Distribution Characterization Of Rare Earth And Ammonium In Ion Adsorption Rare Earth Deposits And Their In-situ Leaching Tailings

The obvious advantage of in-situ leaching ion adsorption rare earths(IAREs) is of small damage to vegetation. However, there still exist many uncertain factors, which lead to low extraction yield, serious soil erosion and even landslide. Therefore, it is necessary to further evaluate the real effects and problems of in-situ leaching technique so as to find out the technical measures to increase rare earth extraction efficiency and reduce environmental impact.In the present study, several typical IAREs and their tailings after in situ leaching were selected as research objects from Longnan, Anyuan and Xunwu, Jiangxi Province. The rare earth and ammonium content of samples taken from different spatial positions in the deposits or tailings were determined using our established methods. To explore the problems of in-situ leaching technology and to provide improving measures, the spatial distribution characteristics of rare earth and ammonium in IAREs and their tailings, as well as the change rule of ratios of heavy to light rare earths(Rh/l) with the depth were comparatively investigated. Results show that due to the good permeability of the full weathered layer, the contents of rare earth and ammonium in the aged in-situ leached tailings(AILTs) are relatively low to the surface layer and half weathered zone. An increase of ammonium and rare-earths residue from weathered layer to half weathering direction is observed, However, the ammonium contents in the being in-situ leached tailings(BILTs) are much higher than that in AILTs, and the total rare earth(TRE) content is inversely proportional with the ammonium content. Meanwhile, the variation relationship of TRE at different positions with the depth is also different. The adsorption isotherms of clay minerals for rare earths and ammonium are determined to be preferential and linear relationship respectively, indicating that the ammonium adsorbed on the clay mminerals is not stable and is easily lost when contacting with water, however, the rare earths are stable. Therefore, the low ammonium content in AILTs is related to the ammonium loss resulted from the rainwater infiltration. The different variation rules of acidity from the surface downward vertical direction in IAREDs and AILTs mean that the ammonium in the tailings can also be degradated via liberating ammonia and releasing proton. Therefore, the distribution of ammonium in AILTs reflect the water and gas permeability. Accordingly, the internal structure and seepage characteristics of deposit can be determined according to the distributin of ammonium and TRE. At the same time, the variation curves of TRE content or Rh/l with depth from the surface downward vertical direction in IAREDs are similar. However, their maximum peak are not synchronized, the peak depth of Rh/l always lag 1 ~ 2 meters behind that of TRE content. In AILTs, it is found that the Rh/l is negative correlation with the leaching rate of rare earth, namely the area of Rh/l is low, its rare earth leaching rate is generally high; Therefore, the distribution of rare earth and ammonium and the Rh/l values in AILTs can all be used to evaluate the completeness of rare earth leaching, provide the basis for the calculation of rare earth recovery.