Passive/biological treatment of waters contaminated by uranium mining

Treatment of radioactively-contaminated and metal-laden mine waters and of seepage from tailings ponds and waste rock piles is among the key issues facing WISMUT GmbH in their task to remediate the legacy of uranium mining and processing in the Free States of Saxony and Thuringia, Federal Republic of Germany. Generally, contaminant loads of feed waters will diminish over time. At a certain level of costs for the removal of one contaminant unit, continued operation of conventional water treatment plants can hardly be justified any longer. As treatment is still required for water protection, there is an urgent need for the development and implementation of more cost efficient technologies. WISMUT GmbH and BioPlanta GmbH have studied the suitability of helophyte species for contaminant removal from mine waters. In a first step, original waters were used for an in vitro bioassay. The test results allowed for the determination of the effects of biotic and abiotic factors on helophytes' tolerance range, growth, and uptake capability of radionuclides and metals. Test series were carried out using Phragmites australis, Carex disticha, Typha latifolia, and Juncus effusus. Relevant contaminant components of the mine waters under investigation included uranium iron, arsenic, manganese, nickel, and copper. Investigations led to a number of recommendations concerning plant selection for specific water treatment needs. In a second step, based on these results, a constructed wetland was built in 1998 as a pilot plant for the treatment of flood waters from the Pohla-Tellerhauser mine and went on-line. Relevant constituents of the neutral flood waters include radium, iron, and arsenic. This wetland specifically uses both physico-chemical and microbiological processes as well as contaminant accumulation by helophytes to achieve the treatment objectives. With the pilot plant in operation for three years now, average removal rates achieved are 95 % for iron, 86 % for arsenic, and 75 % for radium. WISMUT GmbH intends to put a number of other projects of passive/biological mine water treatment into operation before the end of 2001.