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A theoretical study of the potential for metalextraction from the incinerated ashes residing inSwedish landfillsBishal Baniya aa Division of Environmental Technology and Management , Linköping University , Linköping ,SwedenAccepted author version posted online: 03 Sep 2012.Published online: 26 Sep 2012.

To cite this article: Bishal Baniya (2013) A theoretical study of the potential for metal extraction from the incinerated ashesresiding in Swedish landfills, Environmental Technology, 34:7, 891-900, DOI: 10.1080/09593330.2012.722688

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Environmental Technology, 2013Vol. 34, No. 7, 891–900, http://dx.doi.org/10.1080/09593330.2012.722688

A theoretical study of the potential for metal extraction from the incinerated ashes residingin Swedish landfills

Bishal Baniya∗

Division of Environmental Technology and Management, Linköping University, Linköping, Sweden

(Received 20 April 2012; final version received 10 August 2012 )

In Sweden, waste incineration has played a major role in sustainable waste management, as well as generating combinedheat and electricity for many years. Incineration of combustible waste produces residues such as fly ash and bottom ash.The chemical composition of both ashes shows that they consist of bulk metals and scarce metals in significant quantity,in elemental form as well as in small metal pieces, which remain unsorted from the incinerated residues. This shows thepotential for metal extraction from the ashes, which are deposited in Swedish landfills. Thus with the aim of quantifyingselected metals (Al, Cu, Fe, Zn, Sb, Sn, Ni, Co, Mo, Ti and V), and assessing their flows and stocks in different deposits, thisstudy has been carried out. Approximately 50% of grate plants and 30% of fluidized bed plant in Sweden were sampled forthe study. The data collected from the sampled plants were the basis for the calculation of flow of ashes and metals throughall the plants. First of all, annual metal flows for 1985–2010 were estimated, based on which accumulated stocks at differentdeposits were calculated.

Keywords: waste; incineration; bottom ash; fly ash; landfills; metal extraction

1. IntroductionIn Sweden, waste incineration has played a major role insustainable waste management as well as producing heatand electricity for many years. Sustainable waste manage-ment or sustainable handling of waste has been consideredas a cardinal way to advocate efficient material/resourcerecycling and abate the deleterious environmental impactassociated with waste treatment [1]. Sustainable handlingof waste has also been defined in the notion of industrialecology. Industrial ecology aims ‘to generate least damagein industrial and ecological systems through the optimal cir-culation of materials and energy, making the highest use ofthe resource with least dissipation’ [2]. In the context of thisstudy, industrial ecology relates, in a sense, to the possibil-ity of extracting resource from the waste, the bulk of whichis discarded and deposited elsewhere away from the urbanenvironment. The extraction of resource from waste can berecovery of energy by waste incineration, or recycling ofvaluable metals. This study is concerned with the recov-ery of elemental metals and metal pieces in the incineratedashes.

As the countries within the European Union havebecome wealthier, they have generated more and morewaste. Each year in the European Union (EU-27), approx-imately three billion tons of waste is generated [3], and inSweden approximately 90 million tons of waste is gener-ated [4]. These quantities of waste refer to the total waste

∗Email: bishal.baniya@gmail.com

from households and businesses by economic activities.To counter the increasing waste, the EU came up with awaste management policy which included the formulationof a waste hierarchy: (1) prevention/reduction of waste,(2) re-use, (3) recycling, (4) other recovery (energy recov-ery by incineration) and (5) landfilling [5]. Sweden’s wastepolicy is governed by European and national legislation.The European legislation on waste management is thereforeincorporated into Swedish legislation [6]. The adoption ofthe waste hierarchy defined by the EU is corroborated by thefact that, during the last three years the quantity of municipalwaste has decreased and more and more of the waste gener-ated in EU-27 and Sweden these days is either recycled orincinerated. According to Eurostat [7] for European com-munities, waste treatment by incineration is not the favouredoption in EU-27, where direct disposal of waste to land-fills and recycling lead the way. However, approximately18% of the total waste was incinerated in Sweden in 2006[8] and ∼50% of total municipal solid waste (MSW) wasincinerated in 2009 [9].

