While silicate has been known to affect metal sorption on mineral surfaces, the mechanisms remain poorly understood. We investigated the effects of silicate on Zn sorption onto Al oxide at pH 7.5 and elucidated the mechanisms using a combination of X-ray absorption fine structure (XAFS) spectroscopy, Zn stable isotope analysis, and scanning transmission electron microscopy (STEM). XAFS analysis revealed that Zn–Al layered double hydroxide (LDH) precipitates were formed in the absence of silicate or at low Si concentrations (≤0.4 mM), whereas the formation of Zn–Al LDH was inhibited at high silicate concentrations (≥0.64 mM) due to surface-induced Si oligomerization. Significant Zn isotope fractionation (Δ⁶⁶Zn_{sorbed-aqueous} = 0.63 ± 0.03‰) was determined at silicate concentrations ≥0.64 mM, larger than that induced by sorption of Zn on Al oxide (0.47 ± 0.03‰) but closer to that caused by Zn bonding to the surface of Si oxides (0.60–0.94‰), suggesting a presence of Zn–Si bonding environment. STEM showed that the sorbed silicates had a close spatial coupling with γ-Al₂O₃, indicating that >Si–Zn inner-sphere complexes (“>” denotes surface) likely bond to the γ-Al₂O₃ surface to form >Al–Si–Zn ternary inner-sphere complexes. This study not only demonstrates that dissolved silicate in the natural environment plays an important role in the fate and bioavailability of Zn but also highlights the potential of coupled spectroscopic and isotopic methods in probing complex environmental processes.

中文翻译：

---

将分子尺度光谱与稳定同位素分析相结合，研究 Si 对氧化铝上 Zn-Al LDH 形成机制的影响

虽然已知硅酸盐会影响金属在矿物表面的吸附，但其机制仍然知之甚少。我们研究了硅酸盐在 pH 7.5 下对 Zn 吸附在氧化铝上的影响，并结合 X 射线吸收精细结构 (XAFS) 光谱、Zn 稳定同位素分析和扫描透射电子显微镜 (STEM) 阐明了机制。XAFS 分析表明，Zn-Al 层状双氢氧化物 (LDH) 沉淀在没有硅酸盐或低 Si 浓度 (≤0.4 mM) 时形成，而在高硅酸盐浓度 (≥0.64 mM) 时 Zn-Al LDH 的形成受到抑制) 由于表面诱导的 Si 齐聚。显着的 Zn 同位素分馏 (Δ ⁶⁶ Zn_吸附-水= 0.63 ± 0.03‰）在硅酸盐浓度 ≥ 0.64 mM 时测定，大于 Zn 在氧化铝上吸附引起的值（0.47 ± 0.03‰），但更接近于 Zn 键合到 Si 氧化物表面引起的值（0.60-0.94 ‰），表明存在 Zn-Si 键合环境。STEM表明吸附的硅酸盐与γ-Al ₂ O ₃具有紧密的空间耦合，表明>Si-Zn内球络合物（“>”表示表面）可能与γ-Al ₂ O _3键合表面形成 >Al-Si-Zn 三元内球配合物。这项研究不仅证明了自然环境中溶解的硅酸盐对锌的命运和生物利用度起着重要作用，而且突出了光谱和同位素耦合方法在探测复杂环境过程中的潜力。