rexresearch.com
Justin CHALKER, et al.
Mercury Sequestration
http://freshscience.org.au/2015/red-yellow-toxic-mercury-gone
24 August 2015
Red to yellow, and toxic mercury is
gone
Mercury that hangs around after mining and coal production spells
bad news for the environment and can retard brain development in
children.
Now a team of chemists lead by Justin Chalker at Flinders
University has developed a new material to permanently remove
mercury from soil and water. It’s called Sulfur-Limonene
Polysulfide, or SLP for short.
“SLP is a polymer that looks like red rubber, and is made quite
cheaply from industrial by-products,” says Justin. “We can make it
into any shape we want.”
By lining storage containers with SLP, Justin and his colleagues
have successfully removed mercury from river and pond water, and
soil. The product is self-indicating: the red polymer turns yellow
when it binds mercury.
“This means we know when the SLP is saturated, and needs to be
changed,” Justin explains.
After contact with SLP, mercury remains permanently bound and can
be stored safely without further environmental risk.
Justin has published his results, and filed an international
patent application for SLP and its use in removing toxic mercury
from the environment. He is currently in discussion with industry
partners to develop the material further.
Fresh Scientist Justin Chalker (right)
http://onlinelibrary.wiley.com/doi/10.1002/anie.201508708/full
DOI: 10.1002/anie.201508708
Sulfur-Limonene Polysulfide: A Material
Synthesized Entirely from Industrial By-Products and Its Use
in Removing Toxic Metals from Water and Soil
Abstract
A polysulfide material was synthesized by the direct reaction of
sulfur and d-limonene, by-products of the petroleum and citrus
industries, respectively. The resulting material was processed
into functional coatings or molded into solid devices for the
removal of palladium and mercury salts from water and soil. The
binding of mercury(II) to the sulfur-limonene polysulfide resulted
in a color change. These properties motivate application in
next-generation environmental remediation and mercury sensing.
The exploration of sustainable feedstocks is important in the
synthesis of functional materials.[1] Herein, we report the
utility of a polysulfide synthesized directly from two industrial
by-products: sulfur[2] and d-limonene[3] (Scheme 1). This study
was inspired by classic reports on the reaction of sulfur and
limonene,[4] the use of limonene as a renewable monomer,[5] and
the recent and innovative applications of “inverse vulcanization”
to access a variety of advanced materials with high sulfur
content.[6] We found that the sulfur-limonene polysulfide can be
processed into coatings and solid devices that remove metal salts
such as palladium(II) and mercury(II) from water and soil. We also
report the discovery of a chromogenic response when the
polysulfide is exposed to mercury(II). As sulfur is produced
annually in excess of 60 million tons as a by-product of petroleum
refining[2] and more than 70 thousand tons of limonene are
isolated each year from orange zest in the citrus industry,[3] the
sulfur-limonene polysulfide is inexpensive—further motivating its
use in metal sequestration, sensing, and environmental
remediation.
As a starting point, sulfur was melted (T>120 °C) and then
heated to 170 °C. Above 150 °C, S−S bond scission occurs,[7]
thereby generating thiyl radicals that could add to limonene. An
equal mass of limonene was added to the molten sulfur, which
produced a two-phase mixture that becomes a single, dark red phase
upon reaction. An equal mass of sulfur and limonene was chosen to
maximize the content of both industrial by-products in the final
material. 1H NMR analysis of the reaction mixture indicated
limonene's exocyclic alkene was consumed more rapidly than its
endocyclic alkene, with complete consumption of all olefins within
90 min (see Figures S6–S8 in the Supporting Information). Little
change was observed by 1H NMR spectroscopy on further heating.
The emergence of aromatic signals in the 1H NMR spectrum indicated
the oxidation of limonene. The conversion of limonene into
p-cymene by reaction with sulfur has been reported,[8] but the
complicated 1H NMR signals between 6.9 and 7.6 ppm suggested other
aromatic material was also present in the product (Scheme 2).
Prolonged distillation of the product mixture allowed isolation of
p-cymene as well as volatile thiol and sulfide by-products (see
Figures S11 and S12 in the Supporting Information).[8a] Good mass
balance was observed, with the volatile fraction typically
constituting 20 % of the product and the nonvolatile portion 80 %
of the mass.
Cooling the nonvolatile component to room temperature produced a
red waxlike material. Differential scanning calorimetry (DSC)
revealed a glass transition (Tg) at −21 °C and simultaneous
thermal analysis (STA) indicated substantial thermal decomposition
above 200 °C (see Figure S32–S35 in the Supporting Information).
The material is insoluble in water, sparingly soluble in methanol,
and fully soluble in dichloromethane, chloroform, and
tetrahydrofuran. A band with a λmax=420 nm was observed in the
UV/Vis spectrum of a solution of the material in dichloromethane.
Combustion analysis revealed an elemental composition of 38.97 %
C, 4.97 % H, and 56.6 % S, consistent with the high sulfur content
envisioned for this product. Less than 4 % of this sulfur was
unreacted S8, as determined by GC-MS (see Figures S16–S18 in the
Supporting Information), thus indicating a high conversion in the
reaction between sulfur and limonene. The product was also
optically active, which indicates that at least a portion of the
product derived from limonene maintained its stereochemical
integrity ([α]D=−27.3 (c=1.0, CHCl3).
Expecting a polymeric product, the sulfur-limonene material was
examined by size-exclusion chromatography (SEC). The SEC trace of
the sulfur-limonene material revealed a higher molecular volume
than limonene (see Figures S21 and S22 in the Supporting
Information). Mass spectrometry, however, indicated a lower
molecular weight product than expected. In this analysis, the
sulfur-limonene material was chemically ionized by coordination to
silver(I) prior to infusion into the MS source.[9] A cluster of
signals from m/z=495 to 886 was observed and assigned as [M+Ag]+
ions, based on the doublets present for the two abundant isotopes
of Ag (106.9 and 108.9 Da; see Figures S29–S31 in the Supporting
Information). This result suggested that the mass range of the
limonene-sulfur material that ionized under these conditions
varied between 386 and 777 Da. Unlike recent reports of inverse
vulcanization where sulfur is cross-linked with dienes,[6] the
reaction of sulfur and limonene did not appear to form a
high-molecular-weight polymer. Instead, the material is more
appropriately described as a low-molecular-weight polysulfide.
Raman spectroscopy of the material revealed a dominant signal at
464 cm−1, which corresponds to various stretching modes of S−S
bonds,[10] and additional bands at 149, 215, 589, and 2918 cm−1.
Further evidence for S−S bonds was provided by the reaction of the
material with LiAlH4. SEC and GC-MS analysis after the reaction
with LiAlH4 revealed a product with a lower molecular weight,
consistent with decomposition of S−S cross-links in the
sulfur-limonene material (see Figures S23–S28 in the Supporting
Information). This experiment illustrated that the polysulfide can
be broken down by a reducing agent. We also note that the STA
analysis mentioned previously is consistent with a polysulfide
structure, where significant S−S scission occurs above 200 °C.
Interestingly, this thermal depolymerization proceeded similarly
in both air and nitrogen, thus suggesting that the polysulfide is
not prone to aerobic oxidation (see Figures S32–S34 in the
Supporting Information).
