10 The European Journal of Mineral Processing and Environmental Protection Vol. 4, No. 1, 1303-0868, 2004, pp. 10-14 Technical Note Cyanide extraction from contaminated soil: a method comparison T. Rennert, T. Mansfeldt* Arbeitsgruppe Bodenkunde und Bodenökologie, Fakultät für Geowissenschaften, Ruhr-Universität Bochum, Bochum, D-44780, Germany Received 31 July 2002; accepted 15 April 2004 ABSTRACT Soils on sites of former manufactured gas plants are usually contaminated with iron-cyanide complexes. We investigated the extraction of cyanide from 23 contaminated soils by three methods, which are prescribed by the German Federal Soil Protection Act and Ordinance: the soil-saturation extract with water, SSE, with a very narrow soil:solution ratio; the so-called S4 water extract with a soil:solution ratio of 1:10; and 1M NH4NO3 extracts with a soil:solution ratio of 1:2.5. Highest cyanide concentrations were found in the SSEs ranging from 0.1 to 70.5mg/l. However, percental cyanide extraction was lowest in these extracts. Cyanide concentration and percental extraction obtained by the three methods were correlated among the methods with squared correlation coefficients ranging from 0.45 to 0.80. The relationship between extract pH and cyanide extraction was weak. As the results differed among the methods, they cannot be regarded as equivalent with respect to cyanide extraction. Due to the narrow soil:solution ratio, the longer reaction time of 48h, and the strongest similarity between soil and extract pH, we recommend the SSE method to investigate cyanide extraction from contaminated soil. © 2004 SDU. All rights reserved. Keywords: Cyanide; Extraction; Contaminated soil; Manufactured gas plant 1. INTRODUCTION The presence of cyanide, CN, in soil and ground water is caused predominantly by anthropogenic inputs, because cyanide from natural sources is readily consumed by soil microorganisms (Knowles, 1976). Cyanide-containing compounds occurring in the soil environment originate from industrial processes such as coal gasification (Shifrin et al. , 1996), electroplating (Mohler, 1969), gold mining (Boucabeille et al. , 1994), pig iron production (Mansfeldt and Dohrmann, 2001), and paper recycling (Mansfeldt, 2001) or the use of road salt (Paschka et al. , 1999). Sites of former manufactured gas plants, MGP, or coke ovens are widespread in many industrialised countries and in soils on these sites, cyanide is present as the ferric ferrocyanide Berlin Blue, Fe4[Fe(CN) 6]3, and dissolved iron-cyanide complexes, [Fe(CN) 6] 3-/4- (Meeussen, 1992; Mansfeldt et al. , 1998). The total cyanide concentrations in these soils are up 115g/kg (Fowler et al. , 1994) and up to 85mg/l in the ground water of these sites (Ferguson et al. , 2003). In soil extracts of a MGP site soil, cyanide complexes of Fe, Cu, and Ni as well as thiocyanate, SCN - , have been detected with ferrocyanide, [Fe(CN) 6] 4- , as the dominant species (Theis et al. , 1994). Free cyanide, HCNg, aq and CN - aq, were not detected. However, there is no standard procedure to extract particularly cyanide in order to predict possible contamination of the seepage and ground water with cyanide, and, generally, investigations on extractable cyanide from soil have been rarely carried out (Kjeldsen, 1999). Therefore, the aim of this study was to investigate and to compare the cyanide extraction from contaminated MGP site soils by three methods using batch experiments. * Corresponding author. E-mail: Tim.Mansfeldt@rub.de