Rare earth element extraction from secondary sources: understanding environmental impacts and economic feasibility

稀土元素（RE）在各种重要的高科技应用中必不可少。 稀土供应链缺乏多样性，加上初级采矿对环境的重大影响，使从次级来源提取稀土成为一种有吸引力的替代办法。稀土元素存在于各种次级产品中，特别是1）燃煤产品，如飞灰，底灰和焚烧炉灰，2）工业副产品，如炉渣，浮渣，磷石膏和赤泥，以及3）电子废物，包括镍金属氢化物电池，笔记本电脑和台式电脑的硬盘驱动器，手机，扬声器。这项工作的目标是：1）量化新兴的二次稀土提取工艺及其主要替代品的物质和能量流，2）创建一个框架来比较稀土元素的主要和二次来源的经济和环境绩效，以及3）为可行的国内供应链和制造业的发展提出建议。将综合生命周期评估、商品市场建模、材料表征和技术经济分析等方法，以评估从煤灰、磷石膏、赤泥和电子废物等副产品中回收稀土的工艺。这项研究的智力价值包括：1）建立一个框架和结果，为从废物中回收稀土的过程的研究和开发提供信息，2）改进稀土共生产品分配的核算，3）加强解决开发过程环境/经济评估中的不确定性的方法，以及4）解决废物质量驱动的可变性，包括建立一个不同废物流的稀土元素含量的开放数据库。将采用组合情景分析方法，阐明实现经济可行性和环境效益所需的参数值组合。这项工作的更广泛影响包括提高美国-该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rare earth elements (REEs) are essential in a variety of important high-tech applications. Lack of diversity in the supply chain for REEs, coupled with significant environmental impacts of primary mining, have made extraction of REEs from secondary sources an attractive alternative. REEs exist in a variety of secondary products, in particular 1) coal combustion products such as fly ash, bottom ash, and incinerator ash, 2) industrial byproducts like slags, dross, phosphogypsum, and red mud, and 3) electronic wastes including nickel-metal hydride batteries, hard drives from laptops and desktop computers, cellular phones, speakers. The objectives of this work are to 1) quantify the material and energy flows of emerging secondary REE extraction processes and their primary alternatives, 2) create a framework to compare economic and environmental performance of primary and secondary sources of rare earth elements, and 3) make recommendations for development of viable domestic supply chains and manufacturing. Methodologies from life-cycle assessment, commodity market modeling, material characterization, and techno-economic analysis will be synthesized to assess processes to recover REEs from byproducts, e.g. coal ash, phosphogypsum, red mud, and electronic waste. The intellectual merit of this research includes 1) establishment of a framework and results to inform research and development for processes to recover REEs from waste products, 2) improved accounting of co-product allocation in REE, 3) enhancing methods to address uncertainty in environmental/economic assessment of developing processes, and 4) addressing variability driven by the quality of the waste, including construction of an open database of REE content of different waste streams. A combinatorial scenario analysis method will be employed that clarifies combinations of parameter values necessary to achieve economic feasibility and environmental benefits. The broader impacts of this work include the potential to enhance U.S.-based manufacturing and reduce environmental impacts of green technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.