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st
a,, Res
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Article history:Received 24 July 2014Accepted 13 October
2014Available online 6 November 2014
Keywords:Waste incinerationZn recovery
bottom ash and air pollution control (APC) residues, namely
yashes (including boiler ash and lter ash) and lter cake. While
inmany countries bottom ash is already processed in order to
recoversome of the metals contained (mainly iron scrap, but also
alumin-ium and copper), APC residues (which amount in total to
about2 million tons in the European Union) have been hardly
consideredfor resource recovery so far. In all European countries
they are clas-
s are either land-lso the bact or other
cals in order to complywith regulatory limit values for
wastetance at non-hazardous landlls. Both practices are
associatesignicant costs, ranging between 200 and 250/t y ash
(2008) and the loss of valuable materials (e.g. metals). Contrary
tothat, only a small portion of APC residues, mainly from uidized
bedincineration, can be landlled in non-hazardous landlls
withoutprior treatment.
Only in fewEuropean countries attempts aremade to
recycleAPCresidues (Astrup, 2008) or at least parts of them. In the
Netherlands,for instance, y ashes partly substitute ller material
in asphalt Corresponding author.
Waste Management 37 (2015) 95103
Contents lists availab
an
els(Eurostat, 2014), which amounts, together with commercial
waste,to about 78 million tons of total waste fed toWaste to Energy
(WtE)plants (CEWEP, 2011). Besides the production of electricity
andheat, MSW incineration (MSWI) goes along with the generation
of
other hand.Due to these characteristics most APC residue
lled at hazardous waste landlls (this includes aof former salt
mines) or are stabilized with
cemenhttp://dx.doi.org/10.1016/j.wasman.2014.10.0100956-053X/ 2014
Elsevier Ltd. All rights reserved.kllingchemi-accep-d withAstrup,1.
Introduction
In 2011 about 23% of Municipal Solid Waste (MSW) generatedwithin
the European Union has been thermally valorised
sied as hazardous waste, which results from environmental
con-cerns regarding the leachability of easily soluble salts (such
as Cl,Na or K) and heavy metals (such as Cd, Pb, Cu or Zn) on the
onehand, as well as the total content of As, Cd, Hg, and dioxins on
theResource evaluationResource classicationa b s t r a c t
Solid residues generated at European Waste to Energy plants
contain altogether about 69,000 t/a of Zn, ofwhich more than 50%
accumulates in air pollution control residues, mainly boiler and
lter ashes. Inten-sive research activities aiming at Zn recovery
from such residues recently resulted in a technical scale
Znrecovery plant at a Swiss waste incinerator. By acidic leaching
and subsequent electrolysis this technol-ogy (FLUREC) allows
generating metallic Zn of purity > 99.9%. In the present paper
the economic viabilityof the FLUREC technology with respect to Zn
recovery from different solid residues of waste incinerationhas
been investigated and subsequently been categorised according to
the mineral resource classicationscheme of McKelvey. The results of
the analysis demonstrate that recovery costs for Zn are highly
depen-dent on the costs for current y ash disposal (e.g. cost for
subsurface landlling). Assuming current dis-posal practice costs of
220 /ton y ash, resulting recovery costs for Zn are generally
higher than itscurrent market price of 1.6 /kg Zn. With respect to
the resource classication this outcome indicates thatnone of the
identied Zn resources present in incineration residues can be
economically extracted andthus cannot be classied as a reserve.
Only for about 4800 t/a of Zn an extraction would be
marginallyeconomic, meaning that recovery costs are only slightly
(less than 20%) higher than the current marketprice for Zn. For the
remaining Zn resources production costs are between 1.5 and 4 times
(7900 t/a Zn)and 1080 times (55,300 t/a Zn) higher than the current
market value. The economic potential for Znrecovery from waste
incineration residues is highest for lter ashes generated at grate
incineratorsequipped with wet air pollution control.
2014 Elsevier Ltd. All rights reserved.b Institute for Water
Quality, Resource and Waste Management, Vienna University of
Technology, Karlsplatz 13/226, 1040 Vienna, Austriac Institute for
Chemical Engineering, Vienna University of Technology,
Getreidemarkt 9/166, 1060 Vienna, AustriaEvaluation of resource
recovery from waresidues The case of zinc
J. Fellner a,, J. Lederer a, A. Purgar a, A.
WinterstetteraChristian Doppler Laboratory for Anthropogenic
Resources, Institute for Water Quality1040 Vienna, Austria
Waste M
journal homepage: www.e incineration
H. Rechberger b, F. Winter c, D. Laner a
ource and Waste Management, Vienna University of Technology,
Karlsplatz 13/226,
le at ScienceDirect
agement
evier .com/locate /wasman
-
nagpaved roads. Even though the encapsulation in asphalt may
lastlonger than in cement the dilution and dispersion of
pollutants,resulting from this practice has to be criticized froman
environmen-tal perspective. In Switzerland several waste
incinerators treat theiry ashes by applying acidic washing.
