Effect of reductive conditions on metal mobility from wasteland solids: an example from the Mortagne-du-Nord site (France)

Metallurgical industries have created numerous wastelands where large quantities of wastes have been stocked. The presence of micropollutants is not as much of a problem as the fact that this pollution is mobile and could thereby affect human health. Strong reductive conditions present in several natural or anthropogenic situations could influence metal release to the environment. Two waste samples (difference in age: ca. 20 a) from the Mortagne-du-Nord (France) wasteland were studied to evaluate the behaviour of their metal ions under reductive conditions: a recent sample mainly composed of sulphides and an older solid composed of oxidised phases. Under reductive conditions, release of metals increased in the old sample, but no modifications were observed in the recent solid. As shown by a weathering experiment, alteration of the older solid (initially consisting of sulphides) induced the creation of Fe oxyhydroxides, which adsorbed or coprecipitated the other metals. Under reductive conditions, these oxyhydroxides were dissolved, and the metallic content of the sample was released into the aqueous medium.