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Jérôme Jacob

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Reprocessing of the waste produced during acid mine drainage lime treatment by selective leaching 
J. Jacob1, D. Pino-Herrera1, C. Greffié1, G. Wille1, E. Plat1 
1BRGM, 3 avenue Claude-Guillemin 45060 ORLÉANS, France, j.jacob@brgm.fr 
Table S1 Operating conditions and results of leaching tests in reactors 
Test Volume 
(L) 
Solid content 
(% m/m) 
Acid rate 
(g.H2SO4.kg-1) 
Duration 
(h) 
Initial 
pH 
Final 
pH 
Mass balance* 
(%) 
LYliquid (%) 
 
LYsolid (%) 
    
 
  
Zn Cu Zn Cu Cd Zn Cu Fe 
R1 0.5 0.72 157 24 1.7 3.0 
  
78 80  
   
R2 0.5 0.74 157 24 2.2 5.4 
  
37 8  
   
R3 0.5 0.78 157 24 1.8 2.9 
  
75 78  
   
R4 2 0.70 150 24 1.8 3.4 
  
77 76  
   
R5 2 0.70 175 48 1.8 3.0 
  
79 84  
   
R6 2 0.70 201 48 1.8 2.8 
  
81 84 96 
   
R7 2 0.68 251 48 1.7 2.5 
  
81 90  
   
R8 2 0.76 449 24 1.5 2.0 
  
84 91 1001 
   
R9 2 0.70 348 24 1.5 2.3 
  
82 89 97 
   
R10 2 2.9 199 24 1.3 2.5 -6 -9 78 71  86 82 18 
R11 2 2.8 449 24 0.9 1.6 -4 -4 87 86  93 92 62 
R12 2 2.8 650 24 0.8 1.2 -5 -5 87 87  94 93 65 
R13 2 4.5 199 24 1.1 2.5 -1 -1 87 83  89 85 38 
R14 2 8.6 201 24 0.9 2.4 -1 -2 88 82  89 84 42 
R15 2 16 200 24 0.5 2.4 0 2 84 82  84 80 27 
R16 2 2.9 200 24 1.3 2.5 0 1 87 85  88 86 23 
                                                 
1 Due to minor inaccuracies in analysis and mass balance, some values slightly exceeded 100%. To provide a realistic and accurate representation, we have adjusted these values 
to a maximum of 100%, acknowledging the inherent experimental uncertainties. 
R17 2 3.0 200 24 1.2 2.5 -7 -6 80 78  89 86 22 
R18 2 0.76 201 24 1.7 2.7   77 80 100    
*Calculated as: 
𝑚𝑎𝑠𝑠 𝑎𝑡 𝑡0𝑠𝑜𝑙𝑖𝑑 𝑝ℎ𝑎𝑠𝑒−𝑚𝑎𝑠𝑠 𝑎𝑡 𝑡𝑓𝑙𝑖𝑞𝑢𝑖𝑑 𝑝ℎ𝑎𝑠𝑒−𝑚𝑎𝑠𝑠 𝑎𝑡 𝑡𝑓𝑠𝑜𝑙𝑖𝑑 𝑝ℎ𝑎𝑠𝑒
𝑚𝑎𝑠𝑠 𝑎𝑡 𝑡0𝑠𝑜𝑙𝑖𝑑 𝑝ℎ𝑎𝑠𝑒
× 100% 
 
 
 
Table S2 Operating conditions and results of leaching tests in 150-mL shake flasks 
Test Total leaching 
time (h) 
Solid content 
(% m/m) 
Acid rate 
(g.H2SO4.kg-1) 
Initial pH Final pH LY_liquid (%) 
      
Zn Cu Fe 
T1 24 1.09 43 2.7 3.6 75 66 < 0.5 
T2 5.3 1.28 93 2.4 3.5 67 57 0.3 
T3 24 1.28 133 3.4 3.6 75 70 < 0.5 
T4 5.3 0.66 106 2.6 3.5 77 64 0.20 
T5 5.3 0.79 118 3.2 3.5 77 71 0.30 
 
