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Current Applied Polymer Science, 2017, Volume 1
Sorption of rare earth metal ions (La(III), Nd(III) and Er(III)) using
cellulose
Abstract: This paper investigates the sorption properties of cellulose for the recovery of three rare earth (RE) metal ions
from dilute solutions: La(III), Nd(III) and Er(III), which are representative of light, mild and heavy REEs, respectively.
The study presents the influence of the pH with the discussion of the mechanisms involved in metal binding (i.e., possible
contributions of chelation and ion exchange mechanisms). Optimum sorption is obtained at initial pH value close to 5
(with equilibrium pH close to 6.5). The uptake kinetics are carried out and successfully modeled using the pseudo-second
order rate equation. Under selected experimental conditions, the equilibrium is reached within 3 hours. The effect of initial
metal concentration on sorption capacity is investigated and sorption isotherms are fitted by the Langmuir equation
(preferentially to Freundlich, Dubinin-Radushkevich, and Temkin equations). The maximum sorption capacity ranges
between 31 and 53 mg REE g -1, depending on the metal and the temperature. The determination of thermodynamic
parameters confirms that metal sorption is spontaneous and endothermic (entropy change being positive). Nitric acid
solutions (0.5 M) can be used for REE recovery from metal-loaded sorbent, which can be re-used for a minimum of 4
cycles of sorption/desorption: the loss in sorption and desorption efficiencies does not exceed 5 % .
Keywords: Cellulose; sorption isotherms; uptake kinetics; rare earth metal ions; metal desorption; sorbent recycling; sorption
thermodynamics.
*Address correspondence to these authors at the Centre des Matériaux des Mines d’Alès, Ecole des mines d’Alès, 30319 Alès cedex, France; Tel: +33 (0)466782734; E-mails: [anonimizat], [anonimizat]
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Current Applied Polymer Science, 2017, Volume 2
1. INTRODUCTION
The development of high-tech industries is requiring
increasing amounts of precious and strategic metals such as
platinum group metals or rare earth elements (REEs). The
rarefaction of the resources (limitation of primary mining
resources, or geopolitical constraints for the access to target
metals) has been the main incentive over the last decade for
developing new processes for the recovery of valuable
metals from the so-called urban mine (wastes of materials,
WEEs for example) [1-4], infra-marginal ores and industrial
wastes [5-9]. Making a resource from a waste material
recently became a credo for politics all over the world; and
many incentive regulations have been promulgated for
improving the recycling of strategic metals [1, 7, 10, 11].
REEs (including yttrium, scandium and the lanthanide
series) are widely used for photo-electronic and metallurgical
industries and in nuclear energy programs; as a consequence
the demand for rare earth element (and their alloys) are
steadily increasing. The challenge for REE industry consists
of the separation of REEs from base metals and the selective
separation of individual REEs from mixtures of REEs.
Indeed, due to very similar electronic configurations their
physicochemical properties are very close and numerous
theoretical plates are required for separating these REEs
[12].
Hydrometallurgy is offering a wide range of possibilities
for recovering valuable metals from ores, waste materials
and sub-products of industrial activities; leaching and
bioleaching are typical methods that can be used for
extracting metals from non-conventional metal sources [3, 5,
8, 13]. The recovery of target metals from leachates may
involve solvent extraction techniques [9, 14-18]; however,
this process if generally efficient for metal recovery from
effluents with high metal-loading. For less-concentrated
effluents, sorption process using ion-exchange, chelating
resins [19-27] or solvent impregnated resins [28-30] are
generally preferred. Biosorption have recently retained a
great attention for metal binding from dilute solutions [31-
36]. Biosorbents bear reactive groups similar to those found
in synthetic resins; they are obtained from renewable
resources (agriculture wastes, seaweeds, biomass derived
from marine feedstock, etc.) [34, 37]. They are generally less
expensive from conventional resins. In addition, at the end of
their life cycle their elimination is more environmentally
friendly; the thermal degradation of synthetic resins may
generate hazardous sub-products (especially toxic fumes)
contrary to biosorbents. For example, alginate has been used
for the recovery of lanthanum [32, 38] and other REEs [39-
41]. Chitosan-based sorbents have also retained a great
attention for the last decade for the binding of REEs [31, 42-
47], playing with the chemical versatility of the biopolymer
and the possibility to graft specific functional groups.
