Photon Factory Activity Report 2016 #34 (2017)

BL-12C/2015G583

Influence of different drying conditions on Cu speciation in stream sediment, coastal
sea sediment, and soil
Atsuyuki Ohta1*
1Geological Survey of Japan, AIST, Ibaraki 305-8567, Japan
1 Introduction
An element in sediments and soil substances of theearth surface occurs in various physicochemical forms.
The toxicity and bio-availability of elements change
largely with their chemical forms. Although many
speciation techniques have been proposed, a sequential
extraction procedure has been most widely used toelucidate speciation of an element in sediments and soil
substances. However, there is one reference material(BCR-701) available to quality control of speciation
studies only for six elements (Cr, Ni, Cu, Zn, Cd and Pb).
Thus, the provision of various kinds of referencematerials and reference values for many elements
obtained by speciation study would be beneficial for
speciation study.
Thus, we require a wide range of geochemicalreference materials such as stream sediment, marine
sediment, lake sediment, and soil for the speciation study.
To prepare such reference materials, we must knowwhether the initial chemical form in collected samples ispreserved during the manufacturing process ofgeochemical reference materials. Therefore, in this study
we elucidate the influence of different drying conditions
on metal speciation in sediment samples because theprocess would have the largest impact on metal species in
sediments and soils. Ohta and Kubota [1] have confirmed
the validity of Cu speciation obtained by the sequential
extraction using XANES spectroscopy. Thus, we focus on
Cu speciation in stream sediment, coastal sea sedimentand soil.
2 Sample materials
We collected stream sediment associated with Cu mine,
muddy clay-rich coastal sea sediment deposited at anoxic
estuarine condition, and Kuroboku soil (andosol)
originated from volcanic ash and rich in organic materials.
Collected samples were stored in polyethylene bags at4°C, freeze-dried in the laboratory, and stored inrefrigerator. Duplicated samples were stored inpolyethylene bags, air-dried in the laboratory for 14-21
days at room temperature, and stored at ambient
temperature without direct sunlight. Soil sample wassieved with a 2 mm screen. Other samples were sieved
with a 0.18 mm screen. A sequential extraction procedure
was applied to these samples in 2011 and 2013. We haveconfirmed that metal speciation in these samples change
insignificantly by different drying conditions and storage
period. However, sequential extraction procedure isindirect speciation analysis: each chemical form in amaterial is destructively extracted using a chemicalreagent. Thus, we identify and quantify chemical forms inthese materials using X-ray absorption near edge structure(XANES) spectroscopy in 2015.
3 Experimental methods
The Cu in stream sediment, inner bay sediment, andsoil were extracted using the sequential extraction
procedure, which has been standardized by theCommunity Bureau of Reference (BCR) [2]. Table 1
summarizes the procedure used in this study. The BCR
protocol extracts the elements in carbonate minerals or
those weakly adsorbed on materials at step 1. Elementsbound to Fe hydroxide and Mn oxide are extracted at step
2. Metal sulfides and elements bound to organic matter
were extracted at step 3. The residual crystalline phases
were decomposed at step 4. The concentration of Cu
extracted at each stage was determined by ICP-AES.
Table 1: Outline of the sequential extraction procedure
StepExtractant
1
CH3COOH (0.11 mol/L), 16 h
2
NH2OH·HCl (0.5 mol/L), 16 h
H2O2 (8.8 mol/L), 1h at 20–30 °C and 1h at
85 °C, followed by CH3COONH4 (1 mol/L),
3
16 h
4
HF-HNO3-HClO4, 3h 120°C
As for XANES spectroscopy, the residues after eachstep of the BCR extraction was filtrated through a 0.45
μm cellulose acetate membrane filter and freeze dried.
The samples were stored in a refrigerator until XAFS
analysis. The samples untreated with the BCR wereenclosed in a polyethylene resin. As model compounds,
several kinds of Cu compounds (e.g., sulfate salt andaqueous solution), metal doped Fe hydroxide (FeOOH),
metal doped Mn dioxide (MnO2), metal doped humic acid(HA), and sulfide ores, were also prepared. The Cu Kedge XANES spectra were recorded in a fluoresce modeat the BL-12C of KEK-PF. The fluorescence X-ray wasmeasured by a 19 element pure-Ge SSD.
4 Results and discussion
Figure 1 shows the distributions of Cu concentrations
in stream sediment, soil, and coastal sea sediment
samples for the four fractions obtained by the BCR

Photon Factory Activity Report 2016 #34 (2017)

protocol. The high proportion of Cu in stream sediment
samples was extracted at step 1 (45 % of the total Cu),
and at step 2 (30 % of the total Cu) and at step 3 (20 % ofthe total Cu). In soil samples, an extremely highproportion of Cu (70 % of the total Cu) was extracted atstep 3 and the rest was mostly associated with the residual
fraction (step 4). A significant amount of Cu wasextracted at step 2 (35 % of the total Cu) and step 3 (50 %of the total Cu) for coastal sea sediment samples.
Interestingly, there are no significant differences of Cu
speciation determined by the BCR protocol between airdried sample and freeze-dried one.
Stream sed.

Soil

0%

stream sediments have been altered partly to CuSO4 andreacted with Fe hydroxide and humic substances.

Coastal sea
sed.

Fig. 2: LCF of XANES spectra of stream sediments
derived from Hitachi Cu mine.

