Hydrotalcite minerals are layered double hydroxides (LDH) which play an important role in immobilizing hazardous compounds to decontaminate industrial wastewaters. The stability of an LDH is mostly evaluated in terms of its low solubility in water. However, the solubility of divalent trace metals immobilized by Mg-Al-type LDHs is not well known. Hydrotalcites containing Zn in solid solution, (Mg+Zn)₃-Al-LDH, were synthesized by alkaline co-precipitation. A series of eleven LDH phases with Zn mole fractions X_Zn = Zn/(Mg+Zn) of 0–1 were characterized by powder X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry (TGA), scanning and transmission electron microscopy (SEM/TEM), Brunauer-Emmett-Teller (BET) surface area analysis, and inductively coupled plasma mass (ICP-MS) spectrometry. The XRD analysis provided sharp characteristic spacings for d₀₀₃ and d₀₀₆ which occurred for all samples, confirming a layered LDH structure. Cell parameters (a, c) obeyed Vegard’s law and confirmed the formation of a regular solid-solution series without a mixing gap. An aqueous equilibrium time was determined by kinetic dissolution experiments. Steady-state solubility occurred after 120 days, but the experiments continued up to 240 days. The XRD and SEM/TEM analyses indicated no phase changes during the long-term dissolution experiments; neither were phase impurities detected after 240 days. The solubility products of the Mg- and Zn-bearing endmember compositions were calculated from experimentally determined total cation and anion concentrations using the Visual Minteq code for considering element speciation and ion pairing. The solubility product decreased as the Zn mole fraction increased, suggesting that the Zn-bearing LDH phases were more stable than the pure Mg₃-Al-LDHs. Solid-solution aqueous-solution thermodynamic equilibrium modeling using the Lippmann “total solubility product” approach and applying Lippmann diagrams with logarithmic x-axes revealed a log-linear decrease in aqueous Zn solubility. The results are promising for remediation of metal-bearing liquid wastes because the metals that co-precipitated with the LDH were more strongly retained and, therefore, less soluble than the hydroxides or carbonates of the trace metal.

水滑石矿物是层状双氢氧化物 (LDH)，在固定有害化合物以净化工业废水方面发挥着重要作用。LDH 的稳定性主要根据其在水中的低溶解度来评估。然而，由 Mg-Al 型 LDH 固定的二价微量金属的溶解度尚不清楚。采用碱性共沉淀法合成了含Zn固溶体水滑石(Mg+Zn) _{3 -Al-LDH。}一系列具有 Zn 摩尔分数X _{Zn的 11 个 LDH 相}= 0-1 的 Zn/(Mg+Zn) 通过粉末 X 射线衍射 (XRD)、傅里叶变换红外 (FTIR) 光谱、热重分析 (TGA)、扫描和透射电子显微镜 (SEM/TEM)、Brunauer 进行了表征-Emmett-Teller (BET) 表面积分析和电感耦合等离子体质量 (ICP-MS) 光谱法。XRD 分析为所有样品提供了d ₀₀₃和d ₀₀₆的尖锐特征间距，证实了层状 LDH 结构。单元格参数 ( a , c) 遵守 Vegard 定律并确认形成了没有混合间隙的规则固溶体系列。通过动力学溶解实验确定水平衡时间。120 天后出现稳态溶解，但实验持续到 240 天。XRD 和 SEM/TEM 分析表明在长期溶解实验中没有相变；240 天后也未检测到相杂质。使用考虑元素形态和离子配对的Visual Minteq代码，根据实验确定的总阳离子和阴离子浓度计算含 Mg 和 Zn 端元组合物的溶解度积。溶解度积随着 Zn 摩尔分数的增加而降低，表明含 Zn 的 LDH 相比纯 Mg 更稳定₃ -Al-LDH。使用李普曼“总溶解度积”方法和应用具有对数x轴的李普曼图的固溶体水溶液热力学平衡建模揭示了 Zn 水溶液溶解度的对数线性下降。该结果有望用于修复含金属的液体废物，因为与 LDH 共沉淀的金属被更强地保留，因此比痕量金属的氢氧化物或碳酸盐更难溶解。