Sonoleaching: Development of a rapid determination of Pb ... - SER

Sustain. Environ. Res., 21(6), 375-380 (2011) 375
Sonoleaching: Development of a rapid determination of Pb
from stabilized waste using ultrasound assisted leaching
Luzvisminda M. Bellotindos, Maria Lourdes P. Dalida, Genandrialine L. Peralta,
3, 2
Ming-Chun Lu * and Herman D. Mendoza
1 2 2
1
Office of Research and Extension
Universidad de Zamboanga
Zamboanga City 7000, Philippines
2
Department of Chemical Engineering
University of the Philippines-Diliman
Quezon City 1101, Philippines
Department of Environmental Resources Management
Chia Nan University of Pharmacy and Science
Tainan 71710, Taiwan
3
Key Words: Ultrasound assisted extraction, heavy metals, Pb, TCLP
ABSTRACT
This study develops an ultrasonic assisted leaching procedure, known as sonoleaching process
for determination of Pb from stabilized waste that could improve the Toxicity Characteristic Leaching
Procedure (TCLP) of the United States Environmental Protection Agency. The TCLP is a regulatory
procedure which requires 18 h of extraction for the determination of hazardous wastes/contaminants
as to its toxicity characteristic. The results show that it improves this regulatory procedure by shortening
the extraction time by 97%, decreasing the weight of waste to be used in the analysis by 95%
and decreasing the volume of the extraction fluid used by 95%. The significant improvement in the
TCLP is due to the application of ultrasound irradiation using an ultrasonic bath cleaner. Lead is the
major heavy metal selected in this study. The solid waste in this study is slag from a Pb recovery
smelting plant. The sonoleaching of slag and stabilized slag follows a second order kinetics. The
optimal ultrasonic conditions that give a comparable recovery in TCLP are as follows: a sonication
time of 30 min and initial bath temperature of 30 °C. .
*Corresponding author
Email: mmclu@mail.chna.edu.tw
INTRODUCTION
One common consequence of growing population,
new technologies, new products and services is the
increasing volume of wastes produced. These wastes
have to be properly characterized for appropriate treatment,
re-use, recycle, storage and disposal. The United
States Environmental Protection Agency (USEPA)
developed the protocol for the determination of one of
the characteristics for a waste to be classified as hazardous,
the toxicity characteristic (the others being,
corrosive, flammable and reactive). This procedure,
called the Toxicity Characteristic Leaching Procedure
(TCLP designated as USEPA SW-846 Method 1311)
was designed based on a mismanagement scenario of
co-disposal of this waste with municipal waste in a
landfill [1]. This co-disposal of wastes (for design
development purpose was assumed to be 95% municipal
waste, 5% hazardous waste) would produce leachate
from which heavy metals and organic toxic chemicals
from the hazardous waste may leach out to pollute
the environment. The USEPA identified the eight
heavy metals (in addition to the organic compounds)
of concern and has set the standard limits for a waste
to be considered as hazardous. The eight metals are
Arsenic, Barium, Cadmium, Chromium, Lead, Mercu-
ry, Selenium, and Silver.
As a regulatory procedure, USEPA mandates that
wastes must pass the TCLP test before they can be
disposed in a landfill. However, EPA uses the TCLP in
other programs to measure the adequacy of a waste
treatment method, in risk assessment, as a primary test
for evaluating effectiveness of stabilization/solidification
treatment of media contaminated with metals
and as an accepted approach to generate input data for
groundwater risk model [2]. The TCLP was also used
to predict leaching in situations other than the assumptions
that were considered when the procedure was
developed.
Generators of waste must test their wastes using
USEPA SW-846 Method 1311 to determine if the
leaching potential is greater than the toxicity characteristic
specified in 40 CFR 261.24. For compliance to the
regulation, the TCLP must be performed as written or
.
.

376 Bellotindos et al., Sustain. Environ. Res., 21(6), 375-380 (2011)
the results are not valid for the purposes of determining
whether the waste is hazardous based on toxicity
characteristic.
.
