This study focuses on investigating the solubilities of two rare earth element (REE) sulfate salts, Nd₂(SO₄)₃ (representing light REEs) and Dy₂(SO₄)₃ (representing heavy REEs), under various conditions. Four different systems are studied: 1) binary REE₂(SO₄)₃–H₂O system at natural pH and temperatures of 25, 46, 65, and 80 °C, 2) ternary REE₂(SO₄)₃–NaOH–H₂O system, covering a pH range from 7 down to neutral, at temperatures of 25, 46, 65, and 80 °C, 3) ternary REE₂(SO₄)₃–Y₂(SO₄)₃–H₂O system, involving Y₂(SO₄)₃ concentrations ranging from 0 to 20 g/L, pH values of 3 and 7, all at 25 °C, and 4) quaternary REE₂(SO₄)₃–Na₂SO₄–(NH₄)₂SO₄–H₂O system, encompassing Na₂SO₄ and (NH₄)₂SO₄ concentrations varying from 0 to 20 g/L, pH values of 3 and 7, and at 25 °C. Solubilities of Nd₂(SO₄)₃ and Dy₂(SO₄)₃ decrease as temperature rises, attributed to the exothermic dissolution reactions. Within pH 2 to 5, solubilities remain relatively constant, but at higher pH, they decrease due to the formation of REE₂(SO₄)(OH)₄(H₂O)₂ (rare earth sulfate hydroxide hydrate). Addition of Y₂(SO₄)₃ does not significantly affect solubilities because of the relatively low Y₂(SO₄)₃ concentration range (below 0.03 mol/kg of water), but solubilities are lower at pH 7 due to ${\mathit{REE}}_2\left(S{O}_4\right){\left(\mathit{OH}\right)}_4{\left(H_{2}O\right)}_2$ formation. For Nd₂(SO₄)₃, solubility decreases with increasing Na₂SO₄ and (NH₄)₂SO₄ concentrations, especially at pH 3 due to the formation of NaNd(SO₄)₂(H₂O) (sodium neodymium bis(sulfate) hydrate) which is also confirmed by the decrease in Na₂SO₄ concentration compared with the target value. However, at pH 7, the concentration of Na₂SO₄ is much closer to the target range. This suggests that the formation of NaNd(SO₄)₂(H₂O) is less significant at pH 7 and most of Nd precipitates as ${\mathit{Nd}}_2\left(S{O}_4\right){\left(\mathit{OH}\right)}_4{\left(H_{2}O\right)}_2$. For Dy₂(SO₄)₃, solubility increases with increasing sulfate concentrations again due to the to the formation of REESO₄⁺ and REE(SO₄)₂⁻ complexes but the solubility is lower at pH 7 due to ${\mathit{Dy}}_2\left(S{O}_4\right){\left(\mathit{OH}\right)}_4{\left(H_{2}O\right)}_2$ and $\mathit{Dy}\left(S{O}_4\right)\left(\mathit{OH}\right)$ formation. The outcomes of this investigation represent a notable augmentation to the existing repository of solubility data for Nd₂(SO₄)₃ and Dy₂(SO₄)₃. These particular systems were deliberately chosen to emulate the process of extracting rare earth elements (REEs) from ion-adsorbed clays. Nonetheless, the implications of this research extend beyond this context and hold relevance for various procedures that involve the handling of REEs in sulfate-based environments. One prominent application of these findings lies in the augmentation of thermodynamic models, notably the MSE model integrated into the OLI software. Through the incorporation of this new dataset, the OLI software is poised to become a more potent tool for forecasting and simulating the chemistry of rare earth sulfate systems. This advancement bears significant promise for forthcoming research endeavors and industrial applications where precise modeling of REE behavior is of paramount importance.