Incineration is one of the waste treatment options fora variety of wastes and a part of the waste hierarchy asdefined by the EU directive on waste regulation (Direc-tive 2008/98/EC [10]). In Sweden, incineration of solid andcombustible waste was initially adopted to reduce the vol-ume of waste going to landfills, and to capture or destroypotentially harmful substances associated with the waste.

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The mass and volume of solid waste can be reduced byincineration up to 80% and 90%, respectively [11]. Wasteincineration is considered as a well-established energysource in Sweden. Further, an increase in landfill tax andrecent bans on landfilling of combustible and organic wastein Sweden resulted in an increase in waste treatment byincineration. Moreover, the waste handling tax on incinera-tion has been removed from 1 October 2010, so incinerationof solid waste is likely to continue and grow in the nearfuture [12].

Incineration of waste produces two kinds of residues:fly ash (FA) and bottom ash (BA), which are consideredto be of environmental concern, and need to be depositedat some safe place elsewhere to avoid any negative envi-ronmental impact associated with the ashes. Slag/sludge orBA is the non-burnable ashes remaining in the combus-tion chamber after incineration, which is easily the largestresidue in contrast to FA, representing between 200 and350?kg/tons of waste [13]. These two ash types are oftencalled ‘residues’ in this study. The residues from Swedishincineration plants are transported to various landfill sites ofSweden and deposited there, whereas some are transportedto mines in Norway, to use as a neutralizing agent. Althoughthere is significant reduction of mass and volume of wasteby incineration, the final residue (FA & BA) that goes toSwedish landfills is still large in quantity and is generatedcontinuously as long as daily wastes are produced and areincinerated.

The deposited residue contains valuable bulk metalslike aluminium (Al), copper (Cu), zinc (Zn) and iron (Fe),and scarce metals like nickel (Ni), tin (Sn), antimony (Sb),molybdenum (Mo), cobalt (Co), titanium (Ti) and vana-dium (V) in elemental form as well as in metal pieces [14].Resources are becoming valuable day by day, and the soci-eties are tending towards sustainability, thus introducingthe probable option of recycling the metals present in theresidues. Further, the lack of availability of these metals inthe earth crust, increasing metal prices and large environ-mental impacts associated with extraction and refining ofthe metals inspire the study of the geological deposition ofthese metals in landfill sites. Thus, this study focuses on thetheoretical potential for extraction of metals from inciner-ated ashes residing in Swedish landfills. The metal extrac-tion potential depends on the extraction technology. Cur-rently, there are many physical and chemical technologiesevolving for metal extraction from ashes, some of whichare used in industrial scale and others in laboratory scale.

2. Incineration of MSW, composition of ashes andmetal extraction technologies

2.1. Incineration technologies and flow ofwaste/residues

The grate firing (GF) incinerator and the fluidized bed (FB)incinerator are two common incineration plants in Sweden,

Incoming masses:Municipal waste,

Industrial waste and other waste (biofuels and combustible construction

and demolition waste)

Outgoing masses:Residues: Bottom ash (BA)

and Fly ash (FA), metal pieces for FB plant and

emissions during burning of waste fuel

Figure 1. Incoming and outgoing masses for Swedish incinera-tion plants.

with approximately 70% of currently operating incinerationplant being GF, and the rest being FB plants. According to[15], the choice of type of incinerator depends on the com-position of waste to be incinerated. For the major portion ofdomestic and household waste, GF plant is used, whereas ifthe waste is homogeneous then FB plant is used. The typeof plant together with the different method of handling ofwaste within the incineration plant is one of the importantfactors in influencing the metal content in the residues. InFB plant, metal pieces are sorted from MSW prior to incin-eration, whereas, in GF plants, metal pieces are extractedfrom ashes.

Metals extracted before incineration are ferrous met-als, whereas non-ferrous metals go through the incinerationalong with the waste. Thus, BA from FB plant consists offerrous metal only in elemental form and non-ferrous met-als in both elemental form and in the form of pieces. And,FA from FB plant consists of both ferrous and non-ferrousmetals in elemental form.