In the Philippines, Congress enacted many laws to
address the management and control of increasing
volume of wastes produced. One of these laws, the
Toxic Substances and Hazardous and Nuclear Wastes
Control Act of 1990 (Republic Act 6969), was enacted
in response to the increasing problems related to toxic/hazardous
chemicals and nuclear wastes in the country.
The implementing rules and regulations of this Act
require the use of TCLP.
.
Rossi [3] described leaching as a complex dissolution
process that requires suitable reactants in aqueous
solution to come in contact with the mineral particles
to be dissolved. TCLP estimates the extent of leachability
of hazardous constituents from solid wastes under
certain conditions. This procedure consists of many
components, one of which is the extraction with simulated
leaching fluid using a rotary apparatus for 18 h.
This, in addition to the time for sample preparation before
extraction and the final separation of liquid and
solid phases for final analysis of the target constituents,
is time consuming. The total time for a TCLP determination
can reach 22 h.
.
This limitation of TCLP may be addressed by replacing
the 18-h contact time in a rotary extractor with
ultrasound assisted extraction. Ultrasound is the sound
with frequency beyond the human hearing threshold
[4]. The human hearing frequency is normally 16 to 18
kHz. The use of ultrasound in extraction has been
gaining popularity in the past decade although researches
on ultrasonics started in the late 1920s and
into 1940s [5], but interest on the application of ultrasound
dates back more than 100 yr [6]. Ultrasound is a
useful tool in enhancing reaction rates in many reaction
systems. This rate enhancement is called
sonochemistry.
.
Sonochemistry, which is the use of ultrasound to
enhance or alter chemical reactions [6], began in the
late 1800s. However, as mentioned by Thompson and
Doraiswamy [6] in their review paper on sonochemistry,
the term was first used by Neppiras in 1980
in his review of acoustic cavitation. Chemical effects
of ultrasound include improved conversion and yield,
change in reaction pathway or initiation or reactions in
chemical, biological or electrochemical systems.
Ultrasound also results in physical effects which
include increasing the surface area of the reactants and
accelerating dissolution.
.
The driving force in sonochemistry is cavitation;
the formation, growth and implosive collapse of bubbles
in a liquid [7,8] which generates heat and produces
intense local heating (5000 °C) and high pressure
(200 MPa). This type of cavitation resulting from
the application of sound waves is known as acoustic
cavitation [9]. The effect of cavitation within the liquid
depends on the type of system where it is generated. In
the case of a solid-liquid system, cavitation collapse
near a particle can lead to shock waves that can break
the particle apart or force it into rapid motion. These
result in interparticle collisions that cause erosion,
wetting of the particles, surface cleaning and particle
size reduction [4].
Many studies have been conducted on the various
applications of ultrasound including the effects of ultrasound
assisted extractions of metals from soils, sediments
and solid wastes. In these studies, researchers
found that ultrasound provided savings in extraction
time. Collasiol et al. [10] developed and established a
method for mercury extraction in sediment and soil
using ultrasound and results showed that the method
was fast and mercury loss was prevented. The leaching
yield of the silver content of a mining waste was investigated
by Öncel et al. [11]. The experiment showed
that silver may be leached almost completely from the
solid waste of a silver ore plant by means of ultrasound
assisted thiourea leaching method.
Al-Merey et al. [12] investigated the experimental
conditions of an ultrasonic cleaning bath for quantitative
extraction of lead, copper and zinc metals from
soil samples. The results showed that the performance
of the method was equal to a hot-plate digestion method
and significantly reduced the hazardous and
fumehood emissions.
Mason et al. [13] reviewed current laboratory
research and potential for the scale-up of chemical
decontamination using ultrasound and concluded that
the use of ultrasound in the laboratory cleaning of soil
samples proved to be effective and some large scale
trials showed promise. Meegoda and Perera [14] in an
attempt to develop a technology to decontaminate
heavy metals in dredged sediment using ultrasound
coupled with vacuum pressure concluded that although
the clay fraction could not be effectively treated by this
technology, chromium was immobile in the clay fraction
of the treated sediment and was safe for disposal.
Marin et al. [15] developed a method for determination
of zinc and arsenic speciation in soils using focused
ultrasound. The method, which replaced extraction
with mechanical shaking by sonication to simplify
analytical procedures was optimized and validated.