本研究重点研究两种稀土元素 (REE) 硫酸盐 Nd ₂ (SO ₄ ) ₃ （代表轻 REE）和 Dy ₂ (SO ₄ ) ₃（代表重 REE）在不同条件下的溶解度。研究了四种不同的系统：1)自然 pH 值和温度为 25、46、65 和 80 °C 的二元 REE ₂ (SO ₄ ) ₃ –H _{2 O 系统，2) 三元 REE 2} (SO ₄ ) ₃ –NaOH –H ₂ O 系统，pH 范围从 7 到中性，温度为 25、46、65 和 80 °C，3) 三元 REE ₂ (SO ₄ ) ₃ –Y ₂ (SO ₄ ) ₃ –H ₂ O 系统，涉及 Y ₂ (SO ₄ ) ₃浓度范围为 0 至 20 g/L，pH 值为 3 和 7，均在 25 °C 下，以及 4) 四元 REE ₂ (SO ₄ ) ₃ –Na ₂ SO ₄ –(NH ₄ ) ₂ SO ₄ –H ₂ O系统，包括Na ₂ SO ₄和(NH ₄ ) ₂ SO ₄浓度范围为0至20 g/L，pH值为3和7，温度为25 °C 。由于放热溶解反应，Nd ₂ (SO ₄ ) ₃和Dy ₂ (SO ₄ ) ₃的溶解度随着温度升高而降低。在pH 2 至5 内，溶解度保持相对恒定，但在较高pH 下，由于形成REE ₂ (SO ₄ )(OH) ₄ (H ₂ O) ₂（稀土氢氧化硫酸盐水合物），溶解度降低。_{由于 Y 2} (SO ₄ ) ₃浓度范围相对较低（低于 0.03 mol/kg 水），添加Y ₂ (SO ₄ ) ₃不会显着影响溶解度，但由于以下原因，在 pH 7 时溶解度较低${\mathit{稀土元素}}_2\left(S{氧}_4\right){\left(\mathit{哦}\right)}_4{\left(H_2氧\right)}_2$形成。对于 Nd ₂ (SO ₄ ) _{3 ，溶解度随着 Na 2} SO ₄和 (NH ₄ ) ₂ SO ₄浓度的增加而降低，特别是在 pH 3 时，由于形成 NaNd(SO ₄ ) ₂ (H ₂ O)（钕钠）与目标值相比， Na ₂ SO ₄浓度的降低也证实了这一点。_{然而，在pH 7 时，Na 2} SO ₄的浓度更接近目标范围。_{这表明 NaNd(SO 4} ) ₂ (H ₂ O)的形成在 pH 7 时不太显着，并且大多数 Nd 沉淀为${\mathit{钕}}_2\left(S{氧}_4\right){\left(\mathit{哦}\right)}_4{\left(H_2氧\right)}_2$。对于 Dy ₂ (SO ₄ ) ₃，由于 REESO ₄ ⁺和 REE(SO ₄ ) ₂ ^-复合物的形成，溶解度再次随着硫酸盐浓度的增加而增加，但在 pH 7 时溶解度较低，因为${\mathit{镝}}_2\left(S{氧}_4\right){\left(\mathit{哦}\right)}_4{\left(H_2氧\right)}_2$和$\mathit{镝}\left(S{氧}_4\right)\left(\mathit{哦}\right)$形成。这项研究的结果显着增强了现有 Nd ₂ (SO ₄ ) ₃和 Dy ₂ (SO ₄ ) ₃溶解度数据存储库。这些特殊的系统经过精心选择，旨在模拟从离子吸附粘土中提取稀土元素 (REE) 的过程。尽管如此，这项研究的意义超出了这一范围，并与涉及在硫酸盐环境中处理稀土元素的各种程序相关。这些发现的一个突出应用在于热力学模型的增强，特别是集成到 OLI 软件中的 MSE 模型。通过纳入这一新数据集，OLI 软件有望成为预测和模拟稀土硫酸盐系统化学的更有效工具。这一进展为未来的研究工作和工业应用带来了重大前景，其中稀土行为的精确建模至关重要。