Materials Transactions, Vol. 50, No. 6 (2009) pp. 1536 to 1540
#2009 The Japan Institute of Metals
Novel Evaluation Method of Elemental Recyclability from Urban Mine
—Concept of Urban Ore TMR—
Eiji Yamasue1 , Ryota Minamino1 , Takeshi Numata1 , Kenichi Nakajima2 , Shinsuke Murakami3 ,
Ichiro Daigo3 , Seiji Hashimoto2 , Hideyuki Okumura1 and Keiichi N. Ishihara1
1
Graduate School of Energy Science, Kyoto University, Kyoto 606-8501, Japan
National Institute for Environmental Studies, Tsukuba 305-8506, Japan
3
Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
2
In this study, the total materials requirement (TMR) to recycle chemical elements from the urban ore by recycling (urban ore TMR, UOTMR) has been compared with the TMR to extract the element from the natural ore by smelting (natural ore TMR, NO-TMR) in order to
evaluate the urban ore grade on an equal footing with the natural ore. A framework of UO-TMR based on the NO-TMR framework is developed.
To validate the developed framework, the UO-TMR of a laptop PC is estimated assuming gold, silver, copper, iron, aluminum, tantalum and
indium are recycled. It is found that the UO-TMRs for gold, silver, copper, iron, aluminum and tantalum are lower than NO-TMR, but that for
indium is higher. The ratio of ‘‘urban tailings’’ is at most 60% of the total, which is smaller than that of NO-TMR ‘‘tailings’’. In contrast to the
contributions of energy and material inputs for the recycling process, the contribution of transportation is not very large. For the UO-TMR of
indium, the contribution of materials for recycling process is extremely large. The availability and scalability of UO-TMR are also
discussed. [doi:10.2320/matertrans.MBW200816]
(Received October 20, 2008; Accepted March 2, 2009; Published April 22, 2009)
Keywords: total materials requirement (TMR), urban mine, urban ore, recycle, elemental concentration
1.
Introduction
6
10
TMR ¼ ðDirect Material InputsÞ
þ ðIndirect Material InputsÞ þ ðHidden FlowsÞ: ð1Þ
Although no one has confirmed whether TMR reflects
environmental burden, it does imply a disturbance of the
global environment.
log(TMR) = –0.813log(x) + 2.289
TMR (g /g)
Large amounts of valuable resources, such as rare metals
in electric and electronic products, are said to be in ‘‘urban
mines’’,1) which is becoming a common term not only in the
field of environmental studies but also among the general
public. In Japanese urban mines, Halada2) reported accumulated amounts of several chemical elements. For example,
he estimated the following amounts, expressed as percentages of the world’s known deposits: gold 16% (6800 t),
silver 22%, indium 61%, tin 42% and tantalum 10%. From
the viewpoint of the urban mine, each waste product is
considered to be ‘‘urban ore’’, and its effective utilization is a
key issue for resource-poor countries such as Japan. However, one has to carefully consider whether the element
should be smelted from crude (natural) ore or recycled from
urban ore.
In the smelting process of an element, the concentration of
the target element in natural ore is a general index for
evaluating the ore grade. The development of a mineral
deposits with higher elemental concentration is an important
national strategy for resource-abundant countries and results
in less energy, material inputs and cost for smelting, resulting
in higher productivity. To further explain this concept, let us
introduce the total material requirement (TMR)3) as one of
the indices of material intensity,4) described below. TMR
consists not only of direct and indirect material inputs
(economic activities) but also of hidden flows (non-economic
activities), as shown in the following.
4
10
2
10
–4
–2
0
2
10
10
10
10
Elemental concentration in natural ore (%)
Fig. 1 Relationship between TMR and the elemental concentration in
natural ore.
Halada et al. estimated both ‘‘ore-TMR’’ that a follows
hidden flow such as overburden and waste rock to obtain
metal ore5) and, based on the ore-TMR, the ‘‘TMR of metal’’
that considers the total amount of direct, indirect and hidden
flows to obtain a metal, while taking into account the
allocation.6) As shown in Fig. 1, it is found that the logarithm
of the TMR of metal6) generally has a linear relationship with
the elemental concentration in natural ore. This linearity is
present because the amount of tailings, such as overburden
and waste rock (hidden flows), is dominant compared with
energy and material inputs (direct and indirect inputs). In
other words, linearity indicates some equivalence of TMR to
the elemental concentration in crude ore.
