Leaching kinetics of ionic rare-earth in ammonia-nitrogen wastewater system added with impurity inhibitors

• Published in: Journal of rare earths Vol. 32; no. 12; pp. 1175 - 1183
• Main Authors: QIU, Tingsheng, ZHU, Dongmei, FANG, Xihui, ZENG, Qinghua, GAO, Guangkuo, ZHU, Hualei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-12-2014
• Subjects: ammonia-nitrogen wastewater; Diffusion; Impurities; impurity inhibitor; Inhibitors; ionic rare-earth; kinetics; Leaching; Mathematical models; Ores; Rare earth metals; Reaction kinetics; Waste water; impurity inhibitor; ionic rare-earth; leaching; kinetics; ammonia-nitrogen wastewater
• ISSN: 1002-0721; 2509-4963
• DOI: 10.1016/S1002-0721(14)60200-3

Ammonia-nitrogen wastewater is produced during the dressing and smelting process of rare-earth ores. Such wastewater includes a very high concentration of NH4+, as well as other ions (e.g., NH4+, RE3+, Al3+, Fe3+, Ca2+, Cl−, and SiO32–) with a pH of 5.4–5.6. Its direct discharge will pollute, yet it can be recycled and used as a leaching reagent for ionic rare-earth ores. In this study, leaching kinetics studies of both rare earth ions and impurity ion Al3+ were conducted in the ammonia-nitrogen wastewater system with the aid of impurity inhibitors. Results showed that the leaching process of rare-earth followed the internal diffusion kinetic model. When the temperature was 298 K and the concentration of NH4+ was 0.3 mol/L, the leaching reaction rate constant of ionic rare-earth was 1.72 and the apparent activation energy was 9.619 kJ/mol. The leaching rate was higher than that of conventional leaching system with ammonium sulfate, which indicated that ammonia-nitrogen wastewater system and the addition of impurity inhibitors could promote ionic rare-earth leaching. The leaching kinetic process of impurity Al3+ did not follow either internal diffusion kinetic model or chemical reaction control, but the hybrid control model which was affected by a number of process factors. Thus, during the industrial production the leaching of impurity ions could be reduced by increasing the concentration of impurity inhibitors, reducing the leaching temperature to a proper range, accelerating the seepage velocity of leaching solution, or increasing the leaching rate of rare earths.
Leaching kinetics controlled model for ionic RE ore at different particle sizes (Internal diffusion controlled leaching model for rare earth at different particle sizes)