Study On The Stabilization Effect Of Magnetic Hydroxyapatite On Heavy Metal Pollution Of Lead And Cadmium In Soil

Based on the treatment of the most prominent lead and cadmium heavy metal pol-lution in the current domestic industrial site pollution,this paper uses an improved pulsed ultrasound-sol-gel method to load ferroferric oxide powder on hydroxyapatite to prepare nanometers grade magnetic hydroxyapatite with different iron content ratios.Through BET,SEM,FTIR,XRD and hysteresis loop and other characterizations,the results show that nano-ferric oxide and nano-hydroxyapatite are successfully combined with good crystallinity and pore structure.The maximum specific surface area and total pore volume of the material can reach 154.38m²·g^-1and 0.84cm³·g^-1,respectively.Fe-O groups are introduced into the original hydroxyl and phosphate groups to give the material magnetic response properties.The saturation magnetization is above2.02emu·g^-1.Through the 24-hour adsorption performance test of the material to lead and cadmium ions in the aqueous solution,the results show that the maximum adsorp-tion capacity of the material for Pb²⁺and Cd²⁺is 751.04 mg·g^-1and 170.03 mg·g^-1,re-spectively.While the adsorption capacity is similar to that of the material iron and phos-phorus.The ratio shows a weak linear negative correlation.In this paper,the short-term effects and long-term stabilization experiments of magnetic hydroxyapatite and lead and cadmium pollutants in the soil environment are carried out.The results of short-term action experiments based on TCLP leaching tox-icity analysis show that most of the reactions between the material and lead and cad-mium ions are completed within 2 hours.Through the kinetic model fitting,it is found that the action process has the highest correlation with the quasi-secondary model,in-dicating that the adsorption process in the soil simultaneously has the effects of mem-brane diffusion,internal diffusion and chemical adsorption,and chemical adsorption is the main one.When the material content is 0.5%and 4%,the TCLP leaching concen-tration of Pb and Cd in the soil decrease from 20.13 mg·L^-1and 3.07 mg·L^-1 to 3.43mg·L^-1 and 0.34 mg·L^-1,which were all lower than the RCRA/GB5085.3-2007 limit.With the increase of iron-phosphorus ratio,there is almost no difference in the effect of the material.And the material is more suitable for alkaline soil,actually,it maintains good processing performance in the soil p H range from 5.5 to 8.5.The long-term sta-bilization experiment results based on the analysis of TCLP leaching toxicity,soil prop-erty changes,leaching liquid property changes,and heavy metal form distribution changes show that:compared with the leaching toxicity at 1d,the leaching toxicity of lead and cadmium contaminated soil at 90d is reduced by 21.82%and18.27%,respec-tively.The addition of materials slightly increases the p H of the soil,and effectively reduces the content of soluble heavy metals in the soil by changing the lead and cad-mium pollution in the soil from a weak acid extractable state to a more stable reducible state and a residue state,while the oxidized state changed a little.The results of experiments on the stabilization and material separation of soils contaminated by lead and cadmium show that the coexistence of lead and cadmium pollution has a greater impact on the initial effect of the material,but with the extension of the stabilization time,the difference continues to decrease.The soil separation rate is significantly positively correlated with the mixing amount.The mixing amount in-creases from 0.5%to 4%,and the separation rate increases from 35.3%to 73.6%,which proves the separability of magnetic materials.This study has certain reference value for the research and application of in-situ remediation of lead and cadmium contaminated soil.