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The bottom ashes, produced by the industrial incinerators, are an essential secondary raw material resource which has been drawing attention to recover economically important metals. In the present study, a hydrometallurgical process (chemical leaching) has been discussed to recover some economically important metals using lab scale reactors (600 ml and 2L capacity). Prior to the leaching tests, the material was characterized for chemical composition and mineralogical phase analysis through XRD. In addition, the conventional process of magnetic separation was applied before leaching tests to remove some easily separable parts. Two acidic reagents (HCl and H2SO4) and an alkali reagent (NaOH) have been used to compare the recovery of metal values from the pre-treated bottom ash samples at varying concentrations. Process parameters such as acid/alkali concentration, working volume and temperature have been optimized and the recoveries of metal values under optimum conditions were recorded. The studies showed that 3M H2SO4, 1.5 L working volume and 80°C was sufficient to leach 88% Mo, 82% V, 37% Ni, 37% Fe and 28% Cu. Acid leaching tests using H2SO4 was found to be an economical and appropriate solvent for metal recovery from bottom ash.
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Mineral Processing and Extractive Metallurgy Review
An International Journal
ISSN: 0882-7508 (Print) 1547-7401 (Online) Journal homepage: http://www.tandfonline.com/loi/gmpr20
Metal Recovery from Bottom Ash of an
Incineration Plant: Laboratory Reactor Tests
Ismail Agcasulu & Ata Akcil
To cite this article: Ismail Agcasulu & Ata Akcil (2017) Metal Recovery from Bottom Ash of an
Incineration Plant: Laboratory Reactor Tests, Mineral Processing and Extractive Metallurgy Review,
38:3, 199-206, DOI: 10.1080/08827508.2017.1289196
To link to this article: http://dx.doi.org/10.1080/08827508.2017.1289196
Accepted author version posted online: 16
Feb 2017.
Published online: 16 Feb 2017.
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Metal Recovery from Bottom Ash of an Incineration Plant: Laboratory Reactor Tests
Ismail Agcasulu and Ata Akcil
Mineral-Metal Recovery and Recycling (MMR&R) Research Group, Mineral Processing Division, Department of Mining Engineering, Suleyman
Demirel University, Isparta, Turkey
ABSTRACT
The bottom ashes, produced by the industrial incinerators, are an essential secondary raw material
resource that has been drawing attention to recover economically important metals. In the present
study, a hydrometallurgical process (chemical leaching) has been discussed to recover some economic-
ally important metals using lab scale reactors (600 mL and 2L capacity). Prior to the leaching tests, the
material was characterized for chemical composition and mineralogical phase analysis through XRD. In
addition, the conventional process of magnetic separation was applied before leaching tests to remove
some easily separable parts. Two acidic reagents (HCl and H
2
SO
4
) and an alkali reagent (NaOH) have
been used to compare the recovery of metal values from the pre-treated bottom ash samples at varying
concentrations. Process parameters such as acid/alkali concentration, working volume and temperature
have been optimized and the recoveries of metal values under optimum conditions were recorded. The
studies showed that 3M H
2
SO
4,
1.5 L working volume and 80°C were sufficient to leach 88% Mo, 82% V,
37% Ni, 37% Fe, and 28% Cu. Acid leaching tests using H
2
SO
4
were found to be an economical and
appropriate solvent for metal recovery from bottom ash.
KEYWORDS
Bottom ash; incineration
residue; leaching; metal
recovery; molybdenum;
vanadium
1. Introduction
Corresponding to the increase in global population and industrial
developments, the production of several metals have also increased
significantly. Even though metal production from primary
resources has increased (Guine, 1999), our natural resources are
notlimitless(Morfetal.2013). Within the framework of the
production and distribution policies of the countries possessing
these main resources, the access to these resources and their
exploration costs fluctuate. Countries aiming to possess consistent
industrial development must adapt their metal resources and
develop their own production policies in order to minimize the
effects of this unstable and fluctuating environment as much as
possible. Countries with limited natural resources aim at increas-
ing the utilization of solid wastes rather than losing valuable
materials in waste stream (Allegrini et al. 2014). One of the most
important secondary production resources is the waste named as
urban mine (Jung et al. 2004)
With the development of social economy and increase in
life standards, the amounts of domestic and industrial solid
wastes have also significantly increased (Yao et al. 2010). Due
to this acceleration, several technologies have developed and
are applied in many countries for solid waste utilization (Lam
et al. 2010; Tang and Steenari, 2016). It has been found
suitable to apply incineration (waste burning facilities)
which reduces the volume of solid wastes by 90% and the
mass by 70% (Lam et al. 2010). The burning facilities have
become frequent in the current scenario, to treat several
thousand million-tons of solid wastes generated per year.
The electrical and thermal energy generated during the incin-
eration is another appealing fact of these burning processes
(Wan et al. 2006). At the end, different solid residuals such as
bottom ash, fly ash and filter dust are obtained.
Approximately 80% of the residue is the bottom ash
(Chimenos et al. 1999). The amount of bottom ash within
the residue changes depending on the design of incinerator
unit, the conditions of the incineration process and the char-
acterization of the fed waste. Approximately 10-35% of the
combusted input waste remains on bottom ash (Bawkon,
1991; Sabbas et al. 2003; Kuo et al. 2007).
Nowadays the implementations are progressed to complete
recycling of metals from bottom ashes and the generated bottom
ash residues are used as construction material (Brunner and
Rechberger 2015) without being subjected to another process
oroperation (Wiles, 1996). It is very interesting to note that the
bottom ashes are also a significant resource for recovery of some
economically important heavy metals. In reference to investiga-
tion of former studies, heavy metals in MSW (Municipal Solid
Waste) were mostly enriched into the bottom ash while the
incineration process occur (Yao et al. 2010). Based on the
study by Jung et al. (2004), some lithophilic metals like Fe, Cu,
Cr mainly and about two thirds of Pb and Zn remained in the
bottom ash. Zhang et al. (2008) observed that after two years
investigation of two large scale incineration, more than 80% of
As, Cr, Cu and Ni, 7494%ofZn,aswellas4679% of Pb
remained in the bottom ash owing to its high mass ratio (85
93%) in the residues. Belevi and Moench (2000); Belevi and
Langmeier (2000) reported that more than 90% of Cu, Cr, Mn,
CONTACT Ata Akcil ataakcil@sdu.edu.tr Mineral-Metal Recovery and Recycling (MMR&R) Research Group, Mineral Processing Division, Department of
Mining Engineering, Suleyman Demirel University, Isparta TR32260, Turkey.