Salts/brine (e.g. for the regen-erationof ion exchangers or for
de-icing roadsduringwinter time) aswell as heavymetals are thereby
separated from the y ash, and theprocessed almost heavy metal free
y ash cake is landlledtogether with bottom ash at non-hazardous
waste landlls. Theheavy metals enriched ltrate is neutralized and
the hydroxidesludge rich in Zinc (Zn) generated thereby can be sent
to specicZn-oxide recycling facilities (Bhler and Schlumberger,
2010). Overthe last few years this so called FLUWA process has been
furtherdeveloped and extended such that zinc can be recovered
directlyat the incineration plant (Schlumberger, 2010). This new
technol-ogy, called FLUREC, has recently been introduced on large
scale ata Waste-to-Energy (WtE) plant in Switzerland (KEBAG,
2013).
Moreover, the recovery of Zn or other metals out of MSWI yashes
has gained increasing interest in recent times, also outsideof
Switzerland. Numerous research activities in different
Europeancountries have been dedicated to a recovery of heavy metals
con-tained in MSWI APC residues (e.g. Karlfeldt Fedje et al.,
2010a,2012, 2012; Meylan and Spoerri, 2014). However, most
studiesconducted so far focused mainly on the technical and
environmen-tal evaluation of metal recovery (e.g. Boesch et al.,
2014). Economicconsiderations with respect to metal recovery are
rare and limitedto residues of certain WtE plants (Karlfeldt Fedje
et al., 2014). Acomprehensive economic evaluation considering
different MSWIy ashes from plants of various combustion and APC
technologyhas not been carried out so far.
Hence, the aim of the present study is to evaluate the
potentialfor recovery of Zn from incineration residues generated at
Euro-pean WtE plants, focusing on y ashes but also considering
bottomashes generated. Filter cake resulting from water purication
ofincinerators using a wet ue gas cleaning system is not
consideredin this study due to its small mass and low Zn content
(Astrup,2008). The evaluation procedure is based on the framework
forevaluating anthropogenic resources recently developed byLederer
et al. (2014) is applied. Their approach foresees a combina-tion of
analysing material ows of the resource of interest and asubsequent
economic assessment for the recovery of those mate-rial ows. The
nal outcome of the evaluation conducted repre-sents the
classication of Zn ows in incineration residues intodifferent
categories, which have been chosen in analogy to theclassication of
natural resource stocks (discriminating betweenreserves, marginally
economic resources, subeconomic resources,and other occurrences of
low grade).
2. Material and methods
In general, the applied framework for evaluating
anthropogenicresources follows the procedure given in Fig. 1. After
an initialphase of prospection (1), which aims at the identication
of rele-vant stocks and ows, a phase of detailed investigation
comparableto the exploration (2) of natural deposits follows.
Therefore, datafor resource ows and stocks of interest are
collected and furtherprocessed. Thereto the method of material ow
analysis MFA asdescribed by Brunner and Rechberger (2004) is
applied. MFAallows tracing ows and stocks of materials or chemical
substancesof interest with a system dened in space and time.
Whereas dur-ing the prospection macro-level material ow analyses
are con-ducted, the exploration phase is characterized by detailed
MFA,which also accounts for uncertainties and if relevant also for
asso-
96 J. Fellner et al. /Waste Maciated ows of wanted or unwanted
substances. In order to extractthe desired material and produce a
marketable good, a technologyfor Zn recovery is required. By
choosing the technology, a roughestimate on the associated costs
can be given (3). The latter formsthe base for the subsequent
classication of the different types ofows and stocks of interest
(4).
Due to the fact that investigations have a priori been
dedicatedto the MSWI residues annually generated, the initial step
ofresource prospection (step 1) has been left out in the frame
ofthe present investigations. Furthermore, contrary to the
evaluationof Lederer et al. (2014), only ow resources have been
considered.Flow resources are characterized by a continuous
availability atdifferent intervals and are in case of natural
resources also classi-ed as renewable resources, which are in
contrast to non-renew-able stock resources. According to Lederer et
al. (2014) wastesgenerated can be considered as anthropogenic ow
resources.
As for the present case study these ow resources are
partlyclassied as hazardous waste, costs associated with the
conven-tional disposal of these waste have to be accounted for as
revenueswhen accomplishing the economic analysis of the recovery
tech-nology chosen.
