| For the great harm of heavy metal contamination,this study attempts to use natural minerals,industrial by-products and agricultural waste to deal with high concentrations of composite heavy metal contamination.Based on the unconfined compressive strength,leaching toxicity,freeze-thaw cycle and morphological distribution as the indicators,and the environment-friendly stabilizer for the treatment of high concentration Pb（2800 mg/kg）、Ni（2800mg/kg）、Cd（100 mg/kg）composite heavy metal pollution was developed by means of long-term maintenance（180 days）,simulated 5-year aging test,soil column leaching test,and scanning electron microscopy（SEM）.The main results are as follows:（1）Unconfined compressive strength（UCS）: Through the characteristics of natural minerals and biochar to deal with contamination and regulate environmental functions,after several batches of screening the optimal ratio and addition of natural minerals and biochar,the specimen is maintained to 7d,14 d,28d,60 d,90d,180 d to determine its unconfined compressive strength index,and try to develop natural mineral stabilizers,biochar stabilizers,cement-free stabilizers to control heavy metal Pb,Ni,Cd pollution.First,the stabilizer was added to the simulated soil with Pb and Ni concentrations of 2500 mg/kg,and the UCS of 1% Grape-fruit biochar stabilizer 180 d was measured to be 5.24 MPa,compared with 28 days,the UCS increased by 21.86%,and after 10 freeze-thaw cycles,the UCS continued to grow larger;Then add Cd（100mg/kg）to try to use agricultural waste for optimal screening,and the results show that after adding Grape-fruit biochar,the UCS for 7d meets the requirements of the U.S.Environmental Protection Agency’s Legal Provisions on Landfills 28 d.Finally,through the simulation of 5-year aging test,the UCS was measured to be above0.75 MPa,showing good long-term stability.（2）Speciation distribution: Through the analysis of various indicators such as unconditioned compressive strength and freeze-thaw cycle,it was found that the biochar stabilizer had a better effect,and we further used the Tessier sequential extraction method to show that the 1% Grape-fruit biochar stabilizer reduced the exchangeable state of Ni by 100%,and the 1% rice straw biochar stabilizer increased the residue state of Ni by 30%,which greatly reduced the potential harm to the environment.Then,a cement-free stabilizer was developed,and the Grape-fruit biochar was added to the simulated soil with the addition amounts of 0.25%,0.5%,1.5%,1.5% and 2%,and the 2% Grape-fruit biochar stabilizer was the best,which increased the residue states of Pb and Ni by 6% and11% respectively.Finally,through the simulation of 5-year aging and soil column leaching test,the proportion of exchangeable states of Pb,Ni and Cd was significantly reduced,and the proportion of residue states was significantly increased.（3）Long-term stability: By simulating 5-year aging,soil column leaching test,and long-term maintenance methods,the long-term stability of biochar stabilizer and cement-free stabilizer after 180 days,10 aging cycles and 8 leaching cycles was measured,and the fixation rate of Pb,Ni and Cd could reach more than96.66%,and the storage state of Pb,Ni and Cd gradually changed from easy migration and transformation to stable morphology,of which 1% of Grape-fruit biochar stabilizer had the best effect,and the fixation rate of Pb reached 99.65%.（4）Scanning electron microscopy analysis（SEM）: The mechanism of stabilizer treatment of high concentrations of heavy metals Pb,Ni,Cd was discussed,and through SEM means,the rich porous structure of agricultural wastes such as Grape-fruit biochar and rice straw biology was observed,as well as a large number of needle-like crystals and cluster particles in simulated soil,under the joint action of the above structures and substances,the stabilizer adsorbed a large number of Pb,Ni,Cd and its compounds,thus playing a good treatment effect on high concentration of composite heavy metal contamination. |
