Journal of Environmental Protection, 2011, 2, 675-682
doi:10.4236/jep.2011.26078 Published Online August 2011 (
Copyright © 2011 SciRes. JEP
Optimization of Precious Metal Recovery from
Waste Electrical and Electronic Equipment Boards
Massimo Delf ini1, Mauro Ferrini1, A ndre a M ann i2*, P aol o Mass acc i1,2, Luigi Piga1, Ant oni o Sc oppe ttu olo1
1Department of ICMA, University of Rome “La Sapienza” Via Eudossiana, Rome, Italy; 2Consorzio Inteuniversitario Nazionale
Ingegneria Georisorse, Via di Monte Giordano, Rome, Italy.
Received April 21st, 2011; revised May 17th, 2011; accepted June 22nd, 2011.
Recovering noble metals from Waste Electrical Electronic Equipment (WEEE) will provide an additional income within
the disposal process of end-of-life electronic devices. Generally, the recycling process starts with the manual disman-
tling of different devices and with sorting of the subdivided products into useful and hazardous materials. A sample of
about 21 tonnes of WEEE was dismantled in 14 days to remove Printed Circuit Boards (PCBs) that were about 5%
weight of the whole sample. Computer PCBs proved to contain the 96% of all the gold present in all types of PCBs of
the sample. Computer PCBs were manually dismantled to obtain the easy-to-remove components of the board, namely,
the integrated circuits and the processors, which were about 13% weight of the board and 0.1% weight of the whole
WEEE sample and contained about 91% of the gold present in the whole board with an average concentration of 2400
Keywords: WEEE, Recycling, Waste Processing, Precious Metals
1. Introduction
The amount of electronic scrap is increasing all over the
world and each European inhabitant produces about 20
kg each year. Generally, the final destination of such
waste should be a landfill with a high level of environ-
mental protection, due to the content of hazardous com-
pounds. According to the European Commission, the
waste stream of electronic and electrical equipment has
been identified as one of the fastest growing waste
streams in the EU, at present being less in quantity than
Municipal Solid Waste (MSW) but increasing, annually
by more than the growth of MSW. The situation is bound
to worsen because the average life-time of a single com-
puter is decreasing and thus the replacement frequency is
growing. Moreover, LCD and plasma monitors of both
computers and TV-sets will substitute the old cathode ray
tube monitors (CRT), increasing the amount of waste to
dispose of.
The Waste Electrical and Electronic Equipment Direc-
tive (WEEE Directive, 2002/96/EC), issued by the Euro-
pean Commission aims to minimise the impact of end-of-
life electrical and electronic goods on the environment,
by increasing re-use and recycling and then reducing the
amount of WEEE used for landfill. A decision of the
Commission stated that, within December 2006, 4 kg
WEEE/inhabitant should have been collected yearly.
Nevertheless, at present, 19 kg/inhabitant are collected in
Sweden, 16 kg/inhabitant in Norway but less than 2
kg/inhabitant in Italy. According to the Italian Environ-
mental Ministy, 938 ktonnes of WEEE were disposed of
in a controlled landfill in 2006 and a large part of this
came from the domestic circuit. The total quantity of
waste generated from the professional circuit should be
added to that amount, but this figure is not available to
Public waste control bodies. Part of WEEE comes from
the information technology sector and 220 ktonnes
wastes were produced in Italy in 2008 but 126 ktonnes
were not controlled, this amount corresponding to about
4 millions of computers, printers or screens. The cost of
legal collection and disposal is expensive, and waste can
be shipped abroad only if the receiving plants are
equipped to treat and disposed of the waste safely. It has
been supposed that a large part of WEEE from the pro-
fessional circuit, is sent to underdeveloped countries dis-
guised as working second-hand appliances, but 90% of
that is only a waste that is dumped and stockpiled in im-
provised landfills without any environmental protection.
