Experimental Study On Purification Of Gold Mine Underground Water In Gansu

Mining produces a large amount of groundwater due to two effects: one is the digging process disrupts the original aquifer,aquifuge and water conductivity fault;the other is the mining operation leads to movement of rock strata and surface subsidence,causing groundwater and surface water gushing to the well bore or well roadway.Groundwater near mines usually contains a considerable amount of heavy metals,toxic and hazardous substances.If it is not properly treated before releasing to adjacent water system,the waste water will severely contaminate the surrounding surface water and groundwater system.In this paper,the removal of arsenic,antimony,cyanide and COD in gushing water of a gold mine in Gansu province is studied.According to the regulatory requirements of the local environmental protection agency,the natural water quality of that area should meet Grade II standard of surface water environmental quality standard?GB3838-2002?,the maximum arsenic is 0.05mg/L,maximum COD is 15mg/L,chemical limit of ?0.05mg/L,limit of antimony uses the centralized drinking water surface water source specific project standards,the limit is ?0.005mg/L.In the first part of this paper,the removal of arsenic and antimony,cyanide and COD were studied.The removal efficiency of these two pollutants was investigated by combining coagulation sedimentation and oxidation-coagulation.In the second part of this paper,cyanide and COD were investigated for complexation and alkaline chlorination.Based on the result of the two groups of pollutants removal experiments,the paper designed the experimental scheme that the four pollutants can be reduced to reach the standard in one process.The main conclusions are as follows:?1?The effect of oxidation-coagulation-lime precipitation on the removal of arsenic and antimony in underground water was significant.The optimal reaction conditions were as follows: the dosage of FeSO₄ 2000 mg/L,dissolved oxygen 10 mg/L time 60 min,lime dosage is 1000mg/L.?2?In the cyanide and COD removal study,calcium hypochlorite and chlorine dioxide have a good oxidation effect.When the oxidation time was controlled at 45 min,Ca?ClO?₂ dosage was 180mg/L,and the p H was controlled between 10.5-11.5,the effect of Ca?ClO?₂ oxidation on removal of CN-ions and COD produced the best result.In the single-factor experiment of oxidizing CN-ions and COD with chlorine dioxide,when the p H value was controlled at 8.5-10.5,the oxidation time was 30 min,and the dosage of ClO₂ was 7.5mg/L,the effect of ClO₂ oxidation on removal of CNions and COD produced the best result.?3?Based on a priori knowledge of removing arsenic and antimony,cyanide and COD,the optimal combined treatment of ferrous sulfate and calcium hypochlorite and the combined treatment of ferrous sulfate and chlorine dioxide were designed and tested.