 
Figure S1 photograph of the 150 mL experimental set-up (A) and 0.5 L STR reactor (B) 
 
 
 
 
Figure S2 XRD diffractograms of a Delafossite-rich sample 
 
Figure S3 XRD diffractograms of a Lepidocrocite-rich sample 
 
Figure S4 EDS-SEM mapping of sludge after leaching at 150 gacid/kgsolid and 0.7% solid load 
 
Figure S5 initial and final pH as different acid to solid ratio in STRs for low solid contents (from 0.7% to 1.3% m/m) 
 
Figure S6 Ca concentration vs final pH (A) and Ca concentration and Ca LYliquid versus solid load (B) 
 
 
 
 


Reprocessing of waste produced during acid mine drainage lime treatment by selective leaching

Julie Réaux-Durain

Boushra Mortada

Murielle Bertrand

Jérôme Maynadié

Michaël Carboni

Daniel Meyer

Damien Bourgeois

S1 
 
Supporting Information 
Back-Extraction of Major Actinides from Organic 
Phase through Precipitation 
Julie Réaux-Durain,a Boushra Mortada,a Murielle Bertrand,b Jérôme Maynadié,a Michaël 
Carboni,a Daniel Meyera and Damien Bourgeoisa* 
 a. ICSM, CEA, CNRS, ENCSM, University of Montpellier, Marcoule, France 
 b. CEA, DES, ISEC, DMRC, BP 17171, 30207 Bagnols-sur-Cèze Cedex, France 
 
 *Corresponding author: damien.bourgeois@umontpellier.fr; Tel.: +33 4 66 33 94 92 
 
 
 
 
 
Description of experimental set-up 
 
 
Figure S1: Schematic description and pictures of the precipitation stripping experiments. 
 
 
Aqueous solution: 
HNO3 and oxalic acid
Organic solution:
TBP containing U(VI) and Th(IV)
Experimental set-up At the end of 
addition
At the end of 
precipitation
After
centrifugation
Solid after drying
S2 
 
Aqueous-Phase Oxalic Precipitation of Uranium 
500 µL of an oxalic acid (0.057-0.214 M) solution in HNO3 0.1 M were introduced into a 5 mL 
glass vial. This was followed by the addition of 500 µL of a solution of UO2(NO3)2.6H2O (0.326 
M) in HNO3 6 M  in a drop-wise manner while stirring at 500 rpm at ambient room temperature. 
Stirring was maintained for 1 h, after which the aqueous solution and the solid precipitate were 
separated and recovered through centrifugation. The aqueous phase was stored in an Eppendorf 
tube for ICP analyses, whereas the solid precipitate was washed with n-dodecane, then with 
heptane and dried at 40 °C for a few hours. 
 
 
 
 
 
Aqueous-Phase Oxalic-Co-Precipitation of Uranium and Thorium 
In the aim of comparing the efficiency of the precipitation from the organic phase to that from 
the aqueous phase, 500 µL of an oxalic acid (0.057-0.214 M) solution in HNO3 0.1 M were 
introduced into a 5 mL glass vial. This was followed by the addition of 500 µL of a solution of 
UO2(NO3)2.6H2O (0.326 M) and Th(NO3)4.5H2O (0.18 M) in HNO3 6 M (while maintaining a 
U : Th concentration ratio of 9) in a drop-wise manner while stirring at 500 rpm at ambient 
room temperature. Stirring was maintained for 1 h, after which the aqueous phase and solid 
precipitate were separated and recovered through centrifugation. The aqueous phase was stored 
in an Eppendorf tube for ICP analyses, whereas the solid precipitate was washed with minimum 
aqueous phase and dried at 40 °C for a few hours. 
 
