The Research Of Heavy Metal Pollution Soil In An Uranium Mine And The Accumulated Characteristics Of Uranium Enrichment Plants

Heavy metal pollution in soil has become a major environmental issue in the world,and the heavy metal pollution control is regarded as an urgent work. Two approaches, i.e.,physiochemical-remediation and phyto-remediation are commonly used all over the world.Compared with physiochemical-remediation, phyto-remediation has several benefits. Firstand foremost, phyto-remediation is economic and easy to be applied. Seondly,phyto-remediation never cause secondary pollution. Moreover, the correspondingpost-processing of this approach is simple. Last but not least, we are able to recycleuranium from the polluted soil. One of the most important technologies involved in thephyto-remediation is the selection of uranium-hyperaccumulators (U-hyperaccumulators).In this thesis, we propose an innovative microtitration-based method to measure the uraiumcontent of plant rapidly. Based on the measurements, we are able to find out andcharacterize U-hyperaccumulators and thus provides scientific support to thephy-remediation in controlling uranium pollution. Specifically, our contribution includes:1) A “sub-titanium reductive vanadium acid ammonium trace microtitration” basedmethod to rapidly measure the uranium content of plant is constructed.2) We measure the content of uranium and some other heavy metals around one uraniummine. And single factor contaminant index, Nemerow pollution index, geo-accumulationindex and potential ecological risk index are used to provide a comprehensive analysis andevaluation to the heavy metals pollution in soil. The results show that U, Cd and Pbpollution are the most serious. In addition, we find the severity of heavy metal pollution indifferent areas are different. Basically, mine-surrounding is the severest polluted area, nextis the tailing dam and then uranium plant.3) The common plants in that region are investigated. In particular, the uranium contentof these plants are measured to analyze their U-accumulation ability. Totally,52species ofplants which belong to28families and51genera are involved in our investigation. And80.77%of them are herbaceous plants while the others are woody plants. Amont these plants, we find12predominant herbaceous plant species, including Humulus scandens,Polygonum hydropiper, Setaria viridis, Eleusine indica, Phyllanthus, fern, Bidensbipinnata L., Digitaria Sanguinalis, Erigeron annuus, Chrysanthemum indicum L.,Xanthium sibiricum and Phytolacca; and several U-hyperaccumulators, such as Eleusineindica, Cyperus rotundus, Polygonum hydropiper, Setaria viridis, Digitaria Sanguinalis,Bidens bipinnata, plantain, Sedum sarmentosum, Raphanus sativus and fern. Thisinvestigation presents varieties of plants is significant in organic riched area but decreasesas radiation increases.4) In the experiments, we plant one of the U-hyperaccumulators, radish, in87differentflower pots to explore the effects of different pHs and uranium content to the radish.Besides, we also use acetate, oxalic acid and citric acid with different carboxyl as soilamendements to investigate organic acids’ effects on uranium chelation. The results showthat the condition for accumulating uranium the most in radish is: soil-pH=5.2, soiluranium-concentration=280mg/kg, and citric acid amendment=20mmol/kg. In addition,we find that the U-accumulation capability of radish planted with citric acid amendementsis51.7times of the corresponding control group.