2.1. Exploration of Zn ows in MSWI residues
In order to explore residues from waste incineration aspotential
secondary resource for Zn, a detailed literature analysisfocusing
on the following issues has been conducted:
The amounts of waste incinerated in European WtE plants(CEWEP,
2011),
the technology of incineration applied distinguishing
betweengrate incineration & rotary kilns on the one hand and
uidizedbed incinerators on the other hand (ISWA, 2006a, 2013), as
theydetermine the specic amount of different MSWI residues andtheir
respective content of valuable metals,
the technology of air pollution control (APC) systems (wet,
dry& semi-dry residue systems) used at
EuropeanWaste-to-Energyplants and the respective amount of APC
residues (ISWA, 2013,2006a), both again inuencing the content of
valuable metals(e.g. Zn) in APC residues,
the Zn content in different MSWI residues (e.g., Auer et
al.,1995; Hjelmar, 1996; Jakob et al., 1996; Abe et al., 2000;Nagib
and Inoue, 2000; Mangialardi, 2003; Aubert et al., 2004;Hallgren
and Strmberg, 2004; Ferreira et al., 2005; Aubertet al., 2007; Van
Gerven et al., 2007; Chiang et al., 2008;Quina et al., 2008;
Bontempi et al., 2010; Karlfeldt Fedje et al.,2010b; Karlsson et
al., 2010; Lam et al., 2010; Schlumberger,2010; De Boom et al.,
2011; Nowak et al., 2013; Boesch et al.,2014), and
transfer coefcients describing the portioning of Zn to the
differ-ent outputs of incineration plants (e.g., Schachermayer et
al.,1996; Brunner and Mnch, 1986; Morf and Brunner, 1998).
In all parameters of interest numerous data sources (as
indi-cated above) have been utilized, which resulted in particular
forthe Zn content in MSWI residues as well as for the transfer
coef-cients of Zn rather in ranges of values than in exact gures.
Thedeviations observed between the different sources have
beenaccounted for by using uncertainty ranges for the
respectiveparameters in the frame of the subsequent material ow and
eco-nomic analyses.
Based on the results of the literature survey a material owmodel
describing the ows of Zn through European WtE plantshas been
established.
2.2. Economic Evaluation of Zn ows
ement 37 (2015) 95103The MFA model together with detailed
information about therecovery technology, its consumables and costs
for alternative
-
disposal of MSWI residues, form the basis for the economic
evalua-tion of Zn recovery. To the knowledge of the authors the
only tech-nology for recovering Zn from MSWI residues operating at
largescale is the FLUREC process, although other technologies
(e.g.Karlfeldt Fedje et al., 2014) for zinc extraction (producing a
metalconcentrate of lower purity) have been developed in the
recentyears. Therefore, the FLUREC technology has been assumed
forthe economic evaluation of Zn resources present in MSWI
residues.
Fig. 2 gives an overview of the FLUREC technology and
summa-rizes the required operating supplies. Detailed information
aboutthe specic quantities of the latter together with data about
prod-ucts and by-products are of major importance for the
economicevaluation. Boesch et al. (2014) who performed a LCA on
wasteincineration enhanced with new technologies for metal
recovery,
provide detailed information about materials and energy
owsassociated with the recovery of Zn out of MSWI y ash. These
dataabout energy and material ows were subsequently linked
withmarket prices for the different operating supplies pOPi
(includingelectricity) and for the nal product, which is Zn metal
of pur-ity > 99.9%, pZn, as well as with the amount of the
by-product, aconcentrate containing Pb, Cu, Zn and Cd. In addition
specic costsCDPi for landlling the residues generated by the FLUREC
technol-ogy, necessary investment costs of the technology CINV as
well asavoided costs for the prevailing disposal of residues in
Europe CCPare accounted for (see Eq. (1)). The latter include
cement stabiliza-tion with subsequent disposal at non-hazardous
waste landlls ordirect landlling at hazardous waste sites. Due to
the fact that leg-islation for landlling of hazardous waste (e.g.
landll tax) may
Fig. 1. Procedure for the evaluation of anthropogenic resources
(after Lederer et al., 2014).
