27

Sulfurization and Solidification of Wastes Consisting of
Elemental Mercury
Taketoshi KUSAKABE and Masaki TAKAOKA*
Graduate School of Engneering, Kyoto University
C-1-3 Katsura, Nishikyo-ku, Kyoto 615-8540, Japan*E-mail: takaoka.masaki.4w@kyoto-u.ac.jp

Abstract
Entry into force of the Minamata Convention on Mercury has changed the supply-demand balance,
leading to an oversupply of mercury worldwide. We assessed sulfurization and solidification technologies for
wastes consisting of elemental mercury for disposal in specially engineered landfills. For chemical
stabilization of elemental mercury, gas phase sulfurization, wet sulfurization in water phase and drymechanochemical sulfurization were evaluated. Solidification for sulfurized mercury was examined using
cement/mortar/concrete, dicyclopentadiene-modified sulfur and epoxy resin as solidification materials. In thisresearch, crucial environmental requirements (limits of leaching and emission) for sulfurized and solidified
products were defined and evaluated using three Japanese leaching tests (JLT-13, JLT-46 and a tank leachingtest) and a headspace test. Overall, each sulfurization and solidification technology fulfilled the crucial
environmental requirements for sulfurized and solidified products and compressive strength of the solidified
products.
Key words :	
mercury wastes, Minamata Convention on Mercury, multiple protection, solidification,
sulfurization

1. Introduction
The Minamata Convention on Mercury entered into
force on 16 August, 2017 to protect human health and theenvironment from anthropogenic emissions and releasesof mercury and mercury compounds (Art. 1) (UNEP,
2019). Mercury wastes are substances or objects in aquantity above the relevant thresholds and should bemanaged in an environmentally sound manner (ESM),
taking into account the Basel Technical Guideline andrequirements in an additional annex adopted by the
Conference of Parties (COP) (Art. 11, para. 2 & 3)
(UNEP, 2019). The entry into force of the Convention haschanged the supply-demand balance worldwide, notably
decreasing the demand for mercury. Inevitably, there will
be an excess of mercury recovered from mercury wastes
and industrial processes. Herein, the amounts of excess
mercury worldwide and in Japan are estimated to reach
24,000 to 25,000 and 600 to 1,400 metric tons,
respectively, by 2050 (Sodeno & Takaoka, 2017). A
variety of concepts, considerations, operations andcombinations of these are available depending on the typeand source of mercury wastes and the situation of eachcountry. As an example, long-term storage, not disposal,of commodity grade mercury in warehouses with safetymeasures is ongoing at the Hawthorne Army Depot in
Global Environmental Research
24/2020: 027-033
printed in Japan

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Nevada, U.S. (UNEP, 2015). On the other hand, mercury
waste is being disposed of for permanent storage inunderground salt mines at depths of 500 to 800 meters
away from the biosphere, e.g., Herfa-Neurode in Hessen,with natural and artificial barriers in Germany (UNEP,
2015). Japan has also taken a defense-in-depth approach,which is purification, stabilization and solidification of
mercury wastes similar to Spain’s sulfur polymer
stabilization/solidification (SPSS) (Fuhrman et al., 2002).
The stabilized and solidified mercury is disposed of in a
specially engineered landfill (SEL), which has been
mandated by an enforcement order of the Waste
Management and Public Cleansing Law since October,2017 in Japan.
The recovery (purification) of elemental mercury
from mercury wastes is performed through thermal
treatment, e.g., a multiple-hearth furnace (Murase &Matsubara, 2013) or rotary kiln (Hawk & Aulbaugh,1998), due to its low boiling point, 356.73°C/629.88 K(Lide, 1999). The elemental mercury kicked out from thewastes into the gas phase is recovered in a cooled
condenser and further purified by successive distillation.
Chemical stabilization of recovered elemental
mercury is plausible because of its unique nature, theonly metal that exists as a liquid at room temperature andlow boiling point. Elemental mercury is chemically©2020 AIRES