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards
The price of the second-hand appliances supports this
hypothesis. In fact, the price of a single computer item or
screen of about 3 euros for Indonesian buyers, for exam-
ple, is absolutely out-of-market as the test to check
whether a computer is running, before shipping abroad,
is well above 3 euros. Moreover, the Italian law on waste
management of waste if far from being enforced, and so
an important fraction of WEEE produced in the domestic
circuit, is still being left beside the rubbish skips. To
avoid this, producers should be made responsible for
financing the collection, treatment, and recovery of waste
electrical equipment, and distributors should be obliged
to allow private or professional consumers to return free
of charge their end-of-life equipment when buying a new
product. 10 product categories fall in the Directive, such
as information technology and telecommunication equip-
ment, medical devices, monitoring and control instru-
ments, large and small household appliances.
Several authors have described the present status of
the WEEE recycling in different countries such as Korea
[1], Taiwan [2], the USA [3,4], China [5], Scotland [6],
Greece [7], Germany [8], Switzerland [9], Sweden [10]
and India [11].
There are 11.000 companies in Italy, producing Elec-
trical and Electronic Equipment (EEE), with 212000 em-
ployes, chalking up a total turnover of 32 billion euro/y
while there are 44 material recycling facilities (MRF)
throughout the territory for the WEEE recycling.
Ten consortiums of producers consortia have been es-
tablished since the approval of the WEEE Directive,
which pay for the cost of collection and transport, ac-
counting for most of the overall cost of recycling, to
“eco-places” [12], where the end user can leave the
WEEE, and from these to the MRFs. The above costs
will probably be added to the selling cost of a new device
and consortium will reach their own decision on whether
to display this cost to consumers in the invoice, as is
currently the case for the recycling plastic packaging, or
to include it in the price.
WEEE recycling raises a large number of environ-
mental issues, which can differ for each category of
waste: Ba, Pb, Hg and rare earths, contained in CRT
from TVs and Monitors and Pb, Cd, Hg contained in
batteries could easily be leached if left in rubbish dumps,
while Polybrominated Biphenyls (PBB), Polychloro
Dibenzo Dioxins/Furans (PCDD/F), Polybrominated Di-
phenyl Ethers (PBDE), used as flame retardants in the
plastic protection casings and condensers and in the
printed boards, could spread in the environment if ignited.
Likewise for Polychloro Biphenyls (PCB), contained in
capacitors, and for phthalate, in plastics.
In most emerging countries backyard recyclers ignite
the wastes in order to recover metals from the ashes,
thereby creating considerable health problems to the
workers and for the human community surrounding the
This is the case, for example, for the major e-waste
recycling towns in China namely Taizhou, Guiyu and
Chendian, where increased levels of pollutants in body
fluids has been reported; in particular dioxin [13], PCB
[14], Pb, Cd, Cu [15], Cr [16], PBDE [17] and PAH [18].
WEEE scrap, without exception, contains Printed Cir-
cuit Boards (PCBs), whose overall composition has been
reported [19] which are worth recycling to obtain the
valuable elements contained, such as Au, Ag, Pd, Cu and
Therefore, recycling of WEEE, as secondary raw ma-
terials, is becoming extremely important due to their
content of precious metals, i.e 50 - 60 time greater than
in a normally mined ore; and the value can cover a large
part of the costs both of recycling and of disposing of
post-recycling end-of-life products.
Several authors have proposed different processes,
based on physical and chemical methods, to recover the
valuable components located in PCBs. The former in-
volve crushing, milling, screening, magnetic separation,
Eddy current separation and shaking table separation as
the main methods. The latter involve hydrometallurgical
[20] and pyrometallurgical methods [21].
Since PCBs contain more than 20% of Cu [2], after a
preliminary shredding and milling process, they could be
directly feed to copper or lead smelting plants: the main
disadvantages of this process are the transport cost for
the PCBs, as there are very few such plants in the world,
and the environmental problems due to the back-forma-
tion (synthesis ex novo) of PCDD/F due to incomplete
decomposition of precursors in flue gases when the tem-
perature of the flue dust is in the range of 250 - 500˚C
The aim of the present work is to identify the valuable
components in the PCBs and to separate them from the
board to minimize environmental impact, through a
strong reduction in the volume of material to be proc-
essed for precious metal recovery in the successive steps.
