precious metal recovery from nanowaste for sustainable

Precious metal recovery from nanowaste for sustainable nanotechnology:

Current challenges and life cycle considerations

[email protected] [email protected] [email protected]

Dr. Peter Vikesland Dr. Sean McGinnis Paramjeet Pati

SUN-SNO-GUIDENANO

Conference 2015

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1.0 Error bars represent 95% confidence interval

Uncertainty results from gold salt model and energy use


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Strong reducing agents (100% yield assumed)

Reported yields

100% yield (assumed)

75% yield (assumed)

50% yield (assumed)

“Life Cycle Assessment of “Green” Nanoparticle Synthesis Methods”, Environmental Engineering Science (2014). Paramjeet Pati, Sean McGinnis and Peter J. Vikesland.


From a life cycle perspective, gold NP synthesis using bio-based (“green”) reducing agents can have substantial environmental impacts.

Gold Chlorine

Gold Salt

Citric Acid

Sodium Carbonate

Sodium Citrate

Deionized Water

TapWater

CleaningSolvent

HCl HNO3

Electrical Energy

HeatingStirring

1 mg Gold NPs

If gold is the key driver of life cycle impacts, can we reduce impacts

by recovering/recycling gold?


The embodied energy of gold drives most of the life cycle impacts of gold nanoparticle synthesis.

(Red ‘flow’ lines show the energy associated with each input. Thicker lines imply higher energy inputs.)

Recovering gold from nanowaste…

AuBr4-

K(OH2)6+

AuBr4-Hydrogen

bonding

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… using α-cyclodextrin


“Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin”. Nature Communications, Liu et al. (2013)


Gold nanowaste

Precipitation Dissolution in HBr/HNO3

Selective recovery ofgold using

α-cyclodextrin Filtration

Sonication(Resuspension)

Schematic of gold recycling experiments

HAuCl4 solution Gold nanoparticles

HCl/HNO3

Reduction


Precipitation of goldusing Na2S2O5

Powder XRD


0

0,5

1

1,5

2

250 300 350 400 450 500 550 600

Ab

sorb

ance

Wavelength (nm)

Stock_HAuCl4 Recycled_HAuCl4

HAuCl4 solution

UV-vis


2.392.06

1.461.25, 1.19

2.362.04

1.441.23, 1.18

Calculated d-spacing (Å)

d-spacing for gold (Å)

Diffraction

Gold nanoparticles


Can we recover gold from nanowaste? Yes, we can. (But should we?)


1 mg AuNP

DI water

Citrate

Gold

HCl

Aqua regia

HNO3

Stirring HeatingCleaning

waterCooling

water

HAuCl4

Other chemicals

ElectricityWater

Synthesis


Gold nanowaste






HCl/HNO3

Reduction



Dissolution in HBr/HNO3

HNO3

HBr

Gold-CD complex

α-CD

Precipitate & resuspendthe complex

Recover gold

precipitate

NaHSO5

Precipitate

NaCl

To waste treatment

1 mg AuNP

Recycle


HCl

HAuCl4 fromrecovered

gold

HNO3

Electricity

Heating

Synthesis Recycling

Actual LCA model for 90% recycle scenario


10% recycle

50% recycle

90% recycle

Dispose all gold as waste

Note: 10% recycle means: 10% of the gold nanowaste is recovered and reused for gold nanoparticle synthesis.

The rest 90% gold is not recovered, and goes into waste disposal.


10% recycle

50% recycle

90% recycle


Error bars represent 95% confidence intervals


Hmm.. overlapping error

bars… means the difference

isn’t statistically significant,

right? Makes no difference

whether we recycle or not…

WRONG! You have

correlateduncertainties!


Product A Product B

Aluminium 1 kg 0.8 kg

Cast iron 1 kg 0.8 kg

Polystyrene 1 kg 0.8 kg

Q: Which of the two has a lower environmental impact?a) Product Ab) Product Bc) It dependsd) Is this a trick question?

Comparing 1 kg of product A vs. 1 kg of Product B:

(Product B uses 20% less inputs compared to Product A. There are no extra, hidden inputs in products A and B)


Correlated uncertainties in LCA: An example

Q: Which of the two has a lower environmental impact?a) Product Ab) Product Bc) It dependsd) Is this a trick question?

The key here: correlated uncertainties.All three inputs (aluminium, cast iron and polystyrene) have uncertainties that

are common to both Product A and Product B.


Metal depletion


Freshwater ecotoxicity

Metal depletion

Climate change


Fossil depletion

Ozone depletion

Natural land transformationUrban land occupation

Agricultural land occupationIonizing radiation

Marine ecotoxicityFreshwater ecotoxicityTerrestrial ecotoxicity

Metal depletionWater depletion

Climate change

Terrestrial acidification

Particulate matter formationPhotochemical oxidant formation

Human toxicityMarine eutrophication

Freshwater eutrophication


10% recycle

50% recycle

90% recycle


Metal depletion



Metal depletion

Fossil depletion

Ozone depletion



Marine ecotoxicityFreshwater ecotoxicity

Terrestrial ecotoxicity


Climate change



Human toxicityMarine eutrophicationFreshwater eutrophication


Fossil depletion

Ozone depletion






Climate change






Synthesis Recycling

90% recycle scenario


High impacts in climate change and fossil fuel depletion are driven by mainly the boiling step in the recovery process.

Fossil depletion

Ozone depletion






Climate change






Conclusion:

Gold recovery from nanowaste is feasible

Even at low yields, recovery beats regular gold nanowaste disposal


Challenges:

Reducing the energy footprint of the recovery step.

Refining the models to account for different waste disposal and recovery scenarios (e.g., recovery but no reuse).

Acknowledgments

Virginia Tech Centre for Sustainable Nanotechnology (VTSuN)

Institute for Critical Technology and Applied Science (ICTAS)

Dr. Sean McGinnisDirector, Green Engineering

Program, Virginia Tech

Leejoo WiUndergraduate researcher

(Vikesland group)

Email: [email protected]

Spam slides

Here be dragons…

Synthesis Recycling

90% recycle

1

2: Gold from recycling

1: Gold obtained from mining

2

Gold

HAuCl4


Synthesis Recycling

1



2

50% recycle


Synthesis Recycling

1



2

10% recycle


Gold nanowaste






HCl/HNO3

Reduction



Gold-cyclodextrincomplex

Gold nanoparticles

Sodium borohydride

1 2 3 4 5 6 7 8 9 10

keV

0.0

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1.0

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cps/eV

Au Au Au Au Br Br K K

O

EDS spectra showed the signature peaks for

Au, Br, K, O

No AuNPs

AuNPs

(a) SEM images of a crystalline sample prepared by spin-coating an aqueous suspension of α·Br onto a silicon substrate, and then air-drying the suspension. (b) TEM images of α·Br prepared by drop-casting an aqueous suspension of α·Br onto a specimen grid covered with a thin carbon support film and air-dried. (c) Cryo-TEM image (left) and SAED pattern (right) of the nanostructures of α·Br. As the selected area includes several crystals with different orientations and the crystals are so small that the diffraction intensities are relatively weak, we can assign the diffraction rings composed of diffraction dots but not the specific angles between different diffraction dots from the same crystal. The scale bars in a and b are 25 (left), 5 (right), 10 (left), 5 μm (right) and in c are 1 μm(left) and 1 nm−1(right), respectively.


precious metal recovery from nanowaste for sustainable

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