Color versions of one or more figures in the article can be found online at www.tandfonline.com/GMPR.
MINERAL PROCESSING AND EXTRACTIVE METALLURGY REVIEW
2017, VOL. 38, NO. 3, 199206
http://dx.doi.org/10.1080/08827508.2017.1289196
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Ni, and more than 85% of Co and 80% Mo transferred to the
bottom ash based on a full scale incinerators investigation, and
the heavy metal contents in bottom ash was generally higher
than that in soil-forming rocks. It is understood that these ashes
can be used as secondary metal acquisition resources when their
annual production amounts are considered (Simon and
Andersson 1996). Furthermore, it is observed that bottom
ashes of solid waste burning facilities for some metals are richer
than the natural ores (Kuo et al. 2007). It therefore becomes
highly essential to investigate the possibilities of this type of
incineration plant residue as a potential material resource.
Bottom ashes have impurities because their chemical composi-
tion is complex. In this situation, hydrometallurgical techniques
canbemoresuitable(Akciletal.2015). Selective recovery of rare
and valuable metals among a variety of compounds is possible
through these routes (Jha et al. 2001).
In view of the economic importance of bottom ash, the
present study was aimed to evaluate the metal recovery
aspects in laboratory conditions from fresh bottom ash sam-
ples of a Turkish incinerator plant using chemical leaching
methods. Several experimental parameters influencing metal
recovery has been investigated and the recovery yields under
differential conditions are discussed in the sections that
follow.
2. Material and methods
2.1. Samples and pre-treatment procedure
The bottom ash samples from waste burning incinerators
used in the present study were collected from IZAYDAŞ
(Waste And Residue Treatment Incineration And Utilization
Corp., İzmit/Kocaeli, Turkey). The operations flowsheet of the
facility and the rotary kiln exit from which the samples were
collected is shown in Figure 1.
Fresh bottom ash samples from the burning incinerators
were collected and dried at 25°C. The unburnt parts such as
the screw, wire, plastics were separated manually. Prior to
leaching tests (discussed in the next section), the sample was
reduced to a size of 500 microns with a roll crusher in order
to remove the magnetic content (iron removal). Gauss mag-
netic field separation was carried out using Carpco Inc.high-
field intensity dry magnetic separator to obtain the magnetic-
featured part (herein referred to as tailings throughout the
text) and the non-magnetic part (herein referred to as con-
centrates throughout the text).
2.2. Leaching tests
The bottom ash samples (tailings and concentrates) were
subjected to leaching tests in order to notice the amenability
of the samples for metal recovery along with optimization of
parameters. The stepwise experimental procedure adopted is
shown in Figure 2 and the following sections details the
methodology.
2.2.1. Parameter optimization studies
The parameters optimization experiments were conducted in
two steps i.e. the preliminary (pre-leaching) and the main
leaching studies. The preliminary leaching tests were carried
out to optimize the time period required for leaching of
metals with other parameters remaining constant as seen on
Table 1. The constant parameters decided for this experiment
was based on the standard literature values (Kinoshita et al.
2005; Van Gerven et al. 2005; Huang et al. 2011; Barberio
et al. 2010; Fedje 2010a,2010b; Li et al. 2009; Parhi et al. 2013;
Kuboňová et al. 2013; Meawad et al. 2010; Gharabaghi et al.
2013; Zhu et al. 2010; Aarabi-Karasgani et al. 2010; Zhang
et al. 2011). The preliminary leaching tests were carried out in
600 ml Isolab glass reactors (250 ml working volume) at 25°C
for 24 hours operating at 170 rpm. Heidolph RZR 2021 model
digital overhead Teflon tipped 4-stab mixer and Velp Arec
magnetic stirrer was used to control the temperature. For this
study, six kinetic tests were designed using acidic and alkali
reagents (Merck Brand H
2
SO
4,
HCl and NaOH) taking 50g of
each sample type. The operating conditions for the experi-
ment along with the test parameters are shown in Table 1.
Figure 1. IZAYDAŞInc. Corp. Incinerator process flowsheet (Bakoğlu et al. 2003).
200 I. AGCASULU AND A. AKCIL
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Instant pH and ORP (Oxidation Reduction Potential) mea-
surements were recorded using a Thermo Scientific Orion
Dual Star Bench top model device at varied time intervals
up to 24 hours. At each measurement period, 4 ml of the leach
liquor was taken for analysis of metal content which was
compensated with 4 ml of same concentration of the respec-
tive reagent. As a result of these tests, the optimum leaching
period was determined according to the ORP and pH values.
Simultaneously, the main leaching experiments for metal
recovery were designed (based on the observations of the
preliminary experiments) varying the acid and alkali concen-
trations and other parameters as shown in Table 2.
2.2.2. Reactor leaching tests
With the optimized parameters from the initial leaching tests
discussed in the above section, scale-up tests were performed
using KGW Isotherm brand 2L capacity reactor with 1.5 L
working volume (Figure 3). In the present study, the effect of
temperature variation and increase of working volume were
investigated. The reagent concentrations and experimental
conditions used are shown in Table 3.
2.3. Analysis
The bottom ash samples were digested in aqua regia (3:1/HCl:
HNO
3
). The contents were filtered and the filtrate was analyzed
with Agilent 240FS AA brand AAS (Atomic Absorption
Spectrophotometer) instrument for initial metal content. The
leach liquors generated following the leaching tests (parameters
optimization and rector leaching) were also analyzed for respec-
tive metal contents using AAS. The mineralogical phases in the
sample were determined using XRD (Panalytical Empyrean).
