| The problem of soil heavy metal pollution has seriously threatened human health and ecological environment.Soil heavy metal repair is also a hot spot in current research.At present,chemical passivation is a widely used method for soil heavy metal pollution restoration.At present,among the commonly used passivating agents,most of the synthetic passivating agents are expensive,and the effect of natural materials is often unsatisfactory.In this experiment,a passivation containing mercapto group was developed using coal gangue,and the agent has the advantages of low price,good performance and simple preparation process.Furthermore,the prepared mercapto-modified coal gangue?CG-SH?was applied to the repair of heavy metal contaminated soil,and the influencing factors in the repair process were studied.The influence of external factors on the stability after repair was also studied.Through the wheat pot experiment,the effects of passivation of heavy metals on crops in actual restoration work were studied.And the main research contents of this paper are as follows:?1?Preparation,characterization and adsorption performance test of CG-SH.The mercapto-modified coal gangue was prepared by coupling coal gangue and 3-mercaptopropyltrimethoxysilane.The materials were characterized by SEM,XRD,FT-IR,N2-adsorption desorption,X-RF and FT-IR.These characterization results indicated that the sulfhydryl group was successfully grafted onto coal gangue,and the specific surface area,pore volume of CG-SH.have a significant increase.The adsorption performance tests were carried out in aqueous solutions containing Pb???,Cd???and Cu???respectively.It was found that CG-SH has good adsorption effects on three heavy metal ions,and chemical adsorption dominates.The adsorption capacities of CG-SH for three heavy metal ions are:332.8,110.4 and 124.1·mg g-1,respectively.The kinetic characteristics are consistent with the pseudo second-order kinetic model,thermodynamic characteristics and Langmuir model.Consistent;the change in pH of the solution has little effect on the adsorption performance.?2?Effect of repair agent dosage,pH,water content and repair time on repairing effect.For the soil contaminated by Pb???,Cd???and Cu???,the effects of repairing agent dosage,pH,water content and repair time on the repairing effect were studied.The results showed that for the contaminated soils with Pb???addition of 300,500,700 and 900 mg·kg-1,the passivation rate increased with the increase of the repair agent.And the optimum amount of repair agent is 4.0%,4.0%,5.0%and 5.0%;the effect of pH on the passivation rate is not obvious;the change of soil moisture content will affect the passivation rate.The optimum moisture content is 45%.The passivation rate decreases first and then increases with the repair time.On the 28th day,the equilibrium is basically reached.The passivation rate at this time are 80.46%,85.58%,84.95%and 86.63%,respectively.And the subsequent passivation rate fluctuated in a small range,and the stability is generally stable overall.For the contaminated soils with Cd???addition of 5,10,15 mg·kg-1,and20 mg·kg-1,the optimal amount of repair agents were:1.0%,1.0%,1.5%,and 1.5%,respectively.The optimum moisture content is 85%;the passivation rate is basically balanced after 28 days,and the passivation rates at the 28th day are 85.50%,85.58%,84.95%and 86.63%,respectively,and the passivation rate is generally stable thereafter.And the passivation rate is also insensitive to changes in pH.For the contaminated soils with Cu???addition amounts of 100,400,600 and 800 mg·kg-1,the optimum amount of repair agent added was 4.0%,4.0%,5.0%,and 5.0%;the optimum moisture content is 55%;on the 28th day,the change in passivation rate is basically balanced,and the passivation rates are:94.90%,95.67%,95.31%,and 94.99%,respectively.When the repair time continues to increase,the passivation rate floats on a small scale.This indicates that CG-SH has a good repair effect on soil contaminated by Pb???,Cd???and Cu???.?3?Study on the stability of contaminated soil after freezing and thawing cycles and alternating wet and dry cyclesThe frozen-thaw experiment and the dry-wet alternating experiment of the repaired heavy metal contaminated soil were used to simulate the effects of freezing,thawing,drought and flooding on the soil.These factors have some effect on the stability of the soil after repair.The results showed that the effects of freeze-thaw cycles on the stability of Pb???,Cd???and Cu???contaminated soils after repair were almost the same,and the passivation rate decreased significantly after the initial freeze-thaw,and then gradually increased.For contaminated soils with Pb???addition of 300,500,700 and 900 mg·kg-1,the passivation rates before freeze-thaw were 81.67%and 84.92%,83.94%and 85.87%,respectively.And the passivation rates after initial freeze-thaw cycles were 78.42%,82.76%,80.67%and 83.85%,respectively.The passivation rates after 20 freeze-thaw cycles were 84.34%,87.69%,85.82%and 88.47%,the passivation rate at this time is higher than before the freeze-thaw cycle;For the contaminated soils with Cd???addition of 5,10,15 and20 mg·kg-1,the passivation rates before the freeze-thaw were 76.56%,80.39%,80.86%and 77.27%,the passivation rates after initial freeze-thaw were 70.19%,79.19%,75.65%and 73.61%,respectively.The passivation rates after 20 freeze-thaw cycles were:80.38%,82.02%,83.98%and 82.76%,respectively.The passivation rate is also higher than before the freeze-thaw cycle.For the contaminated soils with Cu???addition of 100,400,600 and 800 mg·kg-1,the passivation rates were 88.91%,93.08%,and 89.49,respectively,before the freeze-thaw cycle.