[C2O4H2] 
0.057 M 0.085 M 0.114 M 0.142 M 0.214 M 
U Th U Th U Th U Th U Th 
Aqueous 100 % 29 % 100 % N.D. 98 % N.D. 90 % N.D. 61 % N.D. 
Solid N.D. 71 % N.D 99 % 2 % 99 % 10 % 99 % 39 % 99 %  
(U : Th)s 0 0 0.2 0.8 3.3 
Table S1. Variation of the mass percentage of uranium and thorium in the solid 
precipitate and aqueous phase as a function of the concentration of C2O4H2 after 
aqueous-phase precipitation. Note: [HNO3] is fixed at 0.1 M. 
  
S3 
 
 
Figure S2. PXRD patterns of the precipitates obtained from aqueous-phase precipitation of uranium and 
thorium at variable C2O4H2  concentration and a fixed concentration of HNO3 of  0.1 M. 
 
  
S4 
 
Towards the Characterization of the U-TBP-Ox compound 
The unknown phase obtained during the oxalic-precipitation of uranium from the organic phase 
was intended to be further characterized so as to determine its chemical composition and 
structure. To this end, organic-phase precipitation was realized from a monometallic solution 
of uranium in the aim of reproducing the impurity following the protocol applied to the co-
precipitation of uranium and thorium from a mixture of both actinides. The experimental 
conditions involved adding 500µL of the organic solution highly charged with uranium, which 
was obtained by liquid-liquid extraction of a solution containing UO2(NO3)2.6H2O 0.326 M in 
HNO3 6M by a TBP/n-dodecane 1M solution pre-equilibrated with HNO3 6M, to 500 µL of an 
oxalic acid solution of 0.21 M in HNO3 0.1 M. The reaction mixture was then stirred for 1 h at 
room temperature and at 500 rpm. The obtained precipitate was recovered by centrifugation 
and exhibited a pale yellow color that is similar to the color of UO2(C2O4).3H2O, which may 
also probably indicate that the uranium contained in the material exhibited a +VI oxidation state 
(unlike U(IV) that is usually green). The diffractogram of the obtained precipitate is represented 
in Figure S3.  
 
Figure S3. PXRD patterns of the precipitate obtained from organic-phase precipitation of uranium only 
(at C2O4H2  concentration of 0.21 M and HNO3 concentration of 0.1 M. 
 
Furthermore, the obtained precipitate was not soluble in different solvents, including water, 
ethanol, acetone, diethyl ether, toluene, acetonitrile, tetrahydrofuran and even TBP. EDX 
analysis was also realized and proved the presence of uranium, carbon, oxygen and 
phosphorous in the precipitate, which is in agreement with the results obtained for the impurity 
discussed in the main text. Infrared analysis was also realized on the precipitate and the results 
are represented in Figure S4 and Table S2. The IR spectra reveal that the impurity exhibited 
several peaks in common with uranyl oxalate obtained from aqueous-phase precipitation 
(mainly the corresponding to the vibration of the C-O bond) and with the organic phase 
containing uranyl nitrate in TBP/n-dodecane (mainly corresponding to the vibration of the P=O 
and C-O-P bonds). However, it was complicated to prove the presence of nitrate based on IR 
analyses.  
In
te
ns
ity
(a
.u
.)
support
S5 
 
 
Figure S4. Infrared spectra of the impurity and uranyl oxalate trihydrate. 
 
