Bio-chemical Remediation Of Under-ground Water Contaminated By Uranium In-situ Leaching

In the process of uranium in–situ leaching, it was serious that strong acid, uraniumand heavy metals, and SO42–, NO3–could contaminate under–ground water. To remedythese pollutants, conventional methods are high–cost and low–efficient, so a method thateffective integrated SRB, DNB, A.f to cope with the under–ground water pollution step bystep was proposed in this paper. So the following experiament was carried out for themethod.1. The experiment of corncob leachingTo decrease the treatment cost of wastewater from uranium mining in mines andmake corncob more useful, this paper aims to discuss the impact factors of COD incorncob extract. Firstly, as the variations of the mass concentration of corncob，temperature，time and pH，the changes of COD in corncob extract were analyzedrespectively. Afterwards，through orthogonal test，the best conditions for extracting organicmatter from corncob were determined. The single–factor tests shows that there is a linearrelationship between the mass concentration of the corncob and COD of corncob extractwhen the mass concentration of the corncob is lower than50g/L; COD of corncob extractis higher under acidic or alkaline conditions. The optimum conditions for extractingorganic matter from corncob are as follows: temperature is35℃，the mass concentration is40g/L，pH=3，the extracting time is3hours; under this conditions，the amount of CODreleased from a unit mass of corncob reaches0.0562g.2. The experiment of pre–treated by neutralizationThe pH of wastewater is adjusted to different pH value by sodium hydroxide, calciumhydroxide, sodium carbonate and calcium carbonate. The concentration of U, Fe, Mn, Znwas analyzed under the different pH value. The results shows that the performance ofneutralization agent with stronger alkaline was much better than the neutralization agent of carbonate in the removal rate of U; when neutralization was Ca（OH）₂and CaCO3, theeffect of adsorption coprecipitation was stronger than NaOH and Na₂CO₃; But the totalhardness of the treated water was higher than NaOH and Na₂CO₃, when neutralization wasCa（OH）₂and CaCO3;when neutralization was Ca（OH）₂and NaOH, the concentration of U,Mn, Zn, Fe were in the U, Mn, Zn, Fe tolerance range of DNB and SRB, it can’t forNa₂CO₃and CaCO3.3. The experiament of H₂S adsorptionBecause a lot of H₂S produced in the sulfate reduction bioreactor, the H₂S wouldcause seriously secondary pollution to environment was absorbed and oxidized by A.fsolution. So this paper conducted the experiment of H₂S adsorbed by A.f solution. Theresults shows that the Eh of A.f solution was higher, the effect of H₂S absorption was better.A.f liquid to H₂S showed better absorption effect, can fully meet the process requirementsof H₂S removal.4. The experiament of A.f bioreactorTo reduce the cost of H₂S absorption, this paper designed a A.f bioreactor whichwould make the A.f solution recycles use. This paper discussed the liquid flow and gasflow which had influence on Fe²⁺oxidation rate of A.f bioreactor. The results shows that:when the gas flow was less than0.7Nm³/h, the Fe²⁺oxidation rate would be rise byincreasing of the influent flow; when the liquid flow was less than2L/h, the Fe²⁺oxidationrate would be rise by increasing of the airflow. The bioreactor had worked stably for4days,the max Fe²⁺oxidation rate was6.21g/（l·h） and the Fe²⁺oxidation ratio was95%.