Materials Transactions, Vol. 55, No. 12 (2014) pp. 1885 to 1889
© 2014 The Japan Institute of Metals and Materials
EXPRESS REGULAR ARTICLE
Separation of Tin, Silver and Copper from Waste Pb-free Solder
Using Hydrochloric Acid Leaching with Hydrogen Peroxide
Sookyung Kim1, Jae-chun Lee1, Kwang-sek Lee2,+1, Kyoungkeun Yoo2,+2 and Richard Diaz Alorro3
1
Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, Daejeon, 305-350, Korea
Department of Energy & Resources Engineering, Korea Maritime and Ocean University, Busan, 606-791, Korea
3
Department of Metallurgical and Minerals Engineering, Curtin University, Kalgoorlie, 6430, Australia
2
The waste lead (Pb)-free solder leaching process in hydrochloric acid (HCl) solution with hydrogen peroxide (H2O2) followed by
separation of copper (Cu) and tin (Sn) was investigated to separate tin, silver (Ag), and copper as an individual component from waste Pb-free
solder. The dissolution of Sn increased with increasing temperature and HCl concentration. The concentrations of Sn and Cu increased to
27090 g·m¹3 and 191 g·m¹3, respectively, under the leaching condition with 1 kmol·m¹3 HCl, 0.8 kmol·m¹3 H2O2 at 50°C and 400 rpm for
120 min, while Ag is not detected in all leaching tests. The Sn and Cu components are thus successfully separated from Ag by hydrochloric acid
leaching with hydrogen peroxide. To precipitate selectively Cu ions from the leach solution, the method to add Sn powder has been investigated.
Thus, 92.8 g·m¹3 (1.46 mol·m¹3) of Cu could be removed successfully from the leach solution with Sn under the following conditions; 30°C in
temperature; 400 rpm in agitation speed; 0.3 ml min¹1 in N2 flow rate; 0.1 g Sn powder addition to 100 cm3 leach solution.
[doi:10.2320/matertrans.M2014289]
(Received August 11, 2014; Accepted September 29, 2014; Published November 8, 2014)
Keywords: lead-free solder, hydrochloric acid leaching, cementation process, recycling
1.
Introduction
The environmental regulation such as WEEE (the Waste
of Electrical and Electronic Equipment) and RoHS (the
Restriction of the use of certain Hazardous Substances)
restricts the use of lead (Pb) in electric home appliances due
to its toxicity.1,2) Lead-free solder has been investigated to
substitute the tin/lead solder, and various Pb-free solder
series containing tin, silver, copper, bismuth, antimony, and
zinc were developed.3) Simple melting processes have been
used to reuse waste Pb-free solder.4) The melting processes,
however, could cause air pollution due to the gas emission
generated from combustion of organic flux in the Pb-free
solder.4)
Hydrometallurgical processes have been investigated as
alternative processes for recycling of waste Pb-free solder.
Rhee et al. performed the feasibility study on Sn recovery
from lead frame scrap using sodium hydroxide with sodium
persulfate as an oxidant.5) Kim et al. investigated the
leaching behavior of tin in NaOH solution to recover tin
from waste Pb-free solder.6) There have been a few studies on
the recycling of waste Pb-free solder under the acidic
condition although nitric acid leaching tests were performed
to recover valuable metals from waste Pb-free solder4) and
printed circuit boards.7)
In the previous study,4) a recycling process using nitric acid
leaching was proposed to recover Sn, Ag, and Cu from waste
Pb-free solder as shown in Fig. 1. During nitric acid leaching,
silver and copper are dissolved while tin precipitates into
stannic acid or stannic oxide. Subsequently, silver ion
precipitates selectively from leach liquor by adding NaCl,
and then copper is recovered by electrowinning. Therefore,
Sn, Ag, and Cu could be recovered successfully as individual
component. However, the waste Pb-free solder should be
+1
Graduate Student, Korea Maritime and Ocean University
Corresponding author, E-mail: [email protected]
+2
Waste solder
Nitric acid
HNO3 leaching
Leach solution
with Ag & Cu ions
S/L separating
Precipitate
NaCl
Precipitating
AgCl
Solution
with Cu ions
H2SnO3
HCl leaching
Electrowinning
Electrowinning
Cu
Sn
Fig. 1 Schematic diagram of the recycling process of waste Pb-free solder
using nitric acid leaching.4)
leached twice by nitric and hydrochloric acid to recover tin
metal, and the treatment of NOx gas emission will be
required to avoid air pollution.