3. Results and discussions
3.1. Characterization
The chemical analysis of the as received bottom ash is shown in
Table 4. XRD analysis of the bottom ash is shown in Figure 4.
Based on the results of the chemical analysis, it was found appro-
priate to recover Fe, Cu, Mo, Ni, Zn, and V when compared to the
grades of natural ores by using chemical extraction methods.
3.2. Magnetic separation
During the magnetic enrichment step that was applied before
leaching processes, it was aimed to enrich the metals with a
powerful magnetic separator. As such, some of the metals like
Ni and Cr can be separated up to 50% (Han et al. 2007).
Table 5 shows the targeted metals that were selected based on
their amount in the bottom ashes.
3.3. Leaching studies
In the 24-hour pre-leaching tests with the determined para-
meters, at first ORP measurements were carried out during
the first six hours followed by one measurement in every 6
hours. The chemical reactions were believed to be completed
when no further changes in ORP could be observed. HCl
leaching reached stable ORP values at the end of the 4
th
hour while for H
2
SO
4,
NaOH leaching it reached at the end
of 2
nd
hour. These values were used as time parameters for the
main leaching experiments. The ORP measurements are
shown in Figure 5.
Figure 2. Stepwise experimental procedure adopted for leaching of bottom ash.
Table 1. Experimental conditions of preliminary leaching tests.
Sample
Bottom Ash Concentrate
Bottom Ash Tailings
Parameters Experimental Conditions
Acidic/Basic Concentration 1M HCl
3M H
2
SO
4
6M NaOH
Sample Ratio (S/L) (Constant) 1:5
Mixing Rate (Constant) 170 rpm
Leaching Time (Constant) 24 h
Temperature (Constant) 25°C
Table 2. Experimental conditions of main leaching tests.
Sample
Bottom Ash Concentrate
Bottom Ash Tailings
Parameters Experimental Conditions
Reagent Concentration H
2
SO
4
1M, 2M, 3M, 4M
HCl 1M, 2M, 3M
NaOH 3M, 6M, 9M
Sample Ratio (S/L) 1:50/1:25/1:10/1:5
Temperature (°C) 25
Leaching Time (h) 2, 4
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Figure 6 shows the comparative recovery percentages of the
metals from bottom ash concentrate and tailings respectively
using HCl treatment. As can be seen from the Figure 6a,the
recovery of V (70%) from the bottom ash concentrate was highest
followed by Mo (38%), Ni (30%), Fe (21%) and Cu (16%) respec-
tively at a concentration of 2M HCl in 4h. Increasing the con-
centration of HCl to 3M did not have any significant effect on the
recovery of the target metals. On the other hand, the recovery of
Mo (47%) was highest from the bottom ash tailings followed by V
(26%), Ni (21%), Fe (19%) and Cu (16%) respectively (Figure 6b).
The recovery of the target metals from the concentrate and
tailings samples using H
2
SO
4
is shown is Figure 7.Ascanbeseen
from Figure 7a, the recovery of the Mo (84%) was highest from the
concentrate sample followed by V (44%), Ni (25%), Fe (22%) and
Cu (12%) respectively at 3M H
2
SO
4
. These results indicated that
the concentration of 3M H
2
SO
4
was sufficient to leach the target
metals. A similar trend was also observed in case of the tailings
samples at the same H
2
SO
4
concentration however, the order of
the recovery of target metals was seen to be as Mo (84%), V (25%),
Fe (22%), Ni (21%) and Cu (16%) respectively (Figure 7b).
Following leaching tests using acidic reagents, both the samples
were also tested for the recovery of the target metals using an alkali
reagent (NaOH). In both the cases, no significant recovery of the
target metals were seen except for V and Mo using increased
concentrations of NaOH. As can be seen from Figure 8a,the
maximumachievablerecoveryofMowas47%followedbyV
(18%) at 6M NaOH. Similarly, the recovery of Mo was 38% and
V was 6% respectively from the tailings samples at 9M NaOH as
seen in Figure 8b.
3.4. Reactor leaching tests
The initial attempts to optimize several parameters for recov-
ery of target metals from the bottom ash concentrate and
tailings indicted that the use of acidic reagents are more
beneficial for recovery of the metals. In the present scale-up
Figure 3. Experimental apparatus and schematical demonstration for 2L reactor leaching tests
Table 3. 2L reactor leaching test parameters.
Sample
Bottom Ash Concentrate
Bottom Ash Tailings
Parameters Experimental Conditions
Reagent Concentration (M) 3M H
2
SO
4
2M HCl, 3M HCl
Sample Ratio (S/L) 1:5
Temperature (°C) 25, 80
Leaching Time (h) 2
Table 4. Chemical analysis of bottom ash.
Element %
Al 2.99
As 0.0275
B 0.063
Ca 4.75
Co 0.02
Cr 0.1482
Cu 0.1198
Fe 11.8
Mn 0.1205
Mo 0.1524
Na 2.5700
Ni 0.4130
P 0.2760
Pb 0.0824
S 0.46
Ti 1.79
V 0.20
W 0.065
Zn 0.1843
*Selected elements
202 I. AGCASULU AND A. AKCIL
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reactor study (2L capacity), the effect of temperature on the
recovery of target metals using acidic reagents was studied
additionally.
Prior to the temperature leaching studies, the effect of
increase in the working volume (from 250 ml to 1500 ml) at
same temperature i.e. 25°C on the recovery of metals was studied
using the optimized concentrations of the respective acids. The
studies indicated that the recovery of the respective metals
increased with increase in the working volume. The increased
recovery percentages using 2M HCl are as follows: Cu - 12% to
17%, Fe - 22% to 36%, Ni - 26% to 34% and V - 44% to 63%.
