PAHs-heavy Metal Compound Polluted Soil Study On Combined Repair Process Of Thermal Desorption And Stabilization

《The promulgation of the Soil Pollution Prevention》and 《Control Action Plan and the Soil Pollution Prevention and Control Law 》 has accelerated the industrialization level of contaminated soil remediation technology.Single organic or heavy metal pollution remediation technology has been widely researched and applied in engineering,but as a difficult treatment of organic-heavy metal composite contaminated soil still required multiple processes for joint remediation.Thermal desorption and stabilization had the advantages of simple principle,efficient remediation and stable effect.Respectively,They were both the preferred remediation technologies for organic and heavy metal contaminated soils.However,due to the different process conditions,the change of heavy metal morphology distribution by continuous high temperature in the thermal desorption process and the effect of mixing and stirring of chemicals in the stabilization process on the desorption of organic pollutants in the soil directly,They were both determine the remediation efficiency of the combined thermal desorption-stabilization process for organic-heavy metal composite contaminated soils.In this thesis,we selected the polycyclic aromatic hydrocarbons PAHs-Cd composite contaminated soil around Huludao non-ferrous metal smelter,Starting with the main influencing factors of thermal desorption and stabilization process,The effects of different thermal desorption temperatures and stabilizing agent dosages on PAHs desorption rate and Cd stability were investigated;Analyzing the differences in remediation efficiency between thermal desorption-stabilization(T-S)and stabilization-thermal desorption(S-T)processes in terms of chemical concentration,morphological classification and microscopic morphology.Thermal desorption-Stabilization(T-S)and Stabilization-Thermal desorption(S-T)processes.On this basis,the optimized design of thermal desorption-stabilization remediation process based on the classification of dual desorption-stabilization concentration was constructed,and the differences in energy consumption of different process designs were compared through remediation costing.The main conclusions were obtained as follows:(1)In terms of remediation efficiency and influencing factors of thermal desorption and stabilization,the removal rate of PAHs in the thermal desorption process increased with the increase of desorption temperature 350℃～500℃,the removal rate of total PAHs reached99.2% at 400℃,and the removal rate of benzo(a)pyrene reached 99.5% with content lower than GB36600-2018 "Soil Environmental Quality Risk Control Standards for Soil Contamination of Construction Land Trial risk screening value for Class I sites(0.55 mg/kg);During the stabilization process,the increase of the dosage of traditional medicine(phosphate,0.5%～2.5%)can significantly change the leaching rate and morphological distribution of soil Cd,and the maximum leaching rate of Cd can be reduced from 67.10% to 45.53%,the content of residue state increased significantly(43.8%～50.73%),but the changes of soil Cd leaching and morphological distribution were not in significant after the dosage of pharmaceuticals exceeded 2%.(2)Regarding the effect of thermal desorption-stabilization process on the remediation efficiency,under the same desorption temperature 350℃～500℃,agent dosage 1% and 2% of calcium dihydrogen phosphate,although there was no significant difference between T-S and S-T processes on the desorption efficiency of PAHs,the effect on the stability of soil Cd was significant;Comparing the effect of different processes on the leaching rate of Cd,the leaching rate of Cd in the S-T process ranged from 34.81% to 49.42%,which was lower than that of 35.89% to 51.25% in the T-S process;Comparing the effects of different processes on the morphological distribution of Cd,the percentage of residue state in the S-T process ranged from 23.08% to 38.31%,which was also higher than that of 19.55% to 35.08% in the T-S process;Comparing the microscopic morphology under electron microscopy The degree of crystallization of the soil after S-T process was also significantly higher than that of the T-S process.(3)In terms of optimization and energy consumption accounting for the combined thermal desorption-stabilization process,benzo(a)pyrene and Cd in the samples of this thesis were used as indicators,and the critical concentration calculation for both to reach the standard was calculated based on the effects of different process parameters and procedures on the desorption rate of Bap and stability of Cd,0.55 mg/kg for Bap and 3.76 mg/kg for Cd The design of the thermal desorption-stabilization remediation process was thus constructed for classification and optimization;the differences in energy consumption under different process design conditions RMB 406/ton～RMB 662/ton were evaluated and compared through direct cost accounting of desorption temperature and stabilization agent dosage,which provided a scientific basis for the design and parameter optimization of thermal desorption-stabilization process for compound contaminated soil at the engineering level.