In a study by Perez-Cid et al. [16], the use of focused
ultrasound was applied to a sludge sample to
shorten the operation time in each of the stages corresponding
to a sequential extraction method proposed
by the Community Bureau of Reference (BCR). The
sonication conditions (sonication power and time) were
optimized and extraction of copper, chromium, nickel,
lead and zinc was compared with the conventional
three stage sequential extraction method. The use of
ultrasound represented a valid alternative to the con-
ventional shaking and reduced the operation time.
In a similar work, the use of ultrasound provides a
saving in extraction time relative to a conventional
mechanical shaking as shown by Kazi et al. [17] who
developed a rapid version of the three-stage BCR
sequential extraction to release heavy metals from
.
.
.
.
.

untreated waste samples. The use of ultrasonic bath
offered the advantage of replicate extractions that can
be carried out simultaneously. Munoz et al. [18] proposed
a combination of ultrasonic extraction and stripping
technique (anodic stripping voltammetry) for
routine analysis of copper and lead determination in
lubricating oil samples. The method which used an
ultrasonic bath provided the advantage of simultaneous
sample pretreatment. Bellotindos [19] showed that
sonication is better than extraction by TCLP on extraction
of Pb from synthetic soil. Table 1 lists some
studies on Pb leaching by various sonoleaching operation
(frequency and time). .
Table 1. Some studies on ultrasound assisted
extraction of Pb
Sample
BCR certified
reference sediments
Extraction
time (min)
5-60
Frequency
(kHz)
Edible seaweed 10 35
Sediments 5-35 50-60
To determine the effects of two or more factors or
how these factors interact with each other, experiments
are performed. In the past, the one-factor-at-a-time
approach, where one factor is varied over the range of
given condition while keeping all other factors constant,
was practiced. This method is time consuming
and does not consider the interaction between factors
[23]. The Design of Experiment is a planned approach
in determining cause and effect relationship [24] using
inputs and outputs that can be measured. This approach
has become a strategy of researchers to shorten the
time of the study in terms of the number of experimental
runs and to save on expensive trials. To optimize
multivariate systems, statistical software packages
such as Design-Expert 7 are used by researchers.
Optimization is achieved by Factorial Design analysis
[25,26], Fractional Factorial Design [27,28] or Re-
sponse Surface Methodology [29].
There is a growing concern for the increasing
amount of Pb as a contaminant in the environment and
as an environmental health issue. It poses great risks to
human health due to its proven toxicity. This research
explored the use of an ultrasound assisted leaching for
a rapid determination of Pb from stabilized waste. In
this study, stabilized waste from slag was made to find
out the effects of ultrasound in extracting the metal and
comparing it with TCLP extraction and to find out the
mechanism of extraction with ultrasound. The optimal
conditions comparable to TCLP extraction were determined.
.
MATERIALS AND METHODS
1. Chemicals and Analytical Methods .
Bellotindos et al., Sustain. Environ. Res., 21(6), 375-380 (2011)
% Pb
extracted
48-54
0.6-1.4
-1
(µg g )
7.6 -1
(µg g )
Reference
Canepari et al.
[20]
Dominguez-
Gonzalez
et al. [21]
Elik
[22]
.
The water for all solution preparations was ultrapure
water (18.27 MÙ cm at 29 °C) supplied by
RODA ultrapure water systems. Pb was analyzed using
PerkinElmer AAnalyst 200 Atomic Absorption Spectrophotometer.
The rotary agitator for the TCLP was
supplied by Cherng Huei Co. (Taiwan), Model RA-
326, 40 W, 110 V with timer and rpm control. The
temperature feature of the Suntex conductivity meter
was used to measure temperature.
.
2. Sonoleaching Set-up
The source of ultrasound was DELTA Ultrasonic
Cleaner (tank capacity = 10.8 L, operating frequency
= 40 kHz). The ultrasonic bath has a temperature and
time control which can be changed in increments of 1.
The reaction flask is suspended by the use of a clamp
and the level of the liquid in the reaction bath is kept at
the level of the water bath. The bath temperature is
monitored by the temperature feature of a Suntex conductivity
meter. Figure 1 shows the actual picture of
the set-up.