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28

stabilized via sulfurization, selenization, amalgamation,etc. (Hagemann, 2009). Sulfurization of metallic mercury
with sulfur powder proceeds spontaneously at room
temperature. Mercury sulfide (cinnabar, α-HgS andmetacinnabar, β-HgS) is a stable and water-insoluble
mineral, and an increase of excess sulfur worldwide isalso expected due to IMO regulation on SOx emissions
from fuel oil (IMO, 2016). Mercury selenide (tiemannite,
HgSe) is also a very stable and water-insoluble mineral,
but its formation reaction cannot proceed at room
temperature and the toxicity of selenium itself is aconcern. Mercury can make an alloy (amalgam) withseveral metals, e.g., zinc, copper or gold. However, thevapor pressure of mercury of those amalgams is not so
low even after amalgamation compared to that ofelemental mercury, and some of the counter metals are
expensive. Accordingly, sulfurization has been the maintechnology adopted for chemical stabilization. We
investigated the feasibility of gas phase sulfurization ofelemental mercury and also wet sulfurization in water fora mercury compound compared to our past research on
dry mechanochemical sulfurization using a planetary ballmill for elemental mercury (Fukuda et al., 2014 andNakamura et al., 2017).
Cement/mortar/concrete (Nakayama et al., 2015),
asphalt/bitumen (Wati et al., 1992) and thermoplastic/
thermosetting resins (Ito et al., 1984) have been widelyused as solidification materials for radioactive waste withpros and cons, and they are also thought to be applicableto sulfurized mercury. Modified sulfur, synthesized bymodifying sulfur with dicyclopentadiene (DCPD) etc.,
was adopted in Japan as the sole solidification material in
the Guidelines on Mercury Wastes to satisfy certain
testing standards, e.g., compressive strength andleachability, (Ministry of the Environment, 2017). We
have been developing a solidification method using athermosetting and impervious epoxy resin for sulfurized
mercury comparable to DCPD-modified sulfur
solidification (Uenishi et al., 2018). The relevance of

Gas inlet

solidification of sulfurized mercury using cement, DCPDmodified sulfur and epoxy resin as solidification materials
was investigated at the laboratory scale. The objective
herein was to demonstrate our laboratory-scalesulfurization and solidification technologies for wastes
consisting of elemental mercury. A cement/mortar/
concrete solidification method was newly developed inthis research, and other methods for sulfurization andsolidification were developed and are summarized here.

2. Materials and Methods
2.1 Sulfurization
2.1.1 Gas Phase Sulfurization
The reaction between mercury (99.5%, Wako) andsulfur (98%, Nacalai Tesque) in the gas phase proceeded
in a vertical tubular electric furnace (FT-POT300-VAC,
Full-Tech) at high temperatures (Fig. 1). The inside
dimensions of the furnace were 20 cm D×40 cm H (ca.
12.6 L). This gas phase sulfurization was examined by
optimizing operating factors such as input molar ratio (S/Hg) of sulfur to mercury (1.05, 1.25, 1.50), temperature(500 °C and 600 °C) and reaction time (0.5 h and 1.0 h)(Hamaguchi et al., 2013). The initial input mercury
amount was set at 40.00 g, and the internal total and O2
partial pressures were 1.5×103 Pa and 100 ppm O2,
respectively. After the reaction, the gas inside the vessel
was drawn from the gas outlet of the vessel into an
impinger filled with 1 M NaOH (as an SO2 absorber),following two impingers with 0.01 M KMnO4 with 3%
H2SO4 using a suction pump at 0.9 L/min for 22 min.
After trapping, the mercury concentration in the KMnO4
solutions was determined according to JIS K 0222.
2.1.2 Wet Sulfurization in the Water Phase
The sulfurization of mercuric chloride (99.5%,
Wako) proceeded with sodium sulfide (98%, Wako) in a
5-L stainless beaker. HgCl2 was dissolved into 4.00 L ofpure water or 0.1 mol/L sulfuric acid solution with an
initial mercury concentration of 1,000 mg Hg/L.

our: cock valvegLighting window
Observation window

Gas outlet

Bourdon gauge

Rotary pump
BourdonB
Cooling fansg

Dew point meter

Oxygen partial pressure gauge
Temperature
B controllergHeaterPirani gauge

Fig. 1 Vertical tubular electric furnace for gas phase sulfurization.