Similarly, the increased recovery percentages using 3M H
2
SO
4
are as follows: Cu - 12% to 16%, Fe - 22% to 36%, Ni - 25% to
34% and V - 44% to 52%. The above study clearly indicated that
there is an increase in the percentages of the respective metals
which can be attributed to higher mass transfers due to better
stirring at the higher working volumes.
Figure 4. The XRD pattern of bottom ash samples
Table 5. Characterization of samples after magnetic separation.
Metallic Values, (ppm)
Cu Fe Mo Ni V
Feed of Bottom Ash 1,198 118,000 1,524 4,130 2,900
Bottom Ash Concentrate 772 79,630 1,309 2,500 1,283
Bottom Ash Tailing 1,589 140,800 1,827 5,648 3,360
Figure 5. The ORP measurements of bottom ash concentrate and tailing in
various reagents. (C*: Concentrate, T*: Tailings)
Figure 6. HCl leaching test concentrate (A) and tailings (B) recovery yields.
(Constant parameters: S/L 1:5, 25°C, 170 rpm, 4 h)
MINERAL PROCESSING AND EXTRACTIVE METALLURGY REVIEW 203
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The recovery of the respective metals at varying temperatures
using the optimized concentrations of HCl and H
2
SO
4
are
shown in Table 6. As can be seen in the table, increase in
temperature improved the leaching rates for both the concen-
trate and the tailings. It is regarded that much more dissolution
takes place until the stoichiometric ratio balanced under the
solid/liquid ratio was constant. In Table 6, it can be seen that
the leaching efficiency for the concentrate improved using 3M
H
2
SO
4
at 80°C where the Cu recovery reached 28%, Fe 36%, Mo
88%, Ni 37% and V 82%. The effect of temperature on metal
dissolution can be explained based on the increased kinetic
activities with increased temperature.
4. Conclusion
The chemical recovery of Cu, Fe, Mo, Ni and V metals in
bottom ash have been investigated from the samples of an
incinerator plant. Magnetic and non-magnetic parts were
separated prior to leaching tests. The magnetic-featured part
called Tailingsand the non-magnetic part called
Concentratewas leached using acidic and alkali reagents
and the following conclusions were obtained:
The metal recovery from the bottom ash concentrated
product was 28% Cu, 36% Fe, 37% Ni, 88% Mo and 82%
Vat3MH
2
SO
4
concentration, 80°C, and 1:5 solid/liquid
ratio by the end of 2 hours.
The metal recovery from the bottom ash Tailingsproduct
was 22% Cu, 37% Fe and 28% V at 3 M H
2
SO
4
Figure 7. H
2
SO
4
Leaching test concentrate (A) and tailings (B) recovery yields.
(Constant parameters: S/L 1:5, 25°C, 170 rpm, 2h) Figure 8. NaOH Leaching test concentrate (A) and tailings (B) recovery yields.
(Constant parameters: S/L 1:5, 25°C, 170 rpm, 2 h)
Table 6. Comparison for metal recovery at varying temperatures (Conditions: S/L
1:5, 170 rpm, 2h).
Concentrate Tailings
Metals
Temp.
(25°C)
Temp.
(80°C) % Variance
Temp.
(25°C)
Temp.
(80°C) % Variance
Treatment with 2M HCl, 2h
Cu 17 23 6 16 22 6
Fe 36 35 12633 7
Mo 36 52 16 44 43 1
Ni 34 37 3 20 31 11
V 5266 14 2526 1
Treatment with 3M H
2
SO
4
,2h
Cu 14 28 14 17 22 5
Fe 34 36 2 30 37 7
Mo 80 88 8 68 74 6
Ni 33 37 4 25 29 4
V 6382 19 2528 3
204 I. AGCASULU AND A. AKCIL
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concentration, 80°C and 1:5 solid/liquid ratio by the end of
the 2 hours, while it was 84% for Mo and 31% for Ni by 4
hours at 25°C, 3M H
2
SO
4
. Acid leaching (HCl and H2SO4)
gave higher recovery than alkaline (NaOH) treatment.
While reasonable metal recovery output cannot be obtained
in alkali leach, its positive effect on Mo recovery output may
be seen as striking. Developing the alkali leaching para-
meters, the selective recovery of Mo from other metals is
seen to be higher than acidic conditions. The solid/liquid
ratio has been formed to be the most effective variable
among the leaching parameters. Higher recoveries were
obtained by solid/liquid ratio <1:5. Increasing the working
volume and temperature favored higher recoveries.
Considering the experimental design and operational
processes, recovery of molybdenum and vanadium
from bottom ashes via the acid leaching method proved
efficient. Obtaining low recovery outputs from other
metals may be caused by the in-homogeneous and com-
plex structure of the material investigated.
Acknowledgments
The authors would like to thank IZAYDAS Inc. Company General
Directorate and Project Chief Onur Uludağfor supplying the samples
and Dr. Sandeep Panda for kind support during manuscript preparation.
This study was supported by the OYP Coordination Unit and the
Research Projects Coordination Unit of the Suleyman Demirel
University (Project number: 05275-YL-12)
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... The scrap iron and some other metals of MSWI BA can be separated and utilized by the metal refining industry, followed either by reuse of remaining MSWI BA (e.g., as construction materials) or disposal, if the quality does not allow reuse [2,4,5]. Residual heavy/toxic metals can cause challenges in both reuse and disposal of MSWI BA, but also serve as a secondary source for valuable elements [5][6][7]. ...
... With MSWI BA, it has been observed that Zn and Cu dissolution start at pH 4-5 and pH 3-4, respectively [14,17,18]. In harsh acidic conditions (acid: 3 M H 2 SO 4 , temperature: 80 • C, leaching duration: 2 h, solid/liquid ratio: 20%) and applying reactor apparatus, Mo and V recoveries were high (>80%), but for Ni and Cu low (<40%) [7]. Similar leaching yields for Ni and Cu was observed with HNO 3 ; moreover, Zn leaching yield was found low (<40%) [19]. ...