The present study is aimed to develop a new recycling
process using hydrochloric acid to avoid air pollution due
to NOx gas and to simplify leaching processes. The effects
of the parameters such as hydrochloric acid concentration,
leaching temperature, pulp density, and agitation speed, on
the dissolution of Sn, Ag and Cu are discussed. In addition,
the precipitation of Cu by adding Sn powder was investigated
to separate Cu and Sn from the hydrochloric acid leach
solution.
2.
Experimental Procedure
2.1 Materials
The Pb-free solder of Sn-Ag-Cu series covers approx-
1886
S. Kim, J. Lee, K. Lee, K. Yoo and R. D. Alorro
Sn concentration, C / g m-3
Sn
Intensity (cps)
Ag3Sn
Degree / 2θ
θ
imately 70% of reflowing Pb-free solder market.3,8,9) The
waste Pb-free solder of Sn-Ag-Cu series was obtained from a
recycling company in Korea, which was generated from the
fabricating processes of printed circuit boards for electronic
home appliances. The waste solder was dry-sieved with
125 µm (120 mesh) sieve, and the solder with less than
125 µm contained 90.2% Sn, 4.11% Ag, and 0.65% Cu as
main components and 0.022% Bi and 0.021% Pb as minor
components, and any other metals were not detected. The
X-ray pattern (see Fig. 2) of the solder shows the presence of
phases such as Sn and Ag3Sn. All the chemicals used in this
study are of reagent-grade.
2.2 Leaching procedures
The leaching tests of the waste Pb-free solder in
hydrochloric acid solution were performed in a 500 dm3
three-necked Pyrex glass reactor using a heating mantle to
maintain temperature. The reactor was fitted with an agitator
and a reflux condenser. The reflux condenser was inserted in
one port to avoid solution loss at high temperatures. In leach
solution, the concentrations of HCl and H2O2 were adjusted
to 0.1­1 kmol·m¹3 and 0.3­0.8 kmol·m¹3, respectively, and
then 200 dm3 of the leach solution was placed into the reactor
and allowed to reach the thermal equilibrium (30­90°C). A
2 g of the solder powder under 125 µm was added to the
reactor in the experiments except the pulp density test, and
the agitator was set at 200­600 rpm. During the experiment,
3 cm3 of the solution sample was withdrawn periodically at a
desired time interval (10­120 min) with a syringe.
2.3 Separation test of Cu and Sn
The separation tests for Cu and Sn was performed by
adding Sn powder (75 µm, Junsei Chemical Co. Ltd.). The
leach liquor was obtained under the leaching conditions;
400 rpm agitation speed, 1 kmol·m¹3 HCl concentration,
0.3 kmol·m¹3 H2O2 concentration, 50°C temperature and
1.5% pulp density. The separation tests were conducted in a
250 cm3 Pyrex reactor, which was equipped with water jacket
for temperature control. Tin powders (0.1 to 0.5 g) were
added to 100 cm3 of the leach solution at 400 rpm and 30°C,
with or without introducing nitrogen gas (0.3 ml min¹1 flow
rate). For measuring the concentrations of Cu, 2 cm3 of
solution was sampled with a syringe and was prepared for
analysis following the same procedure as mentioned above
(section 2.2).
Fig. 3 Effect of agitation speed on the dissolution of Sn from the Pb-free
solder in 1 kmol m¹3 HCl at 50°C with 0.3 kmol m¹3 H2O2.
