tion. Chemical oxidation processes have some disadvan-