Vibration (cm-1) Organic phase           TBP-UO2(NO3)2 
Uranyl oxalate trihydrate Impurity                         (mixed composite compound) 
νasym O-H (H2O)  3400 + 2940 (broad peak)  
ν C-H (TBP)   3000-2840* 
νasym C-O and δ O-H  (C2O42- 
and H2O) 
 1670 1685 + 1665 
νasym C-O and ν C=O (C2O42-)  1607 1618 (broad peak) 
νasym ONO (NO3-) 1527  1525 
ν C-H (TBP) 1466  1463 
νsym O-C-O (C2O42-)  1351 1350 
νsym O-C-O (C2O42-)  1312 1309 
νsym ONO (NO3-) 1276  1266 
ν P=O (TBP bonded to U) 1188  1167 
ν C-O-P (TBP) 1028  1026 
νasym UO22+ 939 938 934 
δ H-O-H + δ O-C-O +        
νsym C-O (C2O42- and H2O) 
 868 853 
?   810 
δ O-C-O (C2O42-)  802-797 790 
?  725 (broad peak) 735 
?  636  
?  532 536 
δ O-C-O (C2O42-)  484 478 
Table S2. Variation frequencies of the bonds and attributions to species present in 
a TBP solvent rich in uranium, uranyl oxalate trihydrate and in the impurity (mixed 
composite) obtained from organic-phase precipitation of uranium. * indicates the 
presence of more than one peak. Note that theses attributions are based on 
references [1-4]. 
Unknown compound
Hydrated uranyl oxalate
S6 
 
Theromogravimetric and thermodifferential analyses coupled with mass spectrometry (TGA-
TDA-MS) were also carried out on the impurity. The analyses were realized under air flow 
between 22-1000°C with a heating rate of 5°C/minute. Based on Figure S5, these analyses 
reveal a total percentage mass loss of 45.7%, compared to a theoretical mass loss of 31.9% for 
uranyl oxalate trihydrate when calcined under air, which confirms that the impurity consists of 
a higher percentage of organic material compared to uranyl oxalate trihydrate. [5] Furthermore, 
the liberation of CO, CO2 and water vapor molecules during the analysis is an additional proof 
of the presence of oxalate in the impurity, whereas the formation of NO and NO2 gases confirms 
the presence of nitrates or nitric acid.  
 
Figure S5. TGA-TDA-MS analysis of the mixed composite compound U-Ox-TBP obtained from 
organic-phase precipitation of uranium.  
 
Finally, the residue obtained after calcination to 1000°C was a grey-to-green powder, which 
when analyzed with XRD (Figure S6) revealed the presence of peaks characteristic of a mixed-
uranium-phosphate compound U(UO2)(PO4)2 containing both U (IV) and (VI). Thus, the 
impurity can be assumed to be a mixed composite consisting of uranium, oxalate, nitrate or 
nitric acid and TBP, with a preliminary composition that can be denoted as U-TBP-Ox. 
2 0 1 20 2 20 3 20 4 20 5 20 6 20 7 20 8 20 9 20
-3.6%
-39.9%
-45.7%
S7 
 
Therefore, based on whether nitrate or nitric acid is present in the mixed composite, its chemical 
formula can be either (U(IV))a(UO2)b(C2O4)c(NO3)d(TBP)e or 
(U(IV))a(UO2)b(C2O4)c(HNO3)d(TBP)e. 
 
Figure S6. PXRD patterns of the residue obtained from TGA-TDA-MS analysis and of the mixed-
uranium-phosphate compound U(UO2)(PO4)2 (left side). The grey powder corresponding to the residue is 
also represented (right side). 
 
References 
[1] N.D. Dahale, K.L. Chawla, N.C. Jayadevan and V. Venugopal, X-ray, thermal and infrared 
spectroscopic studies on lithium and sodium oxalate hydrates, Thermochim. Acta 293 (1997), 
pp. 163–166. 
[2] P.A. Giesting, N.J. Porter and P.C. Burns, Uranyl oxalate hydrates: structures and IR 
spectra, Z. Für Krist. - Cryst. Mater. 221 (2006). 
[3] N. Dahale, K. Chawla and V. Venugopal, X-ray, thermal and infrared spectroscopic studies 
on potassium, rubidium and caesium uranyl oxalate hydrates, J. Therm. Anal. Calorim. 61 
(2000), pp. 107–117. 
[4] E.A. Smirnova, E.M. Pazukhin and A.S. Krivokhatskii, Size and shape of thorium oxalate 
crystals as function of preparation conditions, Sov. Radiochem. 30 (1988), pp. 24–29. 
[5] H. Tel, M. Bülbül, M. Eral and Y. Altaş, Preparation and characterization of uranyl oxalate 
powders, J. Nucl. Mater. 275 (1999), pp. 146–150. 
 