20%
Step 1

40%

Step 2
Step 360%

Step 480%

freezedried

air-dried

freezedried

air-dried

freezedried

air-dried

100%

Fig. 1: Distribution of Cu concentrations in stream sediments,soil, and coastal sea sediments determined by the BCR protocol.

XANES spectra of Cu in the untreated stream sediment
samples are shown Figure 2. XANES spectra of Cu in
stream sediment do not differ considerably among the airdried sample and the freeze dried one. The features ofXANES spectra of untreated sample were reasonably
reproduced by the linear combination fitting (LCF) using
five components of CuSO4, Cu-bearing FeOOH, Cubearing HA, JCu-1 (chalcopyrite), and the final residual
phase (the residue after step 3 extraction). The CuSO4(20–25 % of the total Cu) is assumed to be an oxidation
product of chalcopyrite and expected to be extracted atstep 1. The percentages of Cu-bearing FeOOH (15–20 %of the total Cu) indicate the percentages of Cu bound toFe hydroxides, which were extracted at step 2 extractionof the BCR protocol. Cu-bearing humic acid (<10 %) andJCu-1 (35 %) are used as a substitute for Cu bound toorganic materials and metal sulfide ores, which are thetarget phases of the step 3 extraction. However, theestimated proportions of these compounds do notcorrespond to the BCR results perfectly.
Even though stream sediments were collected fromdownstream of Cu mine, XANES analysis suggests thatthe percentage of chalcopyrite to total Cu is only 35 %(Fig. 2). Furthermore, XANES spectra of the sample donot change significantly with the different drying methods.
These facts suggest that chemical form of Cu in the river
system has already been oxidized well: it has been kept ina steady state. We assume that oxidized chalcopyrite in

XANES spectra of Cu in soil samples untreated with
the BCR protocol and their LCF results are shown in
Figure 3. As with the case of stream sediment samples,
XANES spectra of Cu in soil substances do not differ
significantly between the air-dried sample and freeze
dried one. The features of XANES spectra of untreatedsamples were fitted by Cu-bearing HA (55 % of the totalCu), Cu sulfide (JCu-1) (5% of the total Cu), and the finalresidue (the residue after step 3) (40 % of the total Cu).
The presence of Cu-bearing FeOOH was negligible in
XANES spectra. The estimated the proportions of step 3(Cu-bearing HA and JCu-1) and step 4 (the residue afterstep 3) are similar to the concentration ratios of Cu
extracted by the BCR protocol. The high proportions ofCu-bearing HA are reasonable because soil samples arerich in organic materials.

Fig. 3: LCF of XANES spectra of Kuroboku soil.
In contrast, XANES spectra of Cu in the coastal sea
sediments collected from Tokyo Bay differ significantly
among air-dried sample and freeze-dried one (Fig. 4),
nevertheless there are no significant differences of the
distribution of Cu concentrations determined by the BCR
protocol (Fig. 1). XANES spectrum of the air-driedsample rather resembles that of stream sediment samples,
However, XANES spectrum of freeze-dried sample
shows the distinct shoulder peak at the lower energy sideof the main peak and smaller main peak than that of airdried sample.

Photon Factory Activity Report 2016 #34 (2017)

LCF results show that Cu-bearing HA and Cu sulfide(JCu-1) are the most dominant species in air-dried sample
and freeze-dried one, respectively (Fig. 4). A significant
amount of Cu sulfide (77 % of the total Cu) in the freezedried sample indicates that authigenic Cu sulfide wasformed in the inner bay sediment under the anoxic
condition. However, the proportion of Cu sulfide (23 %of the total Cu) in the air-dried sediment is considerably
smaller than those in the freeze-dried one. It is possiblethat authigenic Cu sulfide in sediments has been
considerably oxidized during the air-dried period (14-21days). The activity of aerobic microorganisms in samples
may have accelerated the oxidation reaction of Cu sulfide
in the drying process. The high proportion of Cu-bearing
HA (70%) in XANES spectra of the air-dried sample
indicates that Cu released in the fluid in the oxidation
process of Cu sulfide has selectively bound with organicmatters.

Fig. 4: LCF of XANES spectra of coastal sea sediments
derived from the Tokyo Bay.
5 Summary
We examined the differences of Cu species in the airdried sample and the freeze-dried one using the sequential
extraction procedure (the BCR protocol) and XANES
spectroscopy. Stream sediments associated with Cu mineand volcanic soil substances enriched in organic matterare abundant in reducing compounds of chalcopyrite andorganic matters, respectively. However, there are no
significant differences of Cu speciation in the air-driedsample and the freeze-dried one. In contrast, coastal sea
sediment having an anoxic face has the different resultsfrom stream sediment and soil. XANES analysis revealed
that authigenic Cu sulfide precipitate occurs abundantlyin the freeze-dried sample, but it has been considerably
oxidized in the air-dried sample. Curiously, there are no
meaningful differences of Cu speciation obtained by theBCR protocol.
Acknowledgements
I am also grateful to Hiroaki Nitani, Hitoshi Abe, andYasuhiro Niwa for their technical support in obtaining theexperimental data at the BL-12C in KEK-PF.
References[1] A. Ohta and R. Kubota, Geostand. Geoanal. Res.,40, 117 (2016).
[2]
G. Rauret, et al., J. Environ. Monit., 1, 57 (1999).
* a.ohta@aist.go.jp