Experimental Study On In-situ Immobilization Of Uranium In Soil Of Uranium Tailings Pond

The uranium tailings pond is usually treated with lime alkalization.Under the action of the external environment,the fixed active uranium will be released,which penetrate the soil barrier and threaten the ecological environment.Therefore,uranium-contaminated soil needs to be effectively restored.In this paper,four fixatives including chitosan(CTS),attapulgite(ATP),zero-valent iron(ZVI)and hydroxyapatite(HAP)were separately added to immobilize uranium in soil of uranium tailings pond.The species distribution characteristic of uranium and change at different doping amount and p H was determined by stepwise chemical extraction.In addition,the leaching characteristics and release potential of uranium were measured by the toxicity characteristic leaching procedure(TCLP)and static experiment.Meanwhile,the samples immobilize of HAP was characterized to discussed the immobilization mechanism of uranium.The main research results are as follows:(1)Exchangeable(including water soluble)uranium is changed into other stable states after addition of CTS,ATP and ZVI,and the residual uranium content increases with the introduction of HAP.The effects of fixatives on the species distribution of uranium have significant at doping amount 5%.CTS and ATP had the best fixation effect at p H=5,and ZVI and HAP had the largest conversion ratio at p H=4.The order of anchorage capacity is HAP > ZVI > ATP > CTS.(2)The results of TCLP indicate that the stabilization effect of four kinds of fixatives was the most valid at the dosage of 5%.Uranium is activated by chitosan treatment,and leaching increases by 4%~23%.The leaching amounts of uranium were obviously decreased as the inserting of ATP and ZVI,stabilization increased 24% and 50%,respectively.The hydroxyapatite reduced uranium leaching by nearly 80%,which is the best fixative for the remediation of uranium in uranium tailings pond.(3)The release amounts of uranium in soil of uranium tailings pond implied that less low of p H,the more release of uranium.After the inserting of HAP reduce uranium release was significantly affected by p H.The release amounts of uranium were obviously decreased at p H=3 or p H=4,while at p H 5,6 and 7 were increased compared to the blank control group.(4)The uranium in the soil of the uranium tailings pond was stabilized and immobilized mainly via complex precipitation as investigated by Scanning electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy and morphological change.Hydroxyapatite advances the conversion of uranium to a residue state.In addition,there are also ion exchange,physisorption,and chemisorption.