Assessment of the phytoremediation effectiveness in the restoration of uranium mine tailings

Abstract

Uranium (U) contamination due to mining and metallurgical operations is a serious problem and poses a high potential threat to humans and other organisms. The application of amendments and/or plants, known as assisted phytoremediation, can accelerate the adsorption, complexation and precipitation processes in soil, and therefore can facilitate the restoration of U mining areas. This study located in the central-west of peninsular Spain was focussed on two different U mine waste dumps (MWD), where the assisted phytoremediation process was implemented. At each MWD, an area of 10 ha (approx.) was selected for sugar lime (SL) application, at a rate of 75 T ha −1. In addition, after SL addition, common grasses Cynodon dactylon, Secale cereale, and the leguminosae Vicia sativa were seeded. Evolution of soil physico-chemical properties and plant development was monitored for 69 months in Top, Medium and Low areas of both MWDs. The main results indicated a positive effect of the amendment, improving the development of the spontaneous and induced vegetation and the accumulation of soil organic matter. Values of pH were maintained in the range of the neutrality during all the experimentation period. In general, total concentrations of trace elements (including U) presented a high variability. Values were similar in the different studied areas of each MWD (Top, Medium and Low) and did not change in time. Trace elements contents were, in general, higher than those found in non-contaminated soils. However, U and Mn availability decreased with time, as well as the accumulation of trace elements (especially U and Mn) in the studied plants. Moreover, these contents were lower than the permitted limit for animal consumption. In conclusion, application of phytoremediation contributed to the stabilization of U within the soil-plant system, mainly by its positive effects on vegetation cover and the consequent increase in soil organic matter.