Study On Remediation Of Heavy Metal Contaminated Soil By Geochemical Engineering Technology

The remediation of heavy metal contaminated soil is a hot and difficult issue in the world. There are several traditional methods of remediation, including phytoremediation, microbial remediation, chemical remediation, physical rehabilitation and etc.. But these technologies have not been widely used yet because of their limitations. Geochemical engineering technology reforms environment by geochemical process, which is generally effective and works without secondary pollution. It is also easy to operate and has short cycle of remediation. But most of the current technologies are in the phase of laboratory research, seldom maturely applied in fieldwork.The heavy metal contaminated soil around the mining area in the city of Tongling, Anhui Province was chosen as the object of the study, in which the principle of fixing pollutant in geochemical engineering theory was used. Natural clay minerals were added to the soil as the main repair materials, with effective control technology, to reduce the bioavailability of heavy metal in the soil, so that the content of heavy metals in vegetables could meet the food safety requirements. In this study, small scale pot experiment was taken based on the simulation experiments.Laboratory simulation experiments had been taken to determine the best project, including clay mineral modification test, the selection of main repair material, soil/clay mineral ratio test, and pH test. Simulation findings are as follows:(1) Using AB-DTPA extraction method to indicate the difference of the effect between the parallel tests in simulation is feasible.(2) Sodium bentonite, calcium bentonite and attapulgite are all efficient in the remediation of the contaminated soil with little difference of efficiency.(3) The clay minerals have better efficiency while they are not modified.(4) When the pH of soil is between 8.5-9.5, the clay minerals have the best remediation effect. The results of the simulation experiment were used in pot experiment. Some tests with auxiliary repair material and a variety of clay minerals in the mixed ratio were added in the pot experiment. The conclusion shows that:(1)Clay minerals could reduce the bioavailability of heavy metals in soil, being effective in remediation. The best-fit amounts of attapulgite are different corresponding to different types of vegetables.(2)AB-DTPA extraction method used in the simulation experients is feasible.(3)Superphosphate and organic fertilizer could also effectively reduce the bioavailability of heavy metals as auxiliary repair materials. The best-fit amounts of Superphosphate and organic fertilizer are different corresponding to different types of vegetables.(4)lime is good to support fixing Cu and Zn, but not being sure to be good for Cd and As.Therefore, according to the local conditions, attapulgite without modification would be chosen as the major repair material in the remediation of heavy metal contaminated soil around Tongling mining area. According to the different types of crops, select the best-fit amount of clay minerals, superphosphate, and organic fertilizer to do the remediation, and add appropriate amount of lime timely to adjust pH. Effective repairing materials and technologies, supported by appropriate agricultural managements, would contribute to the success of remediation.