426
[Research Paper] 대한금속･재료학회지 (Korean J. Met. Mater.), Vol. 53, No. 6, pp. 426~431
DOI: 10.3365/KJMM.2015.53.6.426
Recovery of Tin and Nitric Acid from Spent Solder Stripping Solutions
Jae-Woo Ahn*, Seong-Hyung Ryu, and Tae-young Kim
Department of Advanced Materials Sci. & Eng., Daejin University, Gyeonggi-do 487-711 Korea
Abstract: Spent solder-stripping solutions containing tin, copper, iron, and lead in nitric acid solution, are
by-products of the manufacture of printed-circuit boards. The recovery of these metals and the nitric acid,
for re-use has economic and environmental benefits. In the spent solder-stripping solution, a systematic
method to determine a suitable process for recovery of valuable metals and nitric acid was developed.
Initially, more than 90% of the tin was successfully recovered as high-purity SnO2 by thermal precipitation
at 80 ℃ for 3 hours. About 94% of the nitric acid was regenerated effectively from the spent solutions by
diffusion dialysis, after which there remained copper, iron, and lead in solution. Leakage of tin through the
anion-exchange membrane was the lowest (0.026%), whereas Pb-leakage was highest (4.26%). The concentration of the regenerated nitric acid was about 5.1 N.
†(Received
May 9, 2014)
Keywords: tin, nitric acid, diffusion dialysis, recovery, solder stripping solution
1. INTRODUCTION
The recent rise in global concern about environmental
pollution has restricted the use of waste material through
landfill dumping. Instead, material recycling has played a
greater role to reduce environmental pollution, as well as
develop clean and green technology. Waste water that
contains heavy metals of different quantities, which has
been discarded at present, however, needs to be recycled
in a proper way when the volume of the material will be
increased in the future. Among such wastes, the waste solution of printed circuit board (PCB) that undergoes nitric
acid stripping contains valuable metals [1]. Such waste
solution mostly contains metals like copper (Cu), lead
(Pb), tin (Sn), and other nitrate dissolved specific heavy
metals, making it difficult for PCB manufacturing companies to process it in an economical way. Therefore, a
company is usually dependent on an external company to
process these wastes, which adds a processing cost, as well
as material transport cost, considered as ultimate burdens
for a company.
Additionally, waste collection companies do not have
any particular treatment process methodology. Instead they
follow a simple neutralization process and finally dump
the precipitated sludge in sediment. However, such precipitated sludge with high heavy metal content when dumped
in a landfill also creates environmental pollution. Most of
such waste sludge possesses 10~30 g/L Sn, 5.0~10.0 g/L
Cu, 5.0~20.0 g/L Pb, and 5.0~10 g/L Fe; moreover, it has
nitric acid concentration of around 250 g/L which is environmentally hazardous if simply disposed. Therefore such
waste material needs special attention in order to recycle
valuable metal resources. In order to recover metal values
from such waste solution, different technology processes
can be applied such as electrochemical process to recover
Sn metal [2-4]; solvent extraction process to recover nitric
acid and other valuable metals [5,6]; membrane separation
process to separate nitric acid from other metals [7-9]; and
oxalate precipitation to recover Sn and Cu [10].
Based on the contents of valuable metals in the waste
solution, the exact process can be developed and followed.
In order to avoid the generation of a large volume of such
waste solution in the future, the developed processes must
be considered so they may be applied in an effective way.
The techno-economic value of the processes must also be
evaluated properly.
Therefore, in this study a new process has been addressed
to treat the direct waste solder solution collected from the
industry. The collected waste solder solution has been
used for thermal precipitation to recover Sn by precipitation
method, and the remaining tin free solution has been
treated in diffusion dialysis to purify nitric acid. The process
has been developed through basic laboratory experimental
data.
