【作者】 刘海波；

【导师】 陈天虎；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 铁氧化物是地表系统的重要组成矿物。目前已知的铁氧化物矿物共有16种，其中以赤铁矿、针铁矿、磁铁矿、纤铁矿、水铁矿5种矿物最为常见。针铁矿是表生氧化环境最主要的铁氧化物，也是土壤和沉积物中极具表面活性和生物化学活性的重要组分之一。作为天然的纳-微米矿物，针铁矿对地表系统中有机污染物、无机阴离子（团）、重金属等环境有毒有害物质的迁移、转化及最终的环境归宿具有重要的影响，因此，针铁矿结构和表面反应性的研究已成为近年矿物学、环境地球化学等领域的一个研究热点。但目前已有的研究主要集中在针铁矿体相结构及其物理化学性质的研究，对其表面特性与结构间的关系，特别是其原子局域结构对表面反应活性的制约机制缺乏深入的研究，从而影响了人们对矿物环境自净化过程和机制的深入认识，而这是我们理解和掌握地表系统物质循环和污染物环境归趋的关键。另一方面，虽然目前已有的研究非常关注纯相针铁矿的结构及其物理学化学特性，但由于地质条件的复杂性，已有的少数研究表明，针铁矿中往往存在一定程度的类质同象置换(如，Al³⁺→Fe³⁺)，类质同象置换对针铁矿的局域结构、晶体化学特性及其表面反应性有什么影响，对于这一问题的研究至今为止还鲜有报道。为此，本论文从铝代针铁矿的合成入手，采用微区微束技术（场发射扫描电镜、透射电镜等）和现代谱学技术（FTIR、Raman等），结合矿物相和晶体化学表征方法，通过合成铝代针铁矿和天然针铁矿的对比研究，揭示了Al³⁺→Fe³⁺置换对针铁矿及其处理产物局域结构、表面物理化学特征及其热稳定性等的影响及其制约机制，建立了铝代针铁矿的结构演化模式；在此基础上，采用吸附实验方法，阐明了针铁矿局域结构变化的对其吸附、催化性能的影响机理及其反应机制，并取得了如下主要创新成果：1、识别出针铁矿晶体存在的1种结构羟基、3种表面羟基和1种新发现的无氢键作用的Fe-OH，以及3层表面吸附水。2、铝代针铁的合成实验表明，高pH有利于提高铝离子进入针铁矿晶格，形成较高铝含量的铝代针铁矿。发现溶液中铝离子存在不仅阻碍针铁矿的生长、降低结晶度，而且影响针铁矿的晶体形貌，表现为铝替代越多针铁矿长径比越小。铝对Fe的类质同象置换可提高针铁矿结构的稳定性，当铝替代量从0增加到9.1%，针铁矿脱水相变为赤铁矿的峰值温度从225℃提高到了275℃，相应的针铁矿热分解活化能也从117.8kJ/mol增加到126.7kJ/mol。铝替代还提高了针铁矿的热还原转变为赤铁矿、纳米铁的温度。3、查明新桥褐铁矿矿石由呈针状、片状的纳米针铁矿交织排列组成，并形成了具有开放孔隙的纳米孔结构，其中针铁矿含量超过95%，且部分针铁矿晶格铁为铝所替代。在空气气氛中，针铁矿在225℃左右开始转化为赤铁矿。生成的赤铁矿不仅保留了针铁矿原有的形貌，而且由于针铁矿晶体脱水相变多晶化，新生了颗粒间纳米孔。随着煅烧温度升高，赤铁矿颗粒变大，赤铁矿粒间空隙变大，比表面积降低，250-350℃煅烧针铁矿具有最大比表面积。与煅烧前针铁矿相比，产物比表面积从12.7m²/g增加到111.6m²/g，提高了8.8倍。这一成果为天然针铁矿煅烧产物发挥吸附性能和催化剂载体作用提供理论基础。4、基于铝代针铁矿热处理结构演化规律认识和表面反应性响应的理解，对空气气氛煅烧获得的赤铁矿、氢还原获得的磁铁矿和纳米铁等纳米结构化材料在吸附除磷、催化脱焦油、还原净化水中硝酸盐和亚硝酸盐、转化对硝基酚、去除重金属离子等效果进行系统研究，并把天然针铁矿演化产物与合成针铁矿演化产物、商品铁氧化物和纳米铁进行性能对比，发现天然针铁矿演化产物比合成针铁矿的演化产物具有了更好的表面性能和反应活性，其原因归结于天然针铁矿中存在的少量类质同象替代的铝导致了衍生产物赤铁矿、磁铁矿、纳米铁的晶格缺陷增多，比表面积增大、表面活性和化学反应活性的增强。表明天然纳米矿物材料在上述污染物净化方面表现出的特异性能具有巨大的应用潜力。同时实验研究中，对检测方法进行了创新，研究出利用总有机碳分析仪（TOC/N仪）检测气体中有机碳、无机碳、甲烷等含量的方法。更多还原

【Abstract】 Iron oxides are important mineral component of the earth’s surface system. Thereare sixteen kinds of iron oxides were found in natural environments, in which commoniron oxides take up5types, namely hematite, goethite, magnetite, lepidocrocite,ferrihydrite. Moreover, goethite is the most crucial iron oxides in the supergeneoxidation environment as well as the one of the most important components havingstrong surface activity and chemical-biological activities in soils and deposits. As anatural nano-micron mineral, goethite plays an important role in transfer, transforamtionand enrichment of organic pollutions, inorgainc anions and heavy metals in theenvironments. Therefore, the structure and surface reactvity of goethite became the hotpoint in the field of mineralogy and environmental geochemistry. However, the currentstudy mianly concentrates on the bulk structure and its physicochemical properties. Thestudy on the relationship between the surface stucture and reactivity especially for theeffect of the struture of atomic local area was scarely reported, which limited theunderstanding of the role of mineral in environmental self-purification. On the otherhand, the study on the structure and physicochemical properties of pure goethite wasreported extensively. However, the researchs on the effect of isomorphrous substitutionby Al on the local structure, crystal chemical properties and surface reactivity wasrarely reported, although the existence of Al substitution for Fe in the structure ofgoethite has been demonstrated.Therefore, in this present thesis, the techniques of micro-beam and micro district(FESEM, TEM, etc), modern spectroscopy techniques (FTIR, Raman, etc) andcharacterization