Separation of Rare Earth Elements Using Flotation and Emulsion Separation based on Difference of Surface Properties

Abstract

Rare earth elements (REEs) are important resources for many cutting-edge industries. To separate REEs from ore, flotation has commonly been used. However, flotation of REE minerals is very challenging because of low selectivity and efficiency. Therefore, in this study, an emulsion process is developed to separate REE minerals. The major REE mineral of the studied ore samples is monazite. However, the content of iron oxide (goethite) of the ore was over the 50%. The value of d10, d50 and d90 of ore sample are 1.31 m, 11.105 m and 51.285 m respectively. Emulsion separation is a procees similar to flotation whereby surface properties are used to separate minerals. The only difference is that for the hydrophobic phase, oil is used instead of air. Since emulsion separation is the process for separating minerals according to their surface properties, collectors, depressants and activator are used, as they are in flotation. Various factors are examined: the volume ratio of slurry to oil, pH, particle size, type of oil, type and dosage of collectors, and type and dosage of depressants. The optimum volume ratio of slurry to oil is 2:1, and the pH is adjusted to 9.5. Ore samples are separated with a micro sieve with a mesh of 10 m to evaluate the effect of particle size. Fine particles are important to stabilize the emulsion and help coarse particles to become stabilized in the emulsion. However, there is no difference in grade between over and under products, which indicates that only surface properties affect the performance of emulsion separation. Kerosene is the best oil phase, and sodium oleate is selected as the collector. The dosage of the collector is determined based on the number of molecules of REEs in ore sample. Sodium silicate is the best depressant for the REE emulsion separation test. To determine the optimum conditions for the emulsion separation process, the dosages of depressant (sodium silicate) and activator (calcium chloride) are varied. The original feed and deslimed feed are used for emulsion separation for comparison. The optimum condition for emulsion separation is 0.875x calcium chloride and 2.625x sodium silicate for the original feed. 75% of recovery is achieved. The value of TREE (emulsion)/TREE (water) was 1.465, and the value of TREE (emulsion)/TREE (feed) is 1.114. The performance of emulsion separation with the deslimed feed is poor compared with the original feed. This finding is attributed to the size effect and the low degree of liberation in the deslimed feed.