Despite its ready availability and wide range of applications,
cellulose-based materials have received much less attention
for the removal of REEs [48, 49]. Cellulose, like chitosan or
alginate, bears a huge number of hydroxyl groups that make
this biopolymer a very hydrophilic sorbent (at least more
hydrophilic than conventional synthetic materials [50]).The objective of this study consists of investigating the
sorption properties of microcrystalline cellulose for the
recovery of La(III), Nd(III) and Er(III). These three metal
ions are representative of light, middle and heavy REEs [12].
The effect of pH is carried out before testing uptake kinetics
and evaluating sorption isotherms at different temperatures
(for calculating thermodynamic parameters). The desorption
of metal ions from loaded sorbent is tested and the
sorption/desorption performances are compared over 4
cycles in order to evaluate the recycling of the material.
2. MATERIALS AND METHODS
2.1. Materials
Microcrystalline cellulose (C 6H10O5)n, was purchased
from Merck AG (Germany). Other common chemicals were
supplied by Prolabo (France) (they were used as received).
La2O3, NdCl3 and ErCl3.xH2O were purchased from Alfa –
Aesar (USA). These salts were burned off at 900 oC for 3 h;
the residues were mineralized in concentrated hydrochloric
acid under reflux. The solution was then diluted in
demineralized water to prepare stock solutions
(concentration: 1 g metal L-1). The “working” solutions were
prepared at the appropriate concentration and target pH
immediately prior to use by dilution of the stock solution
with demineralized water (to prevent possible micro-
precipitation phenomena when solutions are stored for long
time). The pH of the solutions was adjusted by addition of
drops of aqueous NaOH and/or HCl solutions (0.05-1.0 mol
L-1).
2.2. Characterization of materials
The FT-IR spectra were obtained after incorporation in
KBr pellet using a JASCO-FT-IR-6600 spectrometer (Japan).
X-ray diffraction (XRD) patterns were obtained at room
temperature by X-Ray Diffractometry (RIGAKU, Japan),
using the Cu Kα radiation in the range: 2θ = 10-80°.
Thermogravimetric analysis was carried out using a TG/DTA
6300N, (Seiko Instruments Inc. (SII) Japan), under N 2/O2
atmosphere at a constant heating rate of 10 °C min-1. The
morphology of the sorbents and their energy-dispersive X-
ray analysis were investigated with FE-SEM Hitachi
SU8020 microscope equipped with EDAX analyzer (Japan).
2.2. Adsorption and desorption experiments
Batch experiments were carried out by contact of 0.02 g
of cellulose sorbent with 100 mL of aqueous solution (metal
concentration, C0: 100 mg L-1) in a polypropylene flask
under agitation (300 rpm) at 300 K for 3 hours. After
equilibration and phase separation (filtration on 1.2 µm pore
size membranes), the pH was recorded and the residual metal
concentration in the aqueous phase was estimated by ICP-
AES (inductively coupled plasma atomic emission
spectrometry, Jobin Yvon Activa M, France), whilst the
concentration of metal ions sorbed onto the functionalized
cellulose was obtained by the mass balance equation, Eq.
(1):
qeq = (C0 – Ceq) × V/M (1)
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Cellulose for the sorption of rare-earth metal ions Current Applied Polymer Science, 2017, Vol. 0, No. 0 3
here qeq is the amount of sorbed metal ions (mg metal g-1
sorbent), while C0 and Ceq are the initial and equilibrium
metal ion concentrations (mg metal L-1) in the aqueous
solution, respectively. V is the volume of the solution (0.1 L)
and M is the mass of the sorbent (0.02 g).
Standard experimental conditions were set at T: 27 ± 1°C
and pH: 5.00 ± 0.01; the contact time was fixed to 3 h.
However, when relevant these parameters were varied for
determining pH effect, sorption isotherm characteristics and
uptake kinetics.
Isotherm studies were investigated by mixing 0.02 g of
sorbent with 100 mL of metal RE(III) solution at different
initial concentrations (i.e., 25, 50, 75, 100, 150 and 200 mg
L−1, at pH 5) and shaking for 3 h at 200 rpm. The
experiments were performed in a thermostatic chamber, at
different temperatures (293, 300 ± 1 K, 313 ± 1 K and 323 ±
2 K, respectively ± 2 K).
Uptake kinetics were performed using a sorbent dosage
of 0.2 g L-1 and a concentration of 100 mg metal L-1 at 300±1
K: samples were collected under agitation at standard times
and metal concentration was determined, after phase
separation, by ICP-AES.