The sulfur-limonene polysulfide can be synthesized on a large
scale. We have prepared several kilograms of the material,
typically in 50 and 100 g batches. The sulfur-limonene polysulfide
can then be processed as a coating or molded into a desired shape.
For the former, the distillation step was omitted and the p-cymene
and other volatile materials generated during the synthesis
conveniently served as the solvent. Figure 1 A shows the interior
of a flask spin-coated at 70 °C. Heat, vacuum, or a stream of
nitrogen was used to drive off the residual solvent. For molding,
the sulfur-limonene polysulfide was melted (>100 °C) and poured
into a silicone cast (Figure 1 B) or glass petri dish
(Figure 1 C). In Figure 1 C, it is notable that the polysulfide is
transparent at a thickness of 3 mm.
Figure 1.
Processing the sulfur-limonene
polysulfide into a coating (A) or molded object (B,C). The
polysulfide is transparent at a thickness of 3 mm (C).
We next assessed the ability of the polysulfide to sequester
metals from water. Elemental sulfur has been used in mercury
disposal,[11] but it is difficult to process into useful devices
because of its high crystallinity. The sulfur-limonene
polysulfide, in contrast, can be converted into a coating or solid
object (Figure 1). Should the polysulfide have a high affinity for
metals, this property would motivate applications in environmental
remediation.
As a starting point, the removal of palladium(II) from water was
studied. Palladium is a popular catalyst in organic synthesis,[12]
and its use in water leads to waste streams from which the metal
must be removed. Palladium pollution from catalytic converter
exhausts is another motivation for developing new sequestration
technologies.[13] To test the affinity of the sulfur-limonene
polysulfide for palladium, an aqueous solution of Na2PdCl4
(0.35 mm) was incubated on a 28 cm2 plate of the polysulfide. The
concentration of Na2PdCl4 in the water was then monitored by
UV/Vis spectroscopy.[14] In the event, the palladium concentration
dropped rapidly over the first hour, with 42 % of the palladium
removed from solution within 2 h (see Figures S37 and S38 in the
Supporting Information). After this time, the palladium binding
appeared to reach equilibrium. Importantly, this experiment
demonstrated that the sulfur-limonene polysulfide could remove
soft metal salts from water. Furthermore, a control experiment
demonstrated that the sulfur-limonene polysulfide trapped
palladium as quickly and effectively as elemental sulfur (see
Figures S38 and S39 in the Supporting Information).
Encouraged by this preliminary result, we moved to sequestration
studies of HgCl2. Mercury(II) exposure can result in a compromised
immune system, kidney damage, and embryotoxic effects.[15]
Therefore, effective and inexpensive technologies are needed to
remove mercury(II) from the environment.[15a, 16] When an aqueous
solution of HgCl2 (10 mm) was added to the surface of the
polysulfide, the result was a surprise: a bright yellow deposit
formed that remained immobilized on the polysulfide (Figure 2).
The deposit typically appeared within 30 min and remained on the
polysulfide, even after washing with water. Remarkably, this
deposit was only formed when the polysulfide was exposed to Hg2+.
No color change or deposit was observed when the polysulfide was
treated with Li+, Fe3+, Ca2+, Cu2+, Pb2+, Mg2+, Zn2+, Ni2+, K+,
Mn2+, or deionized water (Figure 2 and see Figure S46 in the
Supporting Information).
Figure 2.
10 mm solutions of metal salts were added
to the sulfur-limonene polysulfide and incubated for 24 h. A
selective color change was observed upon exposure to HgII.
This result does not necessarily mean that the other metals did
not bind to the polysulfide, but only that the color change is
unique to mercury(II). Importantly, this color change was not
observed when S8 was exposed to Hg2+ under the same conditions
(see Figure S43 in the Supporting Information), thus revealing
another advantage of the sulfur-limonene polysulfide over
elemental sulfur in metal sequestration.
Analyzing this yellow deposit by scanning electron microscopy
(SEM) and energy-dispersive X-ray (EDX) spectroscopy revealed the
presence of mercury (Figure 3 and see Figures S47–S63 in the
Supporting Information). The polysulfide appeared to form rippled
sheets and ridges upon exposure to Hg2+ (Figure 3, bottom). The
most distinctive feature, however, was the formation of nano- and
microparticles that adhered to the surface, even after washing
with water (Figure 3, bottom images). These particles contained
high levels of mercury, up to 50 wt % as determined by EDX
analysis. Interestingly, several of these particles penetrated the
surface of the polysulfide (Figure 3, bottom right)—likely the
result of the high density of the mercury particles and the
malleable nature of the polysulfide. We anticipate this particle
entrapment will be useful for the sequestration and disposal of
inorganic mercury.
Figure 3.
Top: SEM pin mount coated with the
polysulfide. Region 5 was exposed to HgCl2. Regions 1–4 did
not contain mercury, as determined by EDX. Bottom:
Representative area in region 5, up to 50 wt % mercury was
detected in the nano- and microparticles formed.
Motivated by these intriguing results, we examined how the
polysulfide responded to HgII in complex mixtures. We spiked river
water and a suspension of pond soil with ≥2 mg mL−1 HgCl2.
Remarkably, the same insoluble mercury deposit was formed on the
polysulfide in both cases (see Figures S42–S44 in the Supporting
Information). For the soil suspension, the silt and pond debris
were removed by washing with water, while the yellow mercury
deposit remained adhered to the polysulfide. This result
demonstrated that the sulfur-limonene polysulfide can remove HgII
from the complex mixtures encountered in environmental
remedyation.
While mercury sensing is an obvious application of the
polysulfide's response to HgII, we noted that the yellow deposit
was only visible for HgII concentrations of 1 mm or higher (see
Figure S45 in the Supporting Information). Therefore, rather than
use this chromogenic response to detect low levels of inorganic
mercury, we envision using it to indicate that a threshold level
of mercury has bound to the polysulfide. This response could be
used to monitor the lifetime of remediation devices made from the
polysulfide. It is important to point out, however, that mercury
binds to the polysulfide at lower concentrations, even when there
is no chromogenic response. For example, an aqueous solution of
2000 ppb HgCl2 was incubated on a 28 cm2 plate of the polysulfide
for 24 h. After this time, the water was removed and analyzed by
cold vapor atomic absorption spectroscopy. A final concentration
of 910 ppb was measured, thus indicating approximately 55 % of the
inorganic mercury was removed with a single treatment. While
alternative, and highly effective, mercury sensors[17] and
adsorbents[18] have been reported, their deployment in
environmental remediation is often limited due to the challenges
and cost of their large-scale synthesis.[15a, 16] We note that the
sulfur-limonene polysulfide is comparatively inexpensive, easy to
produce on a large scale, and displays a useful chromogenic
response.
We envision using the polysulfide to remove inorganic mercury from
water and soil at the site of contamination. Before the
polysulfide can be deployed directly in natural waterways and
ecosystems, however, an assessment of its toxicity must be
completed. Initiating these studies, we treated hepatic cell lines
HepG2 and Huh7 with water that had been exposed to the
sulfur-limonene polysulfide for 24 h. Even when this water made up
50 % of the culture medium, no difference in cell viability was
observed between the treated cells and a negative control sample
that was treated with pure, sterile water (see Figure S64 in the
Supporting Information). This experiment indicates that the
polysulfide does not release harmful materials into water, thus
motivating further studies in soil and water remediation. These
investigations are ongoing.