Statistically significant results have been obtained start-
ing from a very large sample of WEEE, to reproduce a
long working cycle for a typical MRF in Italy.
2. Experimental Schemes
Several schemes have been proposed for the preliminary
treatment of different kind of WEEE. After collection
and transport to MRF, any process should always start
with the pre-treatment of sorting and manual dismantling
of the WEEE, by means of tools such as screwdrivers,
Copyright © 2011 SciRes. JEP
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards
Copyright © 2011 SciRes. JEP
hammers and pliers and with the creation of different
bulk of homogeneous materials. To perform such a
manual job most efficiently, a preliminary sorting of
WEEE into different categories should be carried out in
eco-places. In this way, trucks going from eco-places to
MRF could be loaded according to WEEE categories and
unloaded in the opposite sequence in the large open space
which each MRF is provided. This would allow manual
dismantling with no preliminary sorting by operators. Un-
fortunately, at present, in the collecting sites, all the dif-
ferent items of equipment are kept together and are ran-
domly transferred to the trucks for the transport to MRF
where the sorting before disassembling is time consuming.
For the present study, a large sample of 20961 kg was
collected in an Italian MRF of average size over a 14-
working day period to eliminate variations in feeding. A
smaller random sample to be used for characterization
was sampled from the larger one. Characterization was
carried out on each component of this sample by chemi-
cal analyses according to the procedure described in the
analytical method section.
Analytical Method
To determine the Au, Pd and Pt content, 40 ml of Aqua
Regia (HNO3
HCl 1:3 v/v) was added to a 5 - 10 g rep-
resentative sample and the solution was carefully heated
until dissolution of the metallic components. After
washing and filtering of the residue, the solution was
brought to volume in a 250 ml volumetric flask using
HCl 1:1 (v/v), to avoid AgCl precipitation [24,25].
Measurements were carried out, in triplicate, by means
of ICP-OES (Perkin-Elmer Plasma 400) equipped with a
monochromator with a spectral range of 160 - 800 nm
covered by two gratings. After calibration with NIST
traceable standards (O2SI Llc, Charleston, SC, USA), the
elements were analysed in the wavelength having the
best signal/noise ratio. No noteworthy interferences were
noted. In order to prevent AgCl precipitation, HCl 1:1
(v/v) was employed to prepare standard, blank and
flushing solutions.
3. Results
The results of sampling are reported in Table 1, where
the different categories of waste are set out. 20961 kg of
WEEE were collected in the plant in a 14-working day
period with an average amount per day of 1497 kg.
The PCBs from the three sources, namely, monitors,
personal computers and TV-sets, account for the 5.54%
in weight of the overall sample for a daily average
amount of 83 kg, the amount of keyboards being negligi-
ble (0.02%). The large amount of glass, 568 kg daily
(about 38% of the whole sample) is due to the high spe-
cialization of the plant in processing CRT and TV
screens. The above data are in reasonable agreement with
those reported by other authors [2,4].
A preliminary campaign of chemical analyses was car-
ried out on each category of WEEE by means of a ran-
Table 1. Results of the sampling campaign for 14 days: for each day is reported the weight (kg) for each of the 11 different
bulk of products ready to be further processed, the average per day and the quantity percentage of the overall WEEE.
