XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 175
be of potential interest for the development of aluminum
agromining.
Agromining is the process of using hyperaccumula-
tor plants to extract metals and other elements of interest
from the soil (Ent et al. 2018). This technology is already
being used successfully to produce industrial-grade nickel
salts using a nickel hyperaccumulator. Expanding agromin-
ing to other metals requires first to identify new hyperac-
cumulator, and the to develop process allowing to use their
biomass. Producing aluminum through the mean of phyto-
extraction could prove beneficial for several reasons, such as
a reduced environmental impact (Ent et al. 2018).
Recovering aluminum from plants is already a subject
of research in metallurgic chemistry, mainly focused on the
leaching of coal fly ash (CFA). These ashes are produced
from industrial boilers and thermal plants in very large
quantity, at around 750 million tons per year worldwide
(Blissett and Rowson 2012). The composition of CFAs
can vary depending on their geographical origin however,
they are usually rich in aluminum, iron and other metallic
oxides such as titanium. As of today, a very small fraction of
CFA is reused or recycled in any way, most of them being
landfilled (Blissett and Rowson 2012). However, numer-
ous processes are today being researched in order to valorize
these CFA through their metallic oxide contents, like alu-
minum. This can be achieved by different means, as several
extraction processes have been developed, each with its own
advantages and drawbacks.
The aim of this work is to characterize the biomass of
Qualea rosea to first confirm his aluminum hyperaccumu-
lating properties, and then to determine parameters to be
preferred to develop an aluminum recovery process. Then,
design of experiments (DoE) will be used to identify the
main factors to maximize aluminum extraction.
MATERIALS AND METHODS
Hyperaccumulator Plant Samples
Qualea rosea is a tree native from south America from the
Vochysiceae family. It gets its name from the reddish color-
ation of its wood. Samples of Qualea rosea wood chips were
collected from a wood processing plant in French Guiana,
and dried at 65°C for 72 h before being further processed.
Sample Characterization
Thermogravimetric analysis (TGA) of the biomass was per-
formed using a Mettler Toledo TGA/DSC 1 analyzer, at
a rate of 10°C per minutes up to a maximal temperature
of 1000°C under air to determine the optimal combustion
temperature used for ash production.
The elemental composition of biomass and ash samples,
as well as leachate and leachate residues was characterized
using several elemental analysis techniques. The biomass
and ash contents in carbon, hydrogen, oxygen, nitrogen,
sulfur and chlorine were determined using an elementar
Vario EL cube organic analyzer.
Analysis of leachates, leachate residues and trace ele-
ments content of the ash and biomass were performed by
ICP-OES using a ThermoFisher ICAP 6300 DUO. For
analysis of solid samples, prior to ICP-OES analysis, sam-
ples were digested in 5 mL of nitric acid (Fisher Chemical,
67–69% TraceMetal Grade) in glass vessels during an ultra-
wave assisted digestion step using a Milestone ultraWAVE.
The digested samples were then transferred to 50 mL PTFE
containers and volume was adjusted to 50 mL using deion-
ized water.
The crystalline phase of the ash was characterized by
X-ray diffraction analysis using a Bruker D8-Advance dif-
fractometer with a cobalt probe (λCoKα 1.79 Å).
Scanning electron microscope (SEM) imaging and
energy dispersive X-ray (EDX) elemental cartography of
the biomass, ash and leachates residue were performed
using a Hitachi FlexSEM 1000 II microscope.
Design of Experiment Conception and Results
Exploitation
The design of experiment (DoE) used in this work to dictate
the leaching conditions and the modelling of the obtained
results was done using the DesignExpert software.
It was a factorial design with three factors (leaching
duration, sulfuric acid concentration and leaching temper-
ature) and two levels, intended to be used as a screening
design to identify the most important factors. The limit val-
ues used for each of the factors as well as their correspond-
ing coded value –1 or +1 are presented in Table 1. Leaching
was performed with a 0.5% mass ash concentration.
Experimental Conditions
Leaching experiments were carried out in a borosilicate
round flask equipped with a water refrigerant and a ther-
mometer. The acid used was sulfuric acid H2SO4 (ACS
Reagent 95–97%). The acid concentration was adjusted to
Table 1. Limit values of the leaching experiments coded as
–1 or +1
Experimental parameters –1 +1
Leaching duration (min) 30 120
H
2 SO
4 concentration (mol/L) 0.25 2
Leaching temperature (°C) 25 90
be of potential interest for the development of aluminum
agromining.
