CYANEX® 572 Solvent Extraction Reagent Description CYANEX® 572 is a highly stable phosphorus based chelating extractant that is designed to improve SX performance relative to traditional phosphonic acid extractants. It has been specially formulated for the extraction and purification of rare earth elements. It has an extraction strength profile which allows efficient extraction of the heavy rare earth elements while allowing the back extraction / stripping operation to utilize lower strip acid concentrations. REE3+ + 3HA --> REEA3 + 3H+
Tables 1 and 2 show separation factors for CYANEX 572 and traditional phosphonic acid that were determined using the following criteria: Org.: Org.: 0.2 M ligand in aliphatic diluent Aq.: 0.02 M Rare earth single metal solution containing 0.1 M HCl Conditions: O/A=1, T=25 deg C contact time = 15 minutes Table 1 – Separation Factors for CYANEX 572
Key Benefits • • • •
Substantial acid savings Selective for heavy rare earth metals Manufactured in North America Optimization over traditional phosphonic acid extractants
Properties Active Strength: >2.9 M Appearance: Colorless to light amber liquid Specific Gravity: 0.93- 0.95 g/cm3 Viscosity: @ 25o C <50 cP Viscosity: @ 50o C <25 cP CYANEX 572 exhibits good phase separation characteristics and good physical properties without the requirement of 3rd phase modifiers. To avoid risk of 3rd phase formation it is recommended not to exceed 30% of the theoretical stoichiometric load.
DA = [MA]org/[MA]aq SF = DA/DB Table 2 – Separation factors for (2-ethylhexyl - mono(2-ethylhexyl) ester phosphonic acid
DA = [MA]org/[MA]aq SF = DA/DB
P R O D U C T D ATA S H E E T As shown, CYANEX 572 has similar separation factors to phosphonic acid, however extracts at a higher pH range due to the complex strength formed with the rare earth elements. Figure 1 shows the extraction curves that were determined using the following criteria:
Due to the slightly higher pH of extraction, CYANEX 572 allows stripping of REE utilizing a lower total acid concentration. Table 3 shows the approximate acid requirements to achieve efficient stripping utilizing CYANEX 572 in comparison to the acid requirements of using a phosphonic acid extractant. Table 3 – Acid requirements for stripping
1.0 M CYANEX 572 (~33 % v/v in aliphatic diluent)
0.13 M Rare earth single metal solution containing 0.01 M HCl
O/A=1, T=25 deg C contact time = 15 minutes
Extraction vs. pH curves are shown below for single metal RE feed source Figure 1 – Extraction of REE by CYANEX 572 from chloride solution CYANEX 572 - Extraction vs pH 1M CYANEX 572 in ISOPAR M 0.13M rare earth metals as chlorides
100% 90% 80% Ytterbium 70%
As shown above, the acid savings in strip is approximately 30% by using CYANEX 572.
Holmium Dysprosium Terbium
Lanthanum 10% 0% -1
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