PERFORMANCE OF CARBON BLACK-SLURRY ELECTRODES FOR 4-CHLOROPHENOL OXIDATION J.-L. BOUDENNE* and O. CERCLIER Laboratoire de Chimie-Evironnement (JE No. 438), case 29, Universite de Provence, 3, place Victor Hugo, 13331 Marseille CeÂdex 3, France (First received September 1997; accepted May 1998) AbstractÐThe degradation of 4-chlorophenol (4-CP) by electrochemical oxidation in the presence of carbon black (CB) was studied in a laboratory reactor. This reactor consisted of a stack of Ti/Pt elec- trodes. After the mixing of the solution to be treated with CB, the slurry electrode thus obtained ¯ows through the electrode grids. The reaction pathways and kinetics were studied by means of high per- formance liquid chromatography coupled with a UV detection, ionic chromatography coupled with a conductimetric detection and gaseous chromatography coupled with mass spectrometry. The reaction pathways were thus determined: after the C±Cl bond breaking, phenol and chloride ions were detected in the solution. The formation of 2-chlorophenol was also detected. The in¯uence of the amount of CB used on the degradation yield of 4-CP was also studied. The full mineralization of 4-CP could be reached if CB was present in a sucient amount and, in this case, no chlorine was detected. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐelectrooxidation, 4-chlorophenol, carbon black, reaction kinetics and pathways INTRODUCTION Phenols are important synthesis intermediates in the chemical industry. They are also used for the manufacturing of resins, preservatives, and pesti- cides and they are used in the mechanical industries. They are found in wood, coal and, to a lesser degree, in household garbage (Mathian, 1989). Concerning more speci®cally chlorophenols, they are mainly used for the production of insecticides, antifungal agents or pharmaceutical products. They can also be synthesized during the treatment of wastewaters when a chlorination step exists (Esplugas et al., 1994). These compounds can be found in soils and groundwaters. Most of them are carcinogenic (Flora et al., 1994) and their presence can be harm- ful for life in general. Therefore, chlorophenols are considered to be prioritary pollutants by the US EPA (Environmental Protection Agency). Numerous chemical treatment processes do exist to degrade chlorophenols, but most of them do not lead to the complete mineralization of phenols, or are either expensive or time-consuming. Among these methods, we can mention: ± UV photocatalytic oxidation (Guyon, 1983), with or without an oxidizing agent such as hydro- gen peroxide (H 2 O 2 ) or ozone (O 3 ) (Esplugas et al., 1994); ± photochemical oxidation with a semi- conductor, most often TiO 2 (Mills and Morris, 1993; O'Shea and Cardona, 1994); ± wet oxidation techniques (WOT) (Li et al., 1993); ± chemical oxidation by H 2 O 2 with Fe 2+ ions as a catalyst (Fenton method) (Koyama et al., 1994; Levy, 1995), by ozone (Al-Enezi et al., 1994), or by chlorine dioxide (ClO 2 ) (Wajon et al., 1982). Apart from these well known techniques, the elec- trochemical treatment of industrial wastes seems to be an interesting new way (Walsh and Mills, 1993). The ®rst papers dealing with the electrochemical degradation of phenols were published in the late 50's. But it was only around 1980 that the ®rst electrochemical reactors were used (Mieluch et al., 1975; Mowla, 1982) and that the in¯uence of the nature of the electrodes on the degradation yields began to be studied (Landaez-Machado, 1978). The ®rst electrodes consisted of grids made of graphite, then of PbO 2 pellets, and ®nally of reticulous glassy carbon grids (Gattrell and Kirk, 1990). The main drawback of these electrodes was their rapid passivation which stopped the reaction of degra- dation. The use of electrodes made of platinum (Goncharuk and SapsaõÈ, 1984), and later of bi- metallic electrodes such as Pt + IrO 2 or SnO 2 (Comninellis and Pulgarin, 1993), Ti or RuO 2 (Pulgarin et al., 1994) delayed this passivation phenomenon. In this study, we used an electrochemical reactor having electrodes made of platinized titanium Wat. Res. Vol. 33, No. 2, pp. 494±504, 1999 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/98 $19.00 + 0.00 PII: S0043-1354(98)00242-5 *Author to whom all correspondence should be addressed. [Tel: +33-4-91106376; Fax: +33-4-91106377, E-mail: lceeau@newsup.univ-mrs.fr]. 494