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Sulfurization and Solidification of Wastes Consisting of Elemental Mercury
Following pH adjustment to 7.0 using NaOH or Ca(OH)2,a 10w/v% Na2S solution was added at a molar ratio(S/Hg) of 1.10, and then the excess sulfide was removed
by adding a 10w/v% solution of iron (II) sulfate(99%–102%, Wako). Coagulation was performed tocollect the sulfurized products in the water phase using a
10w/v% aluminum sulfate (>85%, Wako) as a coagulant.
Durations of rapid- and slow-mixings and settlement
were 3, 15 and 10 min respectively. The final products
were obtained by 1.0-μm membrane filtration and driedat 60°C for 48 h (Miyahara et al., 2017).
2.1.3 Dry Mechanochemical Sulfurization
A mechanochemical reaction between elemental
mercury (99.99%, Nomura Kohsan) and sulfur powder(98%, Nacalai Tesque) was attained using a planetary ballmill (BX382, Kurimoto) with two reaction vessels and
25-mm balls. The sulfur powder was added to 1,152 g ofelemental mercury at a molar ratio (S/Hg) of 1.05 in a
2,400-mL vessel, accordingly 2,304 g of metallic mercury
per batch. The operating conditions were ball filling ratio:
30%, centrifugal acceleration: 30×G and reaction time:
60 min (Nakamura et al., 2017). Dry mechanochemicalsulfurization was conducted eleven times (i.e., in
22 vessels) to evaluate its repeatability.
Sulfurized mercury for examination of cement/
mortar/concrete solidification was synthesized usinga planetary mono mill (Pulverisette-6, Fritsch). The
leaching value by Japanese leaching test 46 (JLT-46) andmercury concentration in the headspace were 0.06 μg/L
3
and 1.0 μg/m , respectively (Fukuda et al., 2014).
2.2 Solidification
2.2.1 Cement, Mortar and Concrete Solidifications
The sulfurized mercury was solidified using acement, mortar and concrete. Ordinary Portland cement(Taiheiyo Cement), sand as a fine aggregate (Japan
Cement Association) and gravel as a coarse aggregate(Yura River, Japan) were used as solidification materials
and mixed with sulfurized mercury and water using a29

mixer (KC-8, Kansai Kiki) at a water-cement ratio (w/c)
by weight of 50% (Table 1). Fresh mix was poured into amold (50 mm D×100 mm H) and immediately placed in atemperature and humidity-controlled chamber (25°C and
60%RH) for 24 h. After demolding, membrane curing
was conducted for the cylindrical specimens for 55 days.
Materials recovered after a compressive strength test
were put through a Japanese standard leaching test, JLT13, within a few days.
2.2.2 Modified Sulfur Solidification
Sulfur powder was melted at 135 °C for 10 min in amixer (HIVIS MIX 2P-1, PRIMIX), and modified byadding dicyclopentadiene (DCPD) as a modifier to 5wt%.
After replacement of air by nitrogen gas inside a vessel,
the modification reaction proceeded by mixing at 50 rpm
and 135°C for 1 h. The modified sulfur was cooled atroom temperature for 24 h and then powdered using astamp mill (ANS-143, Nitto Kagaku).
The modified sulfur was melted in the mixer at
130°C for 10 min and mixed with sulfurized mercury at aweight ratio of sulfurized mercury to modified sulfur of
50%. After gas replacement as before, the ingredientswere mixed at 50 rpm and 130°C for 1 h. The mixture
was poured into the mold and allowed to cool at room
temperature for 24 h. (Uenishi et al., 2018). Whentransferring the melted product from the mixer to themold, the mercury concentration in the working
environment was directly monitored using a portablemercury survey meter (EMP-2, Nippon Instruments).
2.2.3 Epoxy Resin Solidification
Two bisphenol A (BPA) epoxy resins and four curing
agents (amines) were selected to explore the optimum
mixing ratio, eight combinations in total, in this research.
A liquid epoxy resin (jER 828) and a curing agent (jER
ST12) were purchased from Mitsubishi Chemical. A lowviscosity liquid epoxy resin (diluted jER 828) and curing
agents (J-882, B-2413, X-7000) were obtained from
Daito Sangyo. The mix ratios were calculated based on
the epoxide equivalent weight (EEW) of the epoxy resins

Table 1 Mix proportions for cement, mortar and concrete solidifications.

