Method developments on the identification of metal-hyperaccumulating plants using XRF and reflectance spectroscopy technique:
A case study of rare earth and nickel
GSQ/UQ Webinar
Imam Purwadi
Thursday, 26 October 2023
Hyperaccumulators
Hyperaccumulator coined for Pycnandra acuminata (Jaffré et al. 1976)
721 identified hyperaccumulators (Reeves et al. 2017)
Reasons to find hyperaccumulators
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Exploration becomes harder (Wood 2012)
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Mining contributes to 2.7% of the world CO2 emission (Holmberg et al. 2017)
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Mining endangers plant species (Whiting et al. 2004)
Benefits to find hyperaccumulators
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Hyperaccumulator indicates metal rich soil (Brooks 1988)
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Hyperaccumulators extract metals from soil (van der Ent et al. 2015) and store carbon in soil (Echevarria et al. 2016)
. -
Some hyperaccumulators become extinct and the remaining needs protection (Erskine et al. 2012)
How?
74% of 721 identified hyperaccumulators are Nickel hyperaccumulator
An easily prepared and deployed test for Ni hyperaccumulator detection exists!
Other reasons
Tool is not the only reasons for the high number of identified Ni hyperaccumulator plants.
Soil concentrations
Wide spread nickel rich soils as the weathering product of ultramafic rocks
Economic value
Nickel is in high demand, while supply is scarce
"As metal prices rise with increased demand, hyperaccumulators are gaining recognition as an alternative means of extracting metals, and so is research in this field."
While rare earth hyperaccumulators were discovered earlier than nickel hyperaccumulators, research progress in the former lags behind that of the latter
A new approach was proposed to expedite the identification of hyperaccumulators
Using a portable X-ray fluorescence instrument to scan herbarium specimens: Rapid analysis, Non destructive test, Abundance Sample
Source: X-Ray Fluorescence Ionomics of Herbarium Collections
How does a portable X-ray fluorescence instrument work?
The instrument shoots X-rays to hit the sample's atoms, and detectors catch any X-rays that come out
The outgoing X-rays from each element are distinct and can be utilized for both quantitative and qualitative analysis
Portable XRF Instruments
Caveats
+ - +
Rare earth XRF peaks often observed but the instrument algorithm failed to report
Why it is important to understand the peak XRF radiation for each element?
XRF is a bulk analysis method that captures not only XRF radiation emitted from the surface of a sample but also includes some XRF radiation originating from beneath the surface that manages to reach the detectors
The depth of penetration: how far the X-ray from the instrument can penetrate the sample, and the escape depth: how far the XRF originated from an atom inside the sample can travel
Thickness?
An illustration of herbarium XRF scanning: Observe titanium plate beneath herbarium specimen
Safety: The X-ray coming out of the instrument is not fully absorbed herbarium and even the desk. Put metal plates under specimen to absorb the excessive x-ray.
Safety: A portion of the X-ray coming out of the instrument is scattered. Put backscatter shield on the instrument to absorb backscatter radiation.
Remember: The XRF of Ti from Ti metal can travel ~2mm in dry leaves
According to Rafał Sitko and Beata Z, 2011, emission-transmission can be used for determining matrix properties (μm), without the knowledge of the sample composition.
(Its - Is)/It = exp[-μm]
Where:
It: the Ti intensities from the Ti plate alone
Is: the Ti intensities from the sample
Its: the Ti intensities the sample on top of the Ti plate
Ti concentration in leaves < 34 μg/g or even less (Cary and Kubota 1990; Tlustoš et al. 2011), thus not producing significant Ti fluorescence. So, equation can be simplified to:
Its = It exp[-μm]
Thickness?
Relationship between sample area density and transmitted Ti signals
Hyperaccumulators in Australia/Queensland
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Few hyperaccumulator
<10 of 721 -
Metal rich soil
Many metal deposits -
Existing data
> 2000 specimens were scanned
Can we reveal any missed hyperaccumulators from the previous studies with the developed method?
Results
Newly identified hyperaccumulators by the developed methods
- Manganese 15
- Nickel 2
- Cobalt 3
- Zinc 3
- Rare Earth 2
- Selenium 1
The two new REE hyperaccumulators were further confirmed in another study by taking new samples from the field, subsequently measured using ICP-AES.