Most GF plants in Sweden sort metal pieces from ashesthese days, but sorting of ferrous metal started during themid-1990s, and non-ferrous metals in the early 2000s.Prior to sorting of metals from ashes, all the metals weretransported along with residues. The incoming and out-going masses through the Swedish incineration plants areshown in Figure 1. According to Avfall Sverige (SwedishWaste Management Authority), industrial waste accountsfor about 40% of incoming waste, and BA and FA constituteabout 15% and 4.5% of incoming waste fuel, respectively.These values differed subtly during all the years from 1985to 2010.

Figures 2 and 3 show the annual quantity of incomingwaste and generated ashes (BA & FA) respectively. Fromthese figures it can also be observed that the quantity ofincinerated waste and generation of both BA and FA areincreasing over the years.

2.2. Composition of ashesAsh quality, composition, and physical and chemical char-acterization depend on the composition of input waste fuel,the technology applied (FB/GF) for incineration, opera-tional difference of various plants, and air pollution controldevices [16,17]. These variables affect the composition

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0

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5,000,000

1985

1987

1989

1991

1993

1995

1997

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2005

2007

2009In

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d W

aste

(to

ns)

Year

Figure 2. Quantity of waste incinerated in Swedish incinerationplants 1985–2009.

0

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1985

1988

1991

1994

1997

2000

2003

2006

2009

Ash

es (

tons

)

Variation of ashes over last 25 years

Bottom Ash (tons)

Fly Ash (tons)

Total

Figure 3. Variation in quantity of generated ashes 1985–2009.

of ashes in different countries [18]. However, regardlessof these variables, major elements such as silica (Si),aluminium (Al), iron (Fe), calcium (Ca), magnesium (Mg),potassium (K) and sodium (Na) are present in all ashes inthe form of their oxides, as seen from the compilation ofash composition in the Värmeforsk Allaska database [19]and from Table 1. Ashes also contain small ferrous and non-ferrous metal pieces that remain unsorted before and afterincineration. Table 1 shows the comtent of various elemen-tal oxides in Sweden and in Japan. Oxide of silicon is thedominant component followed by oxide of Al in both FAand BA. The Värmeforsk Allaska database is a storage placefor all the data related to waste incineration in Sweden. Inrecent years, according to Värmeforsk, occurrence of Al inelemental form is highest in FA, but in BA both Al and Fe inelemental form have almost equal proportion. Among the

scarce metals, Cu and Zn have the highest occurrence forboth FA and BA.

2.3. Metal extraction technologiesExtracting metals from incinerated residues residing inlandfills requires the concept of landfill mining, which bydefinition is the mining of valuable resources from land-fill sites. The technologies used for landfill mining aredivided into two groups: physical and chemical methods.Some of the technologies are applicable on an industrialscale, whereas some of them are only of laboratory scaleand in research phase. Some of the technologies are onlylimited for BA or FA, whereas some technologies are appli-cable for both kinds of ashes. The recent technologiesare: (1) magnet separation, (2) eddy-current separation, (3)Magnus separation, (4) kinetic gravity separation, (5) mag-netic density separation (MDS), (6) carrier-in-pulp (CIP),(7) electrochemical separation, (8) density separation, (9)wet screening, (10) solidification/stabilization, and (11)strong acid attack. These technologies include extractionof metal pieces, as well as separation of elemental metalsfrom ashes. While we can observe some technologies toextract metal from ashes, but how they are extracted is themain question. Svensson and Krook [22] give an insightto a practical mining of metals in landfills. They give twoalternatives: use of semi-mobile technology or use of sta-tionary plant. Both of these methods are physical extractionmethods for extracting metal pieces, which involve pro-cesses such as excavation, coarse screening, star screen, airclassifier and finally separation of ferrous and non-ferrousmetal pieces. Technologies such as MDS, CIP and elec-tromechanical separation techniques can extract elementalnon-ferrous metals (Cu, Zn, Sn, Au, Ag, Pb etc.), but are stillin a rudimentary phase, but once developed as an industrialscale they can follow the landfill mining model as proposedby [22].

3. Materials and method3.1. Data collection and samplingRelevant information was mostly collected from govern-mental reports related to waste management and incinera-tion in Sweden, and from the Värmeforsk allaska database

Table 1. Ash composition.