However, in the recycling process of an element in urban
ore, it is not appropriate to evaluate its grade using the
Novel Evaluation Method of Elemental Recyclability from Urban Mine —Concept of Urban Ore TMR—
elemental concentration. One reason is that the element
in urban ore generally exists in many forms compared
with the elements of natural ore. For example, aluminum
exists as elemental aluminum, duralumin, Al-Cu, Mg, Mn, Si
alloys, etc., in urban ore, but its form is primarily bauxite in
natural ore. Another reason is that the recycling process of
urban ore is different from the smelting process of natural
ore; that is, the required energy and material inputs are
different. Hence, to evaluate the urban ore grade on a scale
comparable to that of natural ore, the TMR for obtaining an
element from urban ore by recycling (urban ore TMR, UOTMR) should be compared with the TMR for obtaining the
element from natural ore by smelting (natural ore TMR, NOTMR).
NO-TMR data has been estimated for almost all the
elements by Halada et al. as shown in Fig. 1.6) However, no
framework or even data has been developed for UO-TMR.
Furthermore, for urban ore, since the amount that corresponds to tailing in natural ore is not expected to be
dominant, it is impossible to estimate UO-TMR directly from
the elemental concentration. Thus, the goal of this study is to
develop the framework of UO-TMR, and then estimate UOTMR according to this framework.
2.
Development of Framework
2.1 Review of TMR
Before presenting the development of the framework,
TMR-related research is briefly described.7) An important
concept common to TMR is ‘‘hidden flow’’, as mentioned
above. From the viewpoint of hidden flow, material inputs
per service unit (MIPS), proposed by Friedrich SchmidtBleek, should be explained.8) MIPS is the material intensity
through the lifecycle of a product, and it reflects the total
amount of involved natural resources for implementation of a
product or service.9) Albert et al. reported the TMR for
national economic activities in Germany, USA, Netherlands
and Japan.4) Stefan et al. compared the change in TMR with
economic growth around the world.3) In Japan, Halada
reported the TMR of metal from natural ore,6) that is, NOTMR. Also, Nakajima et al. reported the TMR of energy and
various materials10) using the same framework as NO-TMR.
In the following section, the framework of NO-TMR is
examined, followed by development of the UO-TMR framework.
2.2 Framework of NO-TMR
To produce an element, not only direct material and energy
inputs such as ore and reductant are required, but also indirect
material and energy inputs, such as energy for transportation,
are needed. Using typical (crude) steelmaking as an example,
coke and concentrated ore to produce pig iron correspond
to indirect inputs, whereas pig iron and energy for heat
generation correspond to direct inputs. The indirect inputs
induce other indirect inputs such as energy for the coke
production and for transportation of concentrated ore from
mines.
It should be noted that the source of concentrated ore is
crude ore, which is mined with a large amount of overburden
and waste rock, etc., (i.e., tailings). Since tailings are
1537
overlooked in the marketplace, they do not appear in
economic statistics; hence, tailings are also called ‘‘hidden
flow’’. In energy production, crude oil as a typical energy
source is generally produced with a large amount of sand,
which is a hidden flow. As a matter of practice, hidden flows
exist for almost all materials and energy. However, in the
framework of NO-TMR, the different compositions of
tailings among various mines are not considered.
In the smelting process, by-products are frequently
produced. Although no clear treatment method of byproducts has been established through life cycle assessments
(LCAs), the employment of system expansion or allocation
methods that disclose the calculation manner are considered
reasonable and proper. In the case of NO-TMR estimation,
Halada allocated the shared input and hidden flow for byproducts in monetary proportion.
2.3 Framework of UO-TMR
In the recycling of an element from urban ore, the
generation of waste products is denoted the starting point of
the evaluation. That is, the amounts of direct inputs, indirect
inputs and hidden flows after the starting point are included.
In steel recycling using an electric arc furnace, the direct
inputs include crude steel, steel scrap recovered from waste
products, electricity for the furnace; indirect inputs include
the pig iron to produce the crude steel, energy for shredding
the waste products and energy to transport the waste
products, etc. These indirect inputs induce further indirect
inputs, as in the smelting process of natural ore. Here, unreclaimed parts of which are defined as ‘‘urban tailings’’ in
this study, in contrast to the terms overburden, waste rock and
tailings, etc., defined for natural ore. The urban tailings are
considered hidden flow. The summation of not only the direct
and indirect inputs but also the urban tailings and hidden
flows accompanied by both inputs is the UO-TMR. As with
NO-TMR, difference in the compositions of the urban
tailings are not considered, and shared inputs and hidden
flows are allocated by recycled elements.
