SYNTHESIS AND PROPERTIES OF REE PHOSPHATES ON THE SURFACE OF CLAY MINERALS

Abstract

Weathered and sedimentary rocks (bauxites, clays, etc.) are promising but poorly investigated and rarely used sources of REE. These rocks are characterized by very low contents of rare-metal minerals in contrast to relatively high bulk REE concentrations. Their forms of occurrence are not yet known, which hampers the development of methods of concentration and technological estimation of these kinds of mineral resources [1]. Our study shows that a significant portion of REE in kaoline and hydromica clays occurs on the surface of major minerals in forms which can be easily decomposed in acids. They are presumably phosphates and cannot be identified by optical and microprobe methods. The important role of sorption by clay minerals was demonstrated in REE accumulations and the creation of favorable conditions for subsequent hydrothermal mineralization on the surface [2, 3]. This paper presents results of the synthesis of hydrous and anhydrous phosphates, both individual and on the surface of muscovite and kaolinite, which are characteristic minerals of weathered rocks. The hydrothermal method of synthesis can serve as an analogy for natural mineral-forming processes occurring in the zones of weathering and sedimentation. The decomposition of the phosphates was studied in sulfuric acid solutions, which is usually applied in the technological treatment of phosphate ores. A comparison of the stability of natural and synthetic compounds in acids, calculation, and comparison of solubility parameters allow us to propose possible forms of REE occurrence in natural rocks.