Ability of Pistia stratiotes L. and Eichhornia crassipes for remediation of uranium-contaminated waste water

The field sampling, laboratory analysis and hydroponic solution culture experiments were conducted on the native aquatic plants, Pistia stratiotes L. and Eichhornia crassipes in-situ repair ability of uranium mine pit water. The results of field sampling analysis show the strong enrichment of uranium from abandoned uranium mine pit water by Pistia stratiotes L. and Eichhornia crassipes. The uranium concentration range of abandoned uranium mine pit water is between 0.4 mg/L to 0.6 mg/L, which is about 10 times higher than the national emission standards of China. The mean uranium concentrations (dry weight) in roots of Pistia stratiotes L. and Eichhornia crassipes are 1015.40 mg/kg and 504.87 mg/kg, and the enrichment coefficients are 2071 and 1001, respectively. The results of hydroponic solution culture experiments show that the uranium removal ability is closely relative to the growing period and fresh weight of per plant and the area of the plant covering water. 100 g of Pistia stratiotes L. or Eichhornia crassipes at the mature stage (fresh weight more than 100 g per plant) are grown in 1 L of uranium mine pit water with the initial concentration of uranium was 1.93 mg/L, after 10 days, the uranium concentration reduces to below the national emission standards of China, and the uranium removal rates are higher than 98%. SEM-EDS results show that a mass of uranium precipitates with nanometer sized schistose structures on the root surface of Pistia stratiotes L. and Eichhornia crassipes are formed at acidic conditions. But there are no similar crystals observed on the surface of Pistia stratiotes L. and Eichhornia crassipes at alkaline conditions. The present work suggests the different repair mechanisms of uranium-contaminated waste water by the Pistia stratiotes L. and Eichhornia crassipes between acidic and alkaline conditions. (authors)