A new method for preparation of RE2(CO3)3 by multi-membrane electroconversion

Abstract

Preparing rare earth carbonates from rare earth chlorides is a common step in the smelting process for all rare earth ores; however, it produces large amounts of ammoniacal nitrogen wastewater and a chloride-rich precipitate. This study proposes a novel, green and simple process for preparing low-chlorine lanthanum carbonate via a multi-membrane electroconversion approach. The effects of the CO2 flow rate, current density, lanthanum chloride concentration, and electroconversion time on the electroconversion process were systematically explored. Under the optimal process conditions (CO2 flow rate = 0.5 L/min, current density = 25 mA/cm2, LaCl3 concentration = 0.3 mol/L, electroconversion time = 60 min), a current efficiency of 75.77% was obtained, along with a unit energy consumption of 5.44 kW h/kg. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and laser particle size analysis results indicate that a pure La2(CO3)3·8H2O product is obtained with a median particle size of 6.53 μm and chlorine content of 0.0021%. In addition, scanning electron microscopy and transmission electron microscopy observations indicate that the crystallisation and growth of La2(CO3)3·8H2O conform to the oriented attachment and Ostwald ripening mechanisms. Thus, the proposed multi-membrane electroconversion method provides guidance toward the clean transformation of rare earth chlorides to low-chlorine lanthanum carbonates.