J. Fellner et al. /Waste Management 37 (2015) 95103 97Fig. 2.
Schematic process diagram of the FLUREC technology (acidic y ash
leaching wseparation of Pb, Cu, Cd during solidication) based on
Boesch et al. (2014).ith integrated Zn recovery, whereby Zn powder
is to be added for the reductive
-
nagmOPi is the specic mass of operating supply i (kg/t y ash)
and spe-cic energy demand (kW h/t y ash),mDPi is specic mass of
residuej (resulting from the FLUREC process) to be disposed of
(kg/t y ash),mZn is specic mass of metallic Zn recovered (kg Zn/t y
ash), mConis specic mass of concentrate containing Pb, Cu and Cd
(kg Zn/t yash), pOPi is market price for operating supply i and
energy demand i(/kg operating supply) or (/kW h), pZn is market
price for metallicZn (/kg Zn), pCon is market price for concentrate
containing Pb, Cuand Cd (/kg concentrate), cZn is specic production
costs for metal-lic Zn (/kg Zn), CDPj is specic costs for the
disposal of residue j (/kg residue), CINV is specic investment
costs for the FLUREC technol-ogy (/t y ash), CFLUREC is specic
overall costs for the FLUREC tech-nology (/t y ash) and CCP is
specic costs for the current practiceof y ash disposal (/t y
ash).
2.3. Classication of Zn ows
The classication of Zn present in MSWI residues has
beenaccomplished in accordance with Lederer et al. (2014) who
basedtheir evaluation framework for anthropogenic resources
onMcKelvey (1972). The approach considers both, the economic
via-bility of extracting a secondary raw material from a resource
andproducing a tradable good, and the knowledge of the existence
ofthe resource. For the economic classication, McKelvey suggeststhe
following terms. Resources are economic or recoverable if theycan
be extracted with a prot. Therefore, the production costs mustbe
below the market price of the product achievable, which meansin our
case cZn < pZn. Resources for which the production costs
arehigher than the price, but not by more than a factor of 1.5,
aremar-vary considerable between different European countries,
ratherlarge uncertainty ranges for CCP had to be considered. The
balance(Eq. (1)) of all expenses and revenues represent the overall
speciccosts or benets of the FLUREC technology CFLUREC. In case
CFLURECbecomes negative, Zn recovery can be considered as
economic,whereas in case CFLUREC results in a positive value, the
applicationof the FLUREC technology is non-economic at current
marketprices.
Assuming that the overall specic costs of the FLUREC technol-ogy
should be zero, specic production costs for secondary Zn cZn(/kg
Zn) can be determined (see Eq. (2)). In case that specic
pro-duction costs czn are lower than the market price pZn for
metallicZn, Zn recycling (using the FLUREC technology) is
economicallyviable and vice versa.
In order to account for the fact that all data required for the
eco-nomic evaluation (physical mass ows, prices, costs for disposal
ofresidues or investment costs) are uncertain, plausible data
rangeswere dened and subsequently used to perform Monte Carlo
sim-ulations. Thereto the software @risk was used. For the denition
ofthe uncertainties temporal (i.e. over the last 5 years) and
spatialvariations in market prices and costs for disposal have been
evalu-ated. The uncertainty of specic materials ows and energy
con-sumption of the FLUREC technology has been estimated based
oninformation provided by Boesch et al. (2014).
Xn
i1mOPi pOPi
Xl
j1mDPj CDPj CINV mZn pZn mCon pCon
CCP CFLUREC 1
cZn Pn
i1mOPi pOPi Pl
j1mDPj CDPj mCon pCon CINV CCPmZn
2
98 J. Fellner et al. /Waste Maginally economic. Resources above
this value are termed as submar-ginal or subeconomic, whereby
according to Lederer et al. (2014) athreshold factor of 10 times
the market price is assumed(pZn < cZn < 10 pZn). Resource ows
whose production costs areabove the threshold (of 10 times the
market price) are countedas other occurrences.
The classication according to the certainty of the existence of
aresource ow is structured as identied demonstrated, identied
inferred, and potentially undiscovered. To perform this
classication,the uncertainties determined for each Zn ow in the
residues ofMSWI are used. Identied demonstrated resources are of
provenexistence and knowledge is highly certain (condence that
theactual ow of Zn is at least this size is 90%). Identied
inferredresources are dened here as the amount of Zn ows between
thelower uncertainty bound (condence 90%) and the mean value ofthe
ow. The same amount of the material (due to symmetricuncertainty
ranges) is designated as potentially undiscoveredresources, which
may exist but are highly uncertain. Finally, across-classication is
accomplished considering both, economicviability and knowledge.
Therein, reserves are resources that areboth identied demonstrated
and economically extractable.The reserve base further includes the
part that is identied dem-onstrated and not protably extractable
with current technologyand market conditions (classied as
marginally economic).