Day of sampling
Component 1 2 3 4 5 6 7 8 9 10 11 1213 14
kg Av/day
kg Qty
CRT PCB 31 46 49 54 76 92 40 97 60 10445 5395 70 912 65 4,4
PC PCB 2 24 11 5 3 14 15 7 6 23 13 8 18 13 162 12 0.77
TV PCB+ KB 0 0 32 2 4 0 10 8 12 4 0 0 6 0 78 6 0.37
HD + FL 2 36 26 0 0 3 6 3 0 18 0 8 16 17
135 10 0.64
RESINS 168 236 297247 164 288247287251400457172461 340 4015 287 19
MATERIAL. 211 539 688157 157 24748914324831240893183 658 4533 324 22
COPPER 84 83 79 45 66 70 10786 58 10243 4482 56
1005 72 4,8
GLASS1) 1016 572 583282 465 509 649464380486182175674 296 6733 481 32
B/W GLASS1) 84 81 76 47 94 89 79 64 42 21217812040 15
1221 87 5.8
TR. + PS 10 22 18 3 15 28 8 4 38 6 19 8 98 87 364 26 1.7
OTHER 118 161 302117 102 14210089 25 59 25676183 73 1803 129 8.5
TOTAL/ DAY 1726 1800 2161959 1146 1482175012521120172616017571856 1625 20,961 1497100
CRT: Monitors; PCB: Printed Circuit Board; PC: Personal Computers; HD: Hard Disk; FL: Flopp Disky; KB: Keyboard; B/W: Black and White; TR + PS:
Transformer + Power Supply; Av/day: Average per day; Qty: Quantity. 1) The amount of glass from CRT and TV was counted after the separation of the panels
from funnels.
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards
dom sampling. The results, not reported here, showed that
interesting concentration and amount of precious metals
were contained in the PCBs coming from the three
sources reported in Table 1, PC, CRT and TV PCB. Ex-
tensive, systematic chemical analyses were then carried
out on the single components of each type of PCBs, in
order to pinpoint more accurately the precious metals
With this aim, analyses were carried out on the com-
ponents of a representative sample of boards, namely 1)
processors (Figure 1), integrated circuits (Figure 2),
varistors, ceramic condensers, relays and MLCC capaci-
tors (Figure 3) and other components belonging to Com-
puter PCBs; 2) integrated circuits and various parts be-
longing to Monitor PCBs, and 3) integrated circuits and
various parts belonging to TV PCBs. In all three types of
PCBs there were easy and difficult parts to remove, sub-
jectively evaluated by the operators during disassembly.
The results of the analyses are reported in Table 2.
The weigths of Computer-PCBs, Monitor-PCBs and
Figure 1. Computer Processors.
Figure 2. Integrated circuits (all applicances).
Figure 3. Varistors, ceramic condensers, relays and MLCC
TV-PCBs contained in the representative sample, were
about 23.0, 28.0 and 18.6 kg respectively and the proc-
essors and the integrated circuits were less than 10% in
each board. The platinum content was negligible.
Although PCBs are the components of WEEE where
precious metals are present, the highest concentrations of
precious metals are in computer-PCBs with an average
gold concentration of 344 μg/g Au and 11.9 Pd μg/g,
monitor and TV-PCBs showing lower concentrations.
As far as distribution of gold is concerned, computer-
PCBs contain the 96% of the entire gold contained in all
three types of PCBs.
Most of gold was found in processors and integrated
circuits in computer-PCB, with gold concentrations of
7004 and 701 μg/g respectively, while minor amounts
were found in other components such as connectors.
Most of the palladium was found in varistors, ceramic
condensers, relays and, mainly, in MLCC capacitors
showing a palladium concentration of 16808 μg/g, that is
the. 80% of the palladium contained in the entire board.
Table 2 also shows an economic balance to determine
the value of the different components contained in the
three types of boards, given by the content in gold and
palladium. The values per gram of each valuable com-
ponent in each board and the distribution of the value in
the entire board are set out.
The most valuable boards are computer boards whose
components are 95 and 43 times more profitable per
gram than monitor and TV boards respectively.
It was noticed during disassembling of the precious-
metal bearing components that a few components, namely
processors and integrated circuits, were more easily re-
ovable than others. m
Copyright © 2011 SciRes. JEP
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards679
Table 2. Grade and distribution of gold and palladium among the precious-metal bearing components of Computer, Monitor
and TV printed circuit boards (PCB). The weight, the commercial value and their distribution among each kind of printed
circuit boards are also reported.