In addition, the recycling of the sorbents was tested by
comparing the sorption capacity at different successive steps
in a series of 4 sorption/desorption cycles: 0.02 g of sorbent
was mixed with 100 mL of a REE solution (C 0: 100 mg
metal L-1) for 3 h at 27 °C in closed polyethylene flask. After
phase separation the sorbent was recovered and the metal
concentration in the supernatant was determined by ICP-
AES: the mass balance equation was used for determining
the sorption capacity and the sorption efficiency. The metal-
loaded sorbent (after being washed with demineralized
water) was mixed with 50 mL of a 0.5 M HNO 3 solution for
60 min at 27 °C. The metal concentration in the supernatant
was used for calculating the desorption yield (by mass
balance) at each step. The duplication or triplication of
selected experiments showed that the standard deviation was
systematically less than 6 %.
3. RESULTS AND DISCUSSION
3.1. Sorbent characterization
FTIR spectrometry can be used for both the identification
of functional groups at the surface of the sorbent and for the
interpretation of sorption mechanisms (identifying the
functional groups involved in metal binding groups: shift,
appearance or disappearance of typical bands). The
interpretation of changes is sometimes made difficult by the
low sorption capacities (and low metal content in the
sorbent). Figure AM1 (see Additional Material Section)
shows the FTIR spectra of both raw microcrystalline
cellulose and metal-loaded sorbent. A large absorption band
is observed around 3200-3300 cm-1; this broad band is
generally assigned to –OH stretching vibration. In raw
microcrystalline cellulose the peak is detected at 3323.7 cm-
1, while the band is shifted to 3339.1 cm-1, 3332.4 cm-1 and
3335.4 cm-1 after the sorption of La(III), Nd(III) and Er(III),
respectively. This shift can be directly associated to the
binding of metal ions (which affects the environment of OHgroups). The peak at 2900 cm-1 (assigned to –CH2 groups) is
not affected by metal sorption. The band at 1425 cm-1 is
assigned to intermolecular hydrogen bonds in the aromatic
ring [51]. The bands in the region 960-1170 cm-1 are
typically representative of pyranose ring skeletal (1160 cm-1).
The band at 1108 cm-1 is assigned to OH association [52].
The C-O stretching and C-O deformation vibrations
(corresponding to C-OH in primary alcohol groups) are
detected around 1060 cm-1. The signals in the wavenumber
range 700-400 cm-1 are usually assigned to C-C stretching
while C-H bonds (aromatic hydrogen) are identified in the
range 700-900 cm-1 [52]. The comparison of the spectra
before and after metal sorption shows very limited
variations; this is probably due to the relatively low sorption
(less than 50 mg metal g-1) that makes difficult the detection
of these differences.
Figure AM2 (see Additional Material Section) shows the
XRD pattern of cellulose before and after the sorption of
REE metal ions. The XRD pattern of microcrystalline
cellulose shows 3 distinct planes at 2θ = 15, 16.4, 22.5 and
34.5 degrees. These peaks are characteristic of
microcrystalline cellulose [53, 54]. Actually, depending on
the source raw chitosan can be constituted of two allomorphs
(the so-called Iα and Iβ forms). The broad peak at 2θ= 15/16.4
is associated to 100 Iα, 110 Iβ and 010 Iβ reflection planes,
while the peak at 2θ= 22.5° is representative of 110 I α and
200 Iβ reflection planes. These peaks are common to both I α
(algal and bacterial cellulose) and I β (wood cellulose)
cellulose forms [55]. However, peak at 2θ= 34.5° is typically
representative of wood cellulose. The sorption of REE metal
ions does not affect the XRD patterns: it is not possible to
detect shift in the angle of diffraction of reference peaks and
the full width at half maximum height (FWHM) is not
significantly affected by the binding of metal ions. The low
sorption capacities (see below) may explain the relatively
limited effect of metal intercalation on the crystallinity of the
biopolymer.
The thermal degradation of cellulose is easy compared to
conventional resins both in terms of temperatures of
degradation (close to T onset: 250-270 °C and to T max: 322 °C
for the temperature on maximum weight-loss rate) (Figure
AM3, See Additional Material Section) and in terms of
degradation products. Indeed, cellulose is degraded into CO 2
by combustion while for synthetic resins some hazardous
volatile sub-products may be generated during combustion
(or require proceeding to the incineration at very high
temperature to prevent their emission) [56]. This is an
important criterion to take into account for the management
of the life-cycle of the sorbent.
3.2. pH effect on metal sorption
The effect of pH on the sorption of La(III), Nd(III) and
Er(III) is reported in Figure 1. The sorption capacity
continuously increases with pH. This behavior can be
directly correlated to the acid-base properties of cellulose.