3. Results
3.1. Exploration of Zn ows in MSWI residues
According to CEWEP (2011) about 78 million tons of waste
havebeen utilized in European (EU-28 + Norway and Switzerland)
WtEplants in 2011. This equals to about 90% of the total waste
inciner-ation capacity (about 86 million tons) installed. Out of
the 78 mil-lion tons, the vast majority (68 million tons) is
thermally valorisedin grate incinerators (GI), the remaining part
of 4.2 million tons iscombusted in uidized bed combustion (FBC)
plants. According toinformation (data of 350 plants out of 470
plants in total have beenavailable) provided by ISWA (2006a, 2013),
about 45% of the incin-eration plants are equipped with wet ue gas
cleaning systems,29% with semidry and 26% with dry systems. The
discriminationof the incineration technology (grate vs. uidized
bed) and APCsystem (wet-semidry-dry) is of signicant importance for
theexploration of Zn ows, since the technologies do not only
stronglyinuence the size and grade (with respect to Zn content) of
yashes (see Table 1), but also the need of operating supplies
(e.g.consumption of additional acids like HCl for acidic washing)
aswell as costs for the current disposal practice. Fly ashes
fromFBC, for instance, are likely to be disposed of at
non-hazardouswaste landlls (due to their comparatively low contents
of heavymetals and salts), whereas y ashes from grate incinerators
areas a rule classied as hazardous and therefore have to be
landlledat hazardous waste sites or stabilized prior landlling at
non-haz-ardous sites. In Table 1 main outcomes of exploring MSWI
residuesas potential resource for Zn recovery are summarized. Based
on thedetailed analysis of data from more than 50 European WtE
plants,it becomes obvious that the APC control but also the type of
y ash(lter ash vs. boiler ash) strongly inuences the Zn content of
they ash generated. Whereas for dry or semidry APC systems
averageZn contents of y ashes amount to about 11,000 mg Zn/kg, wet
sys-tems may generate residues with Zn contents of about 22,000
mgZn/kg y ash (in case boiler and lter ash are collected
together)or even above 40,000 mg Zn/kg y ash (in case that lter ash
iswithdrawn separately). In comparison to the contents given
inTable 1, Zn contents of bottom ashes from waste incineration
arealmost one order of magnitude smaller (11006000 mg Zn/kg bot-tom
ash Hjelmar, 1996; Mller and Rbner, 2006; Dabo et al.,
ement 37 (2015) 951032009; Sorlini et al., 2011).Based on
transfer coefcients describing the partitioning of Zn
duringwaste incineration (between50% and 60%of Zn is
transferred
-
to the y ash and the remaining part to the bottom ash) and the
datagiven in Table 1, the average content of Zn in thewaste feed of
Euro-pean WtE plants have been determined to about 880 110 mg Zn/kg
wet waste. Considering this content and the overall mass ofwaste
combusted, the following material ow analysis diagramhas been
derived (see Fig. 3). In total about 69 9 kt of Zn are annu-ally
fed into European waste incineration plants. Almost half of it(32.5
2.7 kt) accumulates in MSWI residues (bottom ashes andy ashes from
uidized bed combustion) at average concentrationsbelow 6000 mg
Zn/kg ash (see supplementary material). About17 2.4 kt of Zn are
present in boiler and lter ash of grate inciner-ators equipped with
wet APC systems (average Zn content of about23,000 mg Zn/kg ash)
and almost the same amount (18.5 1.8 kt)
et al., 2014) the different MSWI residues have been
evaluatedregarding their specic costs for Zn recovery. In Table 2
all assump-tions made for the economic evaluation of Zn recovery
from lterashes of wet APC systems are summarized. Data for
evaluatingZn recovery from other MSWI residues (e.g. y ash from dry
orsemidry APC systems) are given in supplementary material.
Theresults for lter ashes from wet APC residues indicate that
despitethe comparatively high Zn contents (around 41,000 mg Zn/kg
ash)of these ashes, the specic production costs for Zn (taking
allexpenses and revenues into account) are about 1.8 0.8 /kg Znand
thus in average slightly above the current market price of1.6 /kg
Zn (average price over the last 5 year). Nevertheless, thelarge
uncertainty (standard deviation) in production costs of Zn
Table 1Statistical analysis of y ash (sum of boiler and lter
ash, and APC residues in case of dry or semidry APC) amounts (kg/t
waste) generated at Waste-to-Energy (WtE) plants withdifferent ue
gas cleaning systems and their respective Zn contents (mg Zn/kg y
ash).
Amount of y ash (kg/t waste input) Zn-content inue gas cleaning
residues (mg Zn/kg y ash)
Flue gas cleaning system Boiler and lter ash of Filter ash of
wet systemsa
Wet Semidryb Dryb Wet systems Semidry systemsb Dry systemsb
Mean 22 42 40 22,100 11,000 11,700 41,000Median 22 40 39 19,100
9700 10,800 42,70010% quantile 14 30 30 14,000 6700 7600 20,90090%
quantile 30 53 54 35,700 15,600 18,500 59,600No. of WtE plants 53
33 11 16 14 9 15No. of different countries 11 10 6 11 10 6 5
a Plants with separate collection of lter ash and boiler ash.b
In case of semidry and dry APC system boiler and lter ashes include
air pollution control residues.