... Similar leaching yields for Ni and Cu was observed with HNO 3 ; moreover, Zn leaching yield was found low (<40%) [19]. In addition to low-to-moderate yields of these key metals from MSWI BA, challenges may also be foreseen in high concentrations of iron in the final leachate (treatment costs due to iron removal), as well as in solid-liquid separation due to gel-like formations (filtration costs) [7,19]. Organic acids have also been studied for metals removal from MSWI BA. ...
Article
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Municipal solid waste incineration bottom ash (MSWI BA) is the main output of the municipal solid waste incineration process, both in mass and volume. It contains some heavy metals that possess market value, but may also limit the utilization of the material. This study illustrates a robust and simple heap leaching method for recovering zinc and copper from MSWI BA. Moreover, the effect of autotrophic and acidophilic bioleaching microorganisms in the system was studied. Leaching yields for zinc and copper varied between 18–53% and 6–44%, respectively. For intensified copper dissolution, aeration and possibly iron oxidizing bacteria caused clear benefits. The MSWI BA was challenging to treat. The main components, iron and aluminum, dissolved easily and unwantedly, decreasing the quality of pregnant leach solution. Moreover, the physical nature and the extreme heterogeneity of the material caused operative requirements for the heap leaching. Nevertheless, with optimized parameters, heap leaching may offer a proper solution for MSWI BA treatment.
... MSW incineration bottom ash (IBA), the heavy noncombustible and unburned carbon part of the waste (remains at the bottom of the incinerator furnace), is composed by a complex and heterogeneous mixture of melted products, ceramics, glass, silicate materials, unburnt organic portions, unburned carbon (from wood, food, paper, textiles, and others), and metallic components (Alam et al. 2019a;Wei et al. 2011). The amount varies based on the nature/conditions of the incineration process, the design of the incineration plant, composition of the fed waste into the WTE incineration furnace, waste management strategies adopted at different regions, etc. (Agcasulu and Akcil 2017;Silva et al. 2019). Several strategies have been adopted to recycle the IBA to produce valuable products such as adsorbents, ceramics, building materials, etc.; however, fractions of IBA < 4 mm are seen to be contaminated with heavy and toxic metals (Alam et al. 2019a, b). ...
... However, these methods are seen not to be feasible to remove fine and heavy nonferrous fractions and/or immobilize the metals in IBA rendering metal removal difficult (Jadhav et al. 2018). In this regard, magnetic separation has been seen to be a fruitful pretreatment method for concentrating iron-bearing minerals from coal fly ash, residues from MSWI pollution control, MSWI boiler fly ash, and iron/steel industry residues (Wei et al. 2017), on one hand, and enhancing recovery of metals, on the other (Agcasulu and Akcil 2017;Oehmig et al. 2015). ...
... Since IBA contains impurities, hydrometallurgical (chemical leaching) routes have been the preferred choice for recovery of metals (Agcasulu and Akcil 2017;Zhang et al. 2008). Leaching of metals through this route is promising; however, the use of strong chemicals (basically inorganic acids) is unfavorable to the environment. ...
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Full-text available
Ferrous fractions in incinerated bottom ash (IBA) are linked to lower metal dissolution. In the present study, a novel eco-friendly biotechnological approach has been tested for multi-metal leaching using meso-acidophilic Fe²⁺/S° oxidizing bacterial consortium from magnetically separated IBA, owing to the inherent property of IBA to release Fe²⁺. Comprehensive lab-scale studies, first-of-its-kind, considered all the potential elements to understand targeted metal dissolutions from the sample under differential conditions. Concentrations of metals, Al > Ti > Ni > Zn > Cu, as analyzed by ICP-OES, were targeted to be bioleached. XRD analysis indicated the sample to be amorphous with magnetite (Fe3O4) and iron (Fe) forming major phases in the magnetic part (IBAM) and titano-magnetite (Fe3–x. TixO4) and iron (Fe) for the nonmagnetic part (IBAN). The study indicated that 73.98% Cu, 98.68% Ni, 59.09% Zn, 58.84% Al, and 92.85% Ti could be leached from IBAM when the bioleaching system operates at pH 1.5, 5% pulp density for 8 days. Under similar conditions, within 6 days, 37.55% Cu, 87.99% Ni, 45.03% Zn, 40.72% Al, and 63.97% Ti could be leached from IBAN. Two routes were identified and the mechanism of action has been proposed for the leaching of metals.
... Therefore, to avoid these shortcomings, hydrometallurgy is one of the suitable technologies to apply Panda et al., 2016a). This method has been successfully applied for metal extraction from both primary and secondary resources (Anderson, 2012;Agcasulu and Akcil, 2017;Aktaş and Çetiner, 2020;Zekavat et al., 2021). ...
Article
Developed economies such as the USA and European Union (EU) have classified antimony as a critical raw material. China leads the global antimony production (67% on an average from 2015 to 2019) followed by Russia and Tajikistan. Antimony has been applied in the industry (plastics, etc.) and new/emerging technologies (cell panels, infrared, etc.) where antimony trioxide (Sb2O3) is its most produced and used compound. With technological advances, recent trends indicate a growing demand for this metal; however, with the on-going production rate, antimony is anticipated to become one of the scarcest metals by 2050. Several minerals of antimony exist; nevertheless, stibnite (Sb2S3) is the primary mineral. Extractive metallurgical routes such as pyro and hydro-metallurgy have found industrial applications for stibnite processing; however, bio-hydrometallurgy is slowly gaining momentum. In this piece of review, the world-wide scenario of antimony production, recent market trends along with the common and current research advances related to applications of antimony in emerging technologies is presented. Comprehensive details along with the recent advances related to stibnite processing through the aforementioned extractive metallurgy routes, their technological improvements and antimony purification/recovery methods from leach solutions are also discussed. Furthermore, the future perspectives in terms of research and industrial needs are discussed and summarized.
