【作者】 王冲；

【导师】 刘勇兵；

【作者基本信息】 吉林大学 ， 材料学， 2013， 博士

【摘要】 本文结合生命周期评价（LCA）理论对金属镁从矿石开采直至形成镁合金产品废弃整个生命周期内能耗与环境影响进行分析。针对长白山地区丰富的白云石矿产资源，对其矿物组成、微观组织形貌、热分解机理、分解产物等进行了研究，并结合生命周期理论提出了一套以白云石原料制备金属镁的新工艺，为长白山地区白云石合理开采、有效开发、可持续利用及金属镁冶炼行业提供了一定的参考依据。本文遵循生命周期评价(LCA)的原则和框架，将白云石从矿石开采、制备金属镁、镁合金产品生产、使用、废弃到再生过程中的制造技术和生命周期环境影响、能耗分析、经济成本结合起来进行评价，提出了绿色设计决策模型和热还原煅烧白云石制备金属镁工艺的LCA总体模型。在镁及镁合金生产领域引入工业生态学思想，把资源综合利用和工业领域生态修复与生态重建纳入LCA理论框架体系，提出了相关的评价指标体系。形成绿色材料金属镁从矿石开采→金属镁生产→镁合金加工→镁合金材料回收再生的良性循环，从而建立起节能、环保、高效的镁及镁合金生产体系，实现经济效益和环境效益的良好结合。在现有基础上，从新型镁合金材料与工艺装备、再生理论与技术和绿色设计软件系统三个方向阐述今后绿色设计与绿色制造的工作中心，以推动我国镁及镁合金生产进程的产业化。长白山地区白云石矿中C、O、Mg和Ca的质量分数分别为14.8%、50.1%、12.0%和22.5%，平均含镁量为13.18%，白云石中的镁钙比基本上是1:1，含有少量的以SiO2、Al2O3为主的杂质。矿石为典型的菱面体晶形，隐晶质组成，晶粒间结构致密，菱面体完全，解理平行，大部分为自形晶菱形，晶面呈冰糖状构造，是硅热法冶炼金属镁的理想原料。在白云石煅烧过程中，随着温度的升高，主要生成物MgO晶粒生长速度加快，形成较大晶粒，同时由于分子间的热运动，煅烧温度升高，分子间动能逐渐增大，从而导致MgO晶粒的排列规则受到影响，当煅烧温度超过750℃后，煅烧温度对MgO产物的形貌影响较为敏感，在930℃下恒温煅烧3h开始形成团聚结构，造成白云石表面过烧，从而降低了白云石转化为MgO的反应活性。通过对白云石煅烧实验过程中煅烧温度和时间参数的控制，确定煅烧温度为700℃，恒温时间为3h是得到活性MgO和CaCO3的最佳煅烧参数，即长白山地区白云石煅烧的最佳参数是：煅烧温度700℃，恒温时间为3h。通过对白云石矿石显微结构和不同煅烧参数下的煅烧实验研究，得出长白山地区白云石的显微组织与其煅烧质量和冶金性能等存在一定关系。隐晶质颗粒组成的白云石矿石，晶粒细小，且尺寸均匀，由于优先沿解理缝分解所需能量低的缘故，在煅烧分解过程中表现平稳。而显晶质组成的白云石矿石，晶体晶粒尺寸不均匀，取向各异，由于晶粒间受热不均匀，使得热分解反应过程进行缓慢，煅烧性能表现较差，煅烧时间较长，煅烧后产物易于破碎和粉化。文本对长白山地区白云石热分解机理进行了研究，确立了分解动力学方程参数值，研究结果表明：低温阶段（570～730℃），发生反应式CaMg(CO3)2=CaCO3+MgO+CO2，反应是界面收缩机理，CO2-3是迁移扩散的控速步骤；中温阶段（730～750℃），反应式CaMg(CO3)2=CaCO3+MgO+CO2和CaCO3=CaO+CO2协同发生，即界面收缩机理和三维扩散机理同时存在，反应的控速步骤由Mg2+、O2-、CO2-3、Ca2+和生成物CO2决定；高温阶段（750～930℃），发生反应式CaCO3=CaO+CO2，反应是三维扩散机理，CO2是扩散迁移的控速步骤。本文结合生命周期理论，提出了一种白云石炼镁新工艺方法，旨在克服现存工艺镁还原效率低、能耗大、生产周期长和污染严重等问题。该方法包括白云石破碎、真空低温轻煅与CO2回收利用、冷却并回收热量、混合配料球磨、混合料制团、真空高温热还原和取镁块及炉渣利用。真空低温轻煅是利用连续式真空煅烧炉将经过破碎的白云石在煅烧温度范分别为600～700℃和900～1000℃和炉内压力为10000～60000Pa的条件下轻煅1～3h，白云石中的MgCO3与CaCO3依次分解，反应式为：CaMg(CO3)2=CaCO3+MgO+CO2↑和CaCO3=CaO+CO2↑，热分解后得到CO2与MgO和CaO的混合物（煅白）。在炉内流动并加热白云石的CO2被回收利用，高温煅白从连续式真空煅烧炉出料后，直接进入充满非氧化性保护气氛的热交换器中冷却，冷却后将室温状态的煅白与还原剂、熔剂直接放入充满非氧化性保护气氛的混料机中混合成料，对混合料进行研磨后制团。将混合料装入还原装置中与还原剂（硅铁）发生还原反应产生镁蒸气。反应式为：2(MgO·CaO)+Si(Fe)=2Mg↑+2CaO·SiO2+(Fe)，镁蒸汽进入冷凝器冷凝，收集得到金属镁块，还原罐内的残渣可粉磨后制成硅酸钙肥和铸型硬化剂。更多还原

【Abstract】 This article using life cycle assessment (LCA) evaluated the energy consumption and theimpact on environmental in the entire life cycle of magnesium from ore mining to productionabandonment. Aimed at the abundant dolomite mineral resources in changbai mountainarea，this paper investigated the mineral composition, microstructure, thermal decompositionand the decomposition products. A new process for producing magnesium from dolomite isdesigned based on the existing thermal reduction magnesium method. Combined with lifecycle assessment (LCA), both the energy consumption and environmental impact on theentire life cycle from ore mining to abandonment is reasonably analyzed. These resultsprovide a certain valuably reference for the reasonable exploitation of dolomite, effectivedevelopment, sustainable utilization and magnesium metal smelting industry.Following the principles and framework of life cycle assessment (LCA), this paper putforward a green design decision-making model and an LCA general model for heatingmethod to extract magnesium, based on the valuation of the producing technology, the lifecycle of environmental impact during the process from ore extraction to preparing,producing, using, disposing and reproducing magnesium and