11 th Rare Earth Conference Singapore RWTH Aachen workshop on green resources & processing concepts for rare earth metals Eudialyte, an unexploited resource for valuable heavy rare earth elements How to prevent the silica gel formation? Daniel Voßenkaul, B. Friedrich 1 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Eudialyte Empirical chemical fomula (Eudialyte): N 15 [M 1 ] 6 [M 2 ] 3 [M 3 ] M 4 Z 3 [Si 24 O 72 ]O 4 X 2 N = Na, Ca, K, Sr, SEE, Ba, Mn, H 3 O M 1 = Ca, Mn, SEE, Na, Sr, Fe M 2 = Fe, Mn, Na, Zr, Ta, Ti, K, Ba, H 3 O + M 3,4 = Si, Nb, Ti, W, Na Z = Zr, Ti, Nb O = O, OH, H 2 O X = H 2 O, Cl, F, OH, CO 3 2, SO 4 2, SiO 4 4 Johnson, O (2003): The nomenclature of eudialyte groupe minerals 2 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Advantages and Challenges Advantages of Eudialyte: High contents of heavy rare earth elements (HRE) (up to 50%) Easy to digest with mineral acids Contains other valuable metals like Zr, Mn, Nb & Ta Low contents of radioactive elements (Th & U) Available in Europe (Sweden, Greenland, Russia) Challenges for REE processing: Variable and low contents of total rare earth elements (treo) (< 10%) Tendency of gel formation High consumption of acids Difficult digestion of Zr (> 60%), Nb & Ta 3 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Direct Acid Leach of Eudialyte Critical silicon concentration in solution of about 500 mg/l Gelatinous Mass Finely Ground Ore Eudialyte Ore 4 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Mechanism of Silica Gel Formation Monosilicic acid Disilicic acid Polysilicic acid Boundary layer of colloids Fresh silica gel Colloid Enclosed liquid volume 5 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Theo. approach of silica gel prevention Prevention of enclosing water Minimisation of polymerisation Idea: Dry digestion of the Eudialyte concentrate for an immobilization of silica colloids Grinded Eudialyte concentrate Dry digestion with HCl Washing out with H 2 O Theoretical concept of dry digestion process: Similar chemical reaction (formation of an amorphous silica phase) Differences in structure less mobility of colloids individual fragments (less polymerization) Washing out of valuable metal chlorides (no solution of once stabilized silica) 6 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Process Parameter Study (25 g scale) t(dry digest) m(hcl) t(leaching) reproducibility Reproducible results (ore decomposing): No gelation by dry digest (correlation with silicon recovery) REE recovery > 90% Transferable to different Eudialyte occurrences: Khibina Complex Norra Kärr Ilimaussaq Complex (TANBREEZ) 7 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu Metal recovery (R) Processing of Eudialyte (1,5 kg scale) H 2 O HCl Eudialyte Moistening Decomposition Solid Liquid Suspension Leaching 1. Filtration 1. Washing Pregnant Liquor 100% 80% Leaching 1. Washing 2. Washing H 2 O 2. Filtration 2. Washing 60% 40% 20% 3. Filtration Residue 0% Rare Earth Elements 8 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
XRD-Analysis of almost pure Eudialyte Starting material Detection of Eudialyte & Nepheline After decomposition Detection of Sodium chloride & amorphous phase After leaching and washing Main results of XRD: 1. Decomposition with first step: Transformation in light soluble chlorides (NaCl) 2. Leaching with water Solution of soluble chlorides 9 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
QEMSCAN of various Eudialytes Khibina Complex Norra Kärr 54,06% Eudialyte 0,03% Eudialyte 73,35% Eu. RS. 21,66% Eudialyte 2,99% Eudialyte 35,10% Eu. RS. 2000 µm Main results of QEMSCAN: 1. Almost full digestion of Eudialyte mineral 2. Formation of a new silicon rich phase (Eudialyte residue) Ilimaussaq Complex 62,40% Eudialyte 0,02% Eudialyte 84,60% Eu. RS. Eudialyte Catapleiite Aegirine Feldspars Eudialyte residue Others QEMSCAN conducted by N.Stoltz (IML) 10 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Defining of REE metal losses Norra Kärr (EU30) 21,66% Eudialyte 2,99% Eudialyte 35,10% Eu. RS. 2000 µm 2000 µm Surface attack of coarse-grained Eudialyte (process optimization) Optimization of mixing behavior Optimization of grinding 500 µm Eudialyte Catapleiite Aegirine Feldspars Eudialyte residue Others QEMSCAN conducted by N.Stoltz (IML) 11 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Layer Defining of valuable metal losses 0,04% EU, 81,4% R Concentration in % 2,03% EU, 38,4% R 1,09% EU, 47,7% R 2,59% EU, 30,3% R 4,65% EU, 25,0% R 10 mm 2000 µm 12 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Optimization of metal recoveries N 15 [M 1 ] 6 [M 2 ] 3 [M 3 ] M 4 Z 3 [Si 24 O 72 ]O 4 X 2 N = Na, Ca, K, Sr, SEE, Ba, Mn, H 3 O digestion no digestion M 1 = Ca, Mn, SEE, Na, Sr, Fe M 2 = Fe, Mn, Na, Zr, Ta, Ti, K, Ba, H 3 O + M 3,4 = Si, Nb, Ti, W, Na Z = Zr, Ti, Nb O = O, OH, H 2 O X = H 2 O, Cl, F, OH, CO 3 2, SO 4 2, SiO 4 4 Suggested improvements: Grinding and leaching of coarse-grained Eudialyte SEE, Mn & Zr Targeted prozessing of fines (Z-Part of Eudialytstructure) Zr & Nb Johnson, O (2003): The nomenclature of eudialyte groupe minerals 13 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Composition of Pregnant Liquor Solution Norra Kärr ß(metal) 48,9 g/l Ilimaussaq Complex ß(metal) 86,7 g/l 14 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Results of leach liquor processing CaO leach liquor ph-adjustment (ph2) filtration Zr,Fe-residue Main Results: two stage ph-adjustment (ph2 ph4) Fe & Zr-precipitation > 99 % Al-precipitation > 97% CaO ph-adjustment (ph4) solids filtration Al,Zr,Fe-residue liquids suspension REE liquor REE-precipitation solvent extraction Mixed REE concentrate individual REEs 15 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University
Conclusion Main results: The pointed preconditioning step prevents silica gel formation silica liberation << 100 mg/l High recovery rates of valuable metals REE, Mn > 90% (repeated leaching of coarse-grained Eudialyte residue) Zr > 50% (enriched in fine Eudialyte residue) Cheap processing of Eudialyte filtrate by ph-adjustment using CaO 16 Daniel Voßenkaul I Institute of Process Metallurgy and Metal Recycling I RWTH Aachen University