白云石论文：白云石 热分解 动力学 煅烧 纳米氧化镁.doc

【关键词】白云石 热分解 动力学 煅烧 纳米氧化镁【英文关键词】Dolomite thermal decomposition kinetic calcining nano Magnesium oxide白云石论文：白云石的热分解规律及其应用【中文摘要】白云石是冶炼金属镁的重要原料也是冶金行业中炼钢、烧结的重要辅料之一。长白山区拥有丰富的优质白云石矿，但缺乏相关的实验研究。为此，我们采用DTA-7差示热分析仪、X射线衍射仪等仪器及动力学分析对长白山区白云石的热分解过程及微观组织形貌进行了研究。长白山区白云石的平均含镁量为13.04%，白云石中的镁钙比基本上是1：1；块体中细小微晶颗粒较多，微晶集合体颗粒大小不等，微晶的颗粒大小在310m之间，局部有重结晶现象，结构均一。从形态上看，长白山白云石属于晶质白云石类型，呈现典型的菱面体晶形，颗粒间结构致密，解理平行菱面体完全，大部分菱形晶面呈冰糖状构造，可以看到两组解理缝互相交错形成特殊的交织结构。一些样品中含有少量的杂质以SiO2、Al2O3为主。因此，长白山区白云石是冶炼金属镁的较为理想的原料。长白山区白云石的热分解分两步完成，在662734为低温阶段，在734962为高温阶段，第一步热分解的反应产物，人们一般认为是CaCO3和MgO，但在本实验中发现生成物MgO的量比理论值少，同时形成的方解石可能溶解MgO而形成一种固溶体。第一步反应开始时是界面收缩机理，CO32-向外扩散的过程是速度控制步骤。随着反应温度升高，颗粒内质点动能增加，反应由界面收缩机理变为扩散控速机理。第二步反应是由CO2扩散控速的，低温阶段分解反应产生的新相MgO包裹着尚未分解的各物相及CaCO3形成球形界面，所以这一阶段热分解过程是三维扩散，3D（球对称）的机理控制。长白山区白云石的最大失重率约为48.31%。在温度为662时恒温煅烧2h失重现象不明显，在714煅烧2h失重率达到11.11%，说明分解可以进行，但是反应较慢，而在734下分解2h后分解率达到23.2%与MgCO3在白云石中的理论失重率23.5%比较接近，同时失重曲线有一个明显的转折点，说明白云石恒温煅烧过程中MgCO3的分解温度在714734之间。在774煅烧2h失重率为28.64%，说明CaCO3已经开始分解，而在796下分解2h后分解率达到45.17%与白云石的最大失重率48.31%比较接近，同时失重曲线有上升的趋势，表明长白山白云石煅烧发生CaCO3分解的起始温度在774796之间。在相同恒温时间，不同温度下样品的分解率的高低表明在低温阶段白云石分解的速率受温度的影响明显，随温度升高明显加快，而高温阶段白云石的分解速率受温度的影响较小，同时说明白云石低温煅烧阶段温度区间较窄而高温阶段则较宽。无论是高温反应，还是低温反应，当恒温煅烧时间达到一小时，白云石的分解就已经进行得很充分。特别是高温阶段，之后的失重率变化很小，说明煅烧时间不宜过长，否则会浪费燃料。【英文摘要】As we all known, dolomite is an important raw materials of reducing the metalmagnesium and also an important auxiliary of reducing steel and sintering ore.There isa large quantity of high purity dolomite stones in the area of Changbaishan. But it is ashortage of experimental data for this dolomite. Therefore, we take some experiments tostudy the decomposition behavior and mechanism of this dolomite using DTA-7thermal analysis, XRD and some other instruments. We also perform the kinetics,SEMand TEM in order to study the microstructure of dolomite in this paper. The averagemagnesium content of Changbaishan dolomite is13.04%;the atomic ratio ofmagnesium and calcium is1:1.There are many tiny particles of different size in thebluk of Changbaishan dolomite and its size is distribution in310m.It also has somerecrystallization phenomenon in the bluk. According to the research of microstructure,Changbaishan dolomite belongs to crystal dolomite, presenting the typical surface ofrhombohedron and the particles structure is compact.We can observe two group ofcleavage seam in the bluk, appearing a special morphology.The main impurities ofChangbaishan dolomite are SiO2and Al2O3. Therefore, Changbaishan dolomite is anideal raw material for the smelting of magnesium.The process of decomposition can be divided into two steps. The generalreaction path for the first half thermal decomposition of a natural dolomite is differentfrom what people used to persist in. The amount of MgO that can be extracted fromdolomite is less than the theoretical one. This finding may be ascribed to a solid solutionof MgO in calcite. The first step of decomposition is controlled by boundary surfacecontraction in the beginning, followed by diffusion rate-contracting as thedecomposition temperature increases. The contraction step is the diffusion of CO32-.Thesecond step of decomposition is controlled by three-dimensional diffuse （ballsymmetry）. The diffusion of CO2is a rate-controlling step.At the constant temperature of662and calcined for2h, weightlessness is notapparent; at the constant temperature of714and calcined for2h,weightlessness ratereaches11.11%.It indicates the decomposition can undertake at this condition but the process is slow. However,at the constant temperature of734and calcined for2h,weightlessness reaches23.2%,which is close to the theory weight loss of MgCO3in thedolomite.Meanwhile, there is a change in the curve of weightlessness.As a result, thelow temperature of the thermal decomposition of dolomite is between714and734.Accurding to the result of experiments,we can also conclude that the hightemperature of the thermal decomposition of dolomite is between774and796.On the basis of calcining experiment, the result indicate that the temperaturetakes a more obvious influence on the low thermal decomposition stage than that of thehigh thermal decomposition stage,because the weightlessness rate increases obviouslywith the rise of temperature.It suggests that the proper decomposition temperature forthe low stage of dolomite is restricted. When the dolomite was calcining for an hour, nomatter what temperature it was, the decomposition process was nearly completed,especial the high temperature decomposition stage,so it is appropriate to take a shorttime for the calcining of dolomite, otherwise it may be a waste of the fuel.【目录】白云石的热分解规律及其应用摘要4-6Abstract6-7第一章 绪论10-181.1 镁及镁合金10-111.2 金属镁的制备方法11-141.2.1 电解法炼镁11-121.2.2 热还原法炼镁12-141.2.3 炼镁技术进展141.3 镁矿石资源14-161.4 白云石研究与开发中存在的问题16-171.4.1 开发方式161.4.2 白云石热分解机理16-171.5 选题意义及研究内容17-181.5.1 选题意义171.5.2 研究内容17-18第二章 研究方案及实验步骤18-222.1 研究方案18-192.2 实验步骤19-202.2.1 白云石样品的制备和实验仪器参数192.2.2 热分解实验192.2.3 热分解产物分析19-202.3 实验设备20-22第三章 热分解实验结果及讨论22-363.1 白云石的成分及物相分析22-243.1.1 成分分析22-233.1.2 物相分析23-243.2 热分解实验结果及分析24-323.2.1 差热实验24-273.2.2 恒温煅烧实验结果及分析27-323.3 热分解机理及动力学方程32-343.3.1 动力学计算基本原理32-333.3.2 实验结果的动力学分析33-343.4 本章小结34-36第四章 白云石及煅烧产物的微观组织36-464.1 白云石的晶体结构及用途36-374.2 白白云石的的偏光显微微分析37-38