FA: % dry substance

Oxides of various elements in residue SiO2 Al2O3 CaO Fe2O3 MgO K2O Na2O SO3 P2O5 TiO2Värmeforsk 32.3 10.4 23.2 3.92 2.71 2.95 3.42 NA 0.823 2.05Other sources [20,21] 18.8 12.2 24.3 1.6 2.6 4.3 5.8 6.4 2.7 1.5

BA: % dry substanceOxides of various elements in residue SiO2 Al2O3 CaO Fe2O3 MgO K2O Na2O SO3 P2O5 TiO2Värmeforsk 39 9.3 9.89 6.59 1.63 2.18 2.86 NA 0.593 0.881Other sources [20,21] 27.8 9.9 25.9 4 3.3 1.8 3.3 NA 6.9 2

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Table 2. Ash characterization for different time periods (n > 30).

Fly Ash (FA) mg/kg of dry substance Bottom Ash (BA) mg/kg of dry substance

Metal 1985–1990 1991–1995 1996–2005 2006–2010 1985–1990 1991–1995 1996–2005 2006–2010

Al 87,000 52,000 105,000 55,000 104,000 56,900 56,000 49,000Cu 1314 557 3800 3220 4505 3400 4245 4170Fe 15,000 11,000 30,000 27,000 15,000 42,000 69,000 46,000Zn 21,872 14,200 5900 12,100 3830 3080 3480 142Sn 134 134 134 174 130 130 150 129Sb 102 102 160 377 127 127 127 90.1Ni 85 156 160 120 83 138 128 142Co 20 6 20 29.4 13 19.1 21.8 24.5Mo 36 13 10 18 12 16 14.2 11.4Ti 6000 8000 10,000 12,000 5000 6200 7000 5000V 35.6 35.6 60 52.3 58.7 58.7 55.9 72.3

[19]. The related governmental authorities and almost everyincineration plant owner in Sweden were contacted byphone, email and post, and were put a set of questionnairesthat aimed to collect data for the study. There are 31 incin-eration plants in Sweden of which 22 are GF plant, 9 areFB plant, and 2 plants being the common. For this studythe common plant is assumed to operate as FB plant, as thecommon plant has an operation pattern similar to that of FBplant.

Responses to questionnaire were obtained from 13 GFplants and 3 FB plants, which are the sampled data ofthe population (31 plants). Most of the calculations arebased on these data, and hence assumption of character-istics of all plants was made based on the characteristicsof the sampled plants. Similarly, old governmental reports[19,23,24], SWMA annual waste management reports from2000 to 2010, and a recent study [25] provided insightinto the historical data pertinent to incineration and ashcharacterization in Sweden.

3.2. Calculation of flow of ashes and elemental metalsFirst, the quantity of annual waste treated by incineration,and generated bottom ash and fly ash were listed from year1985 to 2010. The waste and residue data from year 1985to 2010 were obtained from SWMA. After the annual flowof incinerated waste, bottom ash and fly ash were estab-lished, annual metal flow for all the years was determinedbased on annual flow of ashes and ash composition data fordifferent time periods as shown in Table 2. Different timeperiods have different metal consumption that finally endsat incineration plant, so different time periods have differentcompositions of metal in the ashes.

Ash characterization data for different time periods weremostly taken from the Värmeforsk Allaska database [19]and other old reports related to waste incineration in Swe-den. In all data sources, the number of samples of the ashes,which determined the composition of metal in ashes in Swe-den, was more than 30. The ash composition data from 1985to 2010 was sometimes obtained as a percentage or mg per

kg of metal oxide, and sometimes obtained as mg per kg ofindividual metal in ashes. For data obtained as metal oxidein ashes, the molecular weight was taken into account. Theweight of metal in the metal oxide was determined, and thensubsequently the weight of metal (mg/kg) per quantity ofash was determined. In this way, for each time period at least15 pieces of data were taken for individual metals. Averagemean data was then calculated for each metal, which wasthen finally incorporated in Table 2.

