【作者】 张晓；

【导师】 魏正贵；

【作者基本信息】 南京农业大学 ， 土壤学， 2011， 硕士

【摘要】 纳米羟基磷灰石与常规体相材料相比,比表面积大、表面原子数多且配位不饱和,使其表面形成大量悬空键和不饱和键,因而具有极高的表面活性。因此,纳米羟基磷灰石对重金属离子的固定能力应大大超过普通含磷材料。本论文研究了纳米羟基磷灰石对水溶液中铅离子的固定效果和机理；探讨了低分子量有机酸在纳米羟基磷灰石表面上的吸附行为及其对含磷材料固定水溶液中铅离子的影响。主要研究结果如下：(1)分别采用中和反应法和溶胶-凝胶法合成了两种不同粒度和结晶度的纳米羟基磷灰石nHAP(A)和nHAP(B),结晶度为:nHAP(A)<nHAP(B).将nHAP(A)和nHAP(B)用于去除水溶液中的铅离子,研究了吸附时间、溶液pH值等因素对纳米羟基磷灰石固定Pb2+的影响,并通过测试溶液pH的变化,进行XRD和TEM分析,研究了纳米羟基磷灰石对Pb2+的固定机理。结果表明：nHAP(A)和nHAP(B)对Pb2+的去除能力随着溶液pH值的升高而降低；在pH值为2-4时,两种材料对Pb2+的去除效果最好；当Pb2+浓度为500mg/L时,由中和反应法合成的纳米羟基磷灰石nHAP(A)对Pb2+的去除能力是溶胶-凝胶法合成的纳米羟基磷灰石nHAP(B)的1.5倍。选用固定铅能力较强的nHAP(A)用于对不同浓度铅溶液进行动力学研究,并测试反应过程中溶液pH值的变化,观察到在反应初始阶段溶液的pH值出现快速下降,这表明纳米羟基磷灰石对铅的固定不但存在溶解-沉淀机制,还存在着表面配位作用,Pb2+能够和纳米羟基磷灰石表面的≡POH配位；XRD分析研究表明溶解-沉淀过程中出现中间相Pb(10-x)Cax(PO4)6(OH)2 (PbCaHAP),Pb2+离子主要占据Ca(Ⅱ)位；通过TEM观察到纳米羟基磷灰石固定Pb2+的最终产物为生物有效性极低的Pb10(P04)6(OH)2(PbHAP)。以上结果表明,纳米羟基磷灰石能够对铅进行有效的固定,其中结晶度较低的nHAP(A)具有较强的反应性能,而且中和反应合成纳米羟基磷灰石方法简便易操作,便于大规模生产,使其在铅污染治理中具有更好的应用前景。(2)研究了纳米羟基磷灰石对有机酸的吸附,以及有机酸对纳米羟基磷灰石和磷矿粉固定铅离子的影响。结果表明,由中和反应法合成的纳米羟基磷灰石nHAP(A)对草酸、苹果酸和柠檬酸有较强的吸附能力,远高于由溶胶-凝胶法合成的纳米羟基磷灰石nHAP(B).通过研究乙酸、草酸、苹果酸、柠檬酸和EDTA对nHAP(A)和nHAP(B)以及磷矿粉(PR)固定铅离子的影响发现：有机酸浓度低于5mmol/L时,有机酸的存在提高了nHAP(B)和PR对铅离子的去除效果,且在有机酸为1 mmol/L时达到最高值；机酸浓度较高(>5 mmol/L)时,乙酸、苹果酸、柠檬酸和EDTA均抑制了nHAP(B)和PR对铅离子的固定,抑制能力的强弱顺序为EDTA>柠檬酸>苹果酸>乙酸；草酸的存在提高了nHAP(B)和PR对铅离子的固定效果；XRD分析表明,草酸是以生成草酸铅沉淀的方式提高了铅离子的固定；但是中和反应法合成的结晶度较低的nHAP(A)对铅离子的固定不受有机酸浓度和种类变化的影响,能够使铅离子完全转化为羟磷酸铅,实现对铅离子最佳固定效果。以上结果表明,纳米羟基磷灰石固定水溶液中铅离子的过程不仅存在溶解-沉淀机制,还有表面配位的作用；采用中和反应法合成的纳米羟基磷灰石性能优越,能够有效地应用于环境中铅污染的治理；通过添加低浓度的低分子量有机酸能够提高含磷材料固定铅离子的效果,使固定产物更为有效地转化为生物有效性极低的羟磷酸铅。更多还原