Back-extraction of major actinides from organic phase through precipitation

Anne-Marie Caminade

Valérie Maraval

Selected properties of phosphorus dendrimers: green approaches to catalysis

Chantal Joseph Abou-Fayssal

Rinaldo Poli

Karine Philippot

Anders Riisager

Eric Manoury

Polymeric nanoreactors for catalytic applications

Sophie Carenco

Frustrated Lewis pairs on nanoparticles for colloidal catalysis: dream or reality?

Salah Jellali

Mejdi Jeguirim

Comptes Rendus
Chimie
Salah Jellali and Mejdi Jeguirim
Foreword to Special Issue “Valorization of biomass and waste: the path for
sustainability and circular economy promotion”
Volume 27, Special Issue S3 (2024), p. 3-6
Online since: 17 March 2025
Part of Special Issue: Materials and Energy Valorization of Biomass and Waste: The
Path for Sustainability and Circular Economy Promotion
Guest editors: Mejdi Jeguirim (Université de Haute-Alsace, Institut de Sciences des
Matériaux de Mulhouse, France) and Salah Jellali (Sultan Qaboos University, Oman)
https://doi.org/10.5802/crchim.392
This article is licensed under the
Creative Commons Attribution 4.0 International License.
http://creativecommons.org/licenses/by/4.0/
C EN T R E
MER S ENN E
The Comptes Rendus. Chimie are a member of the
Mersenne Center for open scientific publishing
www.centre-mersenne.org — e-ISSN : 1878-1543
Comptes Rendus. Chimie
2024, Vol. 27, Special issue S3, p. 3-6
https://doi.org/10.5802/crchim.392
Materials and Energy Valorization of Biomass and Waste: The Path for
Sustainability and Circular Economy Promotion
Foreword to Special Issue “Valorization of biomass
and waste: the path for sustainability and circular
economy promotion”
Salah Jellali ,a andMejdi Jeguirim ,∗,b
a Centre for Environmental Studies and Research, Sultan Qaboos University, Muscat,
Al-Khoud 123, Oman
b The Institute of Materials Science of Mulhouse (IS2M), University of Haute Alsace,
University of Strasbourg, CNRS, UMR 7361, F-68100 Mulhouse, France
E-mails: s.jelali@squ.edu.om (S. Jellali), mejdi.jeguirim@uha.fr (M. Jeguirim)
Abstract. Biomass and wastes are produced in huge amounts all over the world. Even if they have
high potential to be valorized in various sectors including energy, agriculture, and environment, a
big fraction continues to be considered as a serious burden. This situation is worsened by the global
climate change due to important emission of greenhouse gases (GHGs) generated by the consumption
of considerable amounts of fossil fuels and also by the mismanagement of the produced biomass and
wastes. The sustainable valorization of these biomass and wastes for energy recovery, synthesis of
new materials for use in industry, in agriculture, and in environment, will decrease GHG emission,
boost the circular economy, and preserve the environment. The current special issue published in
Comptes Rendus Chimie (CRC) reviews recent advancements in biomass and waste valorization for
the promotion of circular economy and sustainability concepts.
Keywords. Solid wastes, Management, Biomaterials, Adsorbents, Catalysts, Energy recovery and stor-
age.
Manuscript received and accepted 5 March 2025.
1. Introduction
Consumption of resources and production are con-
tinuously increasing in the world. This is mainly
caused by the high rate of population growth, ur-
banization, and industrialization. This has ultimately
induced the production of huge amounts of waste.
Waste can be liquid or solid. Solid wastes are usu-
ally classified according to their source. They in-
clude household waste, institutional waste, indus-
trial waste, medical waste, agricultural waste, and
∗Corresponding author
municipal waste. Biomass is an important part of this
waste. It is defined as renewable organic materials
originating from plants and animals and represents
an important fraction of municipal solid wastes.
According to the latest report of the United Na-
tions Environment Program (UNEP 2024), municipal
solid waste produced globally was evaluated to 2.1
billion tons. This amount will reach more than 3.7
billion tons by 2050. In 2020, only 13% of this amount
