Experimental conditions and results.

Rare Earth Elements (REE) are key to modern technology and industrial processes. They are most used in electronics, although their chemistry enables numerous other applications. Oxides that combine REE, sodium, and molybdenum can be used as catalysts, antibacterial agents, pigments, and even as components in lasers. Although they are heavily in demand, REE supplies are limited in part because the separation of REE from monazite and xenotime (REEPO4), some of the most abundant REE bearing minerals in natural rocks, requires high energy inputs and creates significant environmental hazards. Through an experimental study, here we demonstrate a rapid reaction between REE phosphates and a flux containing molybdenum oxide and sodium carbonate that converts mm-sized REE phosphate into NaREE(MoO4)2 in a period of hours at temperatures <870 °C. This reaction occurs using both lab-grown REEPO4 and naturally occurring monazite as starting materials. The presence of crystalline REEPO4 at higher temperatures (e.g., > 870 °C) limits the grain size of the coexisting oxide. The substantial reactive surface area of the small-grained oxides is advantageous for industrial catalysis processes or for usage as an antibacterial agent. Larger, mm-scale crystalline NaREE(MoO4)2 is produced if mm-scale REEPO4 is not stable in the reaction products at high temperature. Finally, we offer updated details for procedures to grow mm-scale crystals of REEPO4 using the same flux-growth technique, improving the ability to grow those crystals for industrial efforts or for creation of analytical standards.

稀土元素（Rare Earth Elements, REE）是现代科技与工业生产的核心支撑材料。尽管其独特的化学特性赋能了诸多其他应用场景，但稀土元素最主要的应用领域仍为电子工业。由稀土元素、钠与钼结合形成的氧化物，可作为催化剂、抗菌剂、颜料，甚至可用于激光器的核心组件。尽管稀土元素需求旺盛，但供应却相对有限，部分原因在于从独居石（monazite）与磷钇矿（xenotime，化学式为REEPO4）——天然岩石中储量最丰富的稀土承载矿物之一——中分离稀土元素，需要消耗大量能源，且会造成严重的环境危害。本研究通过实验证实，在低于870℃的条件下，稀土磷酸盐与含氧化钼及碳酸钠的熔剂之间可发生快速反应，可在数小时内将毫米级的稀土磷酸盐转化为NaREE(MoO4)2。该反应既可使用实验室合成的REEPO4作为起始原料，也可采用天然产出的独居石作为原料。当反应温度高于870℃等较高温度时，结晶态REEPO4的存在会限制共存氧化物的晶粒尺寸。这类细晶粒氧化物具备可观的反应比表面积，十分适用于工业催化流程或用作抗菌剂。若高温下毫米级REEPO4在反应产物中无法稳定存在，则可生成毫米级的大尺寸结晶态NaREE(MoO4)2。最后，本研究更新了采用同一熔剂生长技术制备毫米级REEPO4晶体的工艺细节，可为该类晶体的工业化制备或分析标准品的研制提供技术支撑。