三相体系下煤基固废富集稀土元素、并兼顾提取烯碳和分离无机材料的基础研究

Graphene and rare earth elements (REEs) are significantly important materials in sustainable energy technologies. We propose the necessities of fundamental researches on recovering graphene pieces and REEs from various waste coal byproducts in a large quantity. The proposed method is based on the breakdown and exfoliation of crystalline carbon and leaching of REEs in an acidic environment being created by the dissolved carbon dioxide in the aqueous water at an ambient temperature and high pressures. A third phase, which is organic esters, helps to form the emulsion, leading the extraction of REEs from the leaching mixture. This method is expected to have a graphene exfoliation efficiency in over 10% by weight of the total carbon content in coal byproducts, and the purity of REEs in over 10% by weight. The left-over solid products, mainly silica and aluminum, should be heavy-metal-free for further safe applications. Carbon dioxide, water and esters can be recycled. We will identify and test critical operational parameters and proper ester groups on phase transitions to help maximize efficiencies of extraction, orientation and separation of graphene pieces and REEs. The collection mechanic and parametric evidence will help on a complete process design for process scale-up, a thorough techno-economic analysis to determine the technical and economical attractiveness of the proposed process and its readiness for scale-up/commercialization and energy and economic feasibility, as well as an evaluation of the environmental impact. The efforts of this basic research will largely secure the removals of technological uncertainties. The efforts will also help on develop a novel process, which bypass the traditional water- and mineral-acids- intensive and environmental polluted extraction process of both aqueous graphene and REEs. The efforts will further bridge the conventional coal industries to the newly developed sustainable energy sector for the acquisition of the necessary novel and important materials.

从大量产出的煤基固废中富集稀土元素、兼顾提取烯碳和分离铝硅，可对固废减量无害化处理，改造、延长现有煤基产业链，开拓稀土、烯碳资源的新途径，支撑战略性新兴产业及新能源材料供应，满足国家重大需求。煤基固废涵盖煤化工焦渣、粉煤灰、劣质煤、煤矸石和煤焦冶金固废，产出端涵盖可资开发利用二级原料，如稀土元素浓缩原料、多孔碳和层状类石墨烯碳片和硅铝。本项目拟采用超临界二氧化碳/水/有机酯三相体系为绿色溶剂并辅以超声等外场强化的方法，对煤基固废中的稀土元素、烯碳及铝硅等进行提取、剥离、分离等基础研究实验。通过探索、调控CO2温压、CO2量及压力等关键技术参数，建立安全、环保，条件温和可调的反应过程。过程具有低能耗、低水耗、无酸碱操作、无氨氮及重金属排放，提取、剥离、分离步骤简单，流程短及环境友好等特点。通过研究形成可靠成熟技术，并评价产出烯碳材料在新能源等领域中的适用性。

煤基固废产量巨大，其中高价值伴生元素众多，但浓度远低于现有工业化可经济提取阈值，同时又高于环境生态影响阈值；因此，煤基固废的全元素资源化利用是解决其堆放占地、降低环境生态影响并提供大宗工业原料的必由之路。本项目明确从大量产出的煤基固废中富集浓缩稀土元素、兼顾提取烯碳和分离铝硅的技术路线，以期开拓新兴产业及新能源材料的关键元素或制品的新途径，并减量无害化煤基固废、延长现有煤基产业链，满足国家的重大战略需求。在项目执行中，我们针对性地收集了主要稀土产区附近煤企的煤基固废样品，涵盖了几乎所有煤基固废品种如劣质煤、煤泥、煤矸石、煤化工焦渣、煤电粉煤灰及冶金焦渣等，研究了煤基固废稀土元素高效率、低能耗、低环境影响释放的机制，获得了利用碱烧解构硅铝晶格以释放稀土元素、利用超临界二氧化碳-水相绿色溶剂以解吸稀土元素、通过酸碱调整以沉降富集稀土元素等关键步骤机制，实现了稀土提取效率高达70-90%、且富集率大于300，形成了一条无或少酸使用、低能耗、简单流程的技术路线和工艺过程，获得了企业重视，推广了两套中试示范系统平台，迈出了煤基固废基稀土二次矿产产业化关键一步。进一步构建了煤基固废制石墨烯量子点荧光探测稀土元素的分析体系、作为锂电电极和替代有机相的吸附剂等应用案例，获得的解构硅铝更方便下一步利用且已净化，因此推动形成煤基固废高值化利用的新途径。考虑环境危害影响，项目建议书提及的有机相提取介质首先在提取浓缩工艺中摒弃、仅以超临界二氧化碳-水相就完成稀土高效提取，但又深入探索了可回收、可生物降解有机相物质，在治理稀土和重金属污染的土壤中取得成功。本项目研究成果已直接应用于两套中试示范建设中、还获批了省级重大研究专项项目一项；同时，申请多项专利、发表高水平SCI论文、 尤其培养了多名青年学者、研究骨干及博士和硕士研究生。经过4年认真项目执行，项目执行最终达到并超过了项目预期，并形成了符合2021年2月国务院关于《加快建立健全绿色低碳循环发展的指导意见》的产业化技术。