J. Fellner et al. /Waste Management 37 (2015) 95103 99can be
found in y ashes from dry and semidry APC systems (aver-age Zn
content of about 11,000 mg Zn/kg ash).
3.2. Economic evaluation and classication of Zn ows
Based on the material and energy demand of the FLUREC
tech-nology and the potential recovery rates for Zn (provided by
BoeschFig. 3. Annual Zn ows (in 1000 t) through European WtE plants
utilizing Municipal Socondence interval, respectively) red ows
indicate ows of MSWI residues with meauidized bed combustion, APC
air pollution control). (For interpretation of the
referencarticle.)(0.8 /kg, which equals 45% of the mean value)
indicates thatdepending on the parameter set chosen (mainly
depending onthe avoided costs for the prevailing disposal of
incineration resi-dues), it may be likely that Zn can be recovered
at costs lower thanthe current market price.
When comparing individual costs, revenues and savings
associ-atedwith the different inputs and outputs of the FLUREC
technologylid Waste MSW and Industrial Waste IW (uncertainties
represent the 10% and 90%n Zn contents above 8000 mg Zn/kg
(abbreviations used: GI grate incinerator, FBCes to colour in this
gure legend, the reader is referred to the web version of this
-
Table 2Economic analysis of Zn recovery from MSWI residues
(using the example of lter ash from wet APC systems) applying the
FLUREC technology.
Means of production and outputs Materials and energy(per 1000 kg
of yash)
Specic costs (positive) andbenets or savings (negative)
Total costs/savings (per1000 kg of yash)
Remarks
Unit Mean sd Unit Mean sd Datasource
Mean
inputsFly ash kg 1000 /kg -0.22 0.02 (1) 220 Savings for current
disposal practiceZinc content of y ash kg 41 1HCl (30%) of wet
scrubbera kg 550 100 /kg 0 0 HCl provided by acidic scrubber
waterHCl (30%) additional kg 40 20 /kg 0.11 0.015 (2) 4.4 Required
for enhanced extraction of
metalsSulfuric acid kg 15 1.5 /kg 0.16 0.02 (2) 2.4Hydrogen
peroxide H2O2 (50%) kg 65 15 /kg 0.30 0.030 19.1NaOH (50%) kg 125
12.5 /kg 0.11 0.015 (3) 13.9 Costs for neutralization of
extracted
residuesSolvents and complexing agents kg 0.4 0.08 /kg 0.4 0.1
(3) 0.2 Required for selective extraction of ZnPrimary Zinc
(powder) kg 5 0.8 /kg 1.6 0.1 (4) 8.5 Zn necessary for reductive
cementation
of Cd, Pb and CuQuicklime kg 200 20 /kg 0.08 0.01 (2) 16.0
Savings of quicklime for subsequent
neutralization of scrubber water incomparison to current
practice
Electricity kW h 347 18 /kWh 0.094 0.005 (5) 32.6 Electrolysis
of Zn and plant operation
Total investment costs for FLUREC (per1000 kg y ash)
180 20 (6) 180 Specic investment costs for FLUREC
outputsLeached y ash (non-hazardous waste
landll)kg 800 30 /kg 0.045 0.005 (7) 36.0 Disposal costs for
leached y ash
Depleted resin material (Hg adsorption) kg 1 0.1 /kg 18 2.8 (8)
18.4 Costs for depleted resin material for Hgremoval from acidic
scrubber water
Residual sludge (re-feeded to incinerator) kg 24 5 /kg 0 0
Concentrate Pb, Cu and Cd kg 9.2 1.5 /kg -1.6 0.2 (9) 14.8 Market
value for concentrate of Pb, Cu
and CdRecovery rate of Zn 0.75 0.025
Necessary revenues from Znproduction
64.7
Secondary Zinc production kg 36.1 1.3 Specic Zn production costs
(/kg) 1.8 0.8
All uncertainties given in table represent standard deviations
sd of normal distribution.Data sources: (1) Astrup (2008) (2)
www.alibaba.com; (3) www.orbichem.com; (4) www.nanzen.net; (5)
Eurostat (2013); (6) based on investment costs provided by
KEBAG(2013); (7) based on data provided by ISWA (2006b); (8)
personal communication of BSH Umweltservice AG (2014); (9) personal
communication of BMG Metall undRecycling GmbH (2014) based on the
assumption that the ratio of Pb and Cu in the concentrate is about
85:15.
a provided by wet APC system.