Figure 2 illustrates the proposed framework of UO-TMR,
and Fig. 3 shows the system boundary of the UO-TMR
estimation. In the following section, UO-TMR is estimated
along with the proposed framework.
3.
Test Estimation of UO-TMR based on the Framework
3.1 Target urban ore, data and assumptions
The UO-TMR of gold, silver, copper, iron, aluminum,
tantalum and indium in a laptop PC weighting 1930 g is
estimated as a test case. The composition was determined
from literature11–13) except for tantalum, neodymium and
titanium which were measured in this study using energy
dispersive X-ray analyzer (0.31, 0.62, 0.18 g/laptop-PC,
respectively).
In the transportation process, it is assumed that the amount
of waste product in each prefecture is proportional to the
number of households in the prefecture and the waste product
is transported to the closest recycling plant actually accepting
laptop PCs. Such plants are located in Hokkaido, Chiba,
Aichi, Kyoto and Fukuoka prefectures. The transportation
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E. Yamasue et al.
Fig. 2 Schematic diagram of proposed framework of UO-TMR.
System boundary
Energy
Materials
Hidden
Materials
input
Transport
UO–TMR
NO–TMR
Energy input
Hidden
Recycling
process
Recycled
element
4
TMR (g /g)
Hidden
Hidden
6
10
Waste product
(urban tailings)
10
2
10
Fig. 3
System boundary of UO-TMR estimation.
distance is estimated using the support system for driving
plan, ‘‘SMAP ver.3’’.14) Here, the prefectural capital is used
as the reference point of the estimation. Based on the
assumptions, the average transportation distance per unit
laptop PC from consumer to recycling plants is estimated to
be 130 km.
In the recycling process for gold, silver, copper, iron and
aluminum, it is assumed that well-established conventional
recycling processes are applied. After the separation processes, iron is recycled using an electric arc furnace, and
aluminum and primary wire-shaped copper are re-melted.
Mixtures including gold, silver and copper from printed
circuit board were subjected to the copper recycling process,
resulting in the recycling of gold and silver as by-products.
The specific energy and material consumption data are
estimated based on Morii’s report15) and the NIMS-EMC
MDE report,16,17) respectively. In the recycling of tantalum
from tantalum capacitors and indium from liquid crystal
displays (LCDs) etc., we assume Mineta’s process18) for
tantalum, and the patented process by Sharp Co., Ltd.19) for
indium.
For shredding and separation processes, it is assumed from
interview investigation that a recycling plant using a shredder
(1 unit, 100 kW of electricity consumption), cyclones (2
0
10
Fig. 4
Au
Ag
Cu
Fe
Al
Ta
In
The estimated UO-TMR compared with NO-TMR.
units, 5 kW for each), magnetic separation (1 unit, 10 kW), a
trammel (1 unit, 10 kW) and others (60 kW in total) can
process 450 tons of waste laptop-PC per month.
For the allocation of shared inputs and flows, two possible
formulas are considered. One is allocation by the number
of recycled elements, and the other is allocation by the
monetary value of recycled elements. Since Halada6) and
Nakajima et al.7) implemented a formula based on monetary
value, we also employ it for comparison in this study. The
detailed calculation method will be presented in a later
publication.
3.2 Results of the estimation
Figure 4 shows the estimated UO-TMR compared with
NO-TMR. As shown in the figure, UO-TMRs are lower than
NO-TMRs except for indium. This result indicates that the
grades of all the elements excluding indium in the product are
higher than those in natural ore. It is interesting that although
Novel Evaluation Method of Elemental Recyclability from Urban Mine —Concept of Urban Ore TMR—
materials for recycling process
1539
Elemental concentration in natural ore (%)
Elemental concentration of natural ore equivalent (%)
energy for recycling process
2.6
Elemental Concentration (%)
shredding/selection
transportation
urban tailings
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
40
10
1
11
12
5
0.1
0.3
0.01
53
0.001
0.0001
Au
Au
Ag
Cu
Fe
Al
Ta
In
Ag
Cu
Fe
Al
Ta
ln
Fig. 6 Elemental concentration of natural ore equivalent (ECNOE)
reduced from UO-TMR compared with elemental concentration of natural
ore.
Fig. 5 The breakdown of the estimated UO-TMR.
the elemental concentration of indium (45 ppm) in the
product is greater than that in natural ore (10 ppm), the
estimated UO-TMR of indium (17000 t/t) is greater than the
NO-TMR of indium (4500 t/t).
Figure 5 shows the breakdown of the estimated UO-TMR.
