An Optimized Method for Determination of Ionic-phase Rare Earth Elements by ICP-MS Using Ammonium Sulfate Leaching

BACKGROUND The accurate determination of ionic phase rare earths in ion-adsorption rare earths is of great significance for the evaluation of rare earth ore bodies. Ionic phase rare earths are adsorbed on clay minerals in the form of hydroxyl or hydrated hydroxyls and can be exchanged and desorbed with strong electrolytes (Mg2+, NH4+, etc.) into solution. The former used ammonium sulfate as the leachate to achieve the desorption and extraction of rare earth ions in the ion phase, but the solution concentration, leaching process and other aspects of choice, leaching rates (60% to 90%) are different. There is no efficient and uniform leaching method conducive to the accurate determination of ionic phase rare earth elements. OBJECTIVES To establish a high-efficiency leaching process by ammonium sulfate solution and determine the accurate contents of ionic-phase rare earth elements. METHODS The leaching parameters (solid-to-liquid ratio, ammonium sulfate concentration, best sample weight, and soaking time) of rare-earth ions by ammonium sulfate were standardized through comparative experiments, which reduced the loss of ionic phase rare earth during leaching. The leaching rates were from 88% to 98%, and ICP-MS was used to accurately determine the ion phase rare earth component. RESULTS The detection limits are 0.05-5.11 ng/g, and the relative standard deviations (RSDs) are 1.80%-10.01% for volcanic rock, 1.06%-7.27% for metamorphic rock, and 1.72%-7.58% for sedimentary rock. CONCLUSIONS The analytical results of the collaborative laboratory verify the reliability and accuracy of the method. This method is easy to operate and has high analysis efficiency. It provides the base for the establishment of relevant industry standards and national standards.