Nano-Catalysts and Colloidal Suspensions of Carbo-Iron for Environmental Application K. Mackenzie, H. Hildebrand, F.-D. Kopinke Helmholtz Centre for Environmental Research – UFZ, Department of Environmental Technology, D-04318 Leipzig, Germany ABSTRACT The present paper shows two different examples for ex- situ and in-situ water treatment using nano-sized materials. Two novel colloidal particles have been developed and tested in initial studies for i) the in-situ generation of sorption/reaction barriers based upon zero-valent iron on sorption-active carbon carriers (carbo-iron) for application in subsurface water treatment and ii) the selective catalytic elimination of halogenated hydrocarbons using Pd on magnetic carriers as agent for ex-situ waste water treatment. The common ground for both applications is the utiliza- tion of nano-particles for dehalogenation reactions in the aqueous phase in order to minimize mass transport limitation and therefore permit high decontamination rates. These water treatment applications have been selected for presentation in order to show the wide applicability of nano-sized materials in environmental technology. Keywords: zero-valent iron, carbo-iron, dechlorination, Pd catalyst, sorption-assisted reaction, water treatment 1 INTRODUCTION During the last ten years, intensive research has been carried out on the development of suitable materials for reactive barriers in subsurface application. Permeable reactive barriers (PRBs) on the basis of zero-valent iron have already been constructed at more than 120 sites worldwide and count as an approved technology [1]. The halogenated organic compounds (HOCs) are removed from the groundwater according to the equation: R-X + Fe 0 + H 2 O ﾆ Fe 2+ + R-H + OH - + Cl - . Recently, the application of nano-sized particles has been advanced, because colloidal solutions of metal particles can easily be injected into the aquifer without the necessity of extensive underground work. This fact and the potential of nano-sized zero-valent iron (ZVI) to migrate in groundwater to form a reactive zone have stimulated the research on nano-particles [2]. Literature studies on nano-sized ZVI reveal on the one hand desirable properties such as high reactivity and injectability. On the other hand, undesirable properties are also described, such as a tendency to agglomeration and untimely sedimentation and hence a limited mobility under aquifer conditions [3]. The hydrophilic nature of the iron surface makes it not well suited for source remediation. The utilization of hydrophilized carriers or poly(acrylic acid) helped to mobilize colloidal suspensions of ZVI [3]. The addition of emulsifying substrates forms emulsion droplets which contain the ZVI particles in water sur- rounded by an oil-liquid membrane. Emulsified zero valent iron (EZVI) has been successfully tested in a field-scale demonstration [4]. EZVI proved miscible with the organic phase; therefore, contact between the reaction partners was realized. Nevertheless, the addition of chemicals to the reactive agent is necessary in order to achieve the close contact between the reactants. In addition, the emulsified particles show even less mobility. The objective of our work is to develop materials with tailored properties for in-situ generation of sorption/ reaction barriers for subsurface water treatment at low cost and without the need for additional chemical supply. The surface properties should be suitable for both plume and source treatment. ZVI in every form and particle size has its limitations concerning the pollutant spectrum which can be treated; e.g. iron completely fails for the dehalogenation of aromatic substances, such as PCBs, halogenated benzenes and phe- nols. However, the utilization of catalytic hydrodehaloge- nation with Pd catalysts can solve this problem. Palladium catalysts have proved to be well suited for promoting hydrodehalogenation reactions in the aqueous phase according to the equation C l H m X n + n H 2 ﾆ C l H m+n + n HX [5]. The present paper aims at a treatment technique de- signed for special industrial wastewater contaminated with only small amounts of halogenated hydrocarbons – amounts which are nevertheless large enough to make a discharge into municipal sewage works impossible. The consequence is the necessity of expensive and energy-intensive incineration of aqueous waste. Therefore, especially for medium-sized enterprises, a decentralized selective waste- water dehalogenation treatment brings not only ecological credibility but also an important economic advantage. Our research in the field of ex-situ water treatment follows the aim of detoxifying the water by a selective destruction of the HOCs in reductive hydrodehalogenation reactions on nano-catalysts containing palladium. By detoxi- fication we mean that the persistent HOCs are converted into dehalogenated organic compounds which can easily be removed by biodegradation in a wastewater treatment plant. 2 EXPERIMENTAL Carbo-iron. The support material activated carbon (AC, e.g. SA Super from Norit), was ground in the presence of deionized water (horizontal mill 200 AHM, Alpine NSTI-Nanotech 2007, www.nsti.org, ISBN 1420061836 Vol. 2, 2007 639