techniques of mineral phase and crystal chemistry were used tocharacterize the synthetic Al-substituted goethite and natural goethite. The objective isto illuminate the effect of Al substitution for Fe in the structure of goethite on the localstructure, surface physicochemical properties and thermal stability of goethite.Eventually, the functionized natural goethite by annealing in air or hydrogen was usedas catalysts or catalysts carrier to catalytic cracking biomass tar, decompose nitrate andPNP, remove phosphate and heavy metals ions from aqueous solution. The maincreative results are list as fellows. Four kinds of hydroxyl and three kinds of surface water were identified accordingto the results of FT-ATR and FT-IES. The four hydroxyl groups contained one structurehydroxyl and three surface hydroxyls.The synthesis of Al-substituted goethite indicated that the high pH favored theformation of Al-substituted goethite. The occurrence of Al susbtitution not onlyhampered the growth of goethite and decreased the crystallinity, but also affected thecrystal morphology reflecting in the decrease of long-width ratio with the increase of Alsubstitution amount. The substitution of Al for Fe increased the thermal stability ofgoethite. The starting temperature of the transforamtion of goethite to hematiteincreased from225oC to275oC and the active energy increased from117.8kJ/mol to126.7kJ/mol as the Al substitution amount increased from0to9.1mol%. In addition,the Al substitution still hindered the transformation of goethite to metallic iron.Limonite obtained from Xinqiao was mainly composed of acicular goethites withopen nano pore structure, in which the content of goethite was over95%. In addition,the existence of Al-substituted goethite was proved in the samples. The transforamtionof goethite to hematite occured at225oC, newly formed hamatite kept the originalshape of goethite and much nanopore was formed due to the dehydroxyl of goethite.The particles of hematite and pore size increased with the increase of annealingtemperature resulting in the reduce of specific surface area. The formed hematite had alargest surface area after annealing at the range of250-350oC. Comparing with thegothite, the surface area of annealed products increased from12.7to111.6m~2/g, whichprovided a crucial predomination for the utilizaiton of annealed goethite as a catalyst orcatalyst carrier.Based on the understanding to the structural evolution of Al-substituted goethite,the annealed products involving hematite, magnetite and zero valent iron were utilizedto catalytic cracking of biomass tar, decompose nitrate and PNP, remove phosphate andheavy metals compared with commercial iron powder. The results showed that naturalgoethite had better property as catalyst carrier than synthetic goethite. In addition, nanozero valent iron (NZVI) prepared by reducing natural goethite had a better surfacereactivity in decomposition of nitrate and PNP, and removal of heavy metals fromaqueous solution than that of commercial iron powder. It was speculated that the strongsurface reactivity of newly formed hematie and this NZVI contributed to the crystaldefects and large surface area. This indicated that natural goethite possesses promisingapplication potential in purifying pollutions. Besides, a new approach to detect theconcentration of carbonaous gases was exploited. The TOC/N was proved to be a goodinstrument for detecting organic carbon, inorganic carbon and methane, etc.更多还原