magnesium alloy, energyconsumption analysis and economic cost. Introducing the idea of industrial ecology into themanufacture of magnesium and its alloy, this paper proposes the related assessment indicatorsystem, bringing integrated use of natural resources, ecological restoration andreconstruction in industry into LCA theoretical framework. In this system, a virtuous circleof green material-green processing-green recycling is formed; an energy efficient,environmentally friendly and highly efficient magnesium alloy producing system isestablished; the combination of economic and social benefits is well achieved. Based on theexisting basis, we expounded the work centers future of green design and greenmanufacturing from the points of new magnesium alloy materials and process equipment,regeneration theory and technology and green design software design, which will promotethe industrialization of the production of magnesium and magnesium alloy in our country.the dolomite mine from Changbai the mass fraction of C, O, Mg and Ca were14.8%,50.1%,12%and22.5%, respectively, average magnesium content is13.18%, calcium and magnesium ratio of dolomite is essentially1:1, containing a small amount of impuritieswhich is mainly composed of SiO2and Al2O3. which is an ideal material for silicon thermalmethod of metallurgy of magnesium metal. Ore belongs to crystalline dolomite type,Itappears to be crystal rhombohedral, dense-particle structure, parallel, and completerhombohedral. Most of the diamond crystal surface appears to be rock candy structure,visible cleavage crack mutually interlaced structure formation. Owing to lower energy areneeded for priority decomposition along cleavages, the process of calcination are stable atdifferent temperatures. As a result, dolomite from Changbai Mountain area is an idealmaterial for silicon thermal method of metallurgy of magnesium metal.In the dolomite calcination process, with the increase of temperature, the grains of themain product MgO grow rapidly, and finally forming large grains. At the same time, becauseof the thermal motion of molecules, the calcination temperature and the intermolecularkinetic energy increase, which affects the distribution rule of the grains of MgO. When thecalcination temperature is over750℃, the formation of MgO is sensitive to the calcinationtemperature. After calcined for3hours constantly under930℃, the dolomite formed intoaggregate structure, resulting in the surface overburned, thereby reducing the reactingactivity of the transformation from the dolomite into MgO.Through the control of thecalcination temperature and the calcination time during the dolomite calcining experiment,the optimal calcining parameters, which will obtain active MgO and CaCO3, are: calcinationtemperature700℃, constant temperature time3h.Through research on the microstructure of dolomite,combined with calcinedexperimental result at different calcining parameters,show that there is a certain relationshipbetween the microstructure of dolomite and calcined quality,metallurgicalproperties.dolomite minerals which is mainly composed of aphanitic particles calcined atdifferent temperature parameters, calcination are stable at different temperatures mainlybecause of Lower energy are needed for priority decomposition along cleavages.Otherwise,significant