Agromining is the process of using hyperaccumula-
tor plants to extract metals and other elements of interest
from the soil (Ent et al. 2018). This technology is already
being used successfully to produce industrial-grade nickel
salts using a nickel hyperaccumulator. Expanding agromin-
ing to other metals requires first to identify new hyperac-
cumulator, and the to develop process allowing to use their
biomass. Producing aluminum through the mean of phyto-
extraction could prove beneficial for several reasons, such as
a reduced environmental impact (Ent et al. 2018).
Recovering aluminum from plants is already a subject
of research in metallurgic chemistry, mainly focused on the
leaching of coal fly ash (CFA). These ashes are produced
from industrial boilers and thermal plants in very large
quantity, at around 750 million tons per year worldwide
(Blissett and Rowson 2012). The composition of CFAs
can vary depending on their geographical origin however,
they are usually rich in aluminum, iron and other metallic
oxides such as titanium. As of today, a very small fraction of
CFA is reused or recycled in any way, most of them being
landfilled (Blissett and Rowson 2012). However, numer-
ous processes are today being researched in order to valorize
these CFA through their metallic oxide contents, like alu-
minum. This can be achieved by different means, as several
extraction processes have been developed, each with its own
advantages and drawbacks.
The aim of this work is to characterize the biomass of
Qualea rosea to first confirm his aluminum hyperaccumu-
lating properties, and then to determine parameters to be
preferred to develop an aluminum recovery process. Then,
design of experiments (DoE) will be used to identify the
main factors to maximize aluminum extraction.
MATERIALS AND METHODS
Hyperaccumulator Plant Samples
Qualea rosea is a tree native from south America from the
Vochysiceae family. It gets its name from the reddish color-
ation of its wood. Samples of Qualea rosea wood chips were
collected from a wood processing plant in French Guiana,
and dried at 65°C for 72 h before being further processed.
Sample Characterization
Thermogravimetric analysis (TGA) of the biomass was per-
formed using a Mettler Toledo TGA/DSC 1 analyzer, at
a rate of 10°C per minutes up to a maximal temperature
of 1000°C under air to determine the optimal combustion
temperature used for ash production.
The elemental composition of biomass and ash samples,
as well as leachate and leachate residues was characterized
using several elemental analysis techniques. The biomass
and ash contents in carbon, hydrogen, oxygen, nitrogen,
sulfur and chlorine were determined using an elementar
Vario EL cube organic analyzer.
Analysis of leachates, leachate residues and trace ele-
ments content of the ash and biomass were performed by
ICP-OES using a ThermoFisher ICAP 6300 DUO. For
analysis of solid samples, prior to ICP-OES analysis, sam-
ples were digested in 5 mL of nitric acid (Fisher Chemical,
67–69% TraceMetal Grade) in glass vessels during an ultra-
wave assisted digestion step using a Milestone ultraWAVE.
The digested samples were then transferred to 50 mL PTFE
containers and volume was adjusted to 50 mL using deion-
ized water.
The crystalline phase of the ash was characterized by
X-ray diffraction analysis using a Bruker D8-Advance dif-
fractometer with a cobalt probe (λCoKα 1.79 Å).
Scanning electron microscope (SEM) imaging and
energy dispersive X-ray (EDX) elemental cartography of
the biomass, ash and leachates residue were performed
using a Hitachi FlexSEM 1000 II microscope.
Design of Experiment Conception and Results
Exploitation
The design of experiment (DoE) used in this work to dictate
the leaching conditions and the modelling of the obtained
results was done using the DesignExpert software.
It was a factorial design with three factors (leaching
duration, sulfuric acid concentration and leaching temper-
ature) and two levels, intended to be used as a screening
design to identify the most important factors. The limit val-
ues used for each of the factors as well as their correspond-
ing coded value –1 or +1 are presented in Table 1. Leaching
was performed with a 0.5% mass ash concentration.
Experimental Conditions
Leaching experiments were carried out in a borosilicate
round flask equipped with a water refrigerant and a ther-
mometer. The acid used was sulfuric acid H2SO4 (ACS
Reagent 95–97%). The acid concentration was adjusted to
Table 1. Limit values of the leaching experiments coded as
–1 or +1
Experimental parameters –1 +1
Leaching duration (min) 30 120
H
2 SO
4 concentration (mol/L) 0.25 2
Leaching temperature (°C) 25 90