... Detailed analyses were performed to investigate the processes involving the leaching of useful elements from fly ash (Agcasulu and Akcil 2017;Behera, Chakraborty and Meikap 2018;Kursun and Terzi 2016;Querol et al. 2000;Yan et al. 2016). Their results suggest that acid leaching is an ecologically and economically efficient process that makes it possible to utilize fly ash in a broader scope of applications. ...
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The zeolitisation of fly ash originating from hard coal combustion in a Polish power plant was conducted using the alkaline hydrothermal method with and without the application of ultrasound. The output ash primarily contained glass, mullite, quartz and hematite, and its dominant chemical components included SiO2 (over 50 wt.%) and Al2O3 (over 28 wt.%). The synthesis of two zeolitic materials was conducted under the following conditions: 3 M NaOH solution, synthesis time – 8 hours, temperature – 80°C. For one of the syntheses, ultrasound with a frequency of 40 kHz and power of 480 W was applied for the first two hours. The identification of mineral components of initial ash and post-synthesis products was conducted using following methods: X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, differential thermal analysis and thermogravimetric analysis. The obtained zeolitic materials varied greatly in phase composition. The product phase composition for the non-ultrasound-assisted synthesis was practically identical to the initial fly ash (mullite, quartz and hematite). The glass underwent minor chemical metamorphosis, recognizable by the presence of new phases in small quantities, typically mutually interlayered, mostly in the form of thin incrustation on the ash grains. The phases included: hydrosodalite, NaP-type zeolite, LTA-type zeolite and A-type zeolite. These phases, where Na⁺ cations should be dominant, contained K⁺, Ca²⁺ and Mg²⁺ cation substitutions. The zeolitic material obtained with the application of ultrasound, apart from initial fly ash phase residues, contained new phases in significant quantities, such as hydrosodalite and NaP-type zeolite, and A-type zeolite in smaller quantities.
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Vanadium-bearing steel slag is a typical solid waste in the steel industry and a valuable secondary resource for vanadium production. In this paper, a direct alkaline leaching process was proposed to extract valuable vanadium and achieve comprehensive utilization of the residue by incorporating the new process into the conventional Bayer alumina production process. The leaching mechanism showed the feasibility of alkaline leaching. The effects of alkaline concentration, temperature, particle size, liquid-solid ratio (mass ratio), and stirring speed on the process were investigated, and the recovery of vanadium was found to achieve 68.4% under optimal conditions. Both the internal diffusion and the interface reaction were found by kinetic analysis to be the controlling steps of the leaching reaction, and the apparent reaction activation energy value of 26.67 kJ/mol was calculated. The valence state of the vanadium in the steel slag was analyzed in detail, finding that low-valent (V³⁺) and high-valent (V⁴⁺ and V⁵⁺) vanadium were both present in the steel slag. By introducing oxygen into the reaction system, the recovery could be improved to 85.6%, which was 17.2% higher than that of non-oxidative leaching.
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With proper leaching tests, health hazards associated with municipal solid waste incineration (MSWI) ashes, i.e., incineration bottom ashes (IBA) and incineration fly ashes (IFA), can be quantitatively defined. However, it must be coupled with specific environmental scenarios to draw the proper conclusions. Several environmental stresses based on current management of MSWI ashes were herein simulated with laboratory leaching studies to understand their impacts. The impact of bulk metal recovery on the IBA leaching potential was firstly investigated, suggesting the promoted release for certain metals including those with a relative high content (> 1000 mg/kg) such as Ba, Cu, Pb and Zn. The impact of seawater was also simulated. Most metal release was altered with the new chemistry established. Batch leaching tests were further performed under both salty and acidic environment to understand their aggregated effects, indicating an overwhelming influence from seawater buffering. Lastly, batch leaching tests of the IBA/IFA mixture were performed under various mass ratios, while data were compared with those by their individuals and the theoretical leaching value, unveiling different leaching characteristics during landfill disposal. Hereby, a comprehensive characteristic metal leaching potential was achieved under various ash managements. It provides insights into environmental risks relevant to their current practices.
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The extraction of valuable elements from high-alumina fly ash was carried out using two methods, the carbochlorination method and the carbothermic method. The carbochlorination experiments were conducted to investigate the impacts of the factors of reaction time, temperature, and carbon content. The carbochlorination of fly ash at a carbon: alumina molar ratio of 4.5 : 1 yielded extractions of Al2O3, SiO2, CaO, and TiO2 of 84.3 72.7, 68.9, and 87.3%, respectively, at 1000°C for 60 min of reaction time with a pellet diameter of 8 mm and a chlorine gas flow of 0.35 L/min. By comparing the decomposition behavior between the carbochlorination and the carbothermic treatment, the carbochlorination mechanism of fly ash was elucidated. Alumina was preferentially chlorinated from mullite in the fly ash. The carbochlorination method provides the potential for the efficient and clean extraction of valuable elements from fly ash.
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The possibility of recovering metals from a mixture of solid industrial waste generated from decommissioning of a coal-fired power plant has been studied in this work. First, a complete characterization of the material was carried out. Results showed that the material contains an interesting amount of metals (Ti, V, Cr, Ni, Zn and Pb) that can be recovered by acid leaching and chemical precipitation. Then, some leaching tests were performed in batch systems with different acid solutions at different operational conditions. The main effects of leaching time, leaching agent and acidity were investigated. High concentrations of metal were achieved in the leachate obtained when a treatment with sulfuric acid solution at a pH value of 1 was used as leaching agent. Finally, the metals presented in leaching solution were precipitated by chemical precipitation with NaOH. A good separation of Ti and V respect to the other dissolved elements between pH 4 and 5 was obtained.
