Multielement analysis of insoluble particulates in solar salt by ICP-AES and ICP-MS in relation to geochemical consideration

The multielement determination of major-to-trace elements in insoluble particulates of solar salt was carried out by ICP-AES and ICP-MS. A solar salt sample (30 g) was dissolved in 1l of pure water to adjust its solution salinity to be almost the same as that of seawater. When the solar salt sample solution was filtered using a membrane filter (pore size 0.45 μm), the residue on the filter was defined as the insoluble particulates and the filtrate as the soluble constituents. The insoluble particulates were decomposed together with the membrane filter by an acid digestion method using HNO3, HF, and HClO4. As a result, 36 elements in the insoluble particulates could be determined at % to sub-μg g-1 levels by ICP-AES and ICP-MS. Taking into consideration the present results along with the analytical results for the soluble constituents reported in a previous paper, alkali elements, alkaline earth elements, Mo and Cd were found mainly in the soluble constituents of solar salt, while Al, Ti, V, Fe, Co, Ga, Y, Sn, and rare-earth elements (REEs) were found in the insoluble particulates. Iron, Co, Y, Sn, and REEs in the insoluble particulates were partly leached into the acid solution when the solar salt sample was dissolved in a 0.1 M HNO3 solution. Thus, it is considered that these elements are dissolved as colloidal matter adsorbed on particulates in seawater. On the other hand, because Mn, Cu, Zn, and Pb were found in both the insoluble particulates and the soluble constituents, these elements in the insoluble particulates were easily leached in a 0.1 M HNO3 solution. These results indicate that Mn, Cu, Zn, and Pb are contained as acidsoluble forms in the insoluble particulates. Moreover, the relative abundances of the elements normalized to the Al concentrations in the insoluble particulates of solar salt and the marine sediment standard material (NIES No. 12) showed a good linear correlation, which suggests that the insoluble particulates in solar salt are an origin of marine sediment.