| Acid mine drainage(AMD)is characterized by low pH,high variety and concentration of heavy metals,which will cause great harm to the health of water and soil.It is one of the most urgent environmental problems in the global mining industry.The traditional lime neutralization technology plays an important role in reducing the acidity of AMD and removing metal pollution.The method and its improved method are widely used because of its high efficiency and stability.However,due to the high concentration of iron ions in the AMD,the consumption of lime and the amount of slag are all large,which causes the water treatment operation cost and the treatment cost of the neutralization slag to be too high.In addition,there is no effective way to recover the heavy metals in the slag,which not only buries the risk of secondary pollution,but also causes waste of this part of the metal resources.In order to solve the problem of high concentration of copper and iron in the AMD,this paper uses the bio-oxidation and biological reduction technology to realize the step-by-step recovery of copper and iron.Compared with the shortcomings of the traditional lime neutralization method,the technical means has the advantages of low processing cost,no secondary pollution risk and effective recovery of valuable metals.The experiment determined the optimal process index by examining bio-oxidation and biological reduction,respectively,and using X-ray diffraction analysis,Raman spectroscopy,Fourier transform infrared spectroscopy,scanning electron microscopy analysis,X-ray energy spectrum analysis and high-through sequencing technology.The means of macrogenomic analysis reveals the mechanism of precipitation of iron,copper and sulfate,which provides a theoretical basis and reference for the application of bio-resources in AMD.The up-flow bio-oxidation reactor and the up-flow biological reduction reactor were designed and constructed according to the scale of the pilot,and continuous experiment was constructed in the laboratory.The simulated waste water is prepared with reference to the actual AMD from a mining area in Tibet.The Fe(II),Cu(II)and SO42-concentration of waste water were 1 700 mg/L,200 mg/L and 15 000 mg/L,respectively.H2SO41l+1)regulates waste water pH2.5.Firstly,the influencing factor test of bio-oxidation process was carried out.The effects of three process parameters of HRT,water temperature and aeration on the operation of the reactor were studied.The optimal process parameters were determined:HRT 15 h,water temperature 35 ?,and aeration.The amount is 4 L/min.Under this condition,the Fe(II)concentration in the effluent of the reactor was reduced to 10 mg/L,and the Fe(II)bio-oxidation ratio was 99.41%.By studying the kinetic model of Fe(II)oxidized by iron oxidizing bacteria,it was found that HRT has a significant effect on the oxidation kinetics of iron oxidizing bacteria.Through high-throughput metagenomic sequencing analysis,it was found that the microbial population structure similarity between the samples is high,whether it was the reactor effluent sample or the bio-filler sample,and the main iron oxidizing bacteria in the system were Leptospirillum,Acidithiobacillus,Acidiphilium and Sulfobacilus.Leptospirillum had the highest proportion in the effluent and the surface of the filler in the reactor,and belonged to the dominant genus in the system.The ratio of iron oxidizing bacteria attached to the surface of the filler is the highest under the condition of HRT of 15 h.Secondly,the iron precipitation test was carried out with the effluent from the bio-oxidation reactor as the test object.The effects of three process parameters such as HRT,waste water pH and water temperature on the effect of iron immersion were studied,and the optimal process parameters were determined:HRT 2 h,control pH is 3.2,water temperature is 30 ?.Under this condition,the total Fe concentration in the effluent of the iron-iron reaction tank decreased to 13.95 mg/L,the total Cu concentration was 190.85 mg/L,and the iron-precipitation ratio reached 99.18%,and the copper loss ratio was only 4.59%.Based on the data of the response surface,it was known that the main factors affecting the process of precipitating iron were the pH value of the waste water and the waste water temperature,and the order of influence of each factor on the immersion iron is:waste water pH>waste water temperature>HRT.By analyzing the structure and morphology of the precipitated material,it was judged that the main component of the precipitated material is schwertmannite.Thirdly,the test of bio-sulfurization was carried out with the waste water after precipitating iron as test object.The effects of four process parameters such as HRT,carbon source type,carbon source dosage and temperature on the operation of the reactor were studied,and the optimal process parameters were determined:HRT was 12 h,formic acid was used as a carbon source and the dosage was 0.5 g/L,and the waste water temperature was 30?.Under the process conditions,the Cu concen-tration in the effluent of the reactor was reduced to 0.043 mg/L,and the recovery ratio of Cu metal was 99.9%.According to the analysis of the structure and morphology of the copper sulfide product,the copper-containing precipitate in the copper precipi-tated tank was mainly copper sulfide.Finally,on the basis of the above-mentioned phased experiments,a continuous test of biological oxidation,iron precipitation and bio-sulfurization was realized,and the test was continuously operated for 5 days.The final effluent pH value was stable above 7 in continuous test,the Fe concentration was about 0.020 mg/L,the Cu concentration was 0.026-0.040 mg/L. |
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