By Susannah Scott, UCSB

1. Ensuring the Sustainability of Critical Materials and Alternatives:
Addressing the Fundamental Challenges in Separation Science and Engineering
244th ACS National Meeting, Philadelphia, August 21, 2012
Findings and opportunities from
the 2012 NSF SusChEM workshop
Chair: Susannah Scott
Department of Chemistry & Biochemistry; Department of Chemical Engineering
University of California, Santa Barbara
Co-chair: Jim McGuffin-Cawley
Department of Materials Science and Engineering
Case Western Reserve University
Disclaimer: The views herein represent the author’s, and are not necessarily those of the NSF.

2. SusChEM
Sustainable Chemistry, Engineering, and Materials
• Systems-level thinking is required:
“There are no sustainable parts of unsustainable wholes.”
Franzi Poldy, CSIRO
• More fundamental research should be use-inspired.
• Green is not synonymous with sustainable.
• Efficiency is necessary but not sufficient, due
to the rebound effect
• Sustainability research and education is multidisciplinary and collaborative.

3. Workshop topics
• Discovering new chemistry and materials that will replace rare, expensive
and/or toxic chemicals with earth-abundant, inexpensive and benign minerals
and chemicals,
• Discovering new processes to economically recycle chemicals and materials
that cannot easily be replaced, such as phosphorus and the REE’s,
• Discovering new chemistry to convert non-petroleum based sources of
organics to feedstock chemicals,
• Discovering new environmentally-friendly chemical reactions and material
processes that use less energy, water, and organic solvents than current
practice,
• Incorporate sustainability into the curriculum; have earth, physical and social
scientists and engineers take common courses; and promote
entrepreneurship.

4. Many separations-relevant issues
• Mineral processing and element recycling (including urban mining)
– Rare earths
– Precious metals
– Phosphorus
• Chemical process intensification
– Integrated reaction/separation in microflow reactors
– Improved separation designs in conventional chemical processing
• Membranes
– Scaleable polymer-inorganic composites
– Highly selective metal-organic frameworks (MOFs)/porous coordination polymers (PCPs)
• Simplifying complex product streams from biomass-derived sources

5. Uses of rare earths
Light rare earths (LREEs) Heavy rare earths (LREEs)
LREEs
HREEs
catalysts
catalysts
Ce Nd La Pr
X. Du, T. E. Graedel, “Global In-Use Stocks of the Rare
Earth Elements: A First Estimate”, Environ. Sci. Technol.,
2011, 45, 4096. Dy Y Gd Sm Tb Eu

6. Concentration of supply
"There is oil in the Middle East; there is rare earth in China…" Deng Xiaoping, 1992
China now produces almost all of the world’s supply of REEs.
Light REEs: from Bastnäsite-containing ores in Inner Mongolia
Heavy REEs: adsorbed on laterites (clays) in Southern China
X. Du, T. E. Graedel, “Global In-Use Stocks of the Rare Earth Elements: A First Estimate”, Environ. Sci. Technol., 2011, 45, 4096.

7. Environmental and social costs
Bayan Obo LREE open pit mine, Acid tanks and run-off ponds at HREE mining
Baotou, Inner Mongolia, China facility near Ganzhou, Jiangxi Province, China
Each ton of rare metals mined releases:
• 10 – 12 x 103 m3 of waste gas (dust, HF, SO2, H2SO4);
• 75 m3 acidic wastewater;
• 1 ton radioactive waste residue (Chinese Society of Rare Earths) Photos by Adam Dean. The Telegraph, 19 March, 2011.

