Cyanide extraction from contaminated soil: a method comparison

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.