In conclusion, we have explored the properties of a polysulfide
synthesized entirely from the industrial by-products sulfur and
limonene. The polysulfide is easy to synthesize on a large scale
and requires no exogenous reagents or solvents. The polysulfide
removes PdII and HgII from water and soil and turns yellow when
exposed to mercury(II). This response is selective for mercury, a
discovery that may find use in sensing applications. We plan to
develop the sulfur-limonene polysulfide as an inexpensive material
for environmental remediation, where it will be used to sequester
toxic metals from complex mixtures. More generally, this research
is part of a growing effort to identify new and useful properties
of materials with high sulfur content[6] and to synthesize them in
an efficient and sustainable fashion.
SULFUR-LIMONENE POLYSULFIDE
WO2016064615
Disclosed is a limonene-sulfur polysulfide and methods for
preparing the same. The polysulfide prepared according to these
methods is flexible, moldable and otherwise capable of being
formed in any manner consistent with a thermoplastic polymer. The
limonene-sulfur polysulfide has been demonstrated to sequester
inorganic palladium and inorganic mercury dissolved in water.
BACKGROUND
[0001 ] Palladium contamination, i.e. palladium (II), of the
environment as a result of large scale organic synthesis processes
and catalytic converter exhaust will continue to necessitate
remediation of lakes, rivers and streams. Similarly, mercury
contamination of the environment has resulted from decades of
mining operations, metal refining processes, coal combustion and
other industrial activities. Mercury, in the form of mercury (II)
is extremely toxic and can cause kidney damage, embryo toxic
effects and other health concerns. Efficient removal of such
contaminants from the environment without exacerbating the problem
by creating additional pollutant wastes will substantially improve
our ecosystems.
SUMMARY
[0002] Disclosed herein is a novel sulfur-limonene polysulfide.
The sulfur-limonene polysulfide has a generally transparent red
colorization. Upon exposure to sufficient levels of mercury (II),
the site of exposure on the sulfur-limonene polysulfide changes
from red to yellow. The sulfur-limonene polysulfide is a reaction
product of limonene, (jf?)-(+)-Limonene, (S)-(-)- Limonene and
mixtures thereof, with elemental sulfur, i.e. Sg. The
sulfur-limonene polysulfide has thermoplastic characteristics.
[0003] Additionally, the present disclosure provides methods for
preparing the sulfur- limonene polysulfide. The method comprises
heating sulfur to a temperature sufficient to melt the sulfur,
adding limonene to the molten sulfur and allowing the two
component mixture to react thereby forming a single phase
comprising sulfur-limonene polysulfide. Typically, the reaction
between the molten sulfur and limonene will occur at temperatures
between about 130°C and about 200°C. When necessary, as determined
by the object formed from the sulfur- limonene polysulfide, the
method includes further steps to remove undesirable volatile
byproducts. The resulting sulfur-limonene polysulfide has
thermoplastic characteristics suitable for forming into an object
using any conventional manufacturing or molding technique.
[0004] Further, the present disclosure describes methods for
sequestering both palladium (II) and mercury (II) from aqueous
solutions. The sequestering methods expose the aqueous solutions
to the sulfur-limonene polysulfide at ambient conditions. [0005]
Finally, the present disclosure also describes methods for
extracting palladium (II) and mercury (II) from soil by an aqueous
extraction process and subsequently sequestering the palladium
(II) and mercury (II) from the aqueous solution using the
sulfur-limonene polysulfide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Figure 1 is a 1H NM for the polysulfide.
[0007] Figure 2 is a<13>C NMR for the polysulfide.
[0008] Figure 3 provides Heteronuclear Single Quantum
Coherence scan of the polysulfide.
[0009] Figure 4 is a UV-Vis spectrum for the polysulfide
dissolved in CH2C12at 5.6 mg/mL and at 1.86 mg/mL.
[0010] Figure 5 is an IR spectrum of the polysulfide.
[0011] Figure 6 is a graph of the size exclusion
chromatography (SEC) analysis of the crude polysulfide prior to
removal of unreacted or by-product volatile materials.
[0012] Figure 7 is a graph of the SEC analysis of the
refined polysulfide.
[0013] Figure 8 depicts the UV-Spectrum of Na2PdCl4solution
after incubation with the polysulfide.
[0014] Figure 9 depicts a molded object formed from the
polysulfide.
[0015] Figure 10 depicts an SEC calibration curve using
polystyrenes having molecular weights ranging from 162 Daltons
to 3,242,000 Daltons.
[0016] Figure 11 depicts the<!>H NMR for the volatile
byproducts produced by the method described herein. The major
product of the volatile material is p-cymene with signals at
7.15- 7.16 ppm (4H, m, ArH), 2.88-2.95 ppm (1H, sept., CHMe2),
2.3 ppm (3H, s, CH3) and 1.28 ppm (6H, d, CHMe2).
[0017] Figure 12 depicts a Raman spectrum for the final
sulfur-limonene polysulfide.
[0018] Figure 13 depicts mass spectrometry results for the
polysulfide using Ag<+>coordination.
[0019] Figures 14-17 are scanning electron microscope
images of the surface of the polysulfide after exposure to
HgCl2.
[0020] Figures 18-19 are scanning electron microscope
images or regions analyzed by energy dispersive x-ray of the
polysulfide. [0021] Figure 20-26 are the scans produced by the
energy dispersive x-ray analysis for each spot identified in
FIG. 19.
[0022] Figure 27 is an enlargement of the scanning electron
microscope image of FIG. 16.
[0023] Figure 28 is an enlargement of the area identified
as EDS Spot 3 with the identified region in the box in FIG. 27.
[0024] Figure 29 is an enlargement of the area identified
as EDS Spot 4 with the identified region in the box in FIG. 27.
[0025] Figure 30 is an enlargement of the area identified
as EDS Spot 5 with the identified region in the box in FIG. 27.
[0026] Figures 31 -35 are the scans produced by the energy
dispersive x-ray analysis for each spot identified in FIG. 27.
[0027] Figure 36 depicts the predicted structure of the
novel polysulfide.
[0028] Figure 37 depicts the structures of the reactants
used to prepare the novel polysulfide.
[0029] Figure 38 depicts the generic reaction process.
[0030] Figure 39 depicts volatile by-products of the
reaction between limonene and sulfur.
[0031] Figure 40 depicts the results of differential
scanning calorimetry analysis of the novel polysulfide.
[0032] Figure 41 depicts a 1H NMR (600 MHz) scan of the
reactants when a radical inhibitor is included in the reaction
mixture.
[0033] FIG. 42 is a 1H NMR (600 MHz) scan of limonene.
&c...
DETAILED DESCRIPTION
[0034] This disclosure provides a novel form of polysulfide and
methods for preparing the disclosed polysulfide. Additionally,
this disclosure describes methods for recovering mercury and
palladium from water using the novel form of polysulfide. The
novel form of polysulfide is a reaction product of limonene,
either (i?)-(+)-Limonene, also known as d-Limonene, or (S)-(-)-
Limonene an enantiomeric form of d-Limonene and elemental sulfur.