Sn concentration, C / g m-3
Fig. 2 XRD pattern of the waste Pb-free solder of Sn-Ag-Cu series used in
this study.
Time, t / min
Time, t / min
Fig. 4 Effect of HCl concentration on the dissolution of Sn from the Pbfree solder at 400 rpm and 50°C with 0.3 kmol m¹3 H2O2.
2.4 Analytical methods
The sample was filtered with 0.45 µm membrane filter and
then the filtrate was diluted with 5% HNO3 solution for Cu
and Ag analyses and 15% HCl solution for Sn analysis,
respectively. The sample solutions were analyzed by an
atomic absorption spectrometry (AA7000, Shimadzu Co.
Ltd.) and an inductively coupled plasma-atomic emission
spectrometry (ICP-AES, JY-38 plus, Jobin Yvon Ltd.).
3.
Results and Discussions
The hydrochloric acid leaching test of the waste Pb-free
solder at agitation speeds in the range 200­600 rpm was
carried out to examine the effect of liquid film boundary
diffusion surrounding the solid particles on the leaching
efficiency of the solder in 1 kmol·m¹3 HCl at 50°C with
0.3 kmol·m¹3 H2O2. As can be seen from Fig. 3, the leaching
efficiencies of Sn are independent of the agitation speeds
after 30 min. Therefore, in all subsequent leaching tests, a
working agitation speed of 400 rpm was selected to ensure
effective particle suspension in the solution while minimizing
the effect of liquid film boundary diffusion surrounding the
solid particles.
Figure 4 shows the effect of HCl concentration on the
dissolution of Sn from the waste solder in 0.1 kmol·m¹3 to
1 kmol·m¹3 HCl solution with 0.3 kmol·m¹3 H2O2. The
leaching efficiencies of Sn increased with increasing HCl
concentration, which would result from the increase in tin
solubility. In the leaching test at 1 kmol·m¹3 HCl, the
leaching efficiency increased to more than 99% so
1887
Sn concentration, C / g m-3
Sn concentration, C / g m-3
Separation of Tin, Silver and Copper from Waste Pb-free Solder Using Hydrochloric Acid Leaching with Hydrogen Peroxide
H 2O 2
H2O2
Time, t / min
Time, t / min
Fig. 7 The leaching behaviors of Sn in 1 kmol m¹3 HCl at 400 rpm and
50°C with 0.8 kmol m¹3 H2O2.
Sn concentration, C / g m-3
Cu concentration, C / g m-3
Fig. 5 Effect of H2O2 addition on the dissolution of Sn from the Pb-free
solder in 1 kmol m¹3 HCl at 400 rpm and 50°C with or without
0.3 kmol m¹3 H2O2.
Time, t / min
Time, t / min
Fig. 6 Effect of temperature on the dissolution of Sn from the Pb-free
solder in 1 kmol m¹3 HCl at 400 rpm with 0.3 kmol m¹3 H2O2.
1 kmol·m¹3 HCl concentration was selected in all subsequent
leaching tests. The effect of H2O2 addition was investigated
in 1 kmol·m¹3 HCl at 50°C and 400 rpm, with and without
0.3 kmol·m¹3 H2O2. Figure 5 shows the H2O2 addition
improved the dissolution of Sn in the 1 kmol·m¹3 HCl
solution. In this experiment without H2O2, 7.2 g·m¹3 Cu was
detected in the leach solution after 120 min leaching while Ag
was not detected.
Figure 6 shows the effect of temperature on the dissolution
of Sn from the waste solder in 1 kmol·m¹3 HCl solution with
0.3 kmol·m¹3 H2O2. The dissolution temperature was varied
in the range 30­90°C, while all other parameters were kept
constant. As can be seen from Fig. 6, higher temperatures
yielded higher dissolution rates of Sn from the solder in the
beginning of the leaching, while the difference of leaching
efficiencies is negligible after 30 min, where the leaching
efficiencies are more than 99%.
