低分子量有机酸对纳米羟基磷灰石固定铅的影响及机理

The utilization of nanosized hydroxyapatite (nHAP) for the immobilization of lead through formation of chloropyromorphite with extremely high geochemical stability，is a promising pollution control technology, which has drawn much attention at home and abroad. Previous researches on the immobilization of lead and other heavy metals by nHAP paid more attention to the immobilization mechanism and influence of coexisting ions, but relatively ignored the effects and mechanism on the immobilization of heavy metals caused by low molecular weight organic acids (LMWOAs), which are ubiquitous in soil, and have significantly higher concentrations in rhizosphere soil than in bulk soil. The main contents of this study include the adsorption of LMWOAs by nHAP, effects of LMWOAs on the surface charge, dissolution propertities, and crystal structure of nHAP; the complexation between lead and LMWOAs and its effect on the immobilization of lead by nHAP; especially the influence of root-secreted organic acids on the stability of immobilization product of lead by nHAP. The objective of this project is to elucidate how the representative LMWOAs (acetic acid, oxalic acid, malic acid and citric acid) in rhizosphere affect the transformation efficiency of lead to chloropyromorphite by nHAP as well as the stability of the immobilization product of lead by nHAP, which will provide theoretical basis for enhancing the remediation efficiency of lead-polluted environment by nHAP.

利用纳米羟基磷灰石（nHAP）将环境中的铅转化为地球化学稳定性极高的氯磷铅矿来实现对铅的固定，是一种极具应用前景的污染控制技术，已引起国内外环境领域极大关注；以往对nHAP固定铅等重金属的研究较多注重固定机理及共存无机离子的影响，相对忽略土壤中广泛存在的、且在根际区域含量较高的低分子量有机酸（LMWOAs）在nHAP固定重金属过程中的作用和机制。本项目通过研究nHAP对LMWOAs的吸附，LMWOAs对nHAP表面电荷、溶解性能和晶体结构的影响；LMWOAs与铅的络合及其对nHAP固定铅效率的影响；特别是根系分泌的LMWOAs对氯磷铅矿稳定性的影响；目的是阐明根际典型LMWOAs（乙酸、草酸、苹果酸和柠檬酸）如何影响nHAP将铅转化为氯磷铅矿的效率，及如何影响nHAP对铅固定产物的稳定性；试图为有效提高nHAP对铅污染环境的修复效果提供理论依据。

利用纳米羟基磷灰石（nHAP）将环境中的铅转化为地球化学稳定性极高的氯磷铅矿（CPY），从而实现对铅的固定得到了环境领域的广泛认可。本研究重点关注了环境中普遍存在的低分子量有机酸（LMWOAs）对nHAP固定铅的影响机理。重要结果如下：. （1）发现LMWOAs在nano-HAP表面的吸附和有机酸的极性大小以及有机酸与nano-HAP表面的Ca配位能力强弱决定，草酸的极性较大，而且与Ca的配位能力较强，因此在nano-HAP表面的吸附量大于苹果酸和柠檬酸；不同有机酸对nano-HAP释放钙和磷能力顺序为柠檬酸 > 草酸 > 苹果酸。. （2）LMWOAs能与Pb2+竞争nHAP表面的吸附位点，阻碍了对Pb2+的吸附固定；草酸能够显著提高nHAP对Pb2+的去除效果，但是XRD和FT-IR光谱显示固定产物为草酸铅；晶化程度较低的nHAP对Pb2+的固定能力最强，且不受LMWOAs的影响，固定产物为CPY。. （3）溶液中Pb2+最容易和带两个负电荷的草酸根络合，其次是和柠檬酸根络合，而与苹果酸的络合能力最弱；柠檬酸和苹果酸能够与铅形成溶解性的稳定络合物促进CPY的溶解，但不改变物相组成，草酸能够将CPY部分转化为草酸铅。. （4）CPY培养植物实验发现，CPY对植物有一定毒性；充足的磷供应能够提高植物对铅的吸收；根际区域CPY的稳定性显著降低，主要是由于根系分泌大量LMWOAs，特别是草酸。. 上述结果极大地丰富了纳米含磷材料环境应用的基础研究，提示我们在应用nHAP固定环境中的铅时，必须充分考虑LMWOAs的影响；同时，对于同样属于溶解性有机质重要组成的天然高分子有机物（胡敏酸、富里酸等）对纳米材料环境应用的影响，今后有必要加强研究。