Component Au Pd Au + Pd
Weight Distribution Conc. UM ValueValueConc.UM Value Value Total ValueValue
Computer PCB g % μg/g g USDc/g% μg/gg USDc/g % USDc/g %
-Processors 811 3.52 7004 5.68 24.7 72 2 1.6 × 10-3 0 0 24.7 71
-Integrated Circuits 2185 9.49 701 1.53 2.5 19 18 39.3 × 10-3 0.19 2 2.69 19
condensors 202 0.88 n - - - 21300.43 2.3 18 2.3 2
254 1.10 n - - - 1600.04 0.2 2 0.2 0
-Capacitors MLCC 111 0.48 n - - - 16,8081.87 17.8 80 17.8 7
-All other components 19,46484.53 37 0.72 0.1 9 n - - 0 0
Total computer PCB 23,028 100 344 7.93 1001022.34 100 100
Monitor PCB
-Integrated Circuits
40 0.14 154 6 × 10-3 0.5004 14 0.6 × 10-3 0 1 0.500 100
-Various parts
27,91099.86 5 140 × 10-3 0 964 112 × 10-3 0 99 0.000 0
Total Monitor PCB 27,950100 5.21 146 × 10-3 1004.0 113 × 10-3 100 100
-Integrated Circuits
415 2.22 315 130 × 10-3 1.1 5912 5.0 × 10-3 0 5 1.100 58
-Various parts
18,22597.78 5 91.1 × 10-3 0.018415 91.1 × 10-3 0 95 0.018 42
Total TV PCB 18,640100 11.9 222 × 10-3 1005 .2 96.1 × 10-3 100 100
n: < 1 mg/kg; 1)subjectively evaluated by the operators; UM: material units; conc: concentration; Quotation: Au 1000 USD/Oz; Pd 300 USD/Oz.
Table 3. Weights and grades of gold and palladium recoverable from the easy-to-remove components of the three types of
printed circuit board found in the 14-day sample.
Easy-to-remove components1) Weight2) Au Pd
Computer PCB (%) (mg/kg) mg/day (mg/kg) mg/day
-Processors 0.027 7004 2831 2 1
-Integrated Circuits 0.073 701 766 18 20
Monitor PCB
-Integrated Circuits 0.006 154 14 14 1
-Integrated Circuits 0.008 315 38 12 1
Total ETR 0.114 2137 3649 13,6 23
Total ETR kg 23.9
Total ETR kg/day 1.71
1subjectively evaluated by the operators; 2) respect to 20961 kg (total WAEE collected in 14 days); 3) ETR: easy-to-remove components.
Copyright © 2011 SciRes. JEP
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards
Characteristics of easy-to-remove (ETR) gold and pal-
ladium-bearing components are reported in Table 3.
Most of gold is contained in these components which
amount to 13% of the whole board and account for only
0.11% of all the RAEE entering the plant with a weight
of 1.70 kg/day. The easily recoverable gold and palla-
dium amount to 3.66 and 0.023 g/day, respectively.
Most of the palladium is contained in not-easy-to re-
moved components (varistors, ceramic condensers and
MLCC capacitors) that constitute about 0.012% of all
theRAEE entering the plant and about 1.36% of the
whole board.
4. Discussion
A method to selectively remove and sort out the valuable
components from PCBs, in order to recover subsequently
the precious metals, should minimize the environmental
impact of the full treatment of the PCBs. At first, two
solutions were considered: heating the board and the use
of robots.
1) Heating of the board to weaken the soldering and
enable the valuable components to be removed manually
is not feasible because it is a very time-consuming proc-
ess and requires environmental precautions for the
worker in order to avoid the contact with the heavy metal
vapours from the board.