.
3. Extraction Procedures
377
For extraction by TCLP, the USEPA SW-846
Method 1311 was used. For ultrasound procedure, distilled
water was poured into the ultrasonic bath to a
level about 5.1 cm from the rim and degassed for 5-10
min. An amount of the sample was weighed into a 250
mL Erlenmeyer flask. The extraction fluid (TCLP ex-
Fig. 1. Sonication set-up.
traction fluid) was added using the solid to liquid ratio
of 1:20. Five flasks were prepared for the different
ultrasound exposure time (15-90 min). The flask was
suspended in the bath such that the level of the extraction
fluid in the flask was at the same level as the water
in the tank. A temperature probe was suspended at the
same level as the bottom of the flask. The duration
time was set and ultrasound was applied. The bath
temperatures at the start and end of sonication were
noted. The concentration of the Pb in the extract was
determined by Atomic Absorption Spectrometer. .
.
.

378
4. Preparation of the Stabilized Slag
The waste sample used in this study is a slag from
a Pb recovery smelting plant. The slag was pulverized
to pass sieve #35 (0.5 mm). Ordinary Portland cement
was used to stabilize the slag. A 1:1 ratio of slag to
cement was used. 750 g of slag and 750 g of ordinary
Portland cement were weighed and thoroughly mixed.
Deionized water was added until a paste like consistency
was obtained. The mixture was then poured into
a mould and allowed to cure for 3 wk. After the curing
period, the stabilized waste was then pulverized again
to pass sieve #35.
.
5. Design of Experiment
The Design-Expert 7 [30] consists of three major
parts, the actual design, the analysis process and the
optimization. In the actual design, the factors, parameters
and expected responses considered in the study
are used to determine the minimum number of runs.
The response data are then used in the analysis process
which includes full analysis of the variance. The optimization
part determines the combination of factors
and responses that simultaneously satisfy the requirements
of the factors and responses.
.
RESULTS AND DISCUSSION
A second order equation based on dissolution [31]
can be expressed in the form:
(1)
Where k = rate constant of second order dissolu-
tion, S = maximum dissolution (g), S = solubility (g),
max
and T = sonication time, min
The equation is then linearized to:
(2)
Where intercept = r = initial dissolution rate =
1/(k S ) and slope = reciprocal of the dissolution
max
equilibrium = 1/S .
max
The straight lines in Figs. 2a and 2b are the graphs
of the linearized form of the second order dissolution
equation (Eq. 2) which shows that dissolution of Pb
with ultrasound follows a second-order kinetics. Table
2 shows the values of S , r and k for the slag and
max
stabilized slag as determined from the lines in Figs. 2a
and 2b.
.
The optimization feature of the Design-Expert 7
can generate a combination of solutions for optimal
conditions. These are ranked in the order of desirability.
Table 3 shows the optimization criteria for the
determination of optimal conditions. For factors [Pb]
and temperature, the criteria are the values used in the
study. 30 min was chosen as the sonication time as
Bellotindos et al., Sustain. Environ. Res., 21(6), 375-380 (2011)
.
.
.
.
.
Table 2. Dissolution rate and rate constant for extraction
of Pb in slag and stabilized slag
-1
S max (% Pb g sample)
Dissolution Rate (r)
-1 -1
(% Pb min g sample)
t / S
Rate constant (k)
12
10
8
6
4
2
Slag Stabilized Slag
31.5 12.1
0.16
0.0064
0.05
0.13
0
0 20 40 60 80 100 120 140
Time (min)
Fig. 2. Second order dissolution of Pb (a) original slag (b)
stabilized slag.
this was the time that equilibrium was attained during
sonication. For the % Pb extraction, the value 80 was
chosen as this was the average of the TCLP extractions.
Of the several combinations that were generated, the
conditions with comparable extraction to TLCP were
sonication time of 30 min and temperature of 30 °C. .
