Study On Pollutant Release Law Of Vanadium-Titanium Magnetite Tailings In Chengde Area

Chengde area is rich in minerals,among which vanadium-titanium magnetite resources are among the top in the country.A large amount of tailings are produced in the process of mining and utilization of mineral resources.Under the action of rainwater leaching,surface runoff and underground seepage,the pollutant components in the tailings are continuously released,which brings certain risks to the surrounding environment.In this thesis,the typical mineral resource vanadium-titanium magnetite in Chengde area is taken as the object to analyze the pollution risk of tailings reservoir,study the leaching release law of typical pollutants in tailings,determine the influence of different factors on the release of pollutants,and construct the leaching release model.The leaching release amount of tailings pollutants is predicted to provide a scientific basis for the prevention and control of tailings reservoir pollution.The physical and chemical characteristics of vanadium titanium magnetite tailings were analyzed.The mineral composition,chemical composition,heavy metal species and particle size distribution of the tailings were analyzed by XRD,XRF and other physical and chemical testing methods.The main heavy metals in the tailings were Cu,Ni,Zn and Cr.The risk of heavy metal pollution in tailings was evaluated.The average content of heavy metals in soil was Cr>Zn>Ni>Cu>Pb>As>Cd.The average content of Cr,Zn,Ni and Cu exceeded the soil background value of Hebei Province,which was2.56,1.05,1.99 and 2.65 times the soil background value of Hebei Province,respectively.The content of heavy metals the in soil decreased gradually with the increase of distance from the tailings pond.The single pollution index method,Nemero comprehensive pollution index method,geological accumulation method and potential ecological hazard index method were used to evaluate the pollution degree of heavy metals in the soil around the tailings pond.According to the results of the four evaluation methods,Cu and Cr pollution is more serious,Ni and Zn pollution is lighter,and other heavy metal elements are pollution-free.The precipitation of Cu,Cr,Ni,Zn,NH₄⁺-N,TP,TN and COD in tailings was studied by static immersion experiment.The effects of initial pH value,tailings particle size,solid-liquid ratio,temperature and stirring on the precipitation of heavy metals in tailings were analyzed.At the initial stage of static soaking,the main pollutants were released rapidly,but with the extension of soaking time,the dissolution and precipitation of pollutants slowed down and gradually stabilized.The heavy metals Cu,Cr,Ni and Zn were leached from the tailings,and the precipitation amount did not exceed the maximum leaching concentration of heavy metals specified in China’s hazardous waste identification standard leaching toxicity identification（GB 5085.3-2007）.The concentration of pollutants in tailings leaching reached the V class standard of’surface water environmental quality standard’（GB 3838-2002）.The dynamic leaching experiment of natural rainfall was carried out to analyze the effects of pH value of leaching solution,particle size of tailings and simulated different rainfall intensity on the dissolution and release of pollutants,and to predict the leaching release of tailings pollutants.The pH value of the leaching solution,the particle size of the tailings,and different rainfall intensities all affected the dissolution and release of pollutants,and the trend of heavy metal concentration was basically the same.With the increase of leaching time,leaching times and leaching amount,the leaching concentration of pollutants decreased gradually.Based on the results of dynamic leaching experiment,the leaching release law of pollutants and the deterministic mathematical model C=C₀V^K were constructed,and the release amount of tailings pollutants was predicted by combining the deterministic mathematical model.The annual average release concentrations of pollutants Cu,Cr,Ni,Zn,NH₄⁺-N,TP,TN and COD were calculated to be 0.008 mg/L,0.002 mg/L,0.001 mg/L,0.013 mg/L,0.085 mg/L,0.016 mg/L,0.301 mg/L and 3.156 mg/L,respectively.According to relevant specifications,the annual average release concentration of tailings pollutants is lower than the specified limit,so the tailings reservoir is safe and harmless to the surrounding soil and groundwater environment,and does not have hazardous waste with leaching toxicity.Although the leaching concentration of the tailings pond has not yet reached the specified limit,it is still possible to pose a threat to the surrounding environment as the leaching continues and the tailings in the tailings pond continue to pile up.