2) Mechanical robots to perform such work automati-
cally are not available everywhere, and are an expensive
investment for small enterprises. At all events, processors
and integrated circuits mainly consist of 2 parts, a lower
one, the base, with pins that are soldered to the PCB and
which it is very hard to remove, and an upper part, fixed
on the base, which it is very easy to remove from the
PCB just using a screwdriver and containing most of the
As a consequence, the manual removal of the valuable
parts of the board is a very simple operation that can be
carried out in a short time, not calling for any particular
skill, and by the same operators who manually disman-
tles each category of WEEE.
On the contrary, the components containing palladium,
namely MLCC capacitors, varistors and ceramic con-
densers, are very small in size (2 - 7 mm) and are spread
all over the board. The removal of such components is
feasible just using a screwdriver, but it is time-con-
suming and its applicability clearly depends on the cost
of labour; therefore the returns on the operation must be
assessed and obviously depend on the cost of the labour
at the place where dismantling takes place. It is not eco-
nomic in Europe or the USA but will probably be very
lucrative in emerging countries, where informal back-
yards recyclers today apply their work to the total
amount of the PCB using simple techniques with an ex-
tremely negative impact on the environment. Instead, and
most importantly, the proposed process will permit the
recovery of precious metal from an inorganic matrix not
containing the precursors for the formation of organic
The obtained results demonstrate that the manual dis-
mantling operation can be regarded as an easy and inex-
pensive method to sort out the valuable components of
PCBs in WEEE and to reduce the volume of waste to be
processed for the recovery the precious metals.
After this, further study was made of the extractive
metallurgy of gold from this kind of sample. The matrix
is the main difference between processing PCBs and pri-
mary raw materials to recover valuable elements. Silicon
is the main component in the former, whereas silica is the
main component in the latter. While this difference does
not greatly affect hydrometallurgical processes, it plays
an important role in pyrometallurgical operations, due to
the difference in the oxidation state of the waste to be
treated. Moreover, another difference between recovering
gold from PCBs and from a primary raw material, is the
volume of material involved in the process which is ex-
tremely small in processing PCBs for an equal amount of
recovered metal.
The importance of the above data is due to the fact that
for this process there is a substantial coincidence in in-
dustrial scale and laboratory scale, and therefore all the
findings from the experiments in extractive metallurgy
could be directly applied either to real industrial cases or
to backyard recyclers in emerging countries.
5. Conclusions
A 20961 kg WEEE sample was collected in a Material
Recycling Facility for 14 days to eliminate variations in
feeding, and the components of Printed Circuit Boards ,
coming from computers, monitors and TV-sets, were
analyzed for their Au and Pd contents. Most of the gold
and palladium is contained in computer PCBs. The gold
is present at an average concentration of 344 µg/g in the
entire board but is also found in processors (72%) and
integrated circuits (19%) of the board at concentrations
of 7004 µg/g and 701 µg/g, respectively and 2400 µg/g
as a total. The amount of these two gold-bearing compo-
nents of computer-PCBs is about 0.11% of the whole
sample collected and 13% with respect to the whole
board. Both components have been considered “easy” to
remove by the operators, hence the gold is easily recov-
erable. As far as palladium is concerned, the metal is
present in MLCC capacitors (80%) and in varistors and
ceramic condensers (18%) at a concentration of 16808
µg/g and 2130 µg/g respectively with an average con-
centration of 102 µg/g in the whole board. The palla-
dium-bearing components represent the 0.012% of the
Copyright © 2011 SciRes. JEP
Optimization of Precious Metal Recovery from Waste Electrical and Electronic Equipment Boards681
entire sample collected and 1.36% of the whole board.
Unfortunately, the palladium-bearing components of
computer-PCBs are hard to remove from the board and
the metal is not easily recoverable.
Extraction of precious metals from monitors and TV
boards does not seem worth studying due to the low val-
ues recoverable.
6. Acknowledgements
This paper is in memory of our collegue Massimo Delfini
who greatly helped us in carrying out the research. The
authors want to thank the Association for Georesource
Engineering of Rome, Italy (CINIGEO) for the precious
contribution supplied to the present work.
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