Table 3. Optimization criteria for the determination of
optimal conditions
Factor
[Pb], ppm
Temperature, °C
Sonication Time, min
% Pb extraction
CONCLUSIONS
(b)
(a)
Criteria
500-5000
25-30
30
80
Using the optimization feature of the Design-
Expert 7 Software, the optimal conditions for an extraction
comparable to TCLP are: sonication time = 30
min and the ultrasonic cleaner bath temperature =
30 °C. The 30 min sonication time as compared to the
TCLP extraction of 18 h, means that the extraction
time has been reduced by about 97% and a bath temperature
of 30 °C means that the temperature can easily
be obtained as it is about the ambient temperature
and there is no need to monitor the ultrasonic bath until
the end of the sonication. The sonoleaching of lead
from slag and stabilized slag is a second order dissolution
process. Extraction with the use of ultrasound did
not result in chemical changes but rather physical
changes occurred. The weight of the waste and the

volume of the extraction fluid used in the procedure
have also been both reduced by 95%.
.
ACKNOWLEDGEMENT
The authors wish to acknowledge the National
Science Council of Taiwan for the financial support
under contract no. NSC 96-2628-E-041-001-MY3. .
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REFERENCES
US Environmental Protection Agency (USEPA),
SW-846 Method 1311: Toxicity Characteristic
Leaching Procedure. USEPA, Washington, DC
(1992).
.
Helms, G., Background Discussion of SAB/EEC
Consultation on Leach Testing. USEPA, Washington,
DC (2003).
.
Rossi, G., Biohydrometallurgy. McGraw-Hill,
Hamburg, Germany (1991).
Sonochemistry Centre, Introduction to
Sonochemistry. Sonochemistry Centre, Coventry,
UK. http://www.sonochemistry.info/introdution.
htm (2007).
.
Abramov, O.V., Ultrasound in Liquid and Solid
Metals. CRC Press, Boca Raton, FL (1994). .
Thompson, L.H. and L.K. Doraiswamy,
Sonochemistry: Science and engineering. Ind. Eng.
Chem. Res., 38(4), 1215-1249 (1999). .
Mason, T.J., Ultrasound in synthetic organic
chemistry. Chem. Soc. Rev., 26(6), 443-451
(1997).
Suslick, K.S., The chemistry of ultrasound. In D.
Calhoun (Ed.). Yearbook of Science and the Future
1994. Encyclopedia Britannica, Chicago, IL, pp.
138-155 (1993).
.
Gogate, P.R., R.K. Tayal and A.B. Pandit,
Cavitation: A technology on the horizon. Curr.
Sci., 91(1), 35-46 (2006).
Collasiol, A., D. Pozebon and S.M. Maia, Ultrasound
assisted mercury extraction from soil and
sediment. Anal. Chim. Acta, 518(1-2), 157-164
(2004).
Öncel, M.S., M. Ince and M. Bayramoglu, Leaching
of silver from solid waste using ultrasound
assisted thiourea method. Ultrason. Sonochem.,
12(3), 237-242 (2005).
Al-Merey, R., M.S. Al-Masri and R. Bozou, Cold
ultrasonic acid extraction of copper, lead and zinc
from soil samples. Anal. Chim. Acta, 452(1), 143-
148 (2002).
Mason, T.J., A. Collings and A. Sumel, Sonic and
ultrasonic removal of chemical contaminants from
soil in the laboratory and on a large scale.
Ultrason. Sonochem., 11(3-4), 205-210 (2004). .
Meegoda, J.N. and R. Perera, Ultrasound to decontaminate
heavy metals in dredged sediments. J.
Hazard. Mater., 85(1-2), 73-89 (2001). .
Marin, A., A. Lopez-Gonzalvez, and C. Barbas,
Bellotindos et al., Sustain. Environ. Res., 21(6), 375-380 (2011)
.
.
.
.
.
.
.
Development and validation of extraction methods
for determination of zinc and arsenic speciation in
soils using focused ultrasound Application to
heavy metal study in mud and soils. Anal. Chim.
Acta, 442(2), 305-318 (2001).
.
16. Perez-Cid, B., I. Lavilla and C. Bendicho, Speeding
up of a three-stage sequential extraction method
for metal speciation using focused ultrasound.
Anal. Chim. Acta, 360(1-3), 35-41 (1998). .
