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

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 Si O32–） with a p H 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 k J/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.

Effects of ionic impurities on crystallization of cobalamin

In this paper,the influence of two typical ionic impurities(Na_(+)and Mg_(2+))is investigated with the focused beam reflectance measurement(FBRM)technique.In this system,the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts.It is noted that impurity Mg_(2+)has a more significant effect than Na_(2+)in crystal growth of the whole crystallization process.From the microscopic observation of crystals,Mg_(2+)has an obvious effect on the crystal habit,while Na_(2+)has little effect.In addition,the crystal habit changes can be monitored by particle vision measurement(PVM).Understanding these effects is helpful to aid optimization and improve process control.