2. MATERIALS AND METHODS
*Corresponding Author: Jae-Woo Ahn
[Tel: +82-31-539-1982, E-mail: [email protected]]
Copyright ⓒ The Korean Institute of Metals and Materials
2.1. Experimental Sample
The collected experimental sample from the industry
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대한금속･재료학회지 제53권 제6호 (2015년 6월)
Table 1. Chemical composition of waste solder stripper (g/L)
Table 3. Characteristic features of diffusion dialysis apparatus
Sn
Cu
Fe
Pb
Na
HNO3
Form
CJ-T-0C
23.41
3.56
4.97
17.31
3.61
3.5~4.0 N
Number of membrane assembly
19
Anion exchange membrane
APS
Membrane size
160 mm×240 mm
Effective membrane size
100 mm×180 mm
Table 2. Chemical composition of solution after thermal precipitation (g/L)
Sn
Cu
Fe
Pb
Na
HNO3
Effective membrane area
0.0172 m2
2.8
4.0
4.3
20.12
4.14
6.2 N
Membrane interval
1.9 mm
Pump
Dosing pump
Tank
PVC 1.0 L
Pipe Material
PVC, PP, PE
was a waste solder solution which was stripped by nitric
acid. The major metal content is given in Table 1. The
solution contained 23.87 g/L Sn, less than 5 g/L of Cu and
Fe, 16.67 g/L Pb, and 3.5~4.0 N nitric acid concentration.
Further, the solution also contained a small amount of
organic component as a stabilizing reagent.
2.2. Experimental Procedures
2.2.1. Selective Precipitation of Tin by Thermal Precipitation
The collected waste solder solution was filtered first and
1.5 L of solution was poured into a 2.0 L reactor, which
was kept in a water bath maintained by constant temperature. The reactor, placed in water bath, was injected
with air at the rate of 4 L/min and was facilitated with a
bottom-up agitation speed of 250 rpm. A periodically supernatant sample was taken from the reactor, filtered initially
with 0.09 mm filter paper followed by membrane filtration
with 0.45 μm cellulose acetate membrane filter. The metal
composition in the final filtered sample was analyzed by
ICP-AES and then the precipitated material was collected.
The collected precipitant was then washed with warm 0.5 M
HCl and distilled water at 60 ℃, and finally dried at 80~
90 ℃ in an oven. A physical property analysis employing
SEM, XRD, and chemical elemental analysis by ICP-AES
followed (PerkinElmer/Optima-4300 DV).
2.2.2 Nitric Acid Recovery by Diffusion Dialysis
After the thermal precipitation of tin from the waste
solder solution, the remaining tin-free solution was used
for nitric acid recovery by a diffusion dialysis process. The
elemental composition of the solution after the thermal
precipitation of tin is given in Table 2. Using the diffusion
dialysis apparatus, the D.I. water flow rate was fixed at
0.48 L/hr while that of feed solution was fixed at 0.42 L/hr.
The reaction temperature was maintained at 30 ℃ throughout the experimental process. The HNO3 concentration in
the solution was measured by using both nitrate electrode
and volumetric titration using NaOH neutralization, along
with Phenolpthaline as the key indicator. The acid recovery
calculation is presented in Equation 1. In addition to this,
the elemental composition in the nitric acid was analyzed
by ICP-AES in order to ascertain the permeability rate
through the ion-exchange liquid membrane. The specific
characteristic features of the diffusion dialysis apparatus
are given in Table 3.
Acidrecovery ( ) 
Qd  Cd
Qf  C f
(1)
Where,
Qd: Flow rate of D.I. water (L/hr)
Cd: Concentration of recovered acid (mol/L)
Qf: Flow rate of feed solution (L/hr)
Cf: Concentration of feed solution (mol/L)
3. RESULT AND DISCUSSION
3.1. Recovery of Tin by Thermal Precipitation
The application of air during high temperature reaction
study has been considered to play important role in the
recovery of Sn from waste solder solution by precipitation
methodology. The occurrence of tin during HNO3 stripping
has been presented in Equations 2 and 3. Equation 2 represented that Sn occurred as Metastannic acid which disperses
more or less small colloidal particles in the solution phase
and is assumed to be precipitated later with heat treatment;
in addition to this, some of the Sn has also been present in
the ionic state in the nitric acid solution.
Sn (in solder) + 2HNO3 → H2SnO3
(2)
Sn (in solder) + 2HNO3 → Sn (NO3)2 + H2 + NO2 (3)
The Eh-pH diagram for tin-nitrate-water shows that in