The quantities of metal in ashes were then determinedby following formula:

metal = mg/kg dry substance × quantity of ashes

(BA or FA) × 1000 tons.

3.3. Calculation of flow of metal pieces from FB andGF plant

The average percentage of metal in MSW that ends atincineration plant is known from the Swedish Waste Man-agement Authority [9], which is different for different timeperiods. For 1985–1995, 1996–2005 and 2006–2010, thepercentages of metals in MSW are 6%, 3% and 3% respec-tively. Similarly, ferrous and non-ferrous metal is 85% and15% of total metal in MSW respectively [9]. Another impor-tant aspect of determining the metal pieces present in theashes is the quantity of metals extracted from MSW beforeincineration in FB plant, and extraction of metal from ashesin GF plants. The quantity of metal pieces extracted beforeand after incineration for all plants is estimated accordingto the data on metal extraction from sampled plants. Thus,the final metal pieces that flow together with ashes are:

for FB plants:

total metal pieces (tons)

= metal pieces going through incineration plant along

with MSW − metal pieces extracted from the

incoming MSW.

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for GF plants:

total metal pieces (tons)

= metal pieces going through incineration plant along

with MSW − metal pieces extracted from the

outgoing ashes.

Further, according to Stena Metall AB (personal contactwith Ingrid Nöred of Stena Metall AB), a Swedish recy-cling company working on extraction of metal from MSWand ashes, and from other sampled plants, the extractionof metal from MSW and from ashes has an efficiency ofapproximately 90%. This value is used for calculation forboth ferrous and non-ferrous metals.

3.4. Accumulated stocks of ashes and metalsThe ashes are transported to different deposits such as inmixed landfills, separate landfills and hazardous landfills,and are used as a construction material around landfills.Based on the data from sampled plant regarding the quantityof transported ash, deposition of all BA and FA at differentlandfills was determined. Once the quantity of deposited ashat various landfills was estimated, the amount of elemen-tal metal going to those landfills was also estimated usingthe same procedure as that for determining the elemental

metal in ashes as described in section 3.2. The calcula-tion of metal pieces in different deposits is as describedin section 3.3.

4. Results and discussion4.1. Annual flow of elemental metalsThe annual flow of all metals from 1985 to 2010 is shownin Table 3. Figure 4 and Figure 5 also show the annual flowof bulk metal and scarce metal, respectively, for all years

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Al

Cu

Fe

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Ti

Figure 4. Annual flow of bulk metals with both BA and FA fromall plants.

Table 3. Annual flow of metals with BA & FA from all plants (1985–2010).

Metals (tons)

Year Al Cu Fe Zn Ti Sn Sb Ni Co Mo V

1985 27,574 1047 6702 2138 1435 29 33 23 4 5 131986 30,442 1156 4553 2361 1584 32 37 25 4 5 141987 33,309 1265 4982 2583 1733 35 40 28 5 6 151988 33,117 1257 4954 2568 1723 34 40 28 5 6 151989 32,924 1250 4925 2553 1713 34 40 27 5 6 151990 32,732 1243 4896 2538 1703 34 40 27 5 6 151991 18,222 907 11,495 1799 2152 43 40 46 5 5 151992 18,170 904 11,463 1794 2146 43 40 46 5 5 151993 18,118 902 11,430 1789 2140 42 39 46 5 5 151994 18,008 896 11,360 1778 2127 42 39 46 5 5 151995 19,425 967 12,254 1918 2294 46 42 49 6 5 161996 23,740 1476 21,516 1427 2724 52 48 48 8 5 161997 24,473 1521 22,181 1471 2808 54 49 50 8 5 171998 29,088 1808 26,363 1748 3338 64 59 59 9 6 201999 30,874 1966 29,104 1862 3578 69 63 63 10 6 222000 29,705 1842 26,804 1784 3405 65 60 60 10 6 202001 30,894 1912 27,801 1855 3539 68 62 62 10 6 212002 34,456 2124 30,806 2068 3941 75 69 69 11 7 232003 38,818 2395 34,755 2330 4441 85 78 78 12 8 262004 41,220 2568 37,482 2478 4734 91 83 84 13 8 282005 47,691 2948 42,821 2863 5460 104 96 96 15 9 322006 38,799 3050 32,182 2169 5059 107 119 106 20 10 442007 42,162 3314 34,955 2364 5502 116 129 115 21 11 482008 44,513 3508 37,063 2419 5767 123 135 121 23 11 512009 46,855 3701 39,154 2478 6034 129 140 128 24 12 542010 45,918 3601 37,926 2644 6029 127 142 125 23 12 51Total 831,246 49,526 56,9928 55,781 87,112 1742 1762 1656 271 180 635

