The elements phase associations of ferromanganese nodules in the seamounts of the South China Sea

The study on the association phase of major and trace elements in ferromanganese nodules is of great significance for further understanding the formation and element enrichment process in ferromanganese nodules. In this paper we applied the in-situ X-ray fluorescence spectrum (XRF) and scanned the transects for 3 nodules collected from the Jiaolong seamount (3 300 meters in depth) in the South China Sea and divided the nodules’ transects into several layers for elements sequential-leaching experiment in order to determine the adsorption phases of main and trace elements. The carbonate phase, manganese mineral phase, iron mineral phase and residual phase components in the nodules were leached respectively, and the contents of major and trace elements before and after leaching in different layers were determined by ICP-OES(MS). The results show that the most of the host phases of elements in nodules are similar to that of hydrogenetic nodules in open oceans, with Al, K, Mg, Li, Ti more enriched in residual phase, showing the unique phase pattern of marginal sea hydrogenetic nodules. From the core to the rim of the nodules, the proportion of Mg, Cu, Ni and Zn in manganese mineral phase increases with the increase of Mn/Fe ratio, which may reflect the changes in chemical and mineral composition. In addition, compared with the previous publications, we found that the experimental reagent and reaction time had a great influence on the leaching result.