羟基磷灰石表面特性差异对重金属污染土壤固化修复的影响

Effect of surface characteristics of hydroxyapatite on the remediation passivation effect of heavy metal contaminated soil

利用两种不同尺寸和形貌的羟基磷灰石(MHA和NHA),通过XRD、TEM、DLS、Zeta电位、FTIR和丁达尔效应等表征分析,结合土壤pH值测定、TCLP提取和形态分析,探究两种羟基磷灰石对铜、镉和铅污染土壤钝化效果差异的原因.研究表明,MHA颗粒呈无定形结构,由大量晶粒聚集组成,NHA颗粒呈棒状,结晶度高,单个晶体粒径尺寸在20—90 nm,MHA和NHA两种材料的平均水合粒径分别为334 nm和3.1μm.MHA颗粒表面OH-分布较多,且水合粒子比表面积更大,更有效地提升了土壤的pH值,增多了铜、镉和铅的难溶盐沉淀,增强了材料颗粒与土壤中铜、镉和铅离子的络合作用; NHA颗粒的Zeta电位绝对值低,其颗粒在土壤溶液中易团聚,造成水合粒子比表面积减小,但NHA颗粒表面Ca2+分布较多,其与土壤中重金属的离子交换作用更强.总之,MHA和NHA颗粒表面主要离子分布的差异以及材料在土壤溶液中水合粒子大小的不同是造成两者钝化修复效果差异的主要原因,MHA对土壤中植物可利用态重金属的钝化效果更好,而NHA更有效地将土壤中植物可利用态重金属转化为植物不可利用态,钝化稳定性更好.

Immobilization performance of two types of hydroxyapatite particles（ MHA and NHA）with different size and morphology on copper, cadmium and lead in contaminated soil was investigated by characterization analysis（ XRD、TEM、DLS、Zeta potential、FTIR and Tyndall effect）and soil remediation experiment（ soil pH value、TCLP extraction and fraction analysis）. The results show that MHA was irregular particle which consisted of a large number of grains,while NHA had rod structure with high crystallinity,and the crystal size of every single rod was 20 to 90 nm. The mean hydrodynamic sizes of MHA and NHA particles were 334 and 3070 nm,respectively. More OH-was found on the surface of MHA and it had higher surface area of hydrodynamic particles compared with NHA,which increased the p H value of the soil effectively,increased the insoluble salt precipitation of copper,cadmium and lead,and enhanced the complexation between MHA and copper,cadmium and lead ions in the soil. The absolute value of Zeta potential of NHA particles was lower,and the particles were easy to agglomerate in the soil solution,resulting in the reduced specific surface area of hydrated particles. However,there was more Ca2＋ ions on the surface of NHA particles,which had stronger ion exchange effect with heavy metallic ions in soil. In summary,the difference in the distribution of main ions on the surface of MHA and NHA particles and the difference of the size of hydrated particles in the soil solution are the main reasons for the different remediation effect. MHA has better effect on the passivation of plant available heavy metals in soil,while NHA can effectively transform the available heavy metals in soil into plant unavailable state,and its passivation durability is better.