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1980 1990 2000 2010 2020

tons

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Sn

Sb

Ni

Co

Mo

V

Figure 5. Annual flow of scarce metals with both BA and FAfrom all plants.

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Al Cu Fe Zn Ti

Ton

s

Bulk metals

Total flow of bulk metals

Figure 6. Total flow of bulk metals with both BA and FA fromall plants.

from 1985 to 2010. From Table 3 and Figure 4 it can beseen that aluminium and iron have larger flow than othermetals, with the most recent flow having a value around40,000 ton/year. Cu, Zn and Ti follow a congruent trend inwhich annual flow has been increasing gradually from 1985to 2010, with the most recent flow having a value of around25,000–30,000 ton/year. However, we can see fluctuationin annual flow of Al and Fe. The numerical figure for scarcemetals is in contrast to the numerical figure for bulk met-als. No scarce metal has an annual flow above 150 ton/yearduring the last 26 years and the scarce metal values arevery much less than the annual flow of bulk metals. How-ever, after 2005 the annual flow of most scarce metals hasbeen increased greatly. This increase is due to the increasedconsumption of more scarce metals.

Figure 6 and Figure 7 show the total flow of bulk metalsand scarce metals, respectively, which has been obtained bythe addition of all annual flows starting from 1985 to 2010.This represents the elemental metal flow. The accumulatedstock of elemental Al and Fe is above 0.5 million tons indi-vidually as seen from Figure 6, and the accumulated stockof Cu and Zn and are below 100,000 ton. For scarce metal,the highest accumulated stock is for Ni and Sb followed byCo. Sb, Ni and Co have an accumulated stock above 1600tons individually as seen in Figure 7. Similarly, V has an

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Sb Ni Co Mo Sn V

Ton

s

Scarce metals

Total flow of scarce metals

Figure 7. Total flow of scarce metals with both BA and FA fromall plant.

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Al Cu Fe Zn Ti

Ton

sBulk metals

Comparison of presence of bulk metals inboth BA & FA from all plants

In BA

In FA

Figure 8. Comparison of bulk metals in BA and FA from allplants.

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1500

Sb Ni Co Mo Sn V

Ton

s

Scarce metals

Comparison of presence of scarce metals inboth BA & FA from all plants

In BA

In FA

Figure 9. Comparison of scarce metals in BA and FA from allplants.

accumulated stock of just over 600 tons, whereas Mo andSn have stocks below 300 tons.

Figure 8 and Figure 9 show the comparison of differentmetals in BA and FA. It can be seen that almost all metalsunder study exist more in BA than in FA; hence the potentialfor extraction of metal is higher in BA than in FA, but thereis an exceptional case for Zn, where Zn is marginally higherin FA than in BA.

4.2. Flow of metal pieces along with ashes in landfillsFerrous and non-ferrous metal pieces that flow with asheswere determined, and are shown in Table 4 and Table 5.Since there was no metal extraction from ashes before 1995,the quantity of non-ferrous metal extracted during the time

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Table 4. Amount of metal pieces flowing through GF plants.

Ferrous Ferrous metal Remaining ferrous metal Non-ferrous Non-ferrous metal Remaining non-ferrous metalTime metal in extracted from with ashes ending in metal in extracted from with ashes endingperiods ashes (tons) ashes (tons) landfills (tons) ashes (tons) ashes (tons) in landfills (tons)

1985–1995 744,952 275,161 469,791 131,462 0 131,4621996–2005 417,309 167,131 250,178 73,643 3535 70,1082006–2010 382,190 172,677 209,513 67,445 14,569 52,876Total 1,544,451 614,969 929,482 272,550 18,104 254,446

Table 5. Metal pieces flowing through FB plants.