The resulting polysulfide is identified as a sulfur-limonene
polysulfide and referred to herein as polysulfide. Either form of
limonene will provide the necessary polysulfide. As such, when
used herein the word limonene refers to both enantiomers.
[0035] The combined carbon and hydrogen content of the polymer may
range from about 25% to about 50% by weight and the sulfur content
may range from about 50% to about 75% by weight. Typically, the
combined carbon and hydrogen content will range from about 40% to
about 50% and the sulfur content may range from about 50% to about
60%. Preferably, the carbon + hydrogen to sulfur ratio will
provide a polymer having a glass transition value sufficient to
impart flexibility to products molded from the polymer.
[0036] The polysulfide having the above characteristics is not
brittle and may be formed into a plurality of objects. See for
example FIG. 9. Differential scanning calorimetry (DSC) revealed a
glass transition (Tg) at -21 °C and simultaneous thermal analysis
indicated substantial thermal decomposition about 200°C. The DSC
scan of FIG. 40 shows a broad step change with a midpoint at -21
°C indicative of a low molecular weight polymer. The polysulfide
prepared according to the method disclosed herein is preferably
free of unreacted or crystalline sulfur. The final solid product
has a red color yet is transparent in nature. The polysulfide is
insoluble in water, sparingly soluble in methanol and fully
soluble in dichloromethane, chloroform and tetrahydrofuran.
[0037] When examined using analytical techniques, the polysulfide
produced the scans provided in FIGS. 1 -7. In view of the
3⁄4<13>C, and HSQC NMR scans, the resulting polysulfide has
an aromatic component. Based on mass analysis and elemental
composition, the final polysulfide is believed to contain an
average of 2 limonene units and 10 sulfur atoms as depicted in
FIG. 36. However, the polysulfide can vary from one to three
limonene units and may contain 2 to 19 sulfur atoms.
The NMR data reflects the following:
• 0.75-2.55 ppm hydrogen associated with limonene domains that are
greater than 2 bonds from sulfur atoms;
• 2.5-4.5 ppm hydrogens positioned within 2 bonds of sulfur;
• 6.75-8.0 ppm hydrogen associated with aromatic rings.
In FIG. 1 , the 1H NMR (400 MHz, CDC13) depicts the following
peaks associated with the polysulfide: 7.62, 7.58, 7.56, 7.38,
7.36, 7.19, 7.15, 7.11 , 7.04, 6.95, 6.93, 6.91, 3.52, 2.65, 2.62,
2.46, 2.40, 2.32, 2.31, 2.28, 2.15, 1.91 , 1.81 , 1.80, 1.71 ,
1.66, 1.50, 1.49, 1.44, 1.39, 1.29, 1.05, 1.04. In FIG. 2,
the<13>C NMR (100 MHz, CDC13) depicts the following peaks
associated with the polysulfide: 144.3, 141.2, 140.5, 137.2,
133.9, 131.9, 129.2, 127.0, 126.7, 126.4, 125.5, 123.6, 122.6,
122.2, 121.3, 120.29, 65.3, 62.8, 61.5, 59.7, 59.1, 58.1 , 57.5,
56.3, 53.9, 52.99, 52.6, 51.2, 47.9, 47.4, 46.3, 37.4, 36.1, 35.4,
34.5, 31.0, 29.1 , 28.9, 28.3, 25.3, 24.5, 23.9, 21.2, 20.9, 18.8.
[0038] To determine the UV-Vis spectrum for the polysulfide, two
samples of the polysulfide were dissolved in C3⁄4C12. The first
sample had a concentration of 5.6 mg/mL and the second sample had
a concentration of 1.86 mg/mL. UV-Vis analysis was carried out
using a quartz cuvette. As reflected in FIG. 4, local absorbance
maximum was observed at 420 nm. The determined absorbance is
consistent with red colorization of the resulting polymer prior to
sequestration of mercury (II). Additionally, with reference to
FIG. 1 , the alkene peaks associated with limonene are not present
in the NMR scan of the polysulfide. The absence of the alkene
peaks reflects the complete or at least substantially complete
consumption of limonene in the polymerization reaction.
[0039] Without intending to be bound by theory, the reaction of
limonene and sulfur is believed to follow a radical mechanism.
First, sulfur cleaves homolytically to provide thiyl radicals.
Next, the thiyl radicals add to the alkenes of limonene. The
resulting radical on limonene propagates the reaction by reacting
further with sulfur. Elimination reactions can lead to
aromatization of a portion of the polysulfide.
[0040] The IR scan of FIG. 5 indicates that the hydrocarbon
framework of limonene is contained in the resulting polysulfide.
To obtain the IR spectrum, several drops of the polysulfide were
dissolved in CH2C12(approx. 2 mg/mL), placed on a sodium chloride
plate and dried. The resulting thin film was analyzed by FT-IR.
The optical activity of the final product [a]D = -27.3 (c = 1.0,
CHC13) reflects the retention of at least a portion of the
stereochemical integrity of the limonene domains in the resulting
polymer. The optical measurement was taken using a polarimeter
using the D-line of a sodium lamp, i.e. at 589 nanometer
wavelength. The Raman spectra provided by FIG. 12 shows a distinct
S-S peak at 464 cm<"1>. The following table identifies the
wavenumber for the peaks specifically identified in FIG. 5.
<img class="EMIRef" id="355830197-imgf000006_0001" />
κ 1509.26 W 704.65
L 1445.84 X 661.05
[0041] The size exclusion chromatography (SEC) graphs of FIGS. 6
and 7 provide a basis for concluding that the resulting
polysulfide has a number average molar mass (M„) of 208.6, a mass
average molar mass (Mw) of 244.9, and a Z-average molar mass of
298.8. The dispersity of the polysulfide (Mw/ Mn) is 1.17. The
values of FIGS. 6 and 7 are relative values because they were
calculated based on a calibration curve for polystyrene as
described herein. The SEC calibration curve of FIG.10 represents
molecular weights for a range of polystyrenes varying from 162
Daltons to 3,242,000. This data does not provide absolute
molecular weight information (as the polysulfide elution profile
was compared to styrene) and is primarily useful to calculate the
polydispersity. Mass spectrometry (see next) was used to determine
absolute molecular weights
[0042] Further analysis with mass spectrometry using
Ag<+>coordination provided additional information about the
molecular weight of the polysulfide. The Ag<+>coordination
mass spectrum scan provided by FIG. 13, reflects a molecular
weight in the range of 386 to 777 Da. Signals were detected from
m/z =411 to m/z = 949. These peaks correspond to the polysulfide
components coordinated to a single Ag+ ion. The m/z therefore
corresponds to [M+Ag]<+>where M is the molecular weight of
the polysulfide component. Considering both mass spectrometry data
and combustible analysis indicate that the polysulfide contains 1
-3 limonene units and up to 19 atoms of sulfur. On average, the
polysulfide contains 2 limonene units and 10 sulfur atoms with the
following elemental composition: C, 38.97%; H, 4.97%; N, 0.0%; S,
56.60%. Key peaks from the mass spectral analysis provided by FIG.
13 are: m/z = 495.4, 509.5, 521.5,
523.5, 537.5, 549.5, 551.5, 563.5, 565.5, 577.5, 579.5, 601.5,
603.5, 607.6, 619.6, 635.6, 649.6, 663.6, 677.6, 691.7, 705.7,
717.7, 731.7, 745.7, 749.7, 829.7, 855.8, 881.8, 886.8.