Spatial distribution of Hyperaccumulators
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Mn Layer -
Co Layer
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Ni Layer
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Zn Layer
The REE hyperaccumulators from Queensland
Helicia glabrifora plants outside of Eungella National Park, Queensland, Australia
Helicia compared to Others
Helicia to regional geology
The Helicia specimens with relatively higher Y concentrations mainly occurred on granitoid and mixed maftes/felsites rock types
Hyperaccumulators
Plants exhibiting concentrations of at least an order of magnitude higher than that found in normal plants
- Manganese 10000µg/g
- Cobalt 300µg/g
- Nickel 1000µg/g
- Copper 300µg/g
- Zinc 3000µg/g
- Rare Earth 1000µg/g
- Arsenic 1000µg/g
- Selenium 100µg/g
Source: Baker & Brooks, 1989; Reeves, 2003b; van der Ent et al., 2013
Assessing hyperaccumulator thresholds
Using XRF and ICP data
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XRF Data
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26942
Total herbarium specimens
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1150
New datasets
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From four countries
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ICP-AES Data
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1710
Total field samples
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From one country
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N < Below detection limits
XRF has a high detection limit
| Element | XRF | ICP-AES |
|---|---|---|
| Manganese | 12517 | 1 |
| Cobalt | 26516 | 115 |
| Nickel | 24684 | 1 |
| Zinc | 23346 | 293 |
| Arsenic | 26865 | Not available |
| Selenium | 26861 | Not available |
| Yttrium | 26837 | Not available |
How to deal with below detection limit values?
Regression on Order Statistics: Lee and Helsel (2005), Lee and Helsel (2005), Dennis R. Helsel and Timothy A. Cohn (1988)
Regression on Order Statistics vs Constant value
Regression on Order Statistics vs Constant value
Determining the threshold between Normal and Hyperaccumulator plants
Hyperaccumulator thresholds in μg/g
| Element | Historical | XRF | ICP-AES |
|---|---|---|---|
| Manganese | 10000 | 1210 | 2850 |
| Cobalt | 300 | 32 | 5 |
| Nickel | 1000 | 280 | 694 |
| Zinc | 3000 | 181 | 7 |
| Arsenic | 1000 | 8 | Not available |
| Selenium | 100 | 10 | Not available |
| Yttrium | Not available | 11 | Not available |
The historical hyperaccumulator thresholds are higher than this study results, so we suggested to not change the historical results because higher values mean safe from false positive
How good is the developed method for different instruments?
3 different instruments
114 leaves
3 different algorithms
The XRF spectra of the three instruments
Mean absolute errors to the highest errors [relative percentage error to highest errors]
| Intrument | Algorithm | Manganese | Iron | Cobalt | Nickel | Copper | Zinc |
|---|---|---|---|---|---|---|---|
| Rocksand | Empirical | 675.1 [5.7%] | 375.4 [32.5%] | 36.8 [1.4%] | 1484.3 [3.2%] | 3.1 [1.7%] | 103.5 [7.7%] |
| independent pipeline | 500.3 [4.2%] | 270 [23.3%] | 25.4 [0.9%] | 636.5 [1.4%] | 3.4 [1.8%] | 65 [4.9%] | |
| Manufacturer | 574.5 [4.9%] | 288.5 [24.9%] | 73.5 [2.7%] | 2930.6 [6.3%] | 8.7 [4.6%] | 131.5 [9.8%] | |
| Goldd+ | Empirical | 395.6 [3.4%] | 375.4 [32.5%] | 36.4 [1.3%] | 1181.9 [2.5%] | 3.1 [1.7%] | 81.9 [6.1%] |
| Independent pipeline | 497.4 [4.2%] | 268.9 [23.2%] | 62.3 [2.3%] | 707 [1.5%] | 2.8 [1.5%] | 132.3 [9.9%] | |
| Manufacturer | 11776.4 [100%] | 1156.5 [100%] | 2719.7 [100%] | 46454.2 [100%] | 188.1 [100%] | 1338.3 [100%] | |
| Tracer 5g | Empirical | 415.5 [3.5%] | 376.6 [32.6%] | 54.7 [2%] | 1018.2 [2.2%] | 3 [1.6%] | 81.9 [6.1%] |
| Independent pipeline | 276.9 [2.4%] | 266.6 [23.1%] | 75.6 [2.8%] | 711.2 [1.5%] | 5.9 [3.1%] | 59.9 [4.5%] |
Benefits of remote sensing technique compared to herbarium XRF
1. No X-ray radiation license needed
2. Applicable from individual plant species to landscape-scale
3. Capable of scanning inaccessible areas
How a leaf reflects light: A visual analysis?
When sunlight shines on a leaf, a portion of this light is reflected.
Metal absorbance bands
Nickel Hyperaccumulator Leaves
- Berkheya coddii 69leaves
- Glochidion bambangan 34leaves
- Glochidion panataran 34leaves
- Phyllanthus rufuschaneyi 35
- Rinorea bengalensis 32leaves
- Rinorea javanica 24leaves
- Actephila alanbakeri 32leaves
- Walsura pinnata 26leaves
Nickel concentration and Spectral reflectance
Mean spectral reflctance of Hyperaccumulator leaves per species
Reflectance vs Concentration
Nickel concentration and Spectral reflectance
Neodymium absorbance band
Neodymium absorbance band vs Lathanum concentration
Targeting rare earth element bearing mine tailings with remote sensing datasets, GSQ-UQ Webinar. 27 August 2020
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Thank you!
This presentation was a modified version of my PhD thesis presentation: https://1mampurwad1.github.io/thesis_presentation
A summary of my thesis: https://github.com/1mampurwad1/thesis_presentation