Assessment of redox-sensitive element mobility : discrepancy between laboratory and field data

Leaching tests have become popular tools to assess the environmental effect of materials containing pollutants e.g. wastes, construction materials, soils. Batch (EN 12457-3) and column (prEN 14405) leaching tests are both standardised. The standardisation regulates how the test should be performed i.e. the procedure, the amount of material to be used and how to handle the leachate. However, standardisation is often misinterpreted as quality insurance that the results of the test are relevant for any type of material and application. The EN 12457-3 test has thanks to the standardisation and its relatively low price become the most popular tests used to assess if waste material could be used in constructions. Basically waste materials fulfilling acceptance criteria for landfill for inert waste are often regarded as acceptable to reuse in the society.The aim of the presentation is to discuss the risk of using tests without a critical assessment of their relevance and limitations. Materials containing sulphides, iron and arsenic are specially challenging to assess as the standard batch leaching test underestimates the risk for leaching.The leaching of arsenic was underestimated by the EN 12457-3 test and the effect of open filtration, sample preparation and test conditions are discussed. The results showed that a material fulfilling criteria for landfill for inert waste leached more arsenic than was acceptable at a landfill for hazardous waste. In the second example, the documented generation of acidic leachate from blast furnace slag in field conditions has never been observed in the laboratory. The main hypothesis is that the development of unsaturated conditions caused the oxidation of sulphidic minerals in the blast furnace slag heap and generation of acid leachate.The selection of appropriate leaching tests should be done with regard to the real conditions that are to be assessed. Standardisation does not mean that the test is automatically adapted to the need. A relevant assessment requires therefore understanding of the geochemical process controlling the pollutant mobilisation and immobilisation in the actual material and its application. Such comprehension is a prerequisite to the selection of appropriate leaching procedures.Godkänd; 2009; Bibliografisk uppgift: Værtspublikationsredaktører: Jacques Mehu; 20090824 (chma