[0043] The following method was used to prepare the polysulfide
for the Ag<+>coordination mass spectrum analysis. A 0.5
mg/mL solution of AgN03in H20 was prepared and mixed with methanol
in a 9: 1 ratio by volume to provide the mass spectrometry
infusion solution. Subsequently, 20 mg of the polysulfide was
added to the MeOH/H20/Ag<+>infusion solution to provide a
saturated solution. A 100 microliter aliquot of the polysulfide
saturated solution was further diluted to 1.0 mL with the
MeOH/H20/Ag<+>infusion solution to provide a final solution
for mass spectrum analysis. The final solution was injected by
direct infusion into the mass spectrometer using atmospheric
pressure chemical ionization with operation in positive mode. A
cluster of peaks was detected between m/z = 495 and 886. Each of
these peaks corresponds to a polysulfide molecule coordinated to a
single silver ion, therefore the mass of the polysulfide detected
in the mass spectrometer varies from approximately 386 to 777 Da.
Note: two abundant isotopes of Ag<+>(106.9 and 108.9)
results in a doublet for the [M+Ag]<+>that is separated by
two mass units. In a control experiment without silver nitrate, a
sample prepared by the same method gave no signal in the mass
spectrometer.
[0044] Finally, the novel polysulfide disclosed herein does not
readily oxidize. Rather, heating of the polysulfide to
temperatures between about 200°C and 300°C will sever the sulfur-
to-sulfur bonds of the polymer leading to depolymerization and
resulting in volatile decomposition products. Thus, recovery of
sequestered materials can be easily achieved by depolymerizing the
polysulfide.
[0045] The method for preparing the novel polysulfide
advantageously utilizes industrial waste. The reactants used are
limonene, either (i?)-(+)-Limonene, also known as d-Limonene, or
(S)-(-)-Limonene an enantiomeric form of d-Limonene and elemental
sulfur. The structures of each enantiomer and elemental sulfur in
the form of S8are shown in FIG. 37.
[0046] Typically, the raw materials will be treated to provide
technical or analytical grade materials thereby enhancing the
percent yield of the polysulfide and reducing the unreacted or
waste material resulting from the polymerization reaction.
However, the following method will consistently produce the
desired polysulfide independent of whether the starting materials
are industrial grade, technical grade or analytical grade.
[0047] In general, the method for preparing the above described
polysulfide entails initially adding sulfur to a reactor and
heating the sulfur sufficiently to melt the sulfur. Typically,
heating sulfur to a temperature between about 1 15°C to about
130°C, preferably of about 120°C to about 124°C, at atmospheric
pressure will be sufficient to melt the sulfur. Preferably, some
form of agitation will be provided to ensure even and consistent
melting of the sulfur. The reactor can be glass, ceramic, or
stainless steel open to the atmosphere but provided with an
extractor vent to remove any volatile materials.
[0048] Following melting of the sulfur, a mass of limonene is
added to the molten sulfur and the temperature of the reactor
increased. Limonene suitable for use in this method may be (R)-
(+)-Limonene, also known as d-Limonene, or (S)-(-)-Limonene an
enantiomeric form of d- Limonene and mixtures thereof. As noted
above any reference to limonene herein refers to either enantiomer
and mixtures thereof. Upon addition of the limonene, a two-phase
mixture results. The two-phase mixture is heated to a temperature
between about 130°C and 200°C; however, when operating at
temperatures above the 176°C boiling point of limonene the
reaction must take place under increased pressure and/or a reflux
system to preclude unnecessary loss of limonene. The reaction
continues until a single phase is present in the reactor.
Typically, the reaction step will occur at temperature between
about 160°C and 175°C. Preferably, the mixture will be heated at a
temperature of about 170°C for a time period sufficient to yield a
single- phase. Depending upon reactor size and operating
temperature, the reaction step may take from about 30 minutes to
about two hours. In general, as noted above, formation of a single
phase within the reactor signals the termination of the reaction
step as the single phase comprises the desired sulfur-limonene
polysulfide, referred to herein as polysulfide. As noted below,
some side reactions occur requiring further purification to yield
predominately the desired polysulfide.
[0049] One alternative reaction condition includes heating the two
phase mixture to a temperature of about 176°C to about 185°C,
preferably 180°C, under a reduced pressure of about 45 mm Hg (6.0
kPa) to about 55 mm Hg (7.3 kPa), preferably 50 mm Hg (6.7 kPa),
as measured with a manometer, for about three to about five hours,
preferably four hours. Another alternative reaction condition
heats the two phase mixture to a temperature of about 90°C to
about 110°C, preferably 100°C, at a pressure of less than 1 mm Hg
(0.13 kPa) for a period of about four hours to about six hours,
preferably five hours. The reactions are schematically depicted by
FIG. 38. The reaction is believed to proceed by a radical
mechanism. To test this theory, the reaction process was repeated
using 500 mg of sulfur. Following heating of the sulfur, 50 mg of
hydroquinone was added to the sulfur prior to addition of 500 mg
of limonene. The mixture was stirred for 15 minutes at 170°C
followed by addition of 50 mg hydroquinone. The mixture was
maintained at 170°C for an additional 105 minutes. Analysis of the
mixture after cooling indicated only partial reaction of limonene.
The final solution was analyzed using<:>H NMR (600 MHz). As
reflected in FIG. 41, the NMR peaks indicate the presence of
alkenes associated with partially reacted limonene and
-benzoquinone. The formation of -benzoquinone is consistent with
hydroquinone acting as an H-atom donor thereby terminating radical
intermediates. FIG. 42 is a 1H NMR (600 MHz) scan of limonene.
Comparison of FIGS. 41 and 42 indicates that the radical inhibitor
precluded the formation of the polysulfide. [0050] Upon completion
of the reaction, the single-phase mixture is allowed to cool to
room temperature. Volatile by-products may also be present along
with the resulting polysulfide. These components, typically
p-cymene and low molecular weight thiols and sulfides, can be
removed by evaporation at 25°C to 100°C, distillation or vacuum
distillation. Vacuum distillation will take place at about 100°C
to about 180°C under a vacuum of about <1 mbar (0.1 kPa) to 100
mbar (10 kPa) for about one to ten hours until substantially all
volatile material is removed from the polysulfide. An optional
vacuum distillation step occurring at 100°C and less than 1 mm Hg
(0.13 kPa) for three to six hours may be applied. Note: the
removal of volatile byproducts may be carried out prior to
allowing the single-phase mixture to cool to room temperature or
after allowing the single phase mixture to cool to room
temperature.
[0051] Following removal of the volatile components, the overall
method typically results in a yield of the desired
limonene-polysulfide of about 70% to 90% of the theoretical yield.
As noted above, the final polysulfide is a transparent, red solid.
FIG. 11 depicts a<l>R NMR (400 MHz, CDC13) of the volatile
byproducts isolated by the distillation step. The scan corresponds
to the presence of p-cymene and other volatile sulfides and
thiols. Representative peaks associated with the volatile
compounds as depicted in FIG. 11 are found at: 7.16, 7.15, 3.37,
3.36, 3.35, 2.95, 2.93, 2.91, 2.90, 2.88, 2.52, 2.38, 2.18, 2.13,
2.06, 1.86, 1.77, 1.55, 1.43, 1.42, 1.29, 1.27, 1.16, 1.12, 1.10.