%and 87.00%,the passivation rates after initial freeze-thaw cycles were 85.27%,86.96%,84.97%and 83.66%,respectively.The passivation rates after 20 freeze-thaw cycles were:91.34%,93.12%,91.38%and 90.20%,respectively.At this time,the passivation rate is also higher than before the freeze-thaw cycle.The effects of dry-wet alternating on the stability of Pb???,Cd???and Cu???contaminated soils after repair were same generally,in the early stage of dry-wet alternating,the passivation rate decreased significantly and then slowly increased,and Keep rising.The addition amount of Pb???was 300,500,700and 900 mg·kg-1,respectively.The passivation rates before dry-wet alternating were 81.67%,84.92%,83.94%and 85.87%,respectively.After the first dry-wet alternating,the passivation rate reached the lowest,they were:62.34%,69.13%,68.82%and 75.08%respectively;after 20 cycles of dry-wet alternating,the passivation rate was 69.43%,74.59%,75.27%,and 80.19%respectively?For the contaminated soils with Cd???addition of 5,10,15 and 20 mg·kg-1,the passivation rates before dry-wet alternating were 76.56%,80.83%,81.83%and 77.10%;after two alternating wet and dry cycles,the passivation rate has reached a low level,and the passivation rates are:58.47%,67.84%,68.23%,and 61.45%,respectively.After 20 cycles of dry and wet alternating,passivation The rates are 60.76%,69.04%,69.62%and 63.13%,respectively;For the contaminated soils with Cu???addition of 100,400,600 and 800 mg·kg-1,the passivation rate was 88.91%and 93.08%,89.49%and 87.00%,respectively,before the dry-wet alternating.After passing through the secondary dry-wet cycle,the passivation rate reached a lower level,namely:82.90%,85.88%,82.83%and80.77%;After 20 cycles of dry and wet alternating cycle,the passivation rate increased significantly.The passivation rates at this time were 86.94%,89.43%,86.95%and 85.27%,respectively.After 20 times of dry-wet alternating,the passivation rate of CG-SH to three heavy metals in the soil did not reach the level before the dry-wet alternating,but it always kept rising.?4?Wheat pot experimentPot experiments of wheat were carried out in heavy metal contaminated soil,and the results showed that:The content of heavy metals in the various organs of wheat produced in the restored soil was significantly lower than that in the soil before the restoration.For the contaminated soils with Pb???addition of 500,700 and 900 mg·kg-1,respectively,the Pb content of the wheat seeds produced before the restoration was 18.00,38.95,49.00 mg·kg-1,and the Pb content of the wheat seeds produced by the repaired soil is 0.00mg·kg-1.For the added amount of Cd???is 5 and 10 mg·kg-1,respectively,and the 15 mg·kg-1 contaminated soil,the Cd content of the wheat seeds produced before the restoration was 0.17,0.27,0.34 mg·kg-1,respectively.The contents are 0.05,0.09 and 0.12mg·kg-1,respectively.For the contaminated soil with Cu???addition of 400,600 and 800 mg·kg-1,respectively.Before the restoration,the content of Cu???in the wheat seeds produced by the soil was 20.23,22.50 and 37.45 mg·kg-1,respectively.After the restoration,the Cu???content in the wheat seeds produced by the soil was 6.85,8.20,and 11.10 mg·kg-1,respectively.When the addition amount of heavy metal Pb in soil was 500,700 and 900mg·kg-1,the content of Pb???in wheat seeds after restoration was in good accordance with national standards;the amount of heavy metal Cd???in soil was respectively When the contents of 5,10mg·kg-1 and Cu???are 400 and 600mg·kg-1,respectively,the content of two heavy metals in the wheat seeds produced by the repaired soil meets the requirements of national standards;when the heavy metals in the soil are Cd???When the added amount was 15 mg·kg-1 and the addition amount of Cu???was 800 mg·kg-1,respectively,the content of two heavy metals in the wheat seeds produced in the soil after repair was slightly higher than the national standard.The Pb???,Cd???and Cu???contaminated soils before and after restoration were subjected to wheat pot experiments,and the relative contents of the stable forms were significantly increased,while the relative forms of the unstable forms were relatively increased.The content has a significant decrease;compared with the soil which before the restoration,the relative content of the three heavy metals in the repaired soil is higher,the relative content of the unstable form is lower,and the difference is more obvious.It indicated that CG-SH had obvious passivation effect on Pb???,Cd???and Cu???in soil,and the stability was good. |
PDF Full Text Request