【作者】 王瑜；

【导师】 魏正贵；

【作者基本信息】 南京农业大学 ， 生态学， 2010， 博士

【摘要】 常规粒径即体相的磷灰石材料可用于治理铅、镉、氟污染的研究。但由于常规粒径磷灰石材料的比表面积小,表面活性不强,因此将其应用于治理铅、镉、氟污染时,修复时间、修复效果均不理想。此外,由于治理过程中受到酸度等因素的影响,往往需要对被治理的场地进行预处理,增加了环境风险。与常规材料相比,纳米材料(1-100nm)巨大的比表面积和高表面活性,不但使纳米粒子表面有快速的溶解-沉淀过程,而且使纳米粒子表现出较大的表面物理吸附,同时由于扩散作用使之还表现出较大的表面离子交换和离子配位能力。因此,从性质上分析,纳米材料吸附、稳定环境污染物的能力,应大大超过常规材料。目前,尽管国内外对常规粒径磷灰石治理环境中铅、镉、氟污染的理论研究和实际应用均较多,但关于应用纳米级磷灰石或者羟基磷灰石治理环境污染的报道较少,尤其是至今没有关于材料结晶度、施加低分子量有机酸影响纳米羟基磷灰石(nanosized hydroxyapatite, nHAP)环境应用的报道。因此,本文研究材料结晶度、施加低分子量有机酸对nHAP稳定水溶液体系中铅、镉、氟污染的影响。一方面希望借助nHAP优越的表面特性和反应特性,解决常规粒径磷灰石在治理环境污染时存在的缺陷；另一方面研究nHAP结晶度、施加低分子量有机酸对nHAP环境应用的影响,期望找到一条既能避免二次污染又能提高磷灰石治理污染效率的途径,建立周期短、高效、环保的化学修复方法。主要的研究内容及结果如下：(1)nHAP粉体的制备及性能的研究采用沉淀法和溶胶-凝胶法合成不同结晶度的nHAP粉体,用固相法合成体相羟基磷灰石(Bulk HAP)粉体作为对比,利用粉末X射线衍射法(XRD)、红外光谱(IR)、透射电镜(TEM)以及扫描电镜(SEM)对其形貌、晶体结构等表面性能进行表征。结果表明沉淀法和溶胶-凝胶法制备的nHAP均为颗粒均匀、纯相态的物质,并且随着烧结温度的升高结晶度增大。此外在恒定pH值(2-7)条件下,对不同结晶度HAP的反应性能进行研究。结果表明在相同pH值条件下,HAP结晶度越小溶解度越大,释放出磷的浓度越高,从而表现出越强的反应性能；2h之内,研究的四种HAP样品中结晶度最小的在pH<5时达到了完全溶解,结晶度最大的在pH<3时也未完全溶解。(2)材料结晶度对nHAP稳定硫酸铅、碳酸铅的影响本实验考察了在各种影响因素条件下(恒定pH值、随时间变化pH值、反应时间以及nHAP加入量),nHAP结晶度对稳定硫酸铅、碳酸铅的影响。实验结果表明,nHAP稳定硫酸铅、碳酸铅污染的机理主要是溶解-沉淀作用,通过把硫酸铅或碳酸铅转化为磷氯酸铅而达到稳定铅污染的目的；在相同条件下(pH值、反应时间和nHAP加入量),nHAP的结晶度越小,从硫酸铅或碳酸铅到磷氯酸铅的转化率越高；由于溶解-沉淀机理的存在,nHAP勺结晶度越小,越容易在较低酸度条件下达到较高的转化率；增加反应时间和nHAP加入量有利于硫酸铅、碳酸铅的稳定；在变化pH值条件下,nHAP能够快速、完全的把硫酸铅、碳酸铅转化为磷氯酸铅。但是nHAP稳定硫酸铅和碳酸铅的过程有所不同。硫酸铅在不同pH值条件下的溶解实验表明其溶解不受pH值影响且在25 min内达到了溶解平衡；而碳酸铅的溶解受pH值影响且溶解过程在2h内没有达到平衡；根据溶解-沉淀机理,在硫酸铅和nHAP共存的体系中,nHAP的溶解速率决定了硫酸铅转化为磷氯酸铅的速率；而在碳酸铅和nHAP共存的体系中,nHAP和碳酸铅的溶解速率共同决定了碳酸铅转化为磷氯酸铅的速率。(3)材料结晶度对nHAP稳定碳酸镉的影响本实验考察了在各种影响因素条件下(恒定pH值、随时间变化pH值、反应时间以及nHAP加入量),nHAP结晶度对稳定碳酸镉的影响。实验结果表明,nHAP稳定碳酸镉的主要机理是表面吸附作用,溶解-沉淀作用不明显；在相同条件下(pH值、反应时间和nHAP加入量),nHAP的结晶度越小,其对碳酸镉的稳定效率越高；在达到相同稳定效率时,nHAP的结晶度越小需要的酸度越低、反应时间越短、nHAP力口入量越少；在变化pH值条件下,nHAP能够快速、完全的把碳酸镉稳定下来,并且存在明显的离子交换过程。(4)施加低分子量有机酸对nHAP去氟能力的影响本实验选择了草酸、柠檬酸、苹果酸作为低分子量有机酸(LMWOAs)的代表。考察在不同nHAP加入量、氟初始浓度、溶液pH值、反应时间、反应温度等条件下,LMWOAs对nHAP去氟能力的影响。运用Langmuir和Freundlich等温吸附方程及一级动力学和二级动力学方程进行拟合,此外还计算了热力学函数ΔG°、ΔS°、ΔH°,并初步探讨了可能的吸附机理。实验结果表明,在各因素条件下,LMWOAs的存在均促进了nHAP对氟的吸附,本研究选择的三种LMWOAs对nHAP去氟能力增强程度为：草酸>柠檬酸>苹果酸；LMWOAs增强nHAP去氟能力的原因是氟吸附位点的增加,新增加的氟吸附位点来源于nHAP表面吸附的LMWOAs;在LMWOAs存在下,随着反应时间、反应温度的增加,nHAP的去氟能力增加；随着nHAP加入量、氟初始浓度、溶液pH值的增加,nHAP的去氟能力降低；LMWOAs存在下nHAP对氟的吸附比较符合Freundlich等温吸附方程(R2>0.98),且运用二级动力学方程能够更好的描述其吸附过程,此外吸附热力学参数说明该吸附过程是自发、吸热过程。更多还原

