| China is one of major countries to produce chromate and the annual output of chromate was more than 160 thousand tons.However,a large amount of chromium-containing slag was discharged from chromate industries.The chromium slag usually contains 0.3~1.5%soluble Cr(?).Through the erosion of rainfall and surface water,soluble Cr(?)would enter the surrounding soil and groundwater,causing serious pollution to the environment.A ferroalloy plant began to test metal chromium in 1959.Due to lack of environmental protection consciousness,chromium slag was piled randomly,causing serious pollution of well water in downstream villages.In some areas,the concentration of hexavalent chromium in groundwater exceeded 600 times now(standards for drinking water quality GB5749-2006)),the water quality is far from meeting the needs of production and domestic water.In order to develop and utilize local groundwater and alleviate hexavalent chromium pollution,it is urgent to carry out research on technical methods for removing hexavalent chromium from groundwater,which could provide theoretical basis and technical support for the treatment of groundwater hexavalent chromium pollution in the ferroalloy plant.This paper is supported by the project“Development of chrome-contaminated groundwater remediation technology in a ferroalloy plant”.For the problem of excessive Cr(?)concentration in groundwater near the Ferroalloy Plant,on the basis of summarizing the data of the study area,the concentration and species of Cr(?)in groundwater were investigated and monitored to determine the pollution range of pollutants;Tracking the current situation and development,determining in situ remediation technology as a method to remove Cr(?)from groundwater;Screening In-situ Cr(?)removal material in groundwater in the well,revealing the mechanism of Cr(?)removal and removal efficiency under different water chemistry conditions.The technical parameters such as the structure and maximum water output of the in-situ repair well are studied,which provides a kind of Cr(?)purification for groundwater purification.Through the research of the thesis,the following understandings have been made:1.Cr(?)in the study area along the groundwater flow direction forms a pollution halo from southwest to northeast.The pollution area(the area where the Cr(?)concentration exceeds the standard of drinking water)is about 8km~2.2.The sponge iron can be selected as the filling material for removing Cr(?)in groundwater.When the pH is 7 and the temperature is 13°C,the equilibrium removal rate of the 30mg/L Cr(?)solution within 15h is about 56%.The removal efficiency of Cr(?)in water by expanded graphite and copper sulfate modified significantly increased to 83.4%.3.Within the range of chemical changes of groundwater,the sponge iron and its modified materials are sensitive to the change of aqueous solution pH,which is reflected as the reaction rate and removal efficiency are pH=6>pH=7>pH=8;salinity has no obvious effect on the removal reaction of Cr(?)by sponge iron and its modified materials;the change of temperature has no effect on the removal reaction of sponge iron and sponge iron copper,but under the condition of low temperature,sponge iron expands graphite has decreased.4.Through microstructure analysis,sponge iron is mainly composed of zero-valent iron,the surface is loose and porous,and the specific surface area is large.After the reaction with Cr(?),the surface Fe-O bond becomes Fe-O-Cr bond,the specific surface area is reduced,and lots of pores are filled.Most of the pores of the sponge iron copper are blocked.It can be clearly seen by SEM-EDX.Chromium is applied to the surface of the three materials.5.According to the selected materials,the key technical parameters of the in-situ repair well are designed:the filling material is above the flower tube and below the ground 1m,the filling material is 9m high,the thickness is 20cm,and the maximum water output speed is 1800L/h.The well can meet the small village basic living and irrigation water needs. |
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