17. Kazi, T.G., M.K. Jamali, A. Siddiqui, G.H. Kazi,
M.B. Arain and H.I. Afridi, An ultrasonic assisted
extraction method to release heavy metals from
untreated sewage sludge samples. Chemosphere,
63(3), 411-420 (2006).
.
18. Munoz, R.A.A., P.V. Oliveira and L. Angnes,
Combination of ultrasonic extraction and stripping
analysis: An effective and reliable way for the determination
of Cu and Pb in lubricating oils.
Talanta, 68(3), 850-856 (2006).
.
19. Bellotindos, L.M., Sonoleaching: Development of
a Rapid Determination of Pb from Stabilized
Waste Using Ultrasound Assisted Leaching. Ph.D.
Dissertation, University of the Philippines
Diliman, Quezon City, Philippines (2009). .
20. Canepari, S., E. Cardarelli, S. Ghighi and L.
Scimonelli, Ultrasound and microwave-assisted
extraction of metals from sediment: A comparison
with the BCR procedure. Talanta, 66(5), 1122-
1130 (2005).
.
21. Dominguez-Gonzalez, R., A. Moreda-Pineiro, A.
Bermejo-Barrera and P. Bermejo-Barrera, Application
of ultrasound-assisted acid leaching procedures
for major and trace elements determination
in edible seaweed by inductively coupled plasmaoptical
emission spectrometry. Talanta, 66(4), 937-
942 (2005).
.
22. Elik, A., Ultrasonic-assisted leaching of trace
metals from sediments as a function of pH.
Talanta, 71(2), 790-794 (2007).
.
23. Montgomery, D.C., Design and Analysis of Experiments.
5th Ed., John Wiley, New York (2001). .
24. Anderson, M.J. and P.J. Whitcomb, DOE Simplified:
Practical Tools for Effective Experimentation.
2nd Ed., Productivity Press, New York
(2007).
.
25. Vila, D.H., F.J.H. Mira, R.B. Lucena and M.F.
Recamales, Optimization of an extraction method
of aroma compounds in white wine using ultrasound.
Talanta, 50(2), 413-421 (1999). .
26. Jalbani, N., T. Kazi, B. Arain, M. Jamali, H. Afridi
and R. Sarfraz, Application of factorial design in
optimization of ultrasonic-assisted extraction of
aluminum in juices and soft drinks. Talanta, 70(2),
307-314 (2006).
.
27. Hsu, J., C. Lin, C. Liao and S. Chen, Evaluation
of the multiple ion competition in the absorption
of As(V) onto reclaimed iron-oxide coated sands
by fractional factorial design. Chemosphere,
72(7), 1049-1055 (2008).
.
379

380
28.
29.
30.
31.
Lima, E., B. Royer, J. Vaghetti, J. Brasil, N.
Simon, A. dos Santos Jr., F. Pavan, S. Dias, E.
Benvenutti and E. da Silva, Adsorption of Cu(II)
on Araucaria angustifolia wastes: Determination
of the optimal conditions by statistic design of
experiments. J. Hazard. Mater., 140(1-2), 211-220
(2007).
.
Rezic, I., Optimization of ultrasonic extraction of
23 elements from cotton. Ultrason. Sonochem.,
16(1), 63-69 (2009).
.
Stat-Ease, Design-Expert 7. Stat-Ease, Inc.,
Minneapolis, MN (2005).
Özkan, M.H., R. Gürkan, A. Özcan and M. Akçay,
Dissolution kinetics of magmatic rocks via ultra-
Bellotindos et al., Sustain. Environ. Res., 21(6), 375-380 (2011)
.
sonic leaching for calcium, magnesium and
aluminum. Gazi U. J. Sci., 21(4), 117-122 (2008). .
32. Özkan, M.H. and M. Akcay, Determination of
manganese and iron in magmatic rocks after
ultrasonic leaching by flame AAS. Turk. J. Chem.,
26(1), 59-76 (2002).
.
Discussions of this paper may appear in the discussion
section of a future issue. All discussions should
be submitted to the Editor-in-Chief within six months
of publication. .
Manuscript Received: August 11, 2010
Revision Received: January 13, 2011
and Accepted: January 26, 2011