Article
In the current study, electrodeposition-redox replacement was applied to a hydrometallurgical solution with the main elements of Ca (13.8 g L⁻¹), Al (4.7 g L⁻¹), Cu (2.5 g L⁻¹), Zn (1.2 g L⁻¹), Fe (1.2 g L⁻¹), S (1 g L⁻¹), Mg (0.8 g L⁻¹), P (0.5 g L⁻¹) and Ag (3.5 ppm). The solution originated from the leaching experiment of incinerator plant bottom ash, which was dissolved into 2 M HCl media at T = 30 °C. The resulting deposit on the electrode surface was analysed with SEM-EDS and the observed Ag/(Cu + Zn) ratio (0.3) indicated remarkable enrichment of silver on the surface, when compared to the ratio of these elements (Ag/(Cu + Zn)) in the solution (6.8 × 10⁻⁵). The enrichment of Ag vs. (Cu + Zn) could be demonstrated to increase ca. 4500 fold compared to the ratio of the elements in solution.
Article
Under the proper setting of boundaries, leaching behaviors of incineration bottom ashes (IBA) may be predicted using geochemical models. The extent of agreement between measurements and the prediction is often affected by the model development. On the other hand, the inconsistency may also be caused by the complexity of the system for modeling. As such, discrepancies between measurements and geochemical modeling on IBA leaching would indicate uncovered yet significant mechanisms which may not be fully understood by the existing setting scenarios. pH-static leaching tests of IBA were performed, followed by simulations with two geochemical models. Simulations based on the surface area calculated with all leachable minerals provided a better matching with experimental data as compared to that calculated with surface area of Fe/Al oxides only. Yet, certain elements remained highly overestimated (up to 3 orders of magnitude, e.g. Cd, Ni, Sr, Zn, Fe, Al and Mg) or underestimated (e.g. Cr) in alkaline pH range. Significant co-complexation during leaching may be susceptible and responsible for the differences. Multivariate factor analysis testified that pH, Fe and Al in acidic environment tended to be clustered and highly loaded under the dominant correlation factor (accounting for 33.3–49.0% of variance). Contrastively, pH, Ca and cationic strength in alkaline environment tended to be clustered and highly loaded under the dominant correlation factor (accounting for 39.9–43.3% of variance). In both cases, co-complexation was evidenced. As the natural pHs of IBA usually fall within the high alkaline range, the comparison study offered quantitative discrimination of leaching potential between measurements and simulation, which would be crucial for decision making during IBA applications. In light of limited leaching potential of IBA under the alkaline pH range, its application with cement (with high alkalinity) seems to be one of the best options.
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Full-text available
lnRec is a new process offering an answer to the increasingly urgent question of what to do with the residues left over from solid waste incineration. State-of-the-art incineration grate technology is the starting point for InRec. Dry bottom ash is discharged from the furnace by the DryExTM system and sorted by DryRecTM - a dry process for separating the iron, other metals and the mineral fraction. The untreated coarse fraction can be used direct in road construction or landfilled. The fine fraction is melted in an AshArcTM furnace, if required with the fly ash from the particulate separation process. Conditioning or solidification are possible as an alternative to energy-intensive melting.
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Full-text available
Ash from municipal solid waste incineration (MSWI) may be quite cumbersome to handle. Some ash fractions contain organic pollutants, such as dioxins, as well as toxic metals. Additionally, some of the metals have a high value and are considered as critical to the industry. Recovery of copper, zinc and lead from MSWI ashes, for example, will not only provide valuable metals that would otherwise be landfilled but also give an ash residue with lower concentrations of toxic metals. In this work, fly ash and bottom ash from an MSWI facility was used for the study and optimization of metal leaching using different solutions (nitric acid, hydrochloric acid and sulfuric acid) and parameters (temperature, controlled pH value, leaching time, and liquid/solid ratio). It was found that hydrochloric acid is relatively efficient in solubilizing copper (68.2±6.3%) and zinc (80.8±5.3%) from the fly ash in less than 24h at 20°C. Efficient leaching of cadmium and lead (over 92% and 90% respectively) was also achieved. Bottom ash from the same combustion unit was also characterized and leached using acid. The metal yields were moderate and the leachates had a tendency to form a gelatinous precipitate, which indicates that the solutions were actually over-saturated with respect to some components. This gel formation will cause problems for further metal purification processes, e.g. solvent extraction.
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Full-text available
Incineration of municipal solid waste is a commonly used management method to take care of our waste. However, the residues produced are a problem. They often contain large amounts of potentially toxic metal compounds and soluble salts, which can cause harm to the environment and human health if released from the ash. These ashes are therefore usually classified as hazardous materials and are deposited in specialized landfills. However, as society strives towards more sustainable material cycles, a larger fraction of the materials today classified as waste will, in the near future, be recycled. Since the ashes produced from waste incineration contain significant amounts of metals, they represent a possible source of these metals. Recovery of metals from waste combustion residues would thus give an opportunity to turn a waste into a valuable resource. This thesis focuses on the leaching and recovery of minor metals, such as Cu and Zn, and proposes a recovery procedure for Cu. The leaching of metal compounds from the ash is a very important step in the recovery process and several factors, such as leaching time, pH, leaching agent used and the liquid-to-solid ratio (L/S), affect the leaching properties. In some cases more or less all Cu was leached from the ash. Recovery of metals from ash leachates can be done using solvent extraction, and the results obtained showed that about 90% of the Cu in the leachates could be selectively recovered. The ash matrix itself is highly affected by leaching, which generally increases the specific surface area and changes the particle size distribution. In landfill leaching tests the release of many ions from pre-leached ash was lower than that measured for the original ash, indicating a possibility to utilize the resulting ash as well. Keywords: MSW ash, leaching, metals, Cu, solvent extraction, speciation, NH3NO4, water, HNO3, pH
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Full-text available
Human activities inevitably result in wastes. The higher the material turnover, and the more complex and divers the materials produced, the more challenging it is for waste management to reach the goals of “protection of men and environment” and “resource conservation”. Waste incineration, introduced originally for volume reduction and hygienic reasons, went through a long and intense development. Together with prevention and recycling measures, waste to energy (WTE) facilities contribute significantly to reaching the goals of waste management. Sophisticated air pollution control (APC) devices ensure that emissions are environmentally safe. Incinerators are crucial and unique for the complete destruction of hazardous organic materials, to reduce risks due to pathogenic microorganisms and viruses, and for concentrating valuable as well as toxic metals in certain fractions. Bottom ash and APC residues have become new sources of secondary metals, hence incineration has become a materials recycling facility, too. WTE plants are supporting decisions about waste and environmental management: They can routinely and cost effectively supply information about chemical waste composition as well as about the ratio of biogenic to fossil carbon in MSW and off-gas.