Materialw/c

HgS (%)
20
40
60

HgS (g)
200
400
300

Cement (g)
800
600
200

FA (g)-CA (g)-

Water (g)
400
300
100

0.60

20
40
60

200
400
600

800
600
400

-

-

480
360
240

Mortar

0.50

5
10
20

60
120
240

400
400
400

740
680
560

-

200
200
200

Concrete

0.50

5
10

75
150

250
250

425
350

750
750

125
125

0.50
Cementw/c: a water-cement ratio by weight, FA: fine aggregate, CA: coarse aggregate.

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T. KUSAKABE and M. TAKAOKA

and the amine hydrogen equivalent weight (AHEW) of
the curing agents. The epoxy resin, sulfurized mercury
and curing agent were mixed in a plastic beaker by handor agitator (BLh300, Shinto Scientific) at weight ratios ofsulfurized mercury of 0%, 50%, 60%, 70%, 80% and
90% against the epoxy resin and curing agent. The 48
combinations (eight epoxy resins and six weight ratios ofsulfurized mercury) were finally examined. The mixtures
were poured into the mold and cured at 40°C for 16 h
(Uenishi et al., 2018).
2.3 Testing and Analytical Methods
2.3.1 Compressive Strength
The testing method for the compressive strength of
concrete (JIS A 1108:2018) was applied to specimens
solidified in the mold (50 mm D×100 mm H). A
minimum compressive strength of 0.98 MPa is required
as a landfill standard in Japan.
2.3.2	Japanese Standard Leaching Tests (JLT-13 andJLT-46)The JLT-13 test is designed to evaluate theleachability from industrial wastes compared to landfill
standards by a single batch extraction. Solidified
specimens were pulverized into 0.5–5 mm and mixed
with water at a liquid to solid ratio (L/S) of 10. Following
shaking at 20 °C for 6 h, the liquid extracts were obtainedby 1.0-μm membrane filtration and the dissolved mercury
concentration determined using a reducing-vaporization
mercury analyzer (RA-4300, Nippon Instruments). The
landfill standard for mercury and its compounds is 5 μg/Lor less in Japan.
JLT-46 is a test method to judge whether theenvironmental standard for soil is met or not. JLT-46 issimilar to JLT-13, but the sample size (less than 2 mm)
and pore size (0.45 μm) of the membrane filter differ.
Japanese environmental standard for mercury and its
compounds in soil is 0.5 μg/L or less.
2.3.3 Headspace Test
The mercury concentration in the headspace above
the samples (sulfurized mercury and sulfurized/solidified
mercury) was determined using continuous mercury
analyzers (MS-1A/DM-6B or WLE-8/EMP-2, Nippon
Instruments) (Fukuda et al., 2014). The headspaceconcentration of mercury for stabilized/solidified mercury
wastes is not regulated in Japan, so the provisional
3
regulatory standard of the EU (3 μg/m )—the limit ofdetection of a used analytical instrument (BiPRO,
2010)—and the working environment evaluation standard
for mercury in Japan (25 μg/m3) were referred to as
temporal criteria in this research.
2.3.4 Tank Leaching Test
The Japanese tank leaching test is a diffusion test toevaluate the leaching behavior from monolithic
specimens using a single static-tank leaching procedure(Ministry of Construction, 2000). After allowing the tankto stand at 20 °C for 28 days, the mercury concentration

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in the 0.45-μm membrane filtered samples wasdetermined using the RA-4300.
2.3.5	Powder X-ray Diffraction (XRD) and Rietveld
Refinement
The XRD (Cu-Kα1) pattern of the sulfurized products
was obtained using an X-ray diffractometer (RINTUltimaPC, Rigaku), and its Rietveld refinement was
conducted to quantitatively calculate the percentage of
cinnabar and metacinnabar in the sulfurized mercury.

