Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines

The occurrence of mine water colloids mainly results from the formation of oxyhydroxides and hydroxysulfates of Fe(III) and Al. In acid rock drainage solutions As and Pb are strongly associated with the colloids. In the near-neutral bulk waters of mines, as for instance in adit waters, trace elements such as As, Pb, Cu and the rare earth elements are sorbed. These trace contaminants can be scavenged by the colloids in the near-neutral mine waters and can be immobilized due to colloid coagulation and aggregate precipitation (‘natural attenuation’). In the pH range of 4–6, a pH range that must be passed through during the flooding of a mine, also U(VI) is adsorbed to the colloids and can be temporarily immobilized by precipitating colloids. The latter can result in a delay of the uranium release of a uranium mine and thus in a flattening and broadening of the uranium concentration profiles during the mineʹs ‘first flush’.