Ferrous Ferrous metal Remaining ferrous metal Non-ferrous Non-ferrous Remaining non-ferrous metalTime metals in extracted from with ashes ending metals in metal extracted with ashes endingperiods MSW (tons) MSW (tons) in landfills (tons) MSW (tons) MSW (tons) in landfills (tons)

1985–1995 196,040 96,098 99,942 29,406 0 29,4061996–2005 243,469 238,696 4774 42,965 0 42,9652006–2010 191,095 187,348 3747 33,723 10,614 23,109Total 630,604 522,142 108,463 106,094 10,614 95,480

period 1985–1995 is null as shown in Table 4. Also, fromTable 4, although the flow of ferrous and non-ferrous metalsin ashes per year is increasing in the second time period,the metals that end up in landfills is decreasing because ofincreased efficiency and frequency of extraction of metalsfrom ashes.

There is a relatively smaller amount of ferrous and non-ferrous metal in ashes from FB plants than in the ashesfrom GF plants. This is because FB plant sorts metal fromMSW before incineration and also there are less FB plantsin Sweden. From Table 5 it can be seen that more and moreferrous metals have been extracted from MSW with eachtime period, thus allowing fewer ferrous metal pieces to endup in landfills. However, most of the FB plants in Swedenhave not adopted a method for extracting non-ferrous metalpieces from MSW. Recently, only a few FB plant opera-tors have started sorting non-ferrous metal pieces beforeincineration.

Figure 10 shows the total amount of metal piecesdeposited in various landfills for three different time periods.It is evident from this figure that more ferrous metal piecesare deposited in landfills than non-ferrous metal pieces.Also, the rate of accumulation of both types of metal piecesis declining with each time period, with the time period1985–1995 having the largest accumulation and the recenttime period 2006–2010 having least accumulation.

0

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1985–1995 1996–2005 2006–2010 Total

Ton

s

Time periods

Total metal pieces for different time periods

Flow of ferrousmetal with ashes indeposits (tons)

Flow of non–ferrousmetal with ashes indeposits (tons)

Figure 10. Total amount of metal pieces for different timeperiods.

4.3. Accumulated stocks of metal at different depositsAshes from incineration plants are deposited mostly in land-fills, as are the metals present in the ashes. From Table 6it can be seen that metals are deposited mostly in separatelandfill cells and in construction material near to landfillareas. Mixed landfills contain the least amount of metal.Hazardous landfills also show some potential for metalextraction, but the flow of ashes and metals to hazardouslandfill has been decreasing in recent years.

Figure 11 and Figure 12 show the division of accumula-tion of metals in different deposits. Most of the bulk metalsreside in separate landfills and in construction material in

Table 6. Total accumulated stock of metals in various deposits.

Metals (tons)

Deposits Al Cu Fe Zn Sn Sb Ni Co Mo Ti V

In construction material 309,334 22,223 276,336 11,147 733 595 694 116 69 31,450 337In separate landfills 326,829 19,200 210,594 17,286 654 622 607 97 65 31,054 258In mixed landfill 9228 226 2158 1488 10 14 15 2 2 892 0In hazardous landfills 155,091 6091 65,877 19,204 248 323 273 40 33 17,088 38

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0 200000 400000

Al

Cu

Fe

Zn

Ti

Tons

Bul

k M

etal

s

Bulk metals at different deposits

Inhazardouslandfills

In mixedlandfill

In separatelandfills

As aconstructionmaterial

Figure 11. Bulk metals in various deposits.

0 500 1000

Sn

Sb

Ni

Co

Mo

V

Tons

Scar

ce m

etal

s

Scarce metals in different deposits

In hazardouslandfills

In mixedlandfill

In separatelandfills

As aconstructionmaterial

Figure 12. Scarce metals in various deposits.