3. Sulfurization
3.1 Gas Phase Sulfurization
Recovered mercury ranged from 60% –70% on
average, and sulfurized mercury existed mainly as
cinnabar in the products of gas phase sulfurization. The
results of gas phase sulfurization are shown in Tables 2
and 3 (Hamaguchi et al., 2013). When the mix ratio of
S/Hg was set to 1.05 and 1.50 at 500/600 °C for 1.0 h,
the resulting products satisfied the environmental
standard for soil under JLT-46. However, the case in thecondition of S/Hg = 1.25 did not satisfy it. The
mercury concentrations in the headspace of the resulting
products were below the EU’s provisional regulatory
3
standard (3 μg/m ) when S/Hg was 1.25 at 500/600°C
and when S/Hg was 1.50 at 500°C for 1.0 h, whereas
the others exceeded the standard. As a result, our gas
phase sulfurization was a little unstable, but the propertiesof the resulting products were comparable to DELA’s
assessment, in which the leaching value was less than
50 μg/L (9 μg/L on average) by German DEV S4/ DIN
38 414-4 and the mercury vapor pressure was below
3 μg/m3 (Hagemann, 2009).
The mercury concentration within the vessel after
the reaction (157–389 μg/m3) was one order of magnitude
Table 2 Leaching values (μg/L) of resulting products in gas phasesulfurization by JLT-46 (mean ± SD, N = 3).
Reaction time (h)0.5Temperature (°C)
1.05
S/Hg

500

1.0
600

500

600

8.42 ± 0.63 8.75 ± 0.20

0.32 ± 0.00 0.24 ± 0.01

1.25

7.86 ± 0.04 6.62 ± 0.14

1.23 ± 0.06 0.68 ± 0.05

1.50

6.10 ± 0.34 4.25 ± 0.02

0.06 ± 0.00 0.20 ± 0.00

Underlines indicate values below the environmental standard (0.5 μg/L).

Table 3 Mercury emissions (μg/m3) from resulting products in gas
phase sulfurization.
Reaction time (h)Temperature (°C)
S/Hg

0.5

1.0

500

600

500

600

1.05

32.9

39.9

35.8

56.9

1.25

54.9

30.7

1.6

0.8

1.50

4.3

9.8

1.6

21.0

Underlines indicate values lower than 3 μg/m3.

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Sulfurization and Solidification of Wastes Consisting of Elemental Mercury

3.2 Wet Sulfurization
Mercuric ion (Hg2+) with an initial concentration of
1,000 mg as Hg/L was quantitatively recovered as amercury sulfide through a wet sulfurization process in theconditions of both pure water and dilute sulfuric acid(0.1 mol/L). XRD analysis demonstrated that the resulting
products were a metacinnabar showing low crystallinity
compared to that by dry mechanochemical sulfurization(Fukuda et al., 2014). The leaching values of all resulting
products from wet sulfurization satisfied the JLT-13
standard (5.0 μg/L) and those mercury emissions were
below 0.1 μg/m3 (Miyahara et al., 2017). A drying process
is additionally necessary due to high water content (ca.
80%) of the products. In the case of dilute sulfuric acid asa solvent, the gypsum content as a by-product exceeded
90% in the products, which is undesirable from theviewpoint of volume reduction.
3.3 Dry Mechanochemical Sulfurization
All resulting products in dry mechanochemicalsulfurization satisfied the JLT-46 standard (0.5 μg/L orless), and the mercury concentration in the headspace was
1.7 ± 1.5 μg/m3 (mean ± SD), with 18 out of 22 samples(86%) satisfying the EU’s provisional regulatory standard(3 μg/m 3). XRD-Rietveld analysis demonstrated thepercentage of cinnabar, which is a relatively more stable
crystal than metacinnabar, in the sulfurized mercury was
48.6%.
Overall, dry mechanochemical sulfurization canstabilize elemental mercury with high repeatability.
Calculated under conditions of five days/week and
52 weeks/year, three operations per day (6.9 kg/day at
optimum conditions) could give an annual treatment
capacity of ca. 1,800 kg/year even with the small pilot
mill machine.
As a conclusion so far, dry mechanochemicalsulfurization has advantages and greater reliability than
the gas phase and wet sulfurization processes.

