Effects Of Coal Gasification Residue On Phytoremediation And Migration Of Pb And Cd Contaminated Soil

Since there are a lot of available resources in the gasification waste residue,simply stacking it will also cause a huge waste of resources.Existing researches generally use coal gasification slag in the construction field,and the treatment of waste slag is inadequate.However,there are relatively few studies on the application of coal gasification slag in environmental fields such as soil pollution remediation due to its rich carbon elements and good adsorption properties.This paper studies the microstructure of coal gasification slag and analyzes the composition of coal gasification slag.The effects of coal gasification slag on the growth of ryegrass and the accumulation and transport of lead and cadmium under lead and cadmium stress were studied using indoor pot experiments.The effect of adding coal gasification slag to soil on the adsorption characteristics of lead and cadmium was explored through batch equilibrium adsorption experiments.Combined with soil column experiments,HYDRUS-1D software developed by the University of California,USA and the USDA Saline Soil Laboratory was used to simulate heavy metals.The characteristic curve in the soil and the prediction of the transport behavior of heavy metals in the soil,the following conclusions are drawn:1.Coal gasification slag is mainly composed of Si O₂,Al₂O₃,Ca O and unreacted carbon.The content of the three main oxides reached 86.27%,the content of acidic oxides exceeded 70%,and they had a large specific surface area.Elemental analysis showed that they did not contain heavy metal elements.2.The addition of coal gasification slag can promote the growth of ryegrass under heavy metal stress.Under different stresses of Cd and Pb,the maximum growth rate of emergence rate is 21.2%and 6.9%respectively;ryegrass plants under different concentrations of Cd pollution Compared with the control group,the maximum growth rate,tiller number and total plant weight reached 14.0%(25 mg/kg),49.9%(50 mg/kg)and 113.2%(25 mg/kg)respectively;under different concentrations of Pb pollution Compared with the control group,the maximum growth rate of ryegrass plant height,tiller number and total plant weight reached 23.3%(500mg/kg),60.9%(300mg/kg),91.4%(200mg/kg).The coal gasification slag added under the condition of slag/soil mass ratio of 1:4 can significantly increase the absorption and translocation of ryegrass to heavy metals,and the TF values of Cd and Pb increase by 16.2%-155.0%and 10.7-120.2%,respectively.The root BCF value increased by 9%-16%and 31.9%-101.1%,respectively.3.In the adsorption thermodynamic test of coal gasification slag/soil mass ratio of 1:4,the equilibrium equilibrium concentration of soil samples for heavy metals increases with the concentration of heavy metal solutions,and the adsorption partition coefficients for different concentrations of heavy metals with the solution concentration Increase and decrease.The addition of coal gasification slag significantly increased the adsorption of heavy metals by the soil,and the adsorption partition coefficient of heavy metals with different concentrations of heavy metals(Cd,Pb:5mg/L,10mg/L,15mg/L,20mg/L,25mg/L)increased by 984.72,582.61,138.59,37.34,71.23-(Cd);76.57,74.9,54.14,46.77,46.29-(Pb).Langmuir and Freundlich can be used to fit the experimental data well,and the correlation coefficients are all above 0.9.4.The dispersion coefficients of different soil samples obtained from soil column experiments were 3.82 cm²/min(control group)and 2.62 cm²/min(experimental group),(Experimental group:coal gasification slag/soil mass ratio is 1:4)and the dispersion degrees were 62.47 cm and 43.80 cm,respectively.The RMSE of the measured and simulated values of the migration behavior of heavy metals and Cd in the soil are RMSE:0.1043;RMSE:0.0544,and the RMSE of the measured and simulated values of the migration behavior of Pb in the soil are the original soil samples:0.0267;Slag+soil sample:0.0389.It shows that HYDRUS-1D can better simulate the movement of heavy metals.At the same time,the migration process of infiltration of heavy metals from the surface of the soil to a depth of 100 cm(Cd:100 mg/kg;Pb:300 mg/kg)was predicted for one year.The concentration of Cd at 100 cm depth in the original soil sample was lower than"Soil Environmental Quality The third-level pollution standard stipulated in the Standards,and the Cd concentration at100cm of the soil sample after adding coal gasification slag was lower than the second-level standard;the concentration of Pb at 100cm after adding coal gasification slag decreased from 0.0799mmol/cm³ to 0.0589 mmol/cm³ And it is far less than the secondary standard stipulated by the state.