TREATMENT OF HEAVY POLLUTED ACID DRAINAGE WATERS BY MEANS OF A PASSIVE SYSTEM

A large dump consisting of low-grade uranium ores and mining wastes located in the uranium deposit Kurilo, Bulgaria, was after rainfall a source of acid drainage waters containing toxic heavy metals, radionuclides, arsenic and sulphates in concentrations much higher than the relevant permissible levels. The generation of these polluted waters was connected with the presence of several acidophilic chemolithotrophic bacteria, which oxidized the sulphide minerals and tetravalent uranium present in the dump. The attempts to prevent these processes by the addition of alkalizing minerals to the dump had only a temporary and a partial effect. For that reason the polluted waters were subjected to an efficient treatment by means of a passive system of the type of the constructed wetlands.

Automated summary

After rainfall, a large dump of low-grade uranium ores and mining wastes in Kurilo, Bulgaria, produced acid drainage waters with high concentrations of toxic heavy metals, radionuclides, arsenic, and sulphates. This pollution was caused by acidophilic chemolithotrophic bacteria oxidizing sulphide minerals and tetravalent uranium in the dump. Efforts to prevent these processes using alkalizing minerals were only temporarily effective, so the polluted waters were treated efficiently with a passive system like constructed wetlands.