Author's personal copy Journal of Hazardous Materials 166 (2009) 978–983 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Treatment of a synthetic solution of galvanization effluent via the conversion of sodium cyanide into an insoluble safe complex Ibrahim Ismail, Nabil Abdel-Monem, Seif-Eddeen Fateen ∗ , Waleed Abdelazeem Department of Chemical Engineering, Cairo University, Giza, Egypt article info Article history: Received 8 July 2008 Received in revised form 26 November 2008 Accepted 1 December 2008 Available online 6 December 2008 Keywords: Industrial wastewater treatment Sodium cyanide Ferrous sulfate abstract Wastewater discharged from metal-finishing processes usually contains cyanide, a hazardous substance that is used extensively in the surface finishing industry. In the present study, a synthetic solution resem- bling the contaminated wastewater was chemically treated using ferrous sulfate. This simple one-step process was applied successfully to remove cyanide from metal finishing wastewater. The experiments were carried out on a synthetic solution containing ions of cyanide and zinc. The effects of mixing veloc- ity, ratio of ferrous ions to cyanide ions, ferrous ions concentration, initial cyanide concentration, pH of solution, temperature, mixing time and zinc ions concentration were studied. The results showed that the removal efficiency of cyanide increased as the mixing velocity increased, ferrous ion molar ratio to cyanide ions increased, temperature increased and time of mixing increased at an optimum of pH 8. The reduction of cyanide concentration reached the allowable limit for wastewater discharge according to the Egyptian Environmental Law decree 44/2000, which is 0.2 mg/l. The formed complexes were analyzed and the stability of each complex was studied under different pH value solutions after 7 days of contact. A typical example of electroplating wastewater from a local company in the field of metal finishing, which contains18 mg/l CN - and 12 mg/l Zn 2+ , was treated according to the determined optimum conditions for the treatment process and the concentration of CN - was reduced to 0.095 mg/l after 15 min of agitation. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Cyanide, a poisonous substance dangerous to humans, animals, plants and aquatic organisms, can be found in the effluent of several industries such as paint and ink formulation, petroleum refining, explosives, case hardening, automobile industry, chem- icals industry, pesticides industries, synthetic fiber production, electroplating, thermoelectric power stations, mining, electronics, and coke [1–18]. Its effects on the human and the environ- ment have been well reviewed by Mudder and Botz [14]. Due to its toxic nature, cyanide must be recovered, removed or destroyed. There are many reported processes for treating cyanide- containing effluents [1–30]. These processes can be categorized as biodegradation [1,24,26]; adsorption on activated carbon [6,18]; oxidation via chemical, electrochemical or photochemical pro- cesses [7,9,10,12,15,19,23]; chemical precipitation [11]; hollow fiber gas membranes [13]; ultrasonic waves [15]; ion exchange [17]; extraction [20]; photocatalytic using Ti catalyst [22,25]; and volatilization then absorption by NaOH [21]. The suitability of any ∗ Corresponding author. Tel.: +20 011 400 888. E-mail addresses: dr ismail@instruchem.org (I. Ismail), nabil a monem@hotmail.com (N. Abdel-Monem), sfateen@alum.mit.edu (S.-E. Fateen). of the above-mentioned processes to a specific cyanide-containing effluent depends on the effluent flow rate, cyanide concentration, associate chemical species, permissible level of cyanide in the efflu- ent after treatment, technical level of the entity’s employees and the economy and finances of the process. In Egypt, electroplating workshops are major sources for cyanide-contaminated wastewater. They are geographically dis- tributed all over the country. Most of them are small size entities operated by a few low technical level labors. Due to these uncom- fortable circumstances, it is not possible to individually treat the effluent of every workshop using an advanced technique or to col- lect the effluent of these small entities to be treated in a centralized treatment unit. Currently, most of these workshops do not treat their waste by any means. They discharge the effluents as is to the nearest sewage line creating a severe environmental problem. A real case study of a medium-size Egyptian electroplating workshop producing effluent of 31 m 3 /day was presented by Abou-Elela et al. [8]. They treated the cyanide-containing effluent using alkaline chlorination, which does not destroy the pollutants completely [27]. In caustic chlorine treatment, cyanide is converted to cyanate which is also toxic. Complete destruction of cyanate is difficult. The chlorination process also produces secondary by-products such as trihalo-methanes, which are highly toxic and carcinogenic [28]. The treated water contains huge amount of dissolved chlorine. Considering the nature of the cyanide effluents of the Egyptian 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.12.005