Exchangeable elements forms in river surface sediments and their influence for migration process of typical elements: a case study from the Nalenggele River basin, Qaidam Basin

The occurrence of elements in sediments is significant to show the migration process of typical elements and their influence mechanism. The terminal salt lake regions of the Nalenggele River basin in Qaidam Basin is an important salt lake resource area rich in Li, K, B in the Qinghai-Tibet Plateau. But, the occurrence fraction of these important resource elements in the migration process is still poorly understood, which hinders the further understanding of the enrichment rule of resource elements in the salt lake area. In this paper, the occurrence states of typical elements (K Li B Ca Mg) in surface sediments of different hydrological environments in the Nalenggele River basin were studied based on the sequential extraction experiments. The results show that the exchangeable elements forms are different in different hydrological environments, which reflects the control of different geological processes on the distribution of exchangeable species of resource elements, including salt mineral precipitation, clay mineral adsorption and Fe-Mn oxide adsorption. ​In particular, the high content of exchangeable Li in the water-soluble fraction and Fe-Mn oxide fraction in the sediments of runoff plot and salt lake regions in study area indicates that the adsorption of Fe-Mn oxides and the precipitation of salt minerals may play an important role in Li isotope fractionation, besides the adsorption of clay minerals in general. Overall, this study has important implications for understanding the migration process of resource elements in the Nalenggele River basin.