[0052] Typically, the method for preparing the polysulfide will
follow these steps. Heat the elemental sulfur to a temperature
sufficient to melt the sulfur. As discussed above, the sulfur will
generally be heated with stirring or agitation to about 120°C to
about 124°C at atmospheric pressure. A wide range of ratios of
limonene to sulfur will perform satisfactorily for the method of
producing the polysulfide. In general, the mass ratio of
limonene/sulfur may range from 1 :1.5 to 1.5: 1. Preferably, the
ratio of limonene to sulfur will be 1 : 1. The ratio of limonene
to sulfur is selected to provide a reaction product, polysulfide
and volatiles, that is at least 70% polysulfide by weight. More
preferably, the reaction product, polysulfide and volatiles, is at
least 80% polysulfide by weight. Additionally, the reaction
product is substantially free of unreacted sulfur. Typically, the
products will have less than 4%> unreacted sulfur by weight.
[0053] Following addition of the limonene to the molten sulfur,
the resulting two-phase mixture is heated to a temperature between
about 130°C and 200°C. Generally, the reaction time required to
provide a single phase of the resulting polysulfide will be about
30 minutes to about two hours. Optionally, to remove volatile
by-products from the polysulfide, the single-phase product is
heated at a temperature greater than the vaporization point of the
probable byproducts. Alternatively, vacuum distillation performed
under the appropriate temperatures as determined by the probable
by-products may be used to remove the unwanted by-products. The
final polysulfide is stable up to 200°C and decomposes at
temperatures above 200°C. Objects formed from the polysulfide will
retain their shape at temperatures between 4°C and 60°C.
[0054] The resulting polysulfide has thermoplastic
characteristics. Thus, the polysulfide may be formed into objects
using conventional techniques suitable for thermoplastic polymers
including but not limited to injection molding and spin casting.
As depicted in FIG. 9, a material formed by pouring the liquid
polysulfide into a mold will retain its shape after cooling. When
applied as a spun coated material, the vacuum distillation steps
may be optionally omitted from the method of preparing the
polysulfide as retained volatile components will aid in the
plasticization of the polymer during the coating process and
evenness of the resulting polysulfide coating. Additionally, the
temperatures used during the coating process will subsequently
drive off the retained volatile components such as / cymene. Thus,
spin coating forms an object from the polysulfide and removes
volatile by-products in a single step. As used herein, a
polysulfide object may take any form as prepared by any suitable
process. As noted above, thermoplastic molding techniques,
including spin molding, may be used to design a variety of useful
objects suitable for carrying out the contemplated use of
sequestering palladium and mercury commonly found as environmental
contaminants. Non-limiting examples may include objects spun
coated on the interior of pipes or injection molded into lattice
type nets. Preferably, the manufacturing process provides a
polysulfide object having a large surface area thereby enhancing
the ability of the polysulfide to sequester palladium and mercury.
[0055] FIGS. 14-35 provide further classification and
understanding of the binding of mercury (II) to the polysulfide.
FIG. 14 depicts the surface of the polysulfide following
application of a drop of HgCl2as a lOmM solution. As depicted, the
circular area corresponds to the drop of the solution. FIG. 15
focuses on the identification box in FIG. 14. FIG. 15 reflects the
demarcation area between the surface of polysulfide exposed to a
solution of HgCl2and the region that has not been exposed to
HgCl2. FIG. 16 provides an enlarged view of the surface of the
polysulfide following exposure to HgCl2. As depicted therein,
following exposure of the polysulfide to HgCl2micro- and
nano-particles in the form of a mercuric sulfide form and adhere
to the surface of the polysulfide. The region, containing the
micro- and nano-particles of mercuric sulfide, corresponds to the
observed color change from red to yellow. FIG. 17 is an
enlargement of the identification box depicted in FIG. 16. As
depicted in FIG. 17, the mercuric particles, as micro- and
nano-particles, not only adhere to the surface (area A) of the
polysulfide but may also become enveloped by the polysulfide and
sink partially beneath the surface (area B) of the polysulfide.
[0056] FIGS. 18-19 provide scanning electron microscope images of
a polysulfide following exposure to HgCl2and after formation of
the micro- and nano-particles of mercuric sulfide. Each identified
location in FIG. 19 has been analyzed using energy dispersive
x-ray spectroscopy (EDS, also known as EDX). FIGS. 20-26 provide
the results of the EDS analysis for each spot, EDS 1 - EDS 7
respectively. EDS spot 1 (FIG. 20) is a control region that lacks
polysulfide and lacks HgCl2. The resulting scan reflects the
detection of aluminum in the SEM sample holder. EDS 2 (FIG. 21) is
a second control that contains the polysulfide that was not
exposed to the HgCl2. As reflected in FIG. 21, the SEM produced a
peaks corresponding to the sulfur and carbon components of the
polysulfide. EDS spots 3 and 4 are on the border of the region
exposed to HgCl2. As depicted in FIGS. 22-23, EDS spots 3 and 4
lack any elements corresponding to HgCl2; therefore, EDS spots 3
and 4 were not exposed to HgCl2. In contrast, EDS spot 5 clearly
lies within the region exposed to HgCl2. The presence of mercury
was confirmed by the SEM analysis depicted in FIG. 24. Based on
the SEM and EDS analysis, this region of the scan had 17% mercury
by weight. EDS spot 6 corresponds to spot A in FIG. 17. The SEM
and EDS analysis depicted in FIG. 25 reflects the higher
concentration (50 weight%) of mercury in the resulting particle.
Further, the SEM analysis of the particle reflects an atomic ratio
of sulfur to mercury of 10.4 to 12.6, a ratio consistent with a
mercury sulfide particle. In contrast to FIG. 25, FIG. 26 depicts
the SEM results for an area exposed to HgCl2and adjacent to a
mercuric sulfide particle. As depicts in FIG. 26, the polysulfide
carries adhered mercury; however, the mercury has not formed a
micro- or nano-particle. Thus, mercury may bind to the polysulfide
without undergoing conversion to a mercuric sulfide particle.
[0057] FIGS. 27-30 provide further SEM images of mercuric sulfide
particles on the surface of the polysulfide. FIG. 28 is an
enlarged view of EDS spot 3 in FIG. 27. FIG. 29 is an enlarged
view of EDS spot 4 in FIG. 27 and FIG. 30 is an enlarged view of
EDS spot 5 in FIG. 27. FIGS. 31-35 depict the results of the EDS
analysis of the spots in FIG. 27. [0058] In FIG. 27, EDS spot 1
corresponds to a region lacking micro- and nano- particles but
exposed to HgCl2. As a result, mercury appears in the resulting
analysis at a concentration of 7.5 weight percent. EDS spot 2
corresponds to a region having an altered surface following
exposure to the HgCl2solution. In the region of EDS spot 2, the
surface has become rippled. The EDS analysis depicted in FIG. 32
reflects the binding of mercury to the surface at ten percent by
weight. Thus, the rippling may evidence the beginning of the
formation of a chemical bind, i.e. the precursor to a particle.
