Remediation Of Lead-cadmium Contaminated Soil By Stabilization Reagent Made From Modified Fly Ash And Chicken Manure

With the development of industrial economy,many heavy metals enter into the soil through automobile exhaust,metal smelting and sewage irrigation,resulting in the heavy metal pollution of soil and serious damage to our living environment.Therefore,it is of great practical significance to take effective methods to control soil heavy metal pollution.The large output,high stockpile and low utilization rate of fly ash have brought serious environmental risks to human production and life.The fly ash has a porous structure with high porosity and specific surface area,which can be used for stabilization and remediation of heavy metal contaminated soil.The modified fly ash has better performance.Chicken manure as an auxiliary stabilizer can neutralize the soil with high alkalinity caused by modified fly ash.The combination of the two promotes plant growth while repairing heavy metal contaminated soil.In this study,four adsorption materials,including coal gangue porous material（SM-1）,acid-modified CFB fly ash（SM-2）,Na OH-roasted hydrothermally synthesized modified PC fly ash（SM-3）and Na OH-roasted hydrothermally synthesized modified CFB fly ash（SM-4）,were used to perform adsorption tests on Cd²⁺and Pb²⁺heavy metal solutions,respectively.Based on the adsorption effect and adsorption isotherm,the optimal adsorbent SM-4 was selected as the base stabilizer.SM-4 was combined with chicken manure to remediate soil contaminated with high concentrations of Pb and Cd,and its effects on soil pH,DTPA extractable state Cd²⁺and Pb²⁺concentrations,soil heavy metal morphology,soil organic matter and nutrients such as nitrogen,phosphorus and potassium,as well as soil urease and alkaline phosphatase were investigated.In order to verify the restoration effect,pot experiments were conducted to investigate the effect of stabilizer on Paspalum notatum under different dosing conditions using Paspalum notatum as the test plant,and the cost analysis of stabilizer was also conducted.The main experimental conclusions are as follows:The adsorption experiments of Cd²⁺and Pb²⁺solutions showed that the order of the adsorption capacity of the four materials for heavy metal ions was:SM-4（29）SM-3（29）SM-2（29）SM-1.When the initial concentration of Cd²⁺solution was 500 mg·L^-1,the adsorption capacity of SM-4 could reach 125.65 mg·g^-1;when the initial concentration of Pb²⁺solution was 800 mg·L^-1,the maximum adsorption capacity of SM-4 could reach 290.91 mg·g^-1.The adsorption of both heavy metal ions by SM-4 was in accordance with the Langmuir model.The results of remediation of soil contaminated with high concentrations of Pb and Cd showed that the addition of SM-4 led to an increase in soil pH value.Chicken manure could neutralize the alkalinity released by SM-4 and act as a buffer against excessive soil pH.The stabilization effect of chicken manure on contaminated soil was weaker than that of SM-4.With the increase of remediation time and stabilizer dosage,the stabilization effect of heavy metals in soil was promoted by different treatment methods.The MS3 treatment group showed the best results,with 72.99%and 68.44%reduction of Cd and Pb in the extractable state of DTPA in the soil,respectively.The addition of stabilizers both led to the development of the chemical forms of Cd and Pb in the contaminated soil from the unstable state to the stable state,where the residual Cd and Pb increased by 6.20%and 5.37%,respectively.Each treatment can increase the content of organic matter,effective nitrogen,effective phosphorus and fast-acting potassium in the soil,and chicken manure was significantly more effective than SM-4 in enhancing the nutrient content of contaminated soil.Each treatment had a certain promoting effect on the activity of urease and alkaline phosphatase in soil,and the results of combined application were better than those of single treatment.The MS3 treatment group had the best compounding effect,and the compounding ratio of SM-4 and chicken manure was 5%and 0.6%,respectively.The results of the pot experiment showed that all treatments were effective in increasing the biomass of Paspalum notatum,with the greatest increase in the MS3 group,which increased the dry weight of Paspalum notatum by 30.39%compared to the CK control group.The stabilization treatment also promoted the increase of chlorophyll content in Paspalum notatum,with the largest increase of chlorophyll a and chlorophyll b under MS3treatment,which were 1.28 times and 1.12 times higher than CK treatment,respectively.The accumulation of Cd and Pb in Paspalum notatum was mainly concentrated in the roots,and the content of Cd and Pb in the roots,stems and leaves in the MS3 treatment were68.20%,71.62%,60.00%and 59.22%,76.79%,67.97%lower than those in CK treatment,respectively.Through economic cost analysis,the cost can be reduced by 29.29%compared with other similar stabilizers.In summary,the composite stabilizer used in this study has excellent remediation ability for high concentration Pb and Cd contaminated soil.Compared with similar stabilizers,it has low cost and excellent economic benefits,and has certain application prospects.