CAS Key Laboratory of Mineralogy and Metallogeny & Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, 510640 Guangzhou, China; CAS Center for Excellence in Deep Earth Science, 511 Kehua Street, 510640 Guangzhou, China; University of Chinese Academy of Sciences, 19 Yuquan Road, 100049 Beijing, China.
CAS Key Laboratory of Mineralogy and Metallogeny & Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, 510640 Guangzhou, China; CAS Center for Excellence in Deep Earth Science, 511 Kehua Street, 510640 Guangzhou, China.
Sci Total Environ. 2021 Jul 15;778:146266. doi: 10.1016/j.scitotenv.2021.146266. Epub 2021 Mar 8.
Dissolution-precipitation processes on the surface of brushite (dicalcium phosphate dihydrate, DCPD) control the migration and transformation of potentially harmful elements (PHEs). The incorporation of impurities could affect the properties of DCPD and its interactions with PHEs. In this study, we synthesized Fe-bearing DCPD via coprecipitation and investigated the influence of Fe incorporation on the crystal structure, hydrolysis process, and Cd removal performance. Fe-bearing DCPD had lattice expansion due to the coupled substitution of Fe and NH for Ca. Therefore, the Cd removal performance of Fe-DCPD was enhanced, with a maximum Cd uptake capacity of 431.6 mg/g, which is 1.77 times that of Fe-free DCPD (244.4 mg/g). Furthermore, Fe-DCPD also exhibited a faster hydrolysis rate, which was up to 2.67 times that of Fe-free DCPD and accelerated Cd's transfer to the stable host mineral, hydroxylapatite. Cd was first caught by the DCPD surface in a weakly crystalline form and then incorporated into the hydroxylapatite structure during crystallization. Based on the X-ray photoelectron spectroscopy and thermogravimetric analysis results, we concluded that the decrease in interstitial water due to Fe incorporation was responsible for accelerating hydrolysis and enhancing Cd immobilization. In all, the incorporation of Fe into DCPD could promote its transformation and improve its Cd uptake capacity. Our results suggest that Fe-DCPD could be a promising candidate for environmental remediation.
沉淀-转化过程控制着潜在有害元素（PHEs）在磷酸氢钙二水合物（DCPD）表面的迁移和转化。杂质的掺入可能会影响 DCPD 的性质及其与 PHEs 的相互作用。在这项研究中，我们通过共沉淀法合成了含 Fe 的 DCPD，并研究了 Fe 掺入对其晶体结构、水解过程和 Cd 去除性能的影响。由于 Fe 和 NH 对 Ca 的耦合取代，含 Fe 的 DCPD 发生了晶格膨胀。因此，Fe-DCPD 的 Cd 去除性能得到了增强，最大 Cd 吸附容量达到 431.6 mg/g，是不含 Fe 的 DCPD（244.4 mg/g）的 1.77 倍。此外，Fe-DCPD 的水解速率也更快，达到不含 Fe 的 DCPD 的 2.67 倍，加速了 Cd 向稳定的宿主矿物羟基磷灰石的迁移。Cd 首先以弱晶态的形式被 DCPD 表面捕获，然后在结晶过程中掺入羟基磷灰石结构。基于 X 射线光电子能谱和热重分析结果，我们得出结论，由于 Fe 的掺入导致间隙水减少，从而加速了水解并增强了 Cd 的固定。总之，Fe 掺入 DCPD 可以促进其转化并提高其 Cd 吸附能力。我们的研究结果表明，Fe-DCPD 可能是一种很有前途的环境修复候选材料。
