Study On The Remediation Of Glyphosate-heavy Metal Co-contamination In Farmland Soil

Organic-heavy metal combined pollution is constantly evolving into the main soil environmental pollution problem worldwide.At present,the research on the treatment of soil with organic-heavy metal combined pollution is relatively scarce.Therefore,this paper explores a synergistic method of heavy metal passivation and advanced oxidation of organic matter.We hope that the method can effectively repair organic-heavy metal combined pollution soil.In this paper,the farmland soil contaminated by glyphosate-cadmium（Cd）was repaired by a combination of chemical oxidation and passivation.MgO/PAL and MgSiO₃/PAL passivators were prepared based on raw palygorskite（RPAL）.A method combining MgO/PAL passivator and peroxymonosulfate（PMS）oxidant was used to repair and evaluate the farmland soil with combined contamination.The main conclusions of the study are as follows:（1）MgO/PAL composite materials were prepared by coprecipitation method.SEM and XRD showed the uniform distribution of MgO on the surface of RPAL nanorods.EDS and XRF results further demonstrated the successful loading of MgO on the surface of nanorods.The BET characterization indicated that the specific surface area of the MgO/PAL composite was decreased compared to RPAL,mainly in the form of mesoporous.And the Zeta results showed the transition from negative potential to positive potential with the increase of magnesium salt addition.Precipitation in situ is the main mechanism of Cd adsorption on the surface of MgO/PAL composites.（2）The MgSiO₃/PAL composite was prepared by a one-pot hydrothermal method.The results of FTIR and XRD characterization showed that the skeleton of palygorskite collapsed,and the chain layer structure was destroyed to form amorphous magnesium silicate during the hydrothermal reaction.BET indicated that the specific surface area of MgSiO₃/PAL composites was significantly increased compared with RPAL.The larger specific surface area was conducive to the adsorption of Cd on its surface,and the pore diameter was mainly mesoporous.The EDS and XRF results further demonstrated the successful synthesis of MgSiO₃.Zeta proved that electrostatic attraction was the primary force for Cd adsorption on MgSiO₃/PAL composite materials.（3）Under the condition of p H 5,adsorbent dosage of 1g/L and reaction time of180 min,the absorption capacities of Cd for three adsorbent RPAL,MgSiO₃/PAL and MgO/PAL on 1000 mg/L solution were 169.76,239.76 and 328.46mg/g respectively.The adsorption process of Cd by MgSiO₃/PAL and MgO/PAL can be well simulated by the quasi-two-stage kinetic model.In addition,the adsorption isotherms of the two kinds of composite materials can be consistent with the Langmuir adsorption model,indicating that the adsorption of Cd by the two adsorbents belongs to monolayer chemical adsorption.（4）The glyphosate-Cd co-contaminated soil was repaired by a combination of chemical oxidation and passivation.The removal rate of glyphosate in the co-contaminated soil reached 73.8%after the application of MgO/PAL+PMS.Meanwhile,the leaching concentration of Cd in the contaminated soil was 0.93mg/kg,which reached the international standard of TCLP.The experimental results show that the combined treatment of PMS+MgO/PAL has a certain repairing effect on glyphosate-Cd co-contamination of farmland soil.