Abstract
Eudialyte, a sodium rich zirconosilicate, is one of the promising sources for REEs (rare earth elements), particularly for HREEs + Y (heavy rare earth elements and yttrium). The key challenge in hydrometallurgical processing is the prevention of silica gel formation and REE separation from resulting multi-element leach solutions. This study deals with the selective extraction of REE from eudialyte concentrate by selective roasting. In this method, metal ions are converted into sulfates, followed by the decomposition of non-REE sulfates in a roasting step and the water leaching of the calcine. The effect of acid addition, roasting temperature, roasting time, pulp density and leaching time is studied. For sufficient conversion of REEs into sulfates, sulfuric acid is added in excess. At a roasting temperature of ≥750 °C sulfates of zirconium, hafnium, niobium, aluminum and iron decompose into sparingly soluble compounds, while REE and manganese sulfates remain stable up to a roasting time of 120 min. The silica present in the calcine is found to be metastable even after roasting. The amount of leached Si4+ is dependent predominantly on the pH value of the leaching medium. Applying the method, REEs can be efficiently separated from zirconium, hafnium, niobium, aluminum and iron. However, only diluted solutions can be produced. Water leaching of calcine at high solid/liquid ratios causes REE losses resulting from formation of double sulfates and gypsum. The acid excess removed from the reaction mixture in the roasting stage can be simply recovered by treatment of the gas phase.
Highlights
There are over 270 known minerals containing REEs, of which~43% are silicates, ~23% are carbonates and ~14% are phosphates/oxysalts [1]
REEs can be efficiently separated from zirconium, hafnium, niobium, aluminum and iron
Eudialyte group minerals (EGMs) are characterized by low melting temperature and high solubility in diluted mineral from EGMs or apatite is of great importance for securing strategic raw materials supply and could acids [7]
Summary
There are over 270 known minerals containing REEs (rare earth elements), of which. Deposits—are used sporadically as zirconium ore and are often enriched with REEs. The development of innovative approaches for the extraction of REEs. EGMs are characterized by low melting temperature and high solubility in diluted mineral from EGMs or apatite is of great importance for securing strategic raw materials supply and could acids [7]. A silica-free solution can be obtained by the challenge.of eudialyte with concentrated acid and subsequent water leaching. The selective eudialyte concentrate byorselective roasting is the very low chemical consumption and the possible recovery of acid excess from the gas phase [20]. Diluted solutions obtained due to the high zirconium, hafnium, aluminum and only iron is achieved by verycan lowbe chemical consumption amounts of released sodium, potassium andHowever, calcium ions. Only diluted solutions can be obtained due to the high amounts of released sodium, potassium and calcium ions
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