Recovery of Rare Earth Elements from coal tailings from British Columbia coalfields by nano-flotation

稀土元素(REE)是元素周期表中的一组17种元素，包括15种稀土元素和两种过渡金属：Sc和Y。这些元素广泛应用于现代电子产品和绿色能源应用。随着新的清洁能源和国防相关技术的出现，稀土的消费量迅速增加，它们已被美国、欧盟和加拿大列为关键元素(Creen，2015)。考虑到供应不足以满足需求的种种风险，目前正在评估未来开采的非常规稀土来源。富含稀土的煤矿已在世界各地被确定为潜在的稀土资源。从美国煤炭及其副产物中提取稀土的方法有磁法、密度法、重力法、浮选法、离子交换法和浸出法等，但分离技术仍处于发展的初级阶段，尚未开发出工业化的提取工艺。煤中的稀土与非常细的矿物(通常小于10微米)伴生；因此，由于这些常见的分离过程(包括泡沫浮选)对这些细颗粒的分离效率的限制，从煤中分离稀土的常规物理浓缩方法是可行的。纳米浮选是一种利用纳米气泡进行泡沫浮选的方法，可以有效地捕获矿物加工中的超细颗粒，是从这些非常规资源中分离稀土矿物的一种很有前途的方法。然而，在从煤中回收稀土的背景下，它以前从未被研究过。之前在我的团队中对不列颠哥伦比亚省(BC)的煤炭进行的研究表明，大多数Rees煤在加工时会被排放到废流中。因此，发展纳米浮选作为从这些废渣中回收稀土的工艺是有机会的。我的发现资助研究项目将研究纳米浮选作为从不列颠哥伦比亚省活跃煤田的煤尾矿中回收稀土的工艺。目前，该省生产的优质冶金煤接近3000万吨，虽然这些煤的加工捕获了大部分细粉煤，但仍有相当数量的(约1-200万吨/年)作为尾矿处置。从煤尾矿中回收稀土有许多优点；不需要采矿，如果清洁煤也可以作为二次产品回收，就有可能消除煤尾矿。煤尾矿的再利用并将其转化为有价值的资源为加拿大提供了巨大的经济效益，特别是如果能够从这种非常规资源中回收稀土，而且减少甚至消除煤尾矿废物将产生明显的环境效益。目前在加拿大还没有进行这类研究的研究。

Rare Earth Elements (REEs) are a group of 17 elements in the periodic table including 15 lanthanides and two transition metals: Sc and Y. These elements are used in a wide variety of modern electronic products and green energy applications. With the emergence of new clean-energy and defense-related technologies, consumption of REEs has increased rapidly, and they have been classified as critical elements by the United States, the European Union and Canada (CREEN, 2015). Considering the myriad risks of insufficient supply to meet demand, unconventional sources of REEs are currently being assessed for future exploitation. Coal deposits with enriched concentrations of REEs have been identified across the world as potential REE resources. The extraction of REEs from US coal and its by-products has been studied using different processes such as magnetic, density and gravity-based methods, flotation, ion-exchange and leaching, but the separation technology is still in the initial stages of development, and a commercial extraction process has not yet been developed. REEs in the coal are associated with minerals that are very fine (usually less than 10 µm in size); as a result, common physical concentration methods of REE from coal are feasible due to limitations of separation efficiency by these common separation processes, including froth flotation, for such fine particles. Nano-flotation which uses nano-bubbles in froth flotation was shown to be efficient in capturing very fine particles in mineral processing applications and it is a promising method for separating REE minerals from these unconventional resources. However, it has never been studied before in the context of REE recovery from coal. Previous studies carried out in my group on the coals from British Columbia (BC) showed that most of the REEs coal report to waste streams when processed. Hence, there is an opportunity for the development of nano-flotation as a process for recovery of REEs from these rejects. My Discovery Grant research program will study the nano-flotation as a process for REE recovery from coal tailings from active coalfields in BC. Currently, close to 30mln tonnes of high-quality metallurgical coal is produced in the province, and while the processing of these coals captures most of the fine coal, a significant amount (~1-2 mln/year) is still disposed as tailings. There are number of advantages of recovering REE from coal tailings; there is no mining required, possible elimination of coal tailings if clean coal can be also recovered as a secondary product. Reutilization of coal tailings and turning them into valuable resources provides Canada with significant economic benefits, especially if the REEs could be recovered from this unconventional resource as well as there will be clear environmental benefits of reducing or even eliminating coal tailings waste. There has been no study currently undertaking this type of research in Canada.