8. “Green” technologies
A Toyota Prius contains 30 kg RE:
NiMH battery (La, Ce)
electric motor/generator (Nd, Pr, Dy, Tb)
LCD screen (Eu, Ce)
A single compact
fluorescent lightbulb
contains 1.5 g RE:
phosphor (principally Eu,
with smaller quantities of
A 3 MW wind turbine contains 600 kg RE:
La, Dy, Ce, Pr and Gd)
permanent magnets (Nd, Pr, Dy, Tb)

9. Rare earth export quotas
• In 2010, China cut REE export quotas dramatically.
• In late 2012, China announced separate export quotas for LREEs and HREEs.
Prices in US $/kg, FOB China
Chinese export quotas, kT
REO 2009 2010 2011 8/2012
La 5 22 104 20
Ce 4 22 102 21
Nd 19 50 234 105
Pr 18 48 197 110
Sa 3 14 103 70
www.bloomberg.com
Dy 116 232 1450 950
Eu 493 560 2843 2020
Tb 362 558 2334 2000
China’s rationales: http://www.lynascorp.com
• Rare earths are strategic resources.
• Manufacturing high value finished products is preferred over export as low value raw materials.
• Need to consolidate and regulate REE production, to better control pollution.

10. Rare earth processing
http://www.gwmg.ca

11. Solvent extraction
Mixer-settlers used for continuous, counter-
current liquid-liquid extraction of RE ions, in a
demonstration plant in Australia.
Ln3+ ions partition into a non-polar organic
solvent containing a ligand such as R2P(O)OH
or R3PO.
About 600 mixer-settler boxes are required for
an integrated separation facility, due to low per-
stage efficiency (typically, < 3).
R. Wormsbecher, Grace

12. Rare earth recovery
Recycling of REEs is almost non-existent, due to the high cost of separation.
“Distribution entropy” affects recovery prospects:
• Nd has a high distribution entropy.
– Hard drives, DC motors, permanent magnets, headphones
• La has a lower distribution entropy.
– Metal hydride battery cathodes, hybrid cars, fluid catalytic cracking (FCC) catalyst
• Active component in FCC catalyst is La-
exchanged USY
• An FCC unit processing 75,000
barrels/day contains 56,000 tons catalyst
with ca. 1,000 tons RE
• Catalyst lifetime is ca. 1 month
• World consumption is ca. 2,300 tons
catalyst/day (10% of all RE use)
• Spent catalyst contaminated with other
metals (Ni, V) is landfilled or used for
construction aggregate
R. Wormsbecher, Grace

13. Challenges for RE separation and recovery
Aim to reduce energy-, water- and chemical-intensity.
Make recycling economically viable.
1. Design new chelating agents for highly selective solvent extraction
Peterman et al., Separ. Sci. Technol. 2010, 45, 1711
2. Replace low efficiency mixer-settlers by high efficiency
centrifugal contactors
3. Explore new solvent systems (e.g., RTIL, scf)
4. Develop high affinity ion-exchange resins
5. Develop rare earth-selective membranes
E. Peterson, Idaho National Lab
R. Wormsbecher, Grace

14. Global food security
Sir William Crookes
Guano mining in the Central Chincha
Islands (Peru), mid-19th century
warned of impending global famine in address
to the British Acad. Sciences (1898)
The Atacama Desert (Chile), with the Andes visible in
the background. The remains of a nitrate plant (late 19th
century) and its tailings pile can be seen in the middle.
P. Marr, “Ghosts of the Atacama: The abandonment of nitrate mining in
the Tarapacá region of Chile”, Middle States Geographer, 2007, 40, 22.

15. The N-revolution
Fritz Haber Alwin Mittasch Carl Bosch
J. W. Erisman, M. A. Sutton, J. Galloway, Z. Klimont, W. Winiwarter, “How a
century of ammonia synthesis changed the world”, Nature GeoSci. 2008, 1, 636.

16. Phosphorus in agriculture
There is no P-analog of the Haber-Bosch process.
“There are no substitutes for phosphorus in agriculture.” USGS
Large pile of bison skulls to be ground into fertilizer, Brazilian corn plants grown on P-treated soil are
ca. 1870. much taller than control plants like those in the
foreground, which did not receive adequate
Photo courtesy of Burton Historical Collection, Detroit Public Library. additional phosphorus. UNEP Year Book 2011.

