Applied Catalysis B: Environmental 53 (2004) 13–20 Removal of toxic cyanide and Cu(II) Ions from water by illuminated TiO 2 catalyst M.A. Barakat a,b,∗ , Y.T. Chen b , C.P. Huang b a Extractive Metallurgy Department, Central Metallurgical R&D Institute, Cairo, Egypt b Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA Received 14 March 2004; received in revised form 26 April 2004; accepted 8 May 2004 Available online 8 June 2004 Abstract Due to its strong complex formation potential, cyanide (CN - ) has been used in a variety of metal processing and metal extracting processes. As a result, the wastewaters generated from such processes always contain a mixture of cyanide and metal ions. Photocatalytic degradation using ultraviolet-irradiated TiO 2 suspension has been investigated for destroying both free and complex cyanide with a concurrent removal of the metal (exemplified by copper). The process uses the photogenerated holes at the surface of TiO 2 upon UV irradiation of 100 W. In contrast to conventional cyanide waste treatment processes, the photocatalytic processes convert both free and complex cyanide species into carbon dioxide and nitrogen with no residual harmful chemicals remaining. Synthetic cyanide wastes (dilute solutions of sodium and copper cyanide) were used. The spent TiO 2 was separated by coagulating then centrifugation. The residual CN - concentration was monitored periodically using spectrophotometric analysis. Results revealed that about 78% of free cyanide (10 -3 M) was removed after illumination for 4 h in the presence of 1 g/L (TiO 2 ) at pH 11. Free copper (10 -2 M) was completely removed in a shorter time (3 h). The co-existence of Cu(II) and CN enhanced the removal efficiency of both CN and copper; the removal (%) increased with increase of Cu:CN molar ratio reaching a complete removal for both copper and cyanide at a ratio of 10:1 at the same previous conditions of free cyanide. © 2004 Elsevier B.V. All rights reserved. Keywords: Cyanide; Cu(II) ions; Water treatment; TiO 2 photocatalyst 1. Introduction Hazardous wastes containing free and complex cyanides are generated in large volumes during various industrial ac- tivities such as mining and metal finishing. Cyanides are common contaminants in the waste streams of chemical synthesis and metallurgical processes. As a class, cyanides are highly toxic and must be destroyed or removed from wastewaters prior to discharge. The most common method for treating free or simple cyanide is alkaline chlorination [1–3]. However, chlorination of cyanide results in highly toxic intermediates (e.g., cyanogen chloride). Among the various treatment processes, photocatalytic oxidation of cyanide at semiconductor surface with UV ∗ Corresponding author. Present address: Department of Material Sci- ence Engineering, University of Delaware, 201 Dupont Hall, Newark, DE 19716, USA. Tel.: +1-302-8311445; fax: +1-302-8314545. E-mail address: barakar@udel.edu (M.A. Barakat). radiation offers distinct advantages for disposing dilute cyanide wastes. It ensures destruction of both free and some cyanide complexes, with weak-acid dissociable met- als such as copper, without creating toxic residues. TiO 2 semiconductor has been studied as an efficient photocata- lyst for remediating polluted water [4–6]. Mihaylov et al. [7] and Peral and Domenech [8] investigated the oxidation of cyanide using various photocatalysts such as TiO 2 , ZnS, ZnO, CdS, V 2 O 5 , SiO 2 and Fe 2 O 3 , and reported that only TiO 2 and ZnO were effective for elimination of cyanide in aqueous solutions. Hudson et al. [9] investigated the crystallinity effect of titanium dioxide (amorphous versus anatase), ultraviolet intensity and oxygen exposure on the rate of cyanide destruction and reported that anatase ex- hibited superior photocatalytic activity to the amorphous form of TiO 2 . The poor activity of amorphous TiO 2 was attributed to the recombination of photo-excited electrons and holes at defects located on the surface and in the bulk of the coatings. As expected, oxygen was found to play a 0926-3373/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2004.05.003