ABSTRACT Titanite (CaTiSiO5) a mineral that has shown promise as an actinide-bearing host phase. Natural titanites contain radionuclides which result in radiation damage to the crystal structure and could even lead to an amorphous state (metamict state). It is imperative to understand how the chemical durability of the titanites would be affected by such radiation damage and leaching solutions. Natural metamict titanite 2974 was studied by static leach tests at 200°C in different solutions, including heavy water (D2O) and heavy-oxygen water (H2 18O). The effects of these solutions on the leaching behaviour of the natural titanite with metamict structures were characterised using scanning electron microscopy (SEM), infrared spectrum (IR), Raman and X-ray diffraction (XRD), and the normalized leaching rates of the elements in the titanite were analysed using inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectroscopy (ICP-OES). The results indicate that in a pH 1 solution as well as a pH 11 solution, the leaching rates are comparatively low, even at a high temperature of 200°C. SiO2 and TiO2 were detected on the surface of the leached 2974, which indicates that the hydrothermal alteration abides to a mechanism of dissolution and re-precipitation. However, 2974 is mostly dissolved in a strongly acidic condition.

中文翻译：

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浸出液对天然变镁钛石化学耐久性的影响

摘要 钛铁矿 (CaTiSiO5) 是一种已显示出作为含锕系元素主相的前景的矿物。天然钛石含有放射性核素，会导致晶体结构受到辐射损伤，甚至可能导致无定形状态（metamict 状态）。必须了解这种辐射损伤和浸出溶液会如何影响钛钛矿的化学耐久性。通过在 200°C 下在不同溶液（包括重水 (D2O) 和重氧水 (H2·18O) 中）的静态浸出试验研究了天然镁钛石 2974。使用扫描电子显微镜 (SEM)、红外光谱 (IR)、拉曼和 X 射线衍射 (XRD) 表征这些溶液对具有变质结构的天然钛石浸出行为的影响，使用电感耦合等离子体质谱法 (ICP-MS) 和光学发射光谱法 (ICP-OES) 分析钛铁矿中元素的归一化浸出率。结果表明，在 pH 1 溶液和 pH 11 溶液中，浸出率相对较低，即使在 200°C 的高温下也是如此。在浸出的2974表面检测到SiO2和TiO2，表明热液蚀变遵循溶解和再沉淀的机制。然而，2974在强酸性条件下大多溶解。在浸出的2974表面检测到SiO2和TiO2，表明热液蚀变遵循溶解和再沉淀的机制。然而，2974在强酸性条件下大多溶解。在浸出的2974表面检测到SiO2和TiO2，表明热液蚀变遵循溶解和再沉淀的机制。然而，2974在强酸性条件下大多溶解。