EDS spot 3 corresponds directly to a particle as identified in
FIG. 27. The EDS scan of FIG. 33 clearly reflects the formation of
a mercuric sulfide compound as the scan evidences the presence of
45.8 weight percent mercury at this location. Similarly, EDS spot
4 corresponds to a mercuric sulfide particle that has been
partially enveloped by the polysulfide. The presence of mercuric
sulfide in the area of EDS spot 4 is confirmed by the EDS analysis
of FIG. 34 which reflects the presence of 46 weight percent
mercury at the indicated location. Additionally, the EDS analysis
indicates the atomic ratio of S to Hg is 21.6 to 8.3. Finally,
FIG. 35 provides the EDS analysis of EDS spot 5. EDS spot 5
corresponds to the same particle as EDS spot 4; however, the x-ray
analysis was conducted through the opening in the surface of the
polysulfide. The resulting EDS scan provides atomic ratios of Hg
to S that generally correspond to the scan of FIG. 34.
[0059] The resulting polysulfide has a high affinity for
sequestering palladium and mercury salts. Over the years, the
extensive use of palladium and palladium salts as catalysts in
organic synthesis has resulted in palladium contamination of soil
and water ways. Likewise, industrial usage of mercury compounds
has also produced environmental contamination. The unique
characteristics of the above described polysulfide offer an
effective route for removing palladium and mercury from the
environment.
[0060] In the method of the current invention, a polysulfide
formed into an object using the methods described above is exposed
to water or a soil/water suspension contaminated with
Pd<2+>and/or Hg<2+>. At temperatures between about 4°C
and 60°C, more typically 4°C to 30°C, a sample of polysulfide
having an area of 28 cm<2>will reduce the concentration of
Pd<2+>(also known as palladium (II)) by approximately 40 to
60 percent over a two hour period. Under the same operating
conditions, the polysulfide will reduce the concentration of Hg
(also known as mercury (II)) by about 40 to about 60 percent over
a two hour period. The method may be practiced by applying the
contaminated water to the surface of the polysulfide or by
immersing the polysulfide in a body of water, e.g. a pond, stream
or lake, and allowing the reaction to progress. During the
reaction process, regular sampling of the contaminated water and
use of conventional UV-Vis analysis will allow one to determine
the progress of palladium remediation. To monitor the progress of
mercury remediation, one can simply monitor the polysulfide for
the color change from red to yellow. Additionally,
Hg<2+>concentration in water can be determined and monitored
using cold vapor atomic absorption spectroscopy.
[0061] Remediation of soil may be carried out by initially
generating a soil in water suspension. Typically, the soil in
water suspension will have from about 400 to 800 grams of soil per
liter of water. The suspension will be maintained by stirring for
about one to thirty minutes at a temperature of about 4°C to 60°C,
more typically 4°C to 40°C. Following establishment of the
suspension, the polysulfide may be immersed or otherwise contacted
with the soil/water suspension for a period of time sufficient to
allow for the reaction of Pd<2+>and/or Hg to occur at the
surface of the polysulfide. Alternatively, an extraction step may
be carried out to isolate the Pd<2+>and/or Hg<2+>in a
solution free of soil. One suitable extraction process is known as
the Soxhlet process. Following extraction of the metals from soil,
the method continues as described when remediating contaminated
water samples.
[0062] The following examples demonstrate the ability of the
polysulfide to sequester inorganic palladium. In particular, the
examples demonstrate that use of a polysulfide having 28
cm<2>surface area in the above described method will result
in the reduction of Pd<2+>concentration by 40% to 60% over a
two hour period of exposure. Increasing the surface area of the
polysulfide will decrease the time period required for remediation
and result in higher removal rates. Additionally, the following
examples demonstrate that a polysulfide having 28
cm<2>surface area has the ability to reduce Hg<2+>by
at least 55% over a three hour period when treated at 15°C to
20°C.
[0063] For each example, the polysulfide was prepared as described
above with removal of volatile materials by vacuum distillation.
The polysulfide was then heated to > 100 °C, poured into a
glass petri dish (6 cm diameter) and allowed to cool to room
temperature, thereby forming a polysulfide object. The 3mm thick
polysulfide object had an optically transparent, red coloration
such that an image can be viewed through the plate. The
polysulfide object had a surface area of 28 cm<2>. [0064] An
aqueous solution of Na2PdCl4was prepared by adding palladium
chloride (3.1 mg, 0.017 mmol) to a 50 mL volumetric flask along
with sodium chloride (5.2 mg, 0.088 mmol) followed by 5 mL
deionized water. The resulting mixture was dissolved by incubation
in an ultrasonication bath for 10 minutes at room temperature. The
resulting solution was then diluted to 50 mL with deionized water
to provide a 0.35 mM aqueous solution of Na2PdCl4.
[0065] A 10 mL aliquot of the Na2PdCl4solution was added to
polysulfi.de products (prepared as described above). The solution
was incubated at room temperature on the plates and the UV-Vis
spectrum was measured every 30 minutes for 2 hours. In this
measurement, an aliquot of the Na2PdCl4solution was transferred to
a quartz cuvette and the UV-Vis spectrum was obtained before
returning the solution to the plate. A clean cuvette was used for
each measurement. The UV-Vis spectrum of FIG. 8 depicts the
removal of Pd<2+>from water. Each line in FIG. 8 reflects
the UV-Vis spectrum after exposure of the polysulfide to Na2PdCl4
solution for the indicated time period. As reflected by the change
in absorption over time, the spectrum depicts approximately 42%
reduction of Pd<2+>after a period of two hours. Thus, the
treatment method lowered the concentration of Pd<2+>from
0.35 mM to 0.15mM after two hours. The treatment process can be
repeated until palladium levels are lower than regulatory
requirements.
[0066] Based on the above example, a polysulfide having a surface
area of 28 cm area can bind between 0.2 and 0.5 mg of
Pd<2+>. In view of the thermoplastic characteristics of the
polysulfide, a polysulfide coated matrix or polysulfide coated
support will permit treatment of contaminated areas such as ponds
and streams or even larger bodies of water by immersing the
supported polysulfide in the contaminated water. Supporting
materials may include, but are not limited to, the interior of a
flask or reactor, a stirring device, a polymeric or stainless
steel mesh, or other high surface area supporting material that
does not react with the polysulfide. Since the reaction occurs at
the surface of the polysulfide, the polysulfide layer need be only
as thick as that required to bind to the support. The examples
discussed herein demonstrate that 28 cm of limonene-polysulfide
surface will remove up to 0.5 mg of Pd<2+>after an hour of
incubation. Subsequently, the supported polysulfide material is
removed from the water (or vice versa) leaving purified water and
Pd<2+>bound to the limonene-polysulfide material. As
described above, one can easily monitor the remediation process
and determine when the polysulfide has become saturated with
Pd<2+>by monitoring water samples with conventional analysis
techniques such as UV-Vis analysis. If the polysulfide has become
saturated with Pd the UV-Vis spectrum will reflect a plateau in
the sequestration curve. Likewise, as reflected in FIG. 8, removal
of Pd<2+>to a safe level will be reflected by the UV-Vis
spectrum.