【Abstract】 Nanosized hydroxyapatite (nHAP) exhibits greater surface area and more active sites on the surface than bulk materials, which lead to an increase in physical adsorption capacity, accompanied by a rise in ion exchange and complexation ability. Thus, the immobilization of heavy metals by nHAP would be more effective than bulk materials. In this work, we studied the immobilization of lead ions by nHAP synthesized through a sol-gel method and a neutralization reaction method, meanwhile, the adsorption of low molecular weight (LMW) organic acids on nHAP, as well as the effect of LMW organic acids on the removal of lead ions by nHAP were investigated. The main results were shown as follows:(1) Two types of nanosized hydroxyapatite (nHAP(A) and (nHAP(B)) with different crystallinity were prepared by a sol-gel method and a neutralization reaction method, respectively. And the crystallinity of nHAP(A) was smaller than nHAP(B). The nHAP(A) and nHAP(B) were used to remove lead ions from the aqueous solution, in order to study the effects of adsorption times and pH. The mechanism was also studied through the variety of pH and the analysis of XRD and TEM. Results showed that the removal ability of two materials decreased with the increasing pH and both have the largest removal amount of lead ions in pH=2～4. When the concentration of lead ions was 500mg/L, the removal capacity of lead ions by nHAP(A) was about 1.5 times higher than nHAP(B). The nHAP(A) which has stronger immobilization ability of lead ions was used to study the kinetics and the variety of pH values with different concentration lead ions in solution. It was found that the addition of nHAP to the solution containing lead ions caused a significant decrease of pH initially. It could be concluded that besides dissolution-precipitation mechanism, surface complexation mechanism should be also contributing to the lead uptake, and lead ions coordinated with≡POH on the suface of nHAP. XRD datas showed the formation of Pb(10-x)Cax(P04)6(OH)2(PbCaHAP) as an intermediate phase in the dissolution-precipitation procedure, and lead ions mainly occupied in Ca(Ⅱ) of nHAP. TEM micrographs showed that the final product was PbHAP with a low bioavailability Nanosized hydroxyapatite was proved to be effective for lead immobilization. Furthermore, poorly crystallized nHAP(A) prepared by neutralization method showed a higher efficiency in lead immobilization, and this method was relatively simple and could be used for mass production. Therefore, nHAP synthesized by neutralization method was expected to be an alternative in the remediation of heavy metal in soil and water.(2) The adsorption behavior of LMW organic acids on nHAP was studied, and five kinds of LMW organic acids were used to sudy their influnces on the removal of lead ions by nHAP and PR, including acetic, malic, oxalic, citric acid and EDTA. The results showed that the poorly crystallized nHAP(A) adsorbed greater amounts of oxalic, citric, or malic acid than the well crystallized nHAP(B). It was found that organic acids such as malic, oxalic and citric acid (<5 mmol/L) could enhance the adsorption of lead ions by nHAP(B) and PR, and having the largest removal amount of lead ions when the concentration was 1 mmol/L. Acetic, malic, citric acid and EDTA (>5 mmol/L) could decrease the removal of lead ions by nHAP(B) and PR, and their inhibitory capacities were in the order: EDTA>citric acid>malic acid>acetic acid. Oxalic acid could enhance the removal of lead ions by nHAP(B) and PR significantly, and XRD datas showed that oxalic acid enhance the removal of lead ions through the formation of lead oxalate. However, organic acids had little effect on the removal of lead ions by nHAP(A). The smaller particle sized nHAP(A) can achieve the best adsorption effect no matter what the changes of organic acid concentrations and species, it could transform the harmful lead ions to insoluble hydroxypyromorphite completely and should be the best adsorbent for the removal of lead ions from aqueous solution.Based on the above results, it could conclude that, in the process of immobilization of lead ions by nHAP in aqueous solution, not only dissolution-precipitation mechanism, but also surface complexation mechanism should be contributing to the lead uptake. In addition, the poorly crystallized nHAP(A) prepared by a neutralization reaction method was proved to be efficient for the remediation of lead-polluted water and soil. Moreover, adding low concerntration of LMW organic acids could enhance the immobilization of lead ions by nHAP and decrease the bioavailability of Pb through the formation of hydroxypyromorphite.更多还原