Fig. 4. Specic costs (+) and revenues/saving () of the FLUREC
technology when treating lter ash fromwet APC systems with an
average Zn content of 41,000 mg/kg y ash.
100 J. Fellner et al. /Waste Management 37 (2015) 95103
-
it becomes obvious that avoided costs for the current disposal
prac-tice of y ash aswell as investment costs for the technology
aremostsignicant for the economic viability (see Fig. 4). The
contribution ofrevenues realized by metallic Zn recovery is below
17% of the totalgross revenues, which amount to approximately
300/kg y ash.
For the other y and bottom ashes of European WtE plants, spe-cic
production or recovery costs of Zn are much higher (see Fig.
5).This can be attributed on the one hand to the lower Zn content
inthese ashes and on the other hand signicant amount of HCl
isrequired for plants with dry or semi-dry APC systems.
Moreoverrecovery costs for Zn contained in non-hazardous waste,
such asy ash fromFBCor bottomash fromgrate incineration, are
distinctlyhigher, as the potential savings for avoideddisposal
costs after treat-ment are minor. Detailed information about the
underlying data forthe economic evaluation of Zn recovery from
different types of yashes and bottom ashes is provided in
supplementary material.
Combining information about the size of Zn ows, incl.
theiruncertainties (see Fig. 3) and the specic recovery costs
(seeFig. 5) allows classifying Zn ows in accordance to the
classica-tion scheme for mineral resources (McKelvey, 1972). The
resultof this classication (Table 3) demonstrate that the total
size ofthe identied Zn ows in European MSWI residues is 69,000
t/a.Based on the average market price for Zn over the last 5
years
(1.6 /kg Zn), none of the Zn in the investigated MSWI
residuescan be economically extracted and thus cannot be classied
as areserve, although Zn extraction from separately collected
lterash from wet APC systems may already be economically viable
incase that avoided costs for the disposal of untreated y ash
areabove 230/ton ash.
The reserve base containing marginally economic and identied
demonstrated resources amounts to 4100 t/a (separately col-lected
lter ash from wet APC systems and assuming a technicalextraction
rate for Zn of 75%). An additional 700 t/a are marginallyeconomic
and inferred resources, leading to a total of 4800 t/a ofmarginally
economic resources. These gures are based on theassumption that at
50% of European WtE plants with wet APC lterand the boiler ash can
be separately collected. A total of 6800 t/a ofZn is classied as
subeconomic and demonstrated, with productioncosts approximately
2.5 times above the current market price of Zn(boiler ash and
jointly collected boiler and lter ash from wet APCsystems and
assuming a technical extraction rate for Zn of 75%).Together with
the inferred portion of 1100 t/a, the total of subeco-nomic
resources is 7900 t/a. The residual bulk of Zn (47,400
t/ademonstrated and 7900 t/a inferred) is either low-grade y
ashfrom dry or semidry APC systems (10,400 t/a of Zn), from
bottomash (21,200 t/a), from y ash generated during FBC (1300 t/a)
and
en i
rtain
price
J. Fellner et al. /Waste Management 37 (2015) 95103 101Fig. 5.
Specic recovery costs for zinc (giv
Table 3McKelvey diagram for annual Zn ows (in t/a) in European
MSWI residues (the unceinferred, and potentially undiscovered
resources).
Identied resources
Demonstrated
Economic 0a
Marginally economic 4100b
Subeconomic 6800b
Other occurrences (low grade) 47,400Low-grade materials
Total 69,000
a An economically viable recovery of Zn from y ashes would (at
current market
disposal of untreated ashes of more than 230 /ton ash.
b Assuming that at 50% of all WtE plants with wet APC systems
lter ashes and boiler75%.n /kg Zn) from different MSWI
residues.
ty ranges of the estimates form the basis for the distinction
between demonstrated,
Potentially undiscovered resources
Inferred
0a 0a
700b 700b
1100b 1100b
7900 7900
9000
s) only be possible at Zn contents above 53,000 mg/kg ash or
avoided costs for theashes can be separately collected and that
technical recovery rates of Zn amount to
-
Current research initiatives with respect to metal recovery
from
The presented work is part of a large-scale research initiative
on
Association Working Group Thermal Treatment, Copenhagen, p.