was valorized for energetic purposes. In develop-
ing countries, direct incineration and landfilling are
generally used for the management of wastes, which
result in negative effects onto the environment and
human health. The same report of UNEP indicates
ISSN (electronic): 1878-1543 https://comptes-rendus.academie-sciences.fr/chimie/
4 Salah Jellali and Mejdi Jeguirim
that, in comparison with 2020 and for a waste man-
agement scenario as usual, by 2050 there will be a
91% increase in GHG emission, a 84% increase in loss
of natural species, and a 87% increase in negative im-
pact on human health.
Valorization of waste, and particularly biomass
has become a promising alternative option to incin-
eration and landfilling. Waste valorization consists in
the application of the 4Rs principle: Reduce, Recy-
cle, Reuse, and Recovery. The last option permits the
conversion of wastes into valuable materials that can
be used in various sectors such as energy, agriculture,
and environment. Indeed, renewable energy can be
recovered from this waste through various mastered
technologies including anaerobic digestion, gasifica-
tion, and pyrolysis. This energy can partially replace
the one generated from fossil fuel combustion and
consequently reduces atmospheric pollution as well
as GHG emission. This will in turn facilitate the tran-
sition to sustainable energy that is regarded as a fo-
cal point in the United Nations Sustainable Develop-
ment Goals and also the Paris Agreement on climate
change. Besides renewable energy production sys-
tems, an intensive research work is being deployed
for its tailored storage. In this context, the synthe-
sis of specific materials is considered an important
challenge to advance the transition to sustainable
and renewable energy. Moreover, new valuable ma-
terials can be also derived from this waste. For in-
stance, organic wastes may be transformed into an
eco-friendly compost (through composting technol-
ogy) that can be used instead of synthetic fertilizers
in agriculture. This operation will boost the circu-
lar economy concept and reduces farmers’ expenses.
Besides that, this waste may be converted into a
valuable biochar through the pyrolysis process. This
biochar, in raw or modified form, may be used for
the treatment of industrial/urban wastewater. More-
over, it can be used for nutrient recovery from ac-
tual wastewater for further use in agriculture. These
nutrients-loaded biochars, when used to amend agri-
cultural soils, usually allow soils to improve their
water holding capacity and microbiological activ-
ity. Furthermore, it can act as slow-release fertilizer
which offers cultivated plants the required nutrients
during a long period and at the same time reduces
the pollution risk to the underlying groundwater.
Likewise, using biochar instead of activated carbons
for the treatment of wastewater and in substitution of
synthetic fertilizers promotes the circular economy
and sustainability concepts, reduces GHG emission,
protects the groundwater against pollution, and of-
fers a high economic added value to farmers.
The present special issue in the journal “Comptes
Rendus Chimie”, is entitled: “Valorization of biomass
and waste: the path for sustainability and circu-
lar economy promotion”. It provides an interest-
ing update on the conversion of wastes, in general
and biomass in particular into high added-value
by-products by using advanced and eco-friendly
technologies. These by-products are intended to
contribute to the promotion of circular economy
and sustainability. Moreover, this special issue aims
to fulfill national and international requirements
regarding sustainable development and climate
change adaptation and mitigation.
2. Outcomes
The current special issue contains 12 papers that
have undergone a peer review process by at least two
skilled reviewers. Published papers address several
subtopics, including: (i) direct valorization of waste
in several domains including concrete, cellulose and
biomaterials extraction, (ii) biomass turned into ad-
sorbents for removal of pollutants from wastewa-
