Precious metal recovery from nanowaste for sustainable

Precious metal recovery from nanowaste for sustainable nanotechnology:

Current challenges and life cycle considerations

pvikes@vt.edu smcginn@vt.edu param@vt.edu

Dr. Peter Vikesland Dr. Sean McGinnis Paramjeet Pati

SUN-SNO-GUIDENANO

Conference 2015

‘Synthetic’ Chemicals

sodium borohydride

hydrazine

Green Chemicals

grape pomace cypress leaves

coriander leaves

soybean

cinnamon

borohydridecitra

hydrazine

soybean seed

sugarbeet pulp

tive E

1.0 Error bars represent 95% confidence interval

Uncertainty results from gold salt model and energy use

borohydrid

ecitra

grape pomace

hydrazine

cypress le

af extra

C. camphora

vitamin B

cinnamon

ginseng

soybean seed

mushroom

C.album extract

D-glucose

sugarbeet pulp

soybean seed extra

coriander

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

… 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

250 300 350 400 450 500 550 600

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

Aqua regia

Stirring HeatingCleaning

waterCooling

HAuCl4

Other chemicals

ElectricityWater

Synthesis

Gold nanowaste

HCl/HNO3

Reduction

Dissolution in HBr/HNO3

Gold-CD complex

Precipitate & resuspendthe complex

Recover gold

precipitate

NaHSO5

Precipitate

To waste treatment

1 mg AuNP

Recycle

HAuCl4 fromrecovered

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

Fossil depletion

Ozone depletion

Marine ecotoxicityFreshwater ecotoxicity

Terrestrial ecotoxicity

Climate change

Human toxicityMarine eutrophicationFreshwater eutrophication

Fossil depletion

Ozone depletion

Climate change

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: pvikes@vt.edu

Spam slides

Here be dragons…

Synthesis Recycling

90% recycle

2: Gold from recycling

1: Gold obtained from mining

HAuCl4

Synthesis Recycling

50% recycle

Synthesis Recycling

10% recycle

Gold nanowaste

HCl/HNO3

Reduction

Gold-cyclodextrincomplex

Gold nanoparticles

Sodium borohydride

1 2 3 4 5 6 7 8 9 10

cps/eV

Au Au Au Au Br Br K K

EDS spectra showed the signature peaks for

Au, Br, K, O

No 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.

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

Precious metal recovery from nanowaste for sustainable

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