On the gel of silica formed by the acid decomposition of eudialite concentrate

We studied silica-rich gel, formed by the acid decomposition of eudialine and nepheline. The gel shows week sorption selectivity of rare metals. Gels of silica are formed in various geological processes, including ultroagpaite rocks and pegmatites as intermediate compounds and can be fixed due to formation of opal, sometime containing significant concentrations of admixture elements. It can be supposed: if the gel of silica is formed in the way of migration of low-temperature solutions, the selective sorption of metals can be effective mechanism of local differentiation of components. Acid leaching is one of the key stage of any technology for recovery rare-element from eudialite. We experimentally studied eudialite decomposition by HCl and HNO3 to search the optimal parameters of obtaining the solutions of rare- and rare-earth elements for their further separation. The sample of eudialite concentrate, provided by the Lovosersky GOK, was used as a starting material. The concentrate contained eudialite (71.1 %), aegirine+arfvedsonite (12.3%), nepheline(8.9%), feldspar (2.4%), loparite (0.4%), lamprpophyllite and lorenzenite (4.41%). During the experiment, the sample of concentrate was treated by the acids for 1-3 days. X-ray diffraction spectra show reflexes of aegegine, arfvedsonite, feldspar and loparite, but do not show presence of nepheline and eudialite. Nepheline and eudialite are decomposed with formation of gel, which can be filtrated through a red-dot filter, but do not penetrate through the white-dot filter. Mass-balance calculations show, that water content in the gel strongly depends on the concentration of used acid: the weak acid (3%) forms gel, containing 90% of water, whereas the gel, formed by the 30% acid contains only 75% of water. The gel also contains rare and rare-earth elements, and this determines the importance of the elaboration of eudialite technology. At study of properties of the gel, the filter cake was washed by distilled water with the use of step-by-step technique. Composition of liquids was determined by ICP-MS and ICP-AS methods (GEOKHI RAS).