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Incineration can reduce solid waste to 85 percent to 90 percent of the incoming volume, or 65 percent to 80 percent of the incoming weight. With some modification, a waste incinerator can be designed to recover energy in the form of steam, hot water or electricity. This latter type is known as a resource recovery or waste-to-energy facility. Most newer waste incinerators are the waste-to-energy type. Incineration facilities can be very costly to develop, but once operational, waste disposal costs tend to remain fairly stable. Also, life-cycle costs can be significantly reduced through the recovery and use or sale of thermal and/or electric energy. Although all incinerators now require pollution control devices, there remain issues and concerns about air quality, ash disposal and environmental impacts.
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With the increase in environmental awareness, the disposal of any form of hazardous waste has become a great concern for the industrial sector. Spent catalysts contribute to a significant amount of the solid waste generated by the petrochemical and petroleum refining industry. Hydro-cracking and hydrodesulfurization (HDS) catalysts are extensively used in the petroleum refining and petrochemical industries. The catalysts used in the refining processes lose their effectiveness over time. When the activity of catalysts decline below the acceptable level, they are usually regenerated and reused but regeneration is not possible every time. Recycling of some industrial waste containing base metals (such as V, Ni, Co, Mo) is estimated as an economical opportunity in the exploitation of these wastes. Alkali roasted catalysts can be leached in water to get the Mo and V in solution (in which temperature plays an important role during leaching). Several techniques are possible to separate the different metals, among those selective precipitation and solvent extraction are the most used. Pyrometallurgical treatment and bio-hydrometallurgical leaching were also proposed in the scientific literature but up to now they did not have any industrial application. An overview on patented and commercial processes was also presented. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
Municipal solid waste incineration (MSWI) plays an important role in many European waste management systems. However, increasing focus on resource criticality has raised concern regarding the possible loss of critical resources through MSWI. The primary form of solid output from waste incinerators is bottom ashes (BAs), which also have important resource potential. Based on a full-scale Danish recovery facility, detailed material and substance flow analyses (MFA and SFA) were carried out, in order to characterise the resource recovery potential of Danish BA: (i) based on historical and experimental data, all individual flows (representing different grain size fractions) within the recovery facility were quantified, (ii) the resource potential of ferrous (Fe) and non-ferrous (NFe) metals as well as rare earth elements (REE) was determined, (iii) recovery efficiencies were quantified for scrap metal and (iv) resource potential variability and recovery efficiencies were quantified based on a range of ashes from different incinerators. Recovery efficiencies for Fe and NFe reached 85% and 61%, respectively, with the resource potential of metals in BA before recovery being 7.2%ww for Fe and 2.2%ww for NFe. Considerable non-recovered resource potential was found in fine fraction (below 2 mm), where approximately 12% of the total NFe potential in the BA were left. REEs were detected in the ashes, but the levels were two or three orders of magnitude lower than typical ore concentrations. The lack of REE enrichment in BAs indicated that the post-incineration recovery of these resources may not be a likely option with current technology. Based on these results, it is recommended to focus on limiting REE-containing products in waste for incineration and improving pre-incineration sorting initiatives for these elements.
Article
Municipal solid waste incineration (MSWI) plays an important role in many European waste management systems. However, increasing focus on resource criticality has raised concern regarding the possible loss of critical resources through MSWI. The primary form of solid output from waste incinerators is bottom ashes (BAs), which also have important resource potential. Based on a full-scale Danish recovery facility, detailed material and substance flow analyses (MFA and SFA) were carried out, in order to characterise the resource recovery potential of Danish BA: (i) based on historical and experimental data, all individual flows (representing different grain size fractions) within the recovery facility were quantified, (ii) the resource potential of ferrous (Fe) and non-ferrous (NFe) metals as well as rare earth elements (REE) was determined, (iii) recovery efficiencies were quantified for scrap metal and (iv) resource potential variability and recovery efficiencies were quantified based on a range of ashes from different incinerators. Recovery efficiencies for Fe and NFe reached 85% and 61%, respectively, with the resource potential of metals in BA before recovery being 7.2%ww for Fe and 2.2%ww for NFe. Considerable non-recovered resource potential was found in fine fraction (below 2mm), where approximately 12% of the total NFe potential in the BA were left. REEs were detected in the ashes, but the levels were two or three orders of magnitude lower than typical ore concentrations. The lack of REE enrichment in BAs indicated that the post-incineration recovery of these resources may not be a likely option with current technology. Based on these results, it is recommended to focus on limiting REE-containing products in waste for incineration and improving pre-incineration sorting initiatives for these elements.
Article
Hydrochloric acid leaching of nickel from spent Ni–Al2O3 catalyst (12.7% Ni, 39.2% Al and 0.68% Fe) has been investigated at a range of conditions by varying particle size (50–180 μm), acid concentration (0.025–2 M), pulp density (0.2–0.4%, w/v) and temperature (293–353 K). Nickel was selectively leached from the catalyst, irrespective of the different conditions. Under the most suitable conditions (1 M HCl, 323 K, stirring at 500 rpm, 50–71 μm particle size), the extent of leaching of Ni and Al after 2 h was 99.9% and 1%, respectively. The XRD pattern of the spent catalyst corresponded to crystalline α-Al2O3 along with elemental Ni. The peak due to elemental Ni was absent in the residue sample produced at the optimum leaching conditions, confirming the complete dissolution of Ni from the spent catalyst. The leaching results were well fitted with the shrinking core model with apparent activation energy of 17 kJ/mol in the temperature range of 293–353 K indicating a diffusion controlled reaction.