The effect of pulp density from 1% to 3% was investigated
under the leaching condition; 1 kmol·m¹3 HCl, 0.8 kmol·m¹3
H2O2, 400 rpm, and 50°C. In the leaching tests, tin was
oxidized with hydrogen peroxide as the following equation.
Sn þ 2H2 O2 þ 4Hþ ¼ Sn4þ þ 4H2 O
ð1Þ
where 0.3 kmol·m¹3 H2O2 could oxidize 0.15 kmol·m¹3 Sn,
because the tin concentration with pulp density of 3% are
0.253 kmol·m¹3, 0.8 kmol·m¹3 H2O2 was used in the pulp
density test considering that hydrogen peroxide is a relatively
unstable compound.10,11)
As shown in Fig. 7, tin concentration increased to
27090 g·m¹3 in the leaching test with 3% pulp density, and
Fig. 8 The leaching behaviors of Sn in 1 kmol m¹3 HCl at 400 rpm and
50°C with 0.8 kmol m¹3 H2O2.
the leaching efficiencies of tin increased to more than 99%
regardless of pulp density. Figure 8 shows the leaching
behavior of Cu obtained in the same experiment shown in
Fig. 7. The concentration of Cu increased to 63 g·m¹3,
131 g·m¹3 and 192 g·m¹3 in the leaching test with 1%, 2%
and 3% pulp density, respectively, while that of Ag was not
detected in all leaching tests (data not shown). Silver ion has
been found to precipitate by reacting with Cl¹ ion by the
following equation
Agþ þ Cl ¼ AgCl #
ð2Þ
The standard Gibbs free energies of Ag+, Cl¹ and AgCl(s)
are 77.16 kJ·mol¹1, ¹131.0563 kJ·mol¹1, and ¹109.86
kJ·mol¹1, respectively.12,13) The solubility product (Ksp) of
AgCl is calculated to be 10¹9.82 using the data at 25°C. This
result indicates that Ag ions precipitate easily and rapidly
as AgCl because the solubility of AgCl is extremely low.
Consequently, Ag could be precipitated and separated
successfully from Sn and Cu by HCl leaching with H2O2.
Cementation is the process of precipitating the metals from
a solution using the electrochemical reaction between two
metals.14) By cementation process using Sn powder, the
precipitate of Cu was expected as shown below.
Cu2þ þ Sn ¼ Cu # þ Sn2þ
2þ
4þ
ð3Þ
2Cu þ Sn ¼ 2Cu # þ Sn
ð4Þ
where the standard redox potentials of eq. (3) and (4) are
calculated to be +0.48 V and +0.33 V, respectively.15)
In eqs. (3) and (4), 1.46 mol·m¹3 or 0.73 mol·m¹3 of Sn
(17.3 mg or 8.7 mg of Sn to 100 cm3 of leach solution) is
S. Kim, J. Lee, K. Lee, K. Yoo and R. D. Alorro
Cu concentration, C / g m-3
Cu concentration, C / g m-3
1888
Time, t / min
Time, t / min
Fig. 9 The behavior of Cu by adding Sn powder in the leach solution at
50°C and 400 rpm without N2 purging.
Fig. 11 The behavior of Cu by adding Sn powder in the leach solution at
50°C and 400 rpm with N2 purging.
Waste solder
Sn powder + Cu precipitate
Eh / V
HCl + H2O2
Leaching
Leach solution
with Sn & Cu ions
S/L separation
Sn powder
Log a Cl-
AgCl
Solvent extraction
Cementation
Electrowinning
Electrowinning
Cu
Sn
Fig. 10 The Eh-log aCl- digram for the Cu2+/Cu+-Cl¹-H2O system at
25°C.16)
required to precipitate 92.8 g·m¹3 (1.46 mol·m¹3) of Cu. As
shown in Fig. 9, Cu concentrations decreased and then
increased by the addition of 0.1 g to 0.3 g of Sn powder,
though the Sn amount of 5 or 10 times more than that
required in eqs. (3) and (4) was added to the leach solution.
