Research On Remediation Of Contaminated Groundwater From Acid In-situ Leaching Uranium Mining By Sulfate Reducing Bacteria

As a new method of mining, in-situ leaching concentrates the role of mining,mill running and smelting. There are many merits of in-situ leaching such as low cost, short constructing periods, high resource reclaim rate, protecting the ground's entironment and so on. But during the course of leaching, some poisonous substances were soaked out by chemical reagent pulled in the underground and the groundwater was polluted. So measures must be taken to decontaminate the polluted water after mining.The study about decontaminating the in-situ leaching groundwater was at primary stage and there is no precedent studying in our country. And in this paper, use of groundwater in situ microbial purification technology by natural microbial sulfate reduction group to replace the chemical or physical methods is employed to remove sulfate,U(VI) and some heavy metals in the contaminated groundwater. This experiment provided an in situ bioremediation strategy for uranium-contaminating groundwater.The reaction activity of SRB was influenced by many environmental fators. The anaerobic incubation experiments showed that the coexistent heavy metal ions[U(VI),Cu(II),Cd(II),Zn(II),Pb(II),Fe(II)] could restrain the reduction rate of SRB in different extent. It was found that SRB was the most susceptible to Cu(II) among these ions. Our research results also suggested that SRB metabolic activity was significantly influenced by environmental pH. Strong inhibition of its growth was detectable with initial pH less than 5.0, yet a maximum sulfate removal efficiency of 75.7% was achieved at neutral pH. The process of microbial sulphate reduction inhibited strongly in the presence of nitrate in concentration above 500mg/L.The tests of U(VI) bioprecipitation indicated that the capacity of SRB to reduct and enrich uranium was achieved the strongest at neutral pH. A maximum yield(99.2%) was attained when the initial pH was adjusted to 6.0. Anaerobic batch testing results showed that no significant effect on U(VI) bioprecipitation was observed when the Zn(II) concentration was less than 20mg/L or Cu(II) less than 10mg/L. However, this process was completely inhibited at a Zn(II) concentration of 25mg/L or Cu(II) 15mg/L due to their toxicity to SRB. No inhibition of U(VI) bioprecipitation was found with the initial sulfate concentration less than 4000mg/L, however, anion levels above 5000mg/L slowed U(VI) bioprecipitation and the inhibitory effect was enhanced with increasing sulfate concentration. Laboratory incubations also suggested that U(VI) reduction will not commence until nitrate(1000mg/L) is completely depleted. Considering the priority of nitrate removal over U(VI) precipitation. The removal efficiency of sulfate and U(VI) were respectively arrived at 75.5% and 93.55% by SRB from the experiments of simulated uranium-containing wastewater.