[0067] To demonstrate the ability to remove inorganic mercury from
water, a stock solution of HgCl2was prepared by dissolving 36.0 mg
HgCl2(133 mmol) in a total volume of 600 μL deionized water. A 0.3
μL aliquot of the stock solution was then diluted to 10.0 mL total
volume in water to provide an aqueous solution that is 2 ppm
HgCl2. All 10 mL of this solution was then added to the petri dish
containing polysulfide prepared as described in the palladium
example. The solution was covered and incubated for 24 hours at
room temperature. After this time, the solution was removed from
the plate and analyzed by cold vapor atomic absorption
spectroscopy. The concentration of mercury(II) was measured to be
910 ppb. This experiment shows that a single incubation on the
polysulfide plate results in removal of 55% of the mercury.
[0068] Additionally, the polysulfide described herein provides the
ability to determine the presence of toxic levels of mercury in
water. As noted above, the polysulfide has an initial red
colorization. However, following exposure to a sufficient quantity
of mercury for a sufficient period of time, the polysulfide will
undergo a color shift to yellow. The color change typically occurs
when 4 cm<2>of the polysulfide has been exposed to at least
5mg of mercury(II) in solution, i.e. the concentration of
mercury(II) in solution is at least 1 mM. Although some areas of
the polysulfide may still be available for further binding of
mercury(II) the color change can be used as a signal to indicate
the need to replace the polysulfide thereby ensuring that binding
of mercury(II) proceeds without delay. However, the lack of color
change does not mean that binding of mercury(II) has not occurred.
For example, incubation of a solution containing only 2000 ppb
HgCl2on 28 cm<2>plate of the polysulfide resulted in a
reduction of Hg(II) to only 910 ppb, as determined by cold vapor
atomic absorption, without changing the polysulfide to yellow.
Thus, the color change is associated with remediation of solutions
having relatively higher concentrations of mercury(II) or due to
long term exposure to lower concentrations of Hg(II). Finally, the
color change from red to yellow is unique to this polysulfide.
While elemental sulfur is known to bind mercury(II), no color
change occurs as a result.
[0069] A 2 μΤ aliquot of the HgCl2 stock solution prepared above
(60 mg/mL HgCl2) was diluted to a total volume of 60 \xL with
deionized water (sample A) and 60 μL of Arkansas River water
(sample B). 30 μΐ, aliquots of these solutions (2 mg/mL HgCl2)
were then added at different locations on the surface of the
polysulfide. The sample plate was incubated for 24 hours at room
temperature. After approximately 4 hours, a yellow deposit began
to form in the samples containing mercury. Control drops of
deionized water (30 μ ) did not produce any change in color. After
the 24 hour incubation period, the drops were removed by
micropipette and the polysulfide surface was washed with deionized
water (3 x 10 mL). Washing did not remove the yellow deposits.
This experiment demonstrates the ability to visualize the binding
of mercury to the polysulfide at certain concentrations and the
adherence of the inorganic mercury to the polysulfide product.
Thus, the color change characteristic reflects both the presence
of mercury in the water supply and the need to replace the
supported polysulfide.
[0070] The method for removing inorganic palladium and inorganic
mercury may take place in the contaminated environment.
Preferably, the method for removing these materials will take
place at temperatures between about 4°C and 30°C. For example, one
test exposed a polysulfide prepared as outlined above and having a
surface area of 4 cm<2>to a solution containing 2 mg/mL of
mercury (II). The polysulfide effectively sequestered 5 mg of
mercury (II) over a period of 180 minutes at a temperature of
15-20 °C. Another test exposed a polysulfide prepared as outlined
above and having a surface area of 28 cm<2>to a solution
containing 2
<img class="EMIRef" id="355830197-imgf000017_0001" />
of mercury (II). The polysulfide effectively sequestered 55% of
the mercury (II) present in the solution over a period of 180
minutes at a temperature of 15-20 °C. Another test exposed a
polysulfide having a surface area of 28 cm<2>to a solution
containing 0.4 mM, i.e. 42% solution, of palladium(II). The
polysulfide effectively sequestered 55%> of the palladium(II)
present in the solution over a period of 120 minutes at a
temperature of 15-20 °C.
[0071] The actual binding reactions occurring during the
sequestering process have not been determined. Upon examination of
the polysulfide post incubation, the surface of the polysulfide
has domains of nano- and micro-particles. Without intending to be
bound by theory, we believe that the sequestering step forms nano-
and micro-particle domains of mercury sulfides having up to 50
weight percent mercury.
[0072] The polysulfide described herein is also useful for
remediating mercury(II) contaminated soil. The method of
remediating soil includes the following steps: (a) preparing a
suspension of contaminated soil in water; (b) maintaining the
suspension of soil in water for a period of time sufficient to
leach substantially all of the mercury(II) out of the soil; (c)
placing the polysulfide in the suspension or passing the water
containing mercury(II) from the suspension over the polysulfide.
In general, the suspension of soil in water may contain from about
400 to 800 grams of soil per liter of water. The suspension will
be maintained by agitation or stirring for about 1 to about 30
minutes at a temperature of about 4 °C to about 60 °C, more
typically 4°C to 40°C, prior to introducing the polysulfide to the
suspension or filtering the solids and isolating the supernatant
containing mercury(II). Suitable equipment for carrying out the
extraction of metal contamination from soil would include a
Soxhlet extractor. In this method, a soil sample would be placed
in the Soxhlet thimble and extracted with hot water for between 30
minutes and 5 hours. The isolated water, now containing
mercury(II), would be sent for polysulfide treatment and the
purified soil could be returned to the environment. Prior to
treating the suspension or supernatant, the concentration of
mercury(II) will be determined and used to determine the square
centimeters of polysulfide necessary to sequester a sufficient
amount of mercury(II) to meet health regulations for water.
[0073] To demonstrate the removal of mercury from soil, soil from
the bank of Flinders University Lake (-100 g) was suspended in 250
mL of water from the same lake. Before the soil settled, an
aliquot of the soil suspension was spiked with HgCl2so that the
final concentration was 100 mM mercury(II). Two samples were then
applied in 100 i aliquots to discrete locations on the surface of
a single polysulfide product contained in a petri dish having a
surface area of 28 cm . One sample was a 100 \ih aliquot of the
mercury-free suspension of pond silt and the other sample was a
100 i aliquot of the pond silt suspension that had been spiked
with 100 mM HgC12. The petri dish was covered and incubated for 24
hours at room temperature. After 24 hours, both drops appeared
brown due to the pond soil. However, after washing the plate with
deionized water (3 x 10 mL), the soil was removed and no soil
residue remained on the mercury-free sample. However, a yellow
deposit remained on the region treated with the
mercury(II)-treated sample. Analysis of the yellow deposits using
energy dispersive x-ray (EDX) analysis determined that the
deposits contained up to 50wt% mercury. Thus, the polysulfide can
sequester mercury from a complex milieu of pond soil and water.
Furthermore, the polysulfide retains the sequestered mercury even
after the step of washing. Thus, the foregoing example
demonstrates the ability of the polysulfide to remove and retain
inorganic mercury from "crude," i.e. unprocessed, soil samples
obtained directly from the contaminated environment by merely
generating a soil/water suspension and immersion of the
polysulfide in the soil/water suspension. [0074] Other embodiments
of the present invention will be apparent to one skilled in the
art. As such, the foregoing description merely enables and
describes the general uses and methods of the present invention.
Accordingly, the following claims define the true scope of the
present invention.