crystalline, especially dolomite mineral which is composed by large particles, hasa poor calcined performance, difficult in calcination process comparied with hidden crystalwhichis composed of small particles, the required calcination time is relatively long.Becausein the process of calcination of dense great grain dolomite, the diffusion prcess of CO2iscarried in the interior of crystals slowly, due to the uneven heating of rooms inside thecrystal grains, the different orientation lead to that the process of hermal decomposition goon slowly and significant crystalline dolomite which is composed of large grains is easy to crushing and pulverizing after calcined.Based on the study of the thermal decomposition mechanism of the dolomite inChangbai Mountain area, we found that in the low temperature stage(570～730℃), thereaction equation is CaMg(CO3)2=CaCO3+MgO+CO2and the reaction mechanism isinterface contraction mechanism. The CO32-is the rate-controlling step in the relocationdiffusion. In the intermediate temperature stage (730～750℃), the reaction equation isCaMg(CO3)2=CaCO3+MgO+CO2and CaCO3=CaO+CO2. The two reactions happencollaboratively. Namely, interface contraction mechanism and diffusion control mechanismsexist at the same time. The speed control step of the reaction is determined by Mg2+, O2-,CO32-, Ca2+and CO2. In the high temperature stage (750～930℃), the reaction equation isCaCO3=CaO+CO2. The reaction mechanism is diffusion control mechanism. CO2is therate-controlling step of the diffusion.This article using life cycle assessment, invented a new process using dolomite meltingmagnesium, aiming to overcome the disadvantages existing in magnesium preparation,which are low efficiency, high energy consumption, long production cycle and pollute theenvironment. The method includes crushing dolomite, vacuum light calcined at lowtemperature, recycling of carbon dioxide, cooling and heat recovery, mixing milling, hot mixbriquetting at high temperature, vacuum reduction and magnesium block and slag utilization.Vacuum low temperature light calcination is to calcinate the crushed dolomite lightly for1～3hours under calcination temperature600～700℃and900～1000℃and the pressure10000～60000Pa in the furnace by using continuous vacuum furnace. The MgCO3andCaCO3in dolomite will break down successively. The reaction equation is CaMg(CO3)2=CaCO3+MgO+CO2↑and CaCO3=CaO+CO2↑, obtaining a mixture of CO2, MgO and CaO.The CO2from floated in the furnace by heating dolomite is recycled. After coming out of thecontinuous vacuum furnace,the mixture were directely poured into heat exchanger whichwas filled with non-oxidizing protective gas for cooling. After cooling process, the calcineddolomite,reducing agent and flux were directly put into the mixing machine which wasfilled with non-oxidizing protective gas at room temperature to get mixture. The mixture wasbriqueted after grinding. Then put the Mixture into reduction device to react with thereducing agent (ferrosilicon). After reduction reaction we will get magnesium vapor. Thereaction equation is2(MgO·CaO)+Si(Fe)=2Mg↑+2CaO·SiO2+(Fe), magnesium vapor willbecome collectable metal magnesium after coming into the condenser condensate. The residue in the reduction tank can be made into calcium silicate fertilizer and mold hardenerby grinding.更多还原