The ratios of urban tailings are, at most, 60% of the total and
are relatively low compared with the ratios of tailings in the
NO-TMR, and the contribution of the transportation is rather
small, whereas the contributions of energy and material
inputs for the recycling process are very large.
It is notable that in indium process, the contribution of
material inputs for the recycling process is extremely large.
This could be because the recycling technique for indium is
still in development. Also, the indium in an LCD is spread
thinly on a huge glass panel, and so excessive amounts of
acid and organic solvent are required to leach the indium.
4.
Discussion
4.1 Application of UO-TMR
It is shown that the elemental grade in the urban ore can be
evaluated by applying the procedures of the NO-TMR.
Furthermore, we can quantify how much a recycling process
should be improved with the UO-TMR. In the case of indium
recycling, the main reason for a huge UO-TMR shown in
Fig. 5 is the excessive amount of acid and organic solvent
required for leaching indium tin oxide. To improve the
recycling process, the materials inputs must be reduced.
For example, the acid and organic solvent could be reused.
Using UO-TMR, a numerical target for the improvement
can be proposed. Although more concrete results will
be shown in another paper,20) it is briefly stated here that
the acid and organic solvent should be re-used more than ten
times to reduce the UO-TMR of indium to the level of the
NO-TMR.
Evaluation using UO-TMR can be applied not only to
e-wastes but also vehicle, urban structure, landfills, etc. Since
UO-TMR depends on the number of recycled elements and
the recycling method, etc., scenario analyses should be used
for detailed evaluation of the recyclability. Furthermore, the
UO-TMRs of various materials such as plastics and alloys
can be derived.
4.2
Elemental Concentration of Natural Ore Equivalent, ECNOE
In the first section, the linear relationship between NOTMR and the elemental concentration in crude ores was
shown. In this study, we estimated UO-TMR, and it can be
reduced to another elemental concentration in the following
manner.
Assuming that the elemental concentration in natural ore is
100% when NO-TMR is equal to 1, the relationship between
NO-TMR and the elemental concentration in crude ores, as
shown Fig. 1 can be recalculated as follows;
logðNO-TMRÞ ¼ 0:982 logðxÞ þ 2
ð2Þ
where x indicates the elemental concentration in natural ore.
If we substitute UO-TMR for NO-TMR in eq. (2), the
obtained ‘‘x’’ is the reduced elemental concentration of the
urban ore. It can be called the ‘‘elemental concentration of
natural ore equivalent’’ (ECNOE).
Figure 6 shows a comparison of the ECNOE with the
elemental concentration in natural ore. As shown in this
figure, the higher the elemental concentration is, the higher
the possibility of recycling becomes. It is found that the
elemental grade of gold in a laptop PC is 50 times greater
than that in natural ore, but elemental grade of indium is 0.3
times at most. Given the current recycling process, indium in
LCDs should not be recycled. The figure also reflects the fact
that tantalum is only slightly recycled in Japan, but it may be
worthwhile to recycle. Finally, although the ECNOE is
essentially same as the UO-TMR, it is thought that the
elemental concentration seems to be a more easily understandable unit (or index) than TMR for non-expert people.
5.
Conclusion
In this study, it was clarified that the total material
requirement for obtaining elements from urban ore by
recycling (urban ore TMR, UO-TMR) can be compared with
the TMR for obtaining elements from natural ore by smelting
(natural ore TMR, NO-TMR) to evaluate the urban ore grade
on the same basis used for natural ore. The framework of UOTMR is developed based on that of NO-TMR. It is found for
laptop PCs that the UO-TMR for gold, silver, copper, iron,
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E. Yamasue et al.
aluminum and tantalum is lower than the NO-TMR for each
element, except the UO-TMR for indium is higher primarily
because the recycling process requires large material inputs.
From the breakdown provided by the UO-TMR, it is found
that the ratio of urban tailings, which is at most 60% of the
total, is relatively small compared with ratio of tailings in
NO-TMR. Also, the contribution of transportation is rather
small, whereas the contributions of energy and material
inputs for the recycling process are great. ‘‘Elemental
Concentration of Natural Ore Equivalent’’ (ECNOE), which
can be induced from the UO-TMR, is proposed as an
understandable index.
Acknowledgement
This research was supported by a Waste Management
Research Grant from the Ministry of the Environment, Japan,
project numbers: K1810, K1930, K2031 (2006–2008),
project leader: Dr. Seiji Hashimoto, project name: ‘‘Development of material stock account framework and its application: strategies for waste/resource management’’.
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