Research On Life Cycle Assessment And The Application In China Magnesium Industry

Life Cycle Assessment (LCA), acts as an important environmental management tool, not only assesses the environmental issues involved in the full life cycle of the products, more importantly, the value of life cycle thinking lies in its ability to provide the decision-making basis for sustainable development, making the products, industry and even the whole industry chain act more in line with the principles of sustainable development. However, life cycle assessment method itself has yet to be further improved, and some controversies still exists in the methodology of this system, for example, the characteristic model and its factor set of the non-renewable resources are under the restriction of the range of the system boundary, thus showing a strong character of being regional. In the aspect of the actual application of the life cycle assessment method, it is required to combine with the specific conditions, such as the national level of industrial technology and the phases of economic development, before giving a full play of the realistic role that life-cycle assessment can provide decision-making basis for sustainable development.The assessment of mineral resources depletion is always a part filled with dispute of Life Cycle Assessment. Based on the different comprehension about the resources depletion, it comes into being several methods and models assessing the depletion of resources with different theories. Case study and results evaluation are conducted in this thesis by choosing current widely-used method of"Grade-Energy", which receives some recognition internationally, as well as the CML method. Based on China's characters in mineral resources and the statistical features in the elementary data, important parameters within both models are amended. The use of amended CML model helps to calculate out the characteristic factors of 14 kinds of metals, 26 non-metals as well as 3 types of depletion of energy and mineral resources, all of which are playing the important roles for China's national economy. Then, on the basis of that, it is calculated that the antimony equivalent of 2.14×1010kg is the normalized benchmark of the assessment on the effect of mineral resources depletion in China, thus establishing the basis to bring this model in line with international practice.In the aspect of the actual application of the life cycle assessment method, this thesis selects magnesium metal—China's advantages resources—as its research subject. The research field covers all of the major phases of the life cycle, including the production of primary magnesium, processing of magnesium products, use and consumption of magnesium products as well as the treatment of magnesium waste. Through constructing the material flow analysis method and model of the magnesium resources and their products, it identifies and quantifies the quantity, structure and characteristics of the substance metabolism of the magnesium metal materials in China's macro level. The input of abiotic resources and the ecological burden in the practice of smelting magnesium with Pidgeon process in China is calculated. The results showed that the technology of smelting magnesium with Pidgeon process in China is leading to a large amount of materials input. While China is contributing to up to 70 percent of market share in the international magnesium output, 80 percent of the ecological pressures are left at home, creating severe impact on the environment in China.The thesis carries out technique-oriented research on the full life cycle of primary magnesium. First, to start with raw materials, the work is done to carry out research on the technology of smelting magnesium with Pidgeon process in which the coal is directly burnt, and to find out where the leading environmental pressures during the production phase lie. Through the analysis on 3 different energy utilization scenarios of primary magnesium production, figure out and work out both the environmental emission inventory and overall life cycle inventory of all phases, ranging from"cradle to gate". Based on the impact assessment results, the major blamer for the environmental load in the practice of smelting magnesium with Pidgeon process is identified, providing improvement advices and decision support on energy-saving and emission-reducing of the magnesium production.In view of the practical situations of production, use and recycling of the magnesium alloy, the thesis, taking AZ91 magnesium alloy as an example, carries out the environmental load analysis on the technologies of producing magnesium alloy with flux protection and gas protection, and calculates the cumulative environmental load of the Mg-Al alloy production. Through constructing the transportation model of the collection and recycling of waste, compare and analyze the environmental emission of two different kinds of loading vehicles during the highway transportation. Taking the practice that uses liquating method to recycle magnesium alloy waste so as to produce AZ91 alloy for example, the work is done to compare the environmental impact of both primary magnesium alloy and recycled magnesium alloy. Combining with the application of several kinds of materials such as steel, alumimum, magnesium in the auto parts, this thesis comprehensively compares the greenhouse effect of the full life cycle of these materials, and reveals the environmental performance of magnesium and its products within their life cycle.Aluminum is an important element adding to Mg-alloy. The accumulative environmental load of primary aluminum production needs to be considered when studying the environmental impact of Mg-Al alloy production. So, based on the current status of China aluminum industry, the thesis, adopting the life cycle assessment method, carries out evaluation on the resources, energy consumption and the pollutants emission in the production of primary aluminum. Based on the inventory, the thesis compared the differences in the primary aluminum production between China and the world average level, and analyzed the potential of energy-saving and emission-reducing and the characterization results of the environmental impact of the functional unit of primary aluminum and primary magnesium. This inventory can not only provide data support for the overall environmental load evaluation of the aluminum and its processed products as well as of the Mg-Al alloy products, but supply basis for the macro decision-making of China's aluminum industry in an effort to conduct the sustainable development ranging from energy-saving and emission-reducing to recycling use of resources and others.Finally, the thesis, on the basis of generalizing of the research results, presents suggestions and prospects for the contents in the aspects ranging from LCA theory and methodology, the workout of China's elementary life cycle inventory, to the extending research on the magnesium-based materials.