Abstract
During the leaching process of ionic rare earth ore (ICREO), ion-exchangeable phase calcium (IEP-Ca) and ion-exchangeable phase aluminum (IEP-Al) are leached along with rare earth, which causes many problems in the enrichment process, such as increasing the precipitant agent consumption and rare earth loss, etc. The agitation leaching kinetics and the column leaching mass transfer process of IEP-Ca and IEP-Al were studied to understand the leaching behavior of impurity in ICREO, which provides guides for the adjustment of the leaching process and to limit the co-leaching of impurities. IEP-Ca and IEP-Al were leached by ion exchange, with the leaching agent cations and the leaching kinetics described by an internal diffusion-controlled shrinking core model with an apparent activation energy of 8.97 kJ/mol and 10.48 kJ/mol, respectively. In addition, a significant reduction in the leaching efficiency of aluminum was caused by the hydrolysis reaction reinforced by the increase in MgSO4 concentration and temperature. The leaching kinetic data of IEP-Ca and IEP-Al was verified by the column leaching mass transfer process. There was a synchronous increase in the peak concentration of the outflow curve and leaching efficiency of calcium with the concentration of MgSO4 since IEP-Ca was easily leached. Therefore, as the leaching efficiency of calcium was already very high in the 0.20 mol/L MgSO4 leaching process, the leaching rate of calcium was limited by the leaching temperature and injection rate of MgSO4. For aluminum, the hydrolysis of Al3+ was promoted by increasing the MgSO4 concentration and the leaching temperature, thereby effectively reducing the content of aluminum in the leachate.
Highlights
The ionic-type rare earth ore (ICREO), in which the ion-exchangeable phase rare earth (IEP-RE) accounts for more than 80% of whole-phase rare earth [1], was first discovered in Ganzhou City in 1969
Rare earth is leached from ICREO by an in situ leaching process with ammonium sulfate leaching agent [2]
A series of strengthening leaching methods and new leaching agents have been developed to reduce or even eliminate the ammonia–nitrogen pollution in the leaching process [6,9,10,11], among which the MgSO4 leaching agent, which was proposed by our team [9,12], can maintain the soil nutrients to reduce the dosage of calcium–magnesium fertilizer, and may be able to realize ecologically friendly leaching of ICREO [12,13]
Summary
The ionic-type rare earth ore (ICREO), in which the ion-exchangeable phase rare earth (IEP-RE) accounts for more than 80% of whole-phase rare earth [1], was first discovered in Ganzhou City in 1969. It is mainly located in seven provinces of southern China. The development of ICREO can solve the problem that bastnaesite and Baotou mixed rare earth ore can only produce light rare earth and lack medium and heavy rare earth elements [2]. Rare earth is leached from ICREO by an in situ leaching process with ammonium sulfate leaching agent [2]. Pilot-plant-scale tests using the MgSO4 leaching agent are being conducted in Yongzhou city (in Hunan Province), Chongzuo city (in Guangxi Province), and Changting city (in Fujian Province)
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