【Abstract】 Bulk apatite can be used to immobilize Pb, Cd and F in water and soil. Previous results indicate that lowering soil pH value or applying sufficient amount of bulk apatite could improve the efficiency and shorten the time of immobilization. But several disadvantages should be noticed when optimizing amendment quantity and pH so that adverse environmental effects are not a by-product, i.e., water entrophication and soils acidifying. Compared with the apatite of normal size, nanosized hydroxyapatite (nHAP) represents a promising application in a variety of areas, due to their higher surface area and reactivity. Therefore, the enhancement of Pb, Cd and F immobilization, worked by the addition of nHAP, could be realized in practice. However, there are some literatures studying the immobilization of Pb, Cd and F by bulk apatite in water, but litter is known about their immobilization by nHAP. In particular, there are no reports about the effect of nHAP crystallinity or low molecular weight organic acids (LMWOAs) on the immobilization of Pb, Cd and F by nHAP. In this study, the main objectives of this work are (1) to investigate whether the decrease of nHAP crystallinity can promote the immobilization of Pb and Cd by nHAP, (2) to evaluate whether the LMWOAs can promote defluoridation capacity of nHAP.Main results are as follows:(1) Sample preparation and their characterizationThe nHAPs were synthesized by the precipitation and sol-gel method. XRD, TEM, IR were used to characterize these nHAPs. Results showed that the samples were pure HAP and crystallinities of samples increased with annealing temperature. In addition, determination of dissolution rates for nHAP was conducted at the controlled pH condition. Results showed that the dissolution was inversely related to pH and the solubility of HAPs increased with decreasing HAP crystallinity. Within 2 h reaction time, the complete dissolution was obtained at pH<5 for the least crystallinity of HAP. However, there were not complete dissolution at pH<3 for the highest crystallinity of HAP.(2) The effect of nHAP crystallinity on the immobilization of anglesite and cerrusite in aqueous solutionIn this section, the effect of nHAP crystallinity on the immobilization of anglesite and cereusite was investigated at various conditions, such as pH, adsorbent dose, contact time. Results showed that the main mechanism involved HAP dissolution, followed by phosphate reacted with dissolved Pb and precipitation of chloropyromorphite. Under the same conditions (pH, contact time or sorbent dose), with the decrease of HAP crystallinity, the complete immobilization was achieved at higher pH, especially at high P/Pb ratio. As sorbent dose and contact time increased, the immobilization of Pb by nHAP was increased. For the reaction between anglesite and nHAP, the soluble Pb level was controlled by the solubility of chloropyromorphite during the entire reaction process. For the reaction between cerrusite and nHAP, the soluble Pb level was controlled by the solubility of cerrusite and chloropyromorphite during the entire reaction process. In the dynamic pH system, a complete transformation of Pb from anglesite or cerrusite to chloropyromorphite was achieved due to the complete dissolution of nHAP and anglesite/cerrusite at the initial low pH.(3) The effect of nHAP crystallinity on the immobilization of CdCO3 in aqueous solutionIn this section, the effect of nHAP crystallinity on the immobilization of Cd from CdCO3 was investigated at various conditions, such as pH, adsorbent dose, contact time. Results showed that the main mechanism involved adsorption. Under the same conditions (pH, contact time or sorbent dose), with the decrease of HAP crystallinity, the percentage of Cd removal from CdCO3 by nHAP was increased. As pH, sorbent dose and contact time increased, the percentage of Cd removal from CdCO3 by nHAP was also increased. The soluble Cd level was controlled by the solubility of CdCO3 and nHAP during the entire reaction process. In the dynamic pH system, a complete immobilization of Cd was achieved due to the complete dissolution of nHAP and CdCO3 at the initial low pH. The main mechanism involves ion-exchange between Cd2+ and Ca2+ in the dynamic pH system.(4) The effect of LMWOAs on the defluoridation capacity of nHAPIn this section, oxalic, citric and malic acids were selected as the representative of LMWOAs. Bath adsorption experiments were carried out to investigate the effects of contact time, initial fluoride concentration, solution pH, and LMWOAs on fluoride adsorption onto nHAP, and to explore the mechanisms of fluoride adsorption onto the nHAP. Results indicated the defluoridation capacity of nHAP was enhanced by the addition of LMWOAs. The nHAP adsorbed LMWOAs on its surface, and the LMWOAs on nHAP were considered to be the newly formed active sites for fluoride adsorption. In addition, the order of the ability of LMWOAs to enhance the defluoridation capacity of nHAP was oxalic acid> citric acid> malic acid, which was the same order as the amounts of LMWOAs adsorbed onto nHAP. In the presence/absence of LMWOAs, the defluoridation capacity increased with increasing the contact time, initial fluoride concentration and contact temperature, while decreased with the increase of the sorbent dose and solution pH. The adsorption isotherms in the presence/absence of LMWOAs were well fitted by the Freundlich model (R2>0.98), and the sorption kinetics were well described by the pseudo-second-order model. Moreover, thermodynamic parameters indicated that the adsorption was spontaneous and endothermic.更多还原