On the other hand the Cu concentration decreased and then
remained constant to nearly zero by adding 0.4 g and 0.5 g of
Sn powder. Figure 10 shows the Eh-log aCl- digram for the
Cu2+/Cu+-Cl¹-H2O system at 25°C where the activity of
each species is assumed to be 1.16) At low Cl¹ concentration,
Cu exists as copper metal or cupric ion (Cu2+), whereas
cuprous ion species become stable with increasing Cl¹
concentration. Since CuCl2¹ ion as Cu+ species is predominant at 1 kmol·m¹3 Cl¹, copper leaching could be expected
as the following equation.
CuClþ þ Cu þ 3Cl ¼ 2CuCl
2
ð5Þ
The cuprous species could be oxidized by oxygen under
the open condition to air as shown in eq. (6).
þ
þ
4CuCl
2 þ O2 þ 4H ¼ 4CuCl þ 2H2 O þ 4Cl
ð6Þ
The remaining copper ion in Fig. 9 could play a role in reoxidizing copper metal precipitated, and the cuprous species
might be oxidized by contacting oxygen. Thus, because the
reactions shown in eqs. (5) and (6) could be repeated, copper
concentration increased with time as shown in Fig. 9.
Therefore, nitrogen gas was introduced into the reactor to
avoid the oxidation by oxygen. Figure 11 shows the copper
behavior by cementation using Sn powder with N2 purging.
The copper concentration decreased and then remained
constant at low Cu concentration. These results indicate that
copper components could be separated successfully from the
leach solution.
Fig. 12 The recycling process of Pb-free solder (Sn-Ag-Cu series)
proposed in this study.
Based on the above results, a recycling process for the
waste Pb-free solder of Sn-Ag-Cu series is proposed as
shown in Fig. 12. Copper and tin are dissolved by hydrochloric acid leaching with hydrogen peroxide, and then
copper ions were selectively precipitated from the leach
solution by cementation process with tin powder, where tin
powder could be substituted by Pb-free solder because it
contains about 90% Sn as a main component. Finally tin
would be recovered by subsequent electrowinning process.
The mixture of copper precipitated and tin powder remained
in the cementation process will be sent to the leaching
process. Accordingly, copper concentration would increase in
the leach solution by repeating the recycling process. When
the copper concentration increased to sufficient level, copper
ions should be removed by another separation process such
as solvent extraction. Further efforts will be required to
recover copper from the leach solution.
4.
Conclusion
The hydrochloric acid with hydrogen peroxide leaching
process for the treatment of waste lead-free solder followed
by separation of Cu and Sn was investigated to recover Sn,
Ag and Cu as an individual component.
The dissolution of Sn is independent of agitation speed
at more than 200 rpm, but increases with increasing the
Separation of Tin, Silver and Copper from Waste Pb-free Solder Using Hydrochloric Acid Leaching with Hydrogen Peroxide
temperature and HCl concentration. Silver is not detected in
the all leaching tests. The Sn and Cu components are thus
successfully separated from Ag by hydrochloric acid leaching
with hydrogen peroxide. To precipitate selectively Cu ions
from the leach solution, a method comprising of the Sn
addition has been investigated. The re-dissolution of Cu was
observed due to the oxidation of remaining cupric ion and
subsequent re-oxidation of cuprous ion by oxygen. The
introduction of nitrogen gas during the cementation process
prevents Cu from re-dissolving. Thus, Cu could be separated
successfully from leach solution containing Sn by the
addition of Sn powder, whereas Sn could be recovered by
electrowinning from the Cu free solution.
Acknowledgments
The paper is based on the Basic Research Project of the
Korea Institute of Geoscience and Mineral Resources
(KIGAM) funded by the Ministry of Trade, Industry &
Energy (MOTIE) of Korea.
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