ter, (iii) use of catalysts to improve the quality of
biomass conversion by-products, (iv) application of
hydrothermal carbonization as an innovative option
for waste management, and (v) test of new materials
for solar energy storage.
The first part of this special issue addresses the
challenges of waste management, direct reuse, and
the extraction of valuable biomaterials [1–5]. For in-
stance, Chaouch et al. [1] investigated the use of re-
cycled Polyvinyl chloride (PVC) powder as a substi-
tute for conventional PVC resin in the expanded layer
of floorcoverings. They showed that mixing recycled
PVC with PVC resin up to 33% did not affect its me-
chanical characteristics (i.e., break strength, elonga-
tion at rupture, and tear resistance). Moreover, with
finer recycled PVC particles (size lower than 200 µm),
this percentage can be pushed further to 86%. In an-
other study, in order to reduce the cost of air con-
dition in arid areas, Siddique et al. [2] tested the
use of four types of recycled plastics: low-density
polyethylene (LDPE), polypropylene (PP), polyester,
and high-density polyethylene (HDPE), as partial
Salah Jellali and Mejdi Jeguirim 5
sand substitutes in concrete for roofing applications.
Their results show that LDPE exhibited the most sig-
nificant economic and environmental benefits. In
the case of New Delhi, a LDPE percentage of 30%
leads to an annual saving of around 1 $/m2 and a
reduction in carbon emissions of 18 kg/kWh. The
third study, by Ben Ali et al. [3], showed that cellu-
lose can be extracted in an eco-friendly way from
prickly pear seeds. The cellulose extraction yield
was 39.3% by maceration and 23.2% when using
the Soxhlet extraction method. Moreover, charac-
terization of the extracted cellulose showed that it
was exceptionally strong and light, allowing its pos-
sible use for the production of carbon fibers for re-
inforcing composite materials used in the aerospace,
automotive, shipbuilding, and other industries. In
the fourth study, Mestour et al. [4] examined the
optimization of using supercritical CO2 for the ex-
traction of bioactive substances from onion waste.
They reported that the optimal oil extraction yield
(24.4%) was achieved for a pressure, temperature,
particle size, and CO2 mass flowrate of 250 bar,
57 °C, 0.25 mm, and 50 g CO2/min, respectively.
The analysis of the oil produced by gas chromatog-
raphy showed that it contained the four follow-
ing fatty acids: 9,12-octadecadienoic acid, methyl
ester; 9,12-octadecadienoic acid (Z,Z)-, methyl es-
ter; 9-octadecadienoic acid (Z)-, methyl ester; and
hexadecanoic acid, methyl ester. Finally, Deffar
et al. [5] studied the extraction of bioethanol from a
pre-treated water hyacinth biomass, a free-floating
perennial plant. Bioethanol extraction was carried
out through a fermentation process by using a lo-
cally isolated thermophilic consortium in a partially
consolidated bioprocessing process. They showed
that the maximum experimental yield (7.7 g/L) was
achieved at 50 °C, 72 h of fermentation time, and an
inoculum dose of 6.64% (v/v).
The second part of this special issue is about
biomass transformation into valuable by-products
including biochar, bio-oil and biogas [6–12]. In this
context, Jellali et al. [6] synthesized three Mg-, Al-,
and Mg/Al-modified biochars from date palm wastes
and valorized them for the recovery of phosphorus
from aqueous solutions under a wide range of ex-
perimental conditions. Their ultimate aim is to use
the phosphorus-loaded biochar in agriculture as a
slow-release fertilizer. They showed that the biochar
modified using a Mg/Al mixture solution exhibited
the best physico-chemical properties and conse-
quently the highest P recovery efficiency (14.1 mg/g).
Moreover, the P recovery process involved both phys-
ical and chemical mechanisms. They conclude that
the P-loaded Mg/Al-modified biochar has a good po-
tential to be used as an attractive slow-release fertil-
izer instead of the costly commercial ones. In another
study, Alfares et al. [7] examined the valorization of
an abundant plant waste in Iraq: pinecones. They