17. P = essential macronutrient
P is required in:
hydroxyapatite, amino acids, nucleic acids, O
43 kg
phospholipids, ATP, creatine phosphate
Adults must ingest 0.7 g P/day in their food.
Children, adolescents, and pregnant women should
consume 1.25 g/day.
Symptoms of P deficiency (hypophosphatemia):
loss of appetite, muscle weakness, bone pain,
C
rickets, fragile bones, increased susceptibility to 16 kg
infection, numbness and tingling of the extremities,
difficulty walking
H
7 kg
Severe hypophosphatemia results in death. N, 1.8 kg
Ca, 1.0 kg
P, 0.8 kg
other, 0.4 kg

18. World phosphorus supply
0.5 Bt phosphate rock has been extracted over the past half-century.
Current global extraction rate is 20 Mt/year.
Production is increasing at 2.5 % / year.
K. Ashley, D. Cordell, D. Mavinic, “A brief history of phosphorus: From the philosopher’s stone to nutrient recovery and reuse”,
Chemosphere, 2011, 84, 737.

19. Mining phosphate rock
Phosphorite, a sedimentary rock
15-20 % phosphate, as Ca5(PO4)3X (X = F, OH)
Open-cast mining of phosphate rock
Togo Florida
Phillippe Diederich for The New York Tim
Florida mines pump 100,000 gallons water/min.
Rock may contain elevated levels of toxic metals (Cr, Cd, Pb, Hg).
Each ton of mined rock generates 5 tons radioactive (U, Th) phosphogypsum.

20. Phosphate use efficiency
P recoveries from phosphate
rock can be as low as 40%.
Only 20% of mined phosphate
ends up in the food we consume.

21. Peak phosphorus?
Peak phosphorus curve derived from US Geological Survey and industry data,
indicating peak production ca. 2035.
Cordell, D.; Drangert, J.-O.; White, S. The story of phosphorus: Global food security and food for thought.
Glob. Environ. Change 2009, 19, 292.

22. Global phosphate reserves
Largest current producers: China (38%), US (15%), Morocco (14%), Russia (6%)

23. Future P-rock needs
Estimated reserves will last 300-400 years at current production rates.
Growing world population, food equity, and changing dietary preferences (increased
protein consumption) could reduce this to 50-100 years.
D. Cordell and S. White, “Peak Phosphorus: Clarifying the Key Issues of a Vigorous Debate about Long-Term Phosphorus Security”,
Sustainability 2011, 3, 2027

24. Supply/price instability
• Prices shot up in 2007–2008, due to
increasing demand driven by more meat- and
dairy-rich diets, especially in China and India,
and to expansion of the biofuels industry.
• In 2008, China imposed a 135 % tariff on
phosphate rock, effectively eliminating exports.
It was lifted in 2009, but new peak season
tariffs were introduced in 2011 and remain in
effect.
• Phosphate recovery becomes economically
viable at $100/t.
“Failure to take a systems approach could result in investment in costly and energy-
intensive phosphorus recovery technologies that do not address the whole system and
hence do not provide the greatest outcome for sustainability, or at worst, conflict with other
related services (such as energy supply).” Cordell, 2011

25. P-recovery from cities
Humans excrete 3 Mt P annually (0.4 kg/person/yr).
Some forms struvite, MgNH4PO4.6H2O (MAP).
Potential use as slow-release fertilizer.
Conventional precipitation-sedimentation- Pipe clogged with struvite, due to increase in
filtration is energy-intensive, and product has phosphate concentration during biological
high water content (60-80 %). wastewater treatment.
In 2012, a municipal Nutrient Recovery Facility
opened in Hillsboro, Oregon. It will produce 1200
tons/yr of CrystalGreen fertilizer.
Ostara reports seven times less energy required
to create Crystal Green than conventional
fertilizer.
www.ostara.com

26. Crystallization in liquid Crystalactor®
fluidized bed
• MgNH4PO4.6H2O is obtained by mixing feed with
MgCl2 and (if necessary) NaOH
• Difficult separation of fine crystals
• fluidized bed crystallizer uses seed (sand or
minerals) to induce pellet formation
• product discharged continuously at bottom
• high purity pellets with low water content (< 5%)
www.dhv.com
Phosphate recovery plant in Westerbork, The Netherlands
Other potential P-recovery approaches: adsorption, ion-exchange, nanofiltration.

