Chemical composition in phosphate materials from the ocean floor

Content, distribution patterns, and speciation of Cl in phosphorites and bone phosphate from the ocean floor, as well as in a set of samples from the land are studied. Total Cl content varies from 0.05 to 4.25% in phosphorites and from 2.48 to 2.75% in recent phosphate-bearing sediments. Recent phosphorites are enriched in Cl relative to ancient ones. Bound Cl content (not extractable by washing), which increases with lithification, varies from 0.17 to 0.60% in ocean and land phosphorites and from 0.02% to 1.30% in bone phosphate. Na content in most samples is higher relative to Na of NaCl due to its incorporation into the crystal lattice of apatite. However, the opposite relationship is observed in some samples indicating partial Cl incorporation into the anion complex of phosphate. Behavior of Cl in phosphorites from the present-day ocean floor is controlled by early diagenetic processes, whereas the role of weathering, catagenesis, and hydrogeological factors may be crucial for phosphorites on continents.

本研究系统探究了海底磷灰岩、骨磷酸盐及陆地系列样品中氯（Cl）的含量、分布规律与赋存形态。磷灰岩的总氯含量介于0.05%至4.25%之间，现代含磷酸盐沉积物的总氯含量为2.48%至2.75%。相较于古磷灰岩，现代磷灰岩的氯元素富集程度更高。结合态氯（即无法通过水洗提取的氯）含量随成岩作用增强而升高：海陆磷灰岩中的结合态氯含量介于0.17%至0.60%，骨磷酸盐中的结合态氯含量则为0.02%至1.30%。多数样品中的钠总量高于以氯化钠形式存在时的钠占比，原因在于钠已掺入磷灰石的晶格之中；但部分样品呈现出相反的规律，表明部分氯元素已掺入磷酸盐的阴离子络合物中。现代海底磷灰岩中氯元素的地球化学行为受早期成岩作用调控，而陆地磷灰岩的氯元素行为则主要受风化作用、成岩后生作用及水文地质因素控制。