Progress in the Low-carbon, Low-salt and Ammonium-Free Separation and Purification Process
of Rare Earths
*Huang Xiaowei
GRINM, GRIREM
Beijing, China
(hxw0129@126.com)
Feng Zongyu
GRINM, GRIREM
Beijing, China
(fengzongyu1120@163.com)
Wang Meng
GRINM, GRIREM
Beijing, China
(warmmer69@163.com)
Xu Yang
GRINM, GRIREM
Beijing, China
(xuyang6959@foxmail.com)
Peng Xinlin
GRINM, GRIREM
Beijing, China
(pxl77@sina.com)
Sun Xu
GRINM, GRIREM
Beijing, China
(sonsong007@163.com)
Yang Guilin
GRINM, GRIREM
Beijing, China
(yangguilin999@126.com)
ABSTRACT
Rare earth elements are difficult to separate and purify because of similar properties.
Therefore, it will consume lots of chemicals including liquid ammonia, liquid alkali, hydrochloric
acid, and ammonium bicarbonate during the process. A large amount of wastes is hard to be
recycled, causing serious environmental pollution.
In order to solve the environmental pollution, a low-carbon, low-salt and ammonium-free
separation and purification process had been developed, as shown in Fig.1. Mg-containing
wastewater is treated and recovered by calcium/magnesium-bearing alkaline compounds, with
subsequent preparation of high-purity Mg(HCO3)2 solution, and CO2 are recycled during this
process to prepare high-purity Mg(HCO3)2 solution by continuous carbonation. The obtained
Mg(HCO3)2 solution was then used for the extraction and separation of rare earths instead of
liquid ammonia or alkali. The concentration of Mg in the organic phase is over 0.27 mol/L after
the saponification of HEH/EHP extractants by Mg(HCO3)2, and the extraction rate of Mg is more
than 95%. After further exchangeable extraction with rare earths, the concentration of rare earths
in organic phase reaches to 0.17 mol/L, and the extraction rate of rare earths is over 99.5%.
Mg(HCO3)2 solution can also be used instead of ammonium bicarbonate, sodium bicarbonate or
oxalic acid to precipitate rare earths. In the progress, CO2 with different concentrations can be
recycled during extraction, precipitation, calcination, boiler combustion and used to prepare
Mg(HCO3)2; MgCl2 produced during solvent extraction can react with Ca(OH)2 to form Mg(OH)2
due to the different basicity of Mg and Ca, and then reused in the preparation of Mg(HCO3)2
solution.
The new technology has been successfully used for the separation of 2000 tons of rare earth
oxides at Jiangsu Guosheng rare earths Co. Ltd. in China. Furthermore, 5 foreign patents and 6
national patents have been authorized, and several companies in China has been implemented this
process.
Mixed rare earths
chloride solution
CO2 gas
Rare earths extraction
separation process
REaCl3
solution
CO2 gas
Novel saponification
agent Mg(HCO3)2
Saponification
process
REbCl3
solution
Precipitation
Calcium/magnesium
mineral
MgCl2
solution
Hydrated/Alkaline
conversion reaction
Mg(OH)2
Carbonation
CaCl2 product
New type of
precipitant
Mg(HCO3)2
RE2(CO3)3
Recovery &
purification
CO2 gas
Calcination
Rare earth
oxide
Fig.1 New rare earths separation and purification process with low-carbon, low-salt, and ammonium-free wastewater
KEYWORDS
Rare earth, Magnesium bicarbonate, Separation and Purification, Clean production