27. Closing the P-cycle
1. Improve recovery of phosphate from phosphate rock, while mitigating impact of waste.
2. Replace as much primary input as possible by secondary input (recycled P)
• Devise efficient ways to recycle P from animal waste
• Recycle P from other phosphorus uses (e.g., phosphines and phosphine oxides
used in chemical processing, phosphors used in lighting)
• Capture P from diffuse sources (detergents in graywater, farm runoff)
K. Lammertsma, Amsterdam

28. Extracting by-products
mining Cu ore
British Geological Survey 1
1 ppm Re
crushing, milling, flotation
2 concentrates Mo
molybdenite 100 ppm Re
Re metal during roasting, Re2O7
3 sublimes in flue gas
500 ppm Re
Re2O7 is dissolved in
4 weak acid solution
Re annual production 50 tons; supply is inelastic. 1000 ppm Re
Used in gas turbines and jet turbines, where fuel efficiency organic solvent extraction
5
increases with operating temperature. In some super-alloys, 2% Re
Re is unsubstitutable.
ion-exchange then
6 crystallization as
Projected need for 30,000 new, fuel-efficient passenger NH4ReO4, 69% Re
planes by 2030. Supply > demand; Re price $12,000/kg in
8/2008. reduction by H2 to metal
• Need to increase extraction efficiency from ores 7 > 99.9% Re
• Reduce dependence on strong acid solutions during processing
• Develop methods to extract Re from alloys for recycle
M. Carducci, D. Honecker, Climax Molybdenum

29. Process intensification
Replace batch reactors with continuous microflow reactors
- superior mixing and heat transfer properties
- safer handling of hazardous intermediates
- possibility of using short-lived reactants
- easy to ‘number-up’
Need to couple with appropriately scaled separations systems
K. Jensen et al., Angew. Chem. Int. Ed. 2007, 46, 5704 K. Jensen et al., Angew. Chem. Int. Ed. 2010, 49, 899

30. New membrane materials
Inorganic-organic hybrid membranes combine the separating ability of the porous
inorganic component with the processibility and scaleability of the organic
component.
Nanodispersion of the inorganic filler increases discrimination between molecules
of different sizes.
Potential uses in CO2 and H2S capture.
AMH-3
3D porous layered silicate
surface functionalized dispersed in cellulose
with organosilane acetate (CA)
S. Nair, Georgia Tech

31. Chemicals from renewables
A = Hydrolysis
B = Isomerization
C = Dehydration
D = Rehydration
E= Hydrogenation
F = Hydrogenolysis
N. Cardona-Martínez, UPRM-Mayagüez

32. Educational needs
• Prepare a qualified, knowledgeable workforce to think
about how its actions affect the sustainability of the
process/product/company/etc.
- Train students in systems-level thinking, economic and safety analyses using case studies
- Ask students to conduct life cycle and material flow analyses
- Expose students to industrial research and design with constraints
- Have students reflect on scaleability, materials availability, desired lifetime and recyclability
- Cultivate communication skills with stakeholders, including the public
• Emphasize multidisciplinary teamwork
(physical scientists/engineers/social scientists)
• Make sustainability training part of professional
accreditation requirements
(ACS, ABET, AIChE, TMS, ACerS, MRS)
• Empower students to create change through
innovation training and experiences

33. Acknowledgements
SusChEM Co-chair Jim McGuffin-Cawley (Case Western Reserve)
NSF Division Directors Matt Platz (CHE), Jim McGrath (CBET), and Ian Robertson (DMR)
Many NSF Program Officer observers, especially Kathy Covert, Tingyu Li, and Lynnette Madsen
All SusChEM workshop participants, from academia, industry, and government, especially our grad students