pyrolyzed different particle sizes (0.26–0.841 mm) of
this waste at numerous temperatures (400–600 °C)
for diverse residence times (30–120 min) and various
heating rates (10–50 °C/min). They showed that the
highest pyrolytic oil yield production (42.1%) was ob-
tained for a particle size of 0.4 mm, a pyrolysis tem-
perature of 500 °C, a residence time of 1 h, and a
heating rate of 30 °C/min. The bio-oil characteriza-
tion indicated that it can be considered as a high en-
ergy fuel since its higher calorific value was evalu-
ated to be around 27.0 MJ/kg. Moreover, the acti-
vation of the corresponding biochar with K2CO3 at
750 °C led to the formation of a highly porous ma-
terial. This activated biochar exhibited a large Cr(VI)
removal capacity under a wide range of experimen-
tal conditions. For their part, Audu et al. [8] stud-
ied the effect of a new catalyst, synthesized by incor-
porating mesoporous iron oxide (FeO) into alumina
(Al2O3), on the quality of the biogas formed from the
pyrolysis of polyethylene terephthalate (PET). They
showed that, in comparison with a blank test, use of
this catalyst at a 5% load decreases oxygen content in
the biogas from 23.3% to 5.3%. Moreover, the pres-
ence of this catalyst significantly improved the con-
tents in H2 and CH4 gases. The highest H2 and CH4
contents were evaluated to 17.1%, and 16.2%, respec-
tively. These yields were obtained for catalyst doses
of 5 and 3%, respectively. In another study, Zheng
et al. [9] synthesized a novel hierarchical calcium-
based catalyst CaO(S) through sol–gel-biotemplate
method using calcium nitrate-ethanol-citric acid as
precursor and rape pollen as biotemplate. Then, they
used it to catalyze oil/methyl acetate/methanol for
no-glycerol biodiesel production. They showed a rel-
atively high yield of no-glycerol biodiesel (96.6%) for
the following optimal parameters: a temperature of
65 °C, a catalyst dosage of 10%, and an oil/methyl
acetate/methanol ratio of 1/1/8. Furthermore, the
regeneration study showed a significant catalytic sta-
bility with a yield of 91.4% after three cycles. Besides
6 Salah Jellali and Mejdi Jeguirim
that, hydrothermal carbonization (HTC) of biomass
was studied in this special issue [10,11]. In this con-
text, Zhang et al. [10] studied the effect of the HTC
experimental conditions on the yield and quality of
the hydrochars produced from sludge. They showed
that the organic matter and ash content in the sludge
as well as the HTC temperature highly affect the fuel
properties of hydrochars. However, the solid loading
had no significant effect on hydrochar quality but did
affect energy consumption by the HTC process itself.
The former lack of effect was confirmed by Bedoui
et al. [11] when studying the HTC of date pits and
pine nut shells at 250 °C for 1 h. These authors also
showed that the hydrochar with the largest higher
heating value (29.7 MJ/kg) was observed for date pits
and a solid/water ratio of 1:48. Moreover, steam ac-
tivation of the hydrochar for 1 h at 850 °C highly im-
proved its physicochemical properties, especially its
porosity and surface area.
In a last but not least contribution, Sharma et al.
[12], studied the effect on freshwater production of
incorporating sensible heat storage materials (i.e.,
bricks, paper napkins wrapped around the brick,
sand bed) in a triangular solar still. They showed
that adding a sand bed reduced the cost of freshwater
generation by around 43%, and the payback period
by 44%.
Declaration of interests
The authors do not work for, advise, own shares in,
or receive funds from any organization that could
benefit from this article, and have declared no affil-
iations other than their research organizations.
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Foreword to Special Issue “Valorization of biomass and waste: the path for sustainability and circular economy promotion”

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On the phase behavior of sorbitol/water/H<sub>2</sub>/CO<sub>2</sub> mixtures at high pressures and temperatures by in situ infrared spectroscopy