Cellulose is usually considered a weak acid [57-59]. Values
of the pKa in the range 3.7.0-4.2 have been reported
depending on the ionic strength of the solution [57] (and
even as high as 5.15 for 0.001 M NaCl solutions). This
means that, depending on the pH of the solution, a partial

4 Current Applied Polymer Science, 2017, Vol. 0, No. 0 A.A. Galhoum et al.
release of protons from –OH groups can be expected. The
pH of zero-charge is frequently reported lower than 2-3 [57,
59, 60]. On the other hand, the proton may be exchanged
with metal cations: this ion-exchange mechanism is
enhanced at the higher pH (increased mobility/release of
protons) [60]. As the pH increases, the competition of
protons from the solution with metal cations decreases and
the sorption capacity increases. This proton exchange may be
influenced by the ionic strength of the solution by
competition effect (negative impact) and by the decrease in
the pKa of hydroxyl groups (positive impact). Zhu et al. [61]
reported the increase in the sorption capacity for La(III) and
Ce(III) using a composite made of acrylic acid,
hydroxypropyl cellulose and attapulgite (crystalline hydrated
magnesium silicate) when the pH increases: in this case they
attribute metal cation sorption to a combination of chelation
between hydroxyl, carboxylate groups and metals ions with
electrostatic interaction between carboxylate groups and
metal ions. The three REEs show very similar patterns
regarding the impact of pH on metal sorption; playing with
the pH is not expected to contribute to their selective
separation in multi-component solutions.
Figure 1: Effect of initial pH on the sorption of La(III) ,
Nd(III) and Er(III) ions using cellulose (a) and pH change
(b). (C0: 100 mg metal ion L-1; T: 300 K; agitation time, t: 3
h; sorbent dosage, SD: 0.2 g L-1).
The pH variation during the sorption is recorded in
Figure AM4 (see Additional Material Section): the pH
change was rather limited in the range pH 1-3 and tended to
increase by 0.3-0.5 pH units above initial pH 3. Under
selected metal concentrations the equilibrium pH was
systematically below the limit pH value for metal
precipitation (calculated by Medusa, [62]).
3.3. pH effect on metal sorption
Figure 2 reports the kinetic profiles for the sorption of
La(III), Nd(III) and Er(III) metal ions from pH 5 solutions
(C0: 100 mg REE L-1; sorbent dosage, SD: 2 g L-1). Two
sections can be clearly identified (Figure 2a). Within the first
60 min of contact the uptake kinetics shows (for all REEs) a
sharp increase in the sorption capacity; this section
represents 81 to 86 % of the total sorption. This step
corresponds to the fast sorption of REE metal ions at thesurface of the sorbent (or within the first external layers of
the particles). The sorption continues with a much slower
step: the remaining 14 to 19 % of residual sorption occurs
within the next 5 hours. This slow sorption is probably
associated to the contribution of the mechanism of resistance
to intraparticle diffusion. In order to gain a better
understanding of controlling steps (which can include
resistance to bulk diffusion, to film diffusion, to intraparticle
diffusion, but also the proper reaction rate, [63]) several
simple models have been used for fitting kinetic profiles.
The pseudo-first order reaction equation (PFORE, the so-
called Lagergren equation) is linearized under the form [64,
65]:
Log(qeq- q(t)) = log qeq – (k1/2.303) t (2)
The pseudo-second order rate equation (PSORE) is
linearized under the form [64]:
t /q(t) = 1/k2 qeq2 + (1/qeq) t (3)
where qeq and q(t) (mg metal ion g-1) are the sorption
capacities at equilibrium and time t (min), respectively; k 1
(min-1) and k2 (g mg-1 min-1) are the rate constant for PFORE
and PSORE, respectively.
The modeling of experimental data with the PFORE and the
PSORE is appearing in Figures 2b and 2c, respectively. The
rate coefficients are reported in Table 1. The comparison of
the determination coefficients (R2) shows that the PSORE
generally fits better experimental data than the PFORE. In
addition, the comparison of experimental values for the
sorption capacity at equilibrium with the calculated (model)
values shows a better correlation with the PSORE.

Cellulose for the sorption of rare-earth metal ions Current Applied Polymer Science, 2017, Vol. 0, No. 0 5
Figure 2: RE(III) uptake kinetics using cellulose: (a) metal
concentration in the sorbent vs. time, (b) PFORE plots, (c)
PSORE plots. (d) sRIDE (pHi: 5; C0: 100 mg metal ion L-1; T
= 300 K; SD: 0.2 g L-1).