0

200000

400000

600000

800000

1000000

1200000

Ton

s

Depositions

Total metal pieces in different deposits

Metal pieces ferrous(tons)

Metal pieces non-ferrous (tons)

As a co

nstru

ction

mate

rial

In se

parat

e lan

dfill

s

Figure 13. Total amount of metal pieces in various deposits.

landfill areas. Al and Fe also exist in considerable quantitiesin hazardous landfills. Similarly, the occurrence of scarcemetals is frequent in separate landfills and as a constructionmaterial. Sb, Ni, V and Sn appear in hazardous landfillswith a value above 200 tons individually, whereas they arealmost absent in mixed landfills.

Figure 13 shows the quantity of metal pieces trans-ported to different deposits along with the ashes. In separatelandfills, ferrous metal pieces occur in larger amounts thannon-ferrous metal pieces, whereas, for the ashes used asconstruction material in landfills, non-ferrous metals are inlarger amounts than ferrous metals. The hazardous landfills

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.080

0.090

0.100

Al Cu Fe Zn Sn Sb Ni Co Mo Ti V

Rel

ativ

e am

ount

Metals

Relative amount

Figure 14. Relative amount of metals.

exhibit very low potential for extraction of metal pieces incomparison to other disposals.

4.4. Relative size of metalsRegardless of the quantity of accumulated metals in vari-ous landfills in Sweden, it is very important to understandthe relationship between the recent flow of metals and theiraccumulated stocks. Figure 14 shows the relative amountof each metal, calculated as the ratio of annual flow in 2010to the accumulated stocks up to 2010. Although Al hasthe largest annual flow and accumulated stock, the rela-tive amounts of Sb, Co and V are highest of all the metals,followed by Cu, Fe, Sn, Mo and Ti. Zn has the smallestrelative amount.

4.5. Environmental potential for metal recovery fromlandfills

Table 7 shows the CO2-equivalent emission (kg) froma unit (kg) of metal extraction. The data is generatedfrom LCA software SimaPro on primary metal production.Environmental potential solely related to CO2 emission isconsidered in relation to metal extraction. The table showsthe kilograms of CO2 emissions that can be avoided fromregular metal mines if a kilogram of metal is extractedfrom landfills. Based on the following conditions, data wereextracted from LCA Software SimaPro.Title: Comparing processesMethod: IPCC 2007 GWP 100a V1.02Indicator: CharacterizationSkip categories: NeverRelative mode: NoneExclude infrastructure

processes: YesExclude long-term

emissions: No

5. Conclusion(1) Al, Fe, Cu, Zn and Ti are present in ashes in greater

quantity than metals like Ni, Co, Sn, Sb, Mo and V.Among bulk metals, in terms of quantity, Al and Feare by far the most concentrated metal in ashes.

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Table 7. Kilograms of CO2-equivalent emissions from unit kilogram of metal extraction.

Database: 1 1 1 1 1 1 1 1 1 2 2

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Ant

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Cob

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Cop

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prim

ary,

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Mol

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num

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ate,

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Cu

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kel,

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plat

inum

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n

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c,pr

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Impact category Unit (kg)

IPCC GWP 100a kg CO2 eq. 12.23 12.87 8.29 3.13 2.92 7.352 3.375 16.63 1.982 45.08 33.14

(2) The concentrations of all metals are higher inbottom ash than in fly ash.

(3) For metal pieces, ferrous metal pieces are presentin higher quantity than non-ferrous metals.

(4) Most of the ashes are deposited in separate land-fills and used as a construction material in landfills.So, the elementary metals are concentrated more inseparate landfills and the least in mixed landfills.Similarly, the metal pieces are deposited more inseparate landfills.

6. Recommendation(1) This is a theoretical study of the potential for metal

extraction from landfills in Sweden. The resultsof the study are based on the data obtained fromvarious agencies working in the field of inciner-ation, recycling and ash handling without makingactual field visit to landfills. The results are thereforeapproximate values, capable of changing if moreextensive study is carried. However, this could bethe basis for starting a extensive and real field study.

(2) The viability of extraction of metal from landfillsdoes not always depend on the potential for metalextraction from landfills. A more wide-rangingstudy comprising environmental and economicconsiderations should be made.

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Advanced Wastewater Treatment Report No. 2, Proceedingsof a Polish-Swedish seminar (Paper 5), KTH, Stockholm,Sweden, 1997.

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