86.
hazardous metals from MSW y ashan evaluation of ash leaching
methods. J.
naganthropogenic resources (Christian Doppler Laboratory for
Anthro-pogenic Resources). The nancial support of this research
initiativeby the Austrian Federal Ministry of Science, Research and
Economywaste incineration y ashes led us to investigate the
potential andeconomic viability of Zn recovery from incineration
residues.Thereto a survey about WtE in Europe with respect to
combustiontechnology applied, air pollution control installed, as
well as quan-tities and qualities (contents of Zn) of solid
residues generated hasbeen conducted. Based on this survey, a MFA
for Zn ows throughEuropean WtE plants has been established.
Moreover the applica-tion of the only technology for Zn recovery
applied so far at fullscale (FLUREC) has been evaluated regarding
its economic viability,when being applied to different incineration
residues.
The evaluation, based on the analysis of Zn ows through
Euro-pean Waste-to-Energy plants and an economic assessment,
indi-cates that approximately 75% of the Zn present in
Europeanincineration residues, which amounts to 69,000 t of Zn, is
hardlyextractable, as production costs would be at 1080 times
higherthan current market price.
The reasons are, rst, comparatively low contents of Zn in
theseresidues (150015,000 mg Zn/kg); and second, the fact that
signif-icant amounts of Zn can only be extracted at low pH
values(pH < 4), requiring in the absence of acidic scrubber
water hugeamounts of HCl; and third, extractions rate for Zn
applying FLURECare at best 75%, which implies that 25% of the Zn
remain in the lea-ched residues.
The 25% Zn ow that is, in theory, recoverable, accumulates iny
ash of grate incinerators equipped with wet APC. Average Zncontents
of these y ashes are about 22,000 mg Zn/kg ash whenboiler and lter
ash are collected together. In case that lter ashis separately
extracted, the Zn content almost doubles. Accordingto the survey of
European WtE plants such separate collection oflter ash seems to be
established or possible at around 50% of grateincinerators with wet
APC. The lter ash of grate incinerators withwet APC also contains
the only Zn (4100 t/a) that could be recov-ered at production costs
in the range or only slightly above the cur-rent market price for
Zn. In case boiler and lter ash are jointlyextracted, Zn recovery
(potential of 6800 t/a) becomes less eco-nomic; the specic
production costs double and thus rise signi-cantly above current
market price.
The results of the analysis demonstrate that with respect to
uti-lizing Zn in incineration residues, grate combustion in
combinationwith wet APC and separate collection of boiler and lter
ash ispreferable.
Nonetheless in comparison to total European Zn import,
whichamounts to about 1.3 million t/a (Spatari et al., 2003), Zn
recoveryfrom marginally economic and subeconomic MSWI residues (y
ashfrom grate incinerators with wet APC) could substitute 0.8%
ofEuropean imports. This share of substitution could
theoreticallybe increased to a maximum of 2.2% in case that all
waste inciner-ated would be combusted in grate incinerators with
wet APC.
Acknowledgmentspotential residues (leached ashes) of the FLUREC
technology(10,900 t/a). Regarding certainty, 87% of the identied
resourcesare demonstrated, and 13% are inferred stocks.
4. Discussion and conclusions
102 J. Fellner et al. /Waste Maand the National Foundation for
Research, Technology and Devel-opment is gratefully acknowledged.
The authors also gratefullyacknowledge the support of Karin
Karlfeldt Fedje and Aurore DeHazard. Mater. 173, 310317.Karlfeldt
Fedje, K., Rauch, S., Cho, P., Steenari, B.-M., 2010b. Element
associations in
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E., Steenari, B.-M., 2012. Initial
studies of the recovery of Cu from MSWI y ash leachates using
solventISWA, 2013. Waste-to-Energy State-of-the-Art-Report,
Statistics, sixth ed.International Solid Waste Association, Vienna,
p. 210.
Jakob, A., Stucki, S., Struis, R.P.W.J., 1996. Complete heavy
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evaporation rates. Environ. Sci.Technol. 30, 32753283.
Karlfeldt Fedje, K., Ekberg, C., Skarnemark, G., Steenari,
B.-M., 2010a. Removal ofBoom, who provided information with respect
to quantities andcomposition of y ashes generated at WtE plants in
Sweden andBelgium.
Appendix A. Supplementary material
Supplementarydata associatedwith this article canbe found, in
theonline version, at
http://dx.doi.org/10.1016/j.wasman.2014.10.010.
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J. Fellner et al. /Waste Management 37 (2015) 95103 103
Evaluation of resource recovery from waste incineration residues
The case of zinc1 Introduction2 Material and methods2.1 Exploration
of Zn flows in MSWI residues2.2 Economic Evaluation of Zn flows2.3
Classification of Zn flows
3 Results3.1 Exploration of Zn flows in MSWI residues3.2
Economic evaluation and classification of Zn flows
4 Discussion and conclusionsAcknowledgmentsAppendix A
Supplementary materialReferences