4. Solidification
Mercury sulfurized by dry mechanochemicalsulfurization was used for examining solidification
methods. The results of JLT-13 and the headspace test forsulfurized mercury were below 5.0 μg/L and 3 μg/m3,
respectively.
4.1 Cement, Mortar and Concrete Solidification
The results of compressive strength, JLT-13 and tankleaching test for cement/mortar/concrete solidified
products are summarized in Table 4. One mortar-

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Table 4 Compressive strength and leaching values of cement,
mortar and concrete solidified products.
Material

w/c HgS (%)

0.50
Cement0.60

Mortar

0.50

Concrete 0.50

20
40
60
20
40
60
5
10
20
5
10

Compressive strength Leaching value (μg/L)(MPa)
JLT-13 Tank leaching

46.2
27.1
31.3
18.3
18.2
16.3
34.0
37.7
39.3
20.8
27.0

0.34
0.20
0.11
0.25
0.32
0.27
0.24
0.34
0.38
0.10
0.07

0.16
0.25
0.06
0.10
0.12
0.22
0.96
0.26
3.41
0.16
0.05

w/c: water-cement ratio by weight. Compressive strength was evaluated ata material age of 56 days.

30

Leaching values (µg/L)

higher compared to the working environment evaluation
standard for mercury in Japan (25 μg/m3). Under thesecircumstances, leakage of mercury from the vessel
becomes a big concern in gas phase sulfurization.

31

JLT-13JLT-46
Linear fit (JLT-13, R2 = 0.746, N = 12)
Linear fit (JLT-46, R2 = 0.710, N = 12)

25
20
15
10
5
0

0

4

8
Cement/HgS (g/g)

1216

Fig. 2 
Relationship between the leaching behavior of mercury
under JLT-13/-46 and the mix ratio of high early strengthPortland cement to sulfurized mercury from a preliminary
examination. Specimens solidified with concrete (HgS = 1,
5, 10 wt%) and cement (HgS = 40 wt %) with a water/cement
ratio of 0.50 were cured in water for a week.

solidified specimen (HgS, 20%) exhibited high leachingvalues in the tank leaching test, whereas all the solidified
specimens including mortar-solidified products satisfied
landfill standards (5 μg/L or less) under JLT-13. All of thecement- and concrete-solidified products satisfied thestandards, but the sulfurized mercury content of theconcrete-solidified specimens was relatively lower thanthat of the cement-solidified ones. Our preliminary
examination of cement and concrete solidification using ahigh early strength Portland cement (Sumitomo Osaka
Cement) demonstrated a positive correlation between theleaching behavior of mercury under JLT-13/-46 and themix ratio of cement to sulfurized mercury (cement/HgS
by weight) (Fig. 2). This is consistent with the fact thatthe solubility of HgS drastically increases under alkalineconditions (pH > 10) (Kadotani et al., 2009), whichsuggests that if the mixture of solidification material(s)and sulfurized mercury can be cured to achieve the2020/07/30

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T. KUSAKABE and M. TAKAOKA

requirements, a lower ratio of cement would be preferable
to suppress mercury leaching.

advantages similar to or better than that with DCPDmodified sulfur.

4.2 Modified Sulfur Solidification
Solidification of sulfurized mercury with DCPDmodified sulfur at a weight ratio of 1:1 was conductedfollowing the Guidelines on Mercury Wastes in thisresearch. The results of compressive strength, JLT-13 andheadspace test for sulfurized/solidified mercury withmodified sulfur were 30.6 MPa, 0.05 μg/L and <0.1 μg/m3, respectively, all of which satisfied standards(Uenishi et al., 2018). The tank leaching test
demonstrated lower leaching behavior (< 0.01 μg/L) of
mercury from a monolith solidified with DCPD-modified
sulfur compared to that (0.05 μg/L) from pulverized
monolith (0.5–5 mm) by JLT-13’s protocol. Modified
sulfur solidification is effective and successful at
encapsulating sulfurized mercury. When opening thevessel, mercury vapor was detected at ca. 5.0 μg/m 3,
which is below the Japanese working environment
evaluation standard (25 μg/m3).

