磷酸盐对铅镉复合污染土壤的钝化修复研究

IMMOBILIZATION OF SOIL CONTAMINATED BY LEAD AND CADMIUM USING PHOSPHATE

通过模拟实验,研究磷酸二氢钾、磷酸二氢钙和磷酸二氢铵3种磷酸盐对铅镉复合污染土壤的钝化效果,采用重金属形态分析和X-射线衍射法(XRD)探讨了钝化剂的修复机制。结果表明:3种磷酸盐处理可使土壤TCLP提取态Pb、Cd含量显著降低,其中磷酸二氢钙钝化效果最好,且随着投加量的增加,在n(P)/n(Pb+Cd)=5∶1时,钝化效率最高,对Pb、Cd的钝化率分别达到69.81%、35.18%。施加磷酸盐可使污染土壤中Pb、Cd从可交换态和碳酸盐结合态向残渣态转化,显著降低Pb、Cd的生物可利用性。X-射线衍射仪(XRD)检测发现,钝化后的土壤中有羟基磷铅矿、磷酸铅、磷酸镉等矿物晶体生成,表明3种磷酸盐对土壤中铅镉的钝化机理主要是生成难溶性磷酸盐沉淀和羟基磷铅镉矿物。

The simulating experiment was implemented to evaluate the remediation effect of three phosphate（ KH2PO4,Ca（ H2PO4）2,NH4H2PO4） on the soil contaminated by Pb and Cd. The immobilization mechanism of phosphate was clarified through X-ray diffraction（ XRD） and analysis of heavy metal fractions. Results showed that the TCLP extractable Pb and Cd decreased significantly after the addition of three phosphates. With the amount of phosphate increased,the immobilization efficiency of Pb,Cd increased. Ca（ H2PO4）2achieved the optimal immobilizing efficiency when the P/（ Pb ＋ Cd） molar ratio was at 5 ∶ 1,which decreased the concentration of Pb,Cd in TCLP leachates by 69. 15% and 35. 18%. Three phosphate prompted the transformation of Pb,Cd of exchangeable and carbonate-bound to the residual fraction,significantly reduced available heavy metals content. X-ray diffractometer（ XRD） was utilized to observe the mineral of three phosphate induced Pb,Cd contaminated soil. It was found that occurrence of hydroxyapatite galena,lead phosphate and cadmium phosphate mineral crystals,indicating the fixation mechanism of heavy metals was the formation of insoluble lead and cadmium in phosphate precipitation and hydroxyapatite.