【摘要】：鋁(Al)作為地殼中第三豐富的元素,在土壤赤鐵礦的形成過程中,它以同晶替代方式進(jìn)入氧化鐵晶格,占據(jù)Fe~(3+)位置。相比于純赤鐵礦,鋁替代赤鐵礦在晶胞參數(shù)、晶粒大小、結(jié)晶度、生長取向、形貌等發(fā)生明顯改變。這些礦物學(xué)性質(zhì)的改變又反過來影響了赤鐵礦的表面電荷特性、吸附能力、熱力學(xué)穩(wěn)定性、磁性質(zhì)以及溶解性等。因此,深刻地理解鋁同晶替代赤鐵礦納米顆粒的生長過程及其對(duì)赤鐵礦礦物學(xué)性質(zhì)的影響具有一定的理論意義。本論文研究了鋁同晶替代對(duì)赤鐵礦納米顆粒結(jié)構(gòu)和形貌的影響;利用密度泛函理論(DFT)進(jìn)一步計(jì)算出鋁對(duì)與赤鐵礦結(jié)構(gòu)的影響;探討了不同鋁同晶替代赤鐵礦對(duì)磷的吸附特征。主要結(jié)論如下;1.鋁同晶替代誘導(dǎo)了赤鐵礦納米顆粒沿垂直c軸方向生長,隨著鋁替代量的增加,赤鐵礦的晶胞體積v和晶胞參數(shù)a、c降低,結(jié)晶度減弱,結(jié)晶尺寸增大,比表面積增大,結(jié)構(gòu)水增加;赤鐵礦納米顆粒的形貌從菱形,過渡到菱形和平板狀混合形貌,最后到平板狀。2.DFT計(jì)算顯示Al以同晶替代方式進(jìn)入赤鐵礦體相結(jié)構(gòu)后,使得體相結(jié)構(gòu)內(nèi)金屬八面體發(fā)生不同程度的扭曲形變。這樣的形變主要導(dǎo)致了六方緊密堆積的O原子網(wǎng)絡(luò)在a軸方向產(chǎn)生較大的收縮,而在c軸方向上基本保持不變。從整體上看,六方緊密堆積的O原子網(wǎng)絡(luò)在ab方向排列更為接近平面六邊形。Al與a-Fe_2O_3表面作用影響了其表面的原子結(jié)構(gòu)以及表面能。影響程度與Al的量及特定晶面有關(guān)。a-Fe_2O_3(001)和(100)與Al作用(吸附),兩個(gè)晶面的表面能發(fā)生明顯的翻轉(zhuǎn),而翻轉(zhuǎn)后表面能較低的(001)也是平板狀a-Fe_2O_3的主導(dǎo)晶面。無論是a-Fe_2O_3體相結(jié)構(gòu)中的結(jié)構(gòu)水還是表面吸附的水都會(huì)增強(qiáng)鋁同晶替代a-Fe_2O_3形貌異質(zhì)性的演化。對(duì)于體相結(jié)構(gòu)水,它加劇了六方緊密堆積的O原子網(wǎng)絡(luò)在a軸方向的收縮,對(duì)于表面吸附水,它鈍化了(001)面,使其表面能進(jìn)一步降低。3.鋁同晶替代赤鐵礦對(duì)磷的吸附過程表現(xiàn)為一個(gè)初始快速吸附過程和隨后的慢速吸附過程。隨著鋁同晶替代量的增加,赤鐵礦對(duì)磷的初始吸附速率是依次增大的,慢速吸附速率也呈現(xiàn)同樣的趨勢(shì),相對(duì)于快速吸附過程,慢速吸附過程的吸附速率要小一個(gè)數(shù)量級(jí)。Langmuir和Freundlich等溫吸附模型均可以描述磷在鋁同晶替代赤鐵礦上的吸附行為。相比于Langmuir模型,Freundlich模型能夠更好的模擬磷在鋁同晶替代赤鐵礦上的吸附過程。
[Abstract]:Aluminum (Al) is the third richest element in the crust. During the formation of soil hematite, it enters the lattice of iron oxide in the form of homocrystalline and occupies the position of Fe~ (3). Compared with pure hematite, the crystal cell parameters, grain size, crystallinity, growth orientation and morphology of aluminum-substituted hematite changed obviously. These changes in mineralogical properties in turn affect the surface charge characteristics, adsorption capacity, thermodynamic stability, magnetic properties and solubility of hematite. Therefore, it is of certain theoretical significance to understand the growth process of Aluminum-isomorphism instead of hematite nanoparticles and its influence on the mineralogical properties of hematite. In this paper, the effect of aluminum isomorphic substitution on the structure and morphology of hematite nanoparticles was studied, and the effect of aluminum on the structure of hematite was further calculated by density functional theory (DFT). The adsorption characteristics of phosphorus by different aluminum-isomorphic hematite substituted hematite were discussed. The main conclusions are as follows: 1. Aluminum isomorphic substitution induces hematite nanoparticles to grow along the vertical c axis. With the increase of aluminum substitution amount, the unit cell volume v and unit cell parameter AOC of hematite decrease, the crystallinity weakens, the crystal size increases, and the specific surface area increases. Increase of structural water; The morphology of hematite nanoparticles changed from rhombic to rhombic and plate-like, and finally to flat. 2.DFT calculation showed that Al entered the structure of hematite by homocrystalline substitution. The metal octahedron in the bulk structure is distorted and deformed to varying degrees. Such deformation mainly results in the large contraction of the hexagonal compact stacked O atom network in the a-axis direction, while it remains basically unchanged in the c-axis direction. On the whole, the closely packed hexagonal O atom network is closer to the hexagonal plane in the ab direction. The interaction between Al and a-Fe_2O_3 surface affects the atomic structure and surface energy of the surface. The degree of influence is related to the amount of Al and the specific crystal planes. A-Fe_2O_3 (001) and (100) interact with Al (adsorption). The lower surface energy (001) is also the dominant crystal plane of flat a-Fe_2O_3. Both the structure water in the bulk structure of a-Fe_2O_3 and the water adsorbed on the surface can enhance the evolution of the morphology heterogeneity of aluminum isomorphism instead of a-Fe_2O_3. For bulk structure water, it intensifies the contraction of the hexagonal tightly packed O atom network in the a-axis direction, and passivates the (001) surface for the adsorbed water on the surface, which further decreases the surface energy. The adsorption of phosphorus on Aluminum-isomorphic hematite is characterized by an initial rapid adsorption process and a later slow adsorption process. With the increase of the amount of aluminum isomorphic substitution, the initial adsorption rate of phosphorus increased in turn, and the slow adsorption rate showed the same trend compared with the rapid adsorption process. The adsorption rate of slow adsorption process is smaller by an order of magnitude. Both Langmuir and Freundlich isothermal adsorption models can describe the adsorption behavior of phosphorus on aluminum-isomorphic hematite instead of hematite. Compared with Langmuir model, Freundlich model can better simulate the adsorption process of phosphorus on aluminum-isomorphic hematite instead of hematite.
【學(xué)位授予單位】：華中農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P579;X505

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