Formulation of sustainable slow-release phosphate (SRP) fertilizers using low-cost carrier materials is a growing area of research. This fertilizer can prevent its nutrient loss caused by surface runoff or soil leaching. Here, we investigated the mechanochemical activation of halloysite-rich kaolin clay by planetary ball milling and produced an enhanced SRP fertilizing substrate. The milling process was carried out under dry (clay only and KH₂PO₄ solution added after milling) and wet conditions (slurry of clay and KH₂PO₄) over varying durations (e.g., 1–8 h). Changes in crystallinity and microstructure of materials induced by milling were characterized by X-ray diffraction and electron microscopy. The retention and release of phosphate from the water-extractable phase of the fertilizer were also analyzed. High-resolution transmission electron microscopy mapped the elemental distribution at the crystal scale. The milling method had a pronounced effect on the phosphate release behavior. Dry-ground materials (3–5 h) showed better retention and controlled release (∼40% phosphate released in the first wash followed by ∼5% in two successive washes). However, wet-ground samples released more phosphate initially (∼50%), leaving less for later release. Compared to wet milling, dry milling caused greater crystal damage, particularly halloysite tube breaks, and increased the amorphousness of the material. These affected the containment of KH₂PO₄ salt into halloysite lumen and the release of phosphate ions in the water phase. This provides a choice of fertilizer formulations simply by adjusting milling conditions. To move forward, we need to study the scale-up of this potentially sustainable slow-release phosphate fertilizer and test it in soil and crops. This will benefit raw mineral resources and improve the nutrient efficiency.

中文翻译：

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机械化学活化的富含埃洛石纳米管的高岭土粘土作为缓释磷肥的载体

使用低成本载体材料配制可持续的缓释磷酸盐 （SRP） 肥料是一个不断增长的研究领域。这种肥料可以防止其因地表径流或土壤浸出而造成的养分流失。在这里，我们研究了行星球磨法对富含埃洛石的高岭土的机械化学活化，并生产了增强的 SRP 施肥基质。研磨过程在干燥（仅粘土和研磨后添加 KH₂PO₄ 溶液）和潮湿条件（粘土浆和 KH₂PO₄）下进行，持续时间不同（例如，1-8 小时）。通过 X 射线衍射和电子显微镜表征研磨诱导的材料结晶度和微观结构的变化。还分析了肥料水溶相中磷酸盐的保留和释放。高分辨率透射电子显微镜绘制了晶体尺度上的元素分布图。研磨方法对磷酸盐释放行为有显著影响。干磨材料（3-5 小时）显示出更好的保留和控释（第一次洗涤释放 ∼40% 的磷酸盐，随后在两次连续洗涤中释放 ∼5%）。然而，湿地样品最初释放的磷酸盐较多 （∼50%），留给以后释放的磷酸盐较少。与湿法研磨相比，干法研磨会导致更大的晶体损伤，尤其是埃洛石管断裂，并增加材料的无定形性。这些影响了 KH₂PO₄ 盐进入埃洛石腔和磷酸根离子在水相中的释放。这提供了只需调整碾磨条件即可选择肥料配方。 为了向前发展，我们需要研究这种可能可持续的缓释磷肥的放大，并在土壤和作物中进行测试。这将使原始矿产资源受益并提高养分效率。