Demand for rare earth elements (REEs) is increasing, and REE production from ores is energy-intensive. Recovering REEs from waste streams can provide a more sustainable approach to help meet REE demand but requires materials with high selectivity and capacity for REEs due to the low concentration of REEs and high competing ion concentrations. Here, we developed a phosphate polymer nanogel (PPN) to selectively recover REEs from low REE content waste streams, including leached fly ash. A high phosphorus content (16.2 wt % P as phosphate groups) in the PPN provides an abundance of coordination sites for REE binding. In model solutions, the distribution coefficient (K_d) for all REEs ranged from 1.3 × 10⁵ to 3.1 × 10⁵ mL g^–1 at pH = 7, and the sorption capacity (q_m) for Nd, Gd, and Ho were ∼300 mg g^–1. The PPN was selective toward REEs, outcompeting cations (Ca, Mg, Fe, Al) at up to 1000-fold excess concentration. The PPN had a K_d of ∼10⁵–10⁶ mL g^–1 for lanthanides in coal fly ash leachate (pH = 5), orders of magnitude higher than the K_d of major competing ions (∼10³–10⁴ mL g^–1). REEs were recovered from the PPN using 3.5% HNO₃, and the material remained effective over three sorption–elution cycles. The high REE capacity and selectivity and good durability in a real waste stream matrix suggest its potential to recover REEs from a broad range of secondary REE stocks.

中文翻译：

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用于选择性和高效稀土元素回收的磷酸盐聚合物纳米凝胶

对稀土元素 (REE) 的需求正在增加，而从矿石中生产 REE 是能源密集型的。从废物流中回收 REE 可以提供一种更可持续的方法来帮助满足 REE 需求，但由于 REE 浓度低和竞争离子浓度高，因此需要对 REE 具有高选择性和容量的材料。在这里，我们开发了一种磷酸盐聚合物纳米凝胶 (PPN)，可以从低 REE 含量的废物流（包括浸出的飞灰）中选择性地回收 REE。PPN 中的高磷含量（16.2 wt% P 作为磷酸基团）为 REE 结合提供了丰富的配位位点。在模型溶液中，所有 REE的分配系数 ( K _d ) 范围为 1.3 × 10 ⁵到 3.1 × 10 ⁵ mL g ^–1在pH = 7，和吸附容量（q_米为钕，钆，和Ho）为约300毫克克^-1。PPN 对 REE 具有选择性，在高达 1000 倍的过量浓度时胜过阳离子（Ca、Mg、Fe、Al）。PPN 对粉煤灰渗滤液 (pH = 5) 中镧系元素的K _d为 ~ ^{10 5} –10 ⁶ mL g ^–1，比主要竞争离子的K _d (~ 10 ³ –10 ⁴ mL )高几个数量级g ^–1 )。使用 3.5% HNO ₃从 PPN 中回收 REE，并且该材料在三个吸附-洗脱循环中保持有效。实际废物流基质中的高 REE 容量和选择性以及良好的耐久性表明它具有从广泛的二次 REE 储备中回收 REE 的潜力。