5. Conclusions

4.3 Epoxy Resin Solidification
Following a screening examination based on JLT-13
and the headspace test, the optimum mix ratio wasdecided as follows: epoxy resin: jER 828, curing agent:
B-2413, and weight ratio of sulfurized mercury: 80%.
B-2413, 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), isa highly-reactive cycloaliphatic diamine, which offers
advantages in UV resistance and clarity owing to its lackof conjugated double bonds; heat resistance due to highglass transition temperature (Tg), curing even at low
temperature and high humidity; and cost saving throughmaterial reduction due to its low AHEW.
The results of compressive strength, JLT-13 and theheadspace test for sulfurized mercury solidified with the
epoxy resin were 107.0 MPa, 0.09 μg/L and < 0.1 μg/m3,
respectively, all of which satisfied standards (Uenishi etal., 2018). The tank leaching test showed lower leaching
behavior (< 0.01 μg/L) of mercury from a monolith
solidified with the epoxy resin compared to that
(0.09 μg/L) from a pulverized monolith (0.5–5 mm)
under JLT-13’s protocol. Epoxy resin solidification is also
effective and successful at encapsulating sulfurized
mercury.
The mercury concentration in the curing chamberincreased up to 1.0 μg/m3 at a maximum as the central
temperature in the mold increased up to 150°C about
15 min after curing started, after which it decreased.
When solidifying the same weight of sulfurized mercury,the volume of the monolith of epoxy resin was roughly
half that of the DCPD-modified sulfur.
Seven epoxy resins other than the optimum one (jER
828 and B-2413) can still solidify sulfurized mercury at aweight ratio of 70% and satisfy standards. As a result,solidification of sulfurized mercury with epoxy resin has

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A comprehensive examination was conducted toestablish stabilization and solidification technologies for
disposal of wastes consisting of elemental mercury in
SELs. We conclude that dry mechanochemicalsulfurization of elemental mercury using a planetary ballmill has advantages and reliability over gas phasesulfurization of elemental mercury and wet sulfurizationof an inorganic mercury compound in the water phase.
However, it is necessary to check whether thesulfurization reaction by the dry mechanochemical
process is properly proceeding for each lot. The drymechanochemical process has an annual treatment
capacity of ca. 1,800 kg/year. Epoxy resin solidification
has advantages similar to or better than DCPD-modified
sulfur solidification, which has been adopted in the
Guidelines on Mercury Wastes in Japan. We propose
epoxy resin solidification as an alternative solidification
technology. Further research will be required to evaluate
and secure long-term stability of sulfurized and solidified
mercury wastes in SELs.

Acknowledgements
We do appreciate the enormous experimental support
by Dr. Akira Sano, Kenji Shiota, Naomichi Fukuda,
Daisuke Hamaguchi, Shunta Nakamura, Mutsumi
Miyahara and Ryuta Uenishi. The pilot-scale sulfurization
was performed using a planetary ball mill offered byBarrick Gold Corporation and Kurimoto, Ltd. This
research was financially supported by the Environment
Research and Technology Development Funds(3K113001, 3K143002, 3-1701) of the Environmental
Restoration and Conservation Agency of Japan.
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Taketoshi KUSAKABE
Taketoshi Kusakabe is an assistant professor at
the Graduate School of Engineering, Kyoto
University, Japan. He graduated from the
Department of Environmental Science andTechnology at Okayama University, receiving his
B.Sc. in 1999. He received his M.Eng. and Ph.D.
in Global Environment Engineering from Kyoto
University in 2001 and 2007, respectively. His current research interests
include stabilization/solidification technologies for mercury wastes,
mercury emission control using impregnated activated carbon,
comprehensive analysis and scientific understanding of natural organic
matter (NOM), linkages between microbial carbon pumps (MCP) andrefractory dissolved organic matter (RDOM), and integrated lake basin
management (ILBM).

Masaki TAKAOKA
Masaki Takaoka is a professor in the Departmentof Environmental Engineering, Graduate Schoolof Engineering, Kyoto University, Japan. He is amember of the Minamata Convention Group ofTechnical Experts on Mercury Waste Thresholds
and a resource person under the UNEP Global
Mercury Partnership ― Waste Management
Partnership Area. His main research subject is management and treatmentof solid waste. He is particularly interested in controlling toxic substancessuch as heavy metals including mercury, persistent organic pollutants andradioactive nuclides in waste treatment processes and waste-to-energy
projects.
(Received 27 December 2019, Accepted 8 June 2020)

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