It is noteworthy that these equations that were initially
developed for modeling chemical reaction in homogeneous
systems are frequently applied to heterogeneous reactions
(such as solid/liquid adsorption). This means that the
parameters of the models should be considered as apparent
rate coefficient that intrinsically integrates the contribution
of the mechanisms of resistance to diffusion. The apparent
rate coefficients were of the same order of magnitude for the
3 REEs (between 1.46 × 10-3 and 1.30 × 10-3 g mg-1 min-1).
This means that the sorption reaction rate cannot be used for
separating the metals from multi-component solutions.
Table 1: Uptake kinetics for La(III), Nd(III) and Er(II)
sorption using cellulose – Parameters for the PFORE, the
PSORE and the sRIDE models (C 0: 100 mg metal L-1; pHi: 5;
sorbent dosage, SD: 0.2 g L-1; T: 27 °C).Metal ionPFORE
qeq,exp K1 ×10-2qeq,calc R2
La(III) 33.85 3.46 34.2 0.982
Nd(III) 42.30 2.56 38.7 0.996
Er(III) 43.65 2.97 41.6 0.987
Metal ionPSORE
qeq,exp K2 ×10-3qeq,calc R2
La(III) 33.85 1.46 35.84 0.995

6 Current Applied Polymer Science, 2017, Vol. 0, No. 0 A.A. Galhoum et al.
Nd(III) 42.30 1.30 44.64 0.996
Er(III) 43.65 1.33 46.08 0.996
Metal ionsRIDE
Kid,1 Kid,2 Kid,3
La(III) 3.70 0.6343 0.1308
Nd(III) 4.22 1.3041 0.0871
Er(III) 4.36 0.9396 0.072
Units: K 1: min-1; K2: g mg-1 min-1; Kid,i: mg g-1 min-0.5; qeq: mg
metal g-1
The resistance to intraparticle diffusion can be modeled
using sophisticated models [63, 66] . However, the simplified
model developed by Weber and Morris [67] has also been
frequently used for evaluating the contribution of resistance
to intraparticle diffusion and for comparing the kinetic
profiles with varying experimental conditions:
q(t) = k id. t0.5 + C (4)
where q(t) (mg metal ion g−1) is the amount of metal ions
sorbed at time t (min), and k id. (mg g−1 min−0.5) is the rate
constant of intraparticle diffusion constant and C (mg metal
g−1) is usually associated to the thickness of the boundary
layer [68]. When the linear plots does not pass through the
origin (i.e., C ≠ 0) this is generally attributed to the
contribution of resistance to film diffusion (and the thickness
of the boundary layer of film). Hameed et al. [69]
commented that when the plot of q(t) vs. t0.5 shows different
linear sections the system is controlled by different
successive steps of resistance to bulk diffusion (generally
negligible), film diffusion and intraparticle diffusion
(including intraparticle diffusion into pores of different sizes:
macro-, meso- or micro-pores). Figure 2d clearly shows the
coexistence of different linear sections: the process is
initially controlled by film diffusion before the mass transfer
is influenced by intraparticle diffusion; the last section
corresponds to pseudo equilibrium (sorbent swelling with
additional sorption on the sorption sites located at the center
of microcrystalline cellulose particles, or sorption into the
micropores). The values of intraparticle diffusion rate
constants: k id,1, kid,2 and k id,3 are reported in Table 1.
Consistently with previous observations using the other
models, the parameters were very close for the three metals.
The first stage was slightly faster for Er(III) according the
sequence: Er(III)>Nd(III)>La(III) while for the second stage
followed a different trend (i.e., Nd(III)>Er(III)>La(III)); the
last step (corresponding to the attainment of equilibrium)
was slightly faster for La(III). In ny cases, the differences
observed with the three REEs are not sufficient to count on
uptake kinetics for effective separation of these metal ions.
Based on the kinetic modeling, sorption mechanism
appears to be controlled by both intraparticle diffusion and
metal binding by sorption on external reactive groups
(surface sorption and within the first layers of the sorbent).
The contribution of resistance to external diffusion cannot be
completely neglected at the early stage of adsorption [70].
3.4. Sorption isotherms and thermodynamic
characteristicsSorption tests were carried out at different metal
concentrations and different temperatures in order to plot the
sorption isotherms (sorption capacity, q eq vs. Ceq, residual
concentration) and determine the thermodynamic
parameters. The sorption isotherm, at fixed temperature,
represents the distribution, at equilibrium, of the solute
(metal) between the solid and aqueous phases, changing
initial metal concentration. Figure 3 shows the results
obtained for La(III), Nd(III) and Er(III) sorption at pH 5 (for
temperatures in the range 20-50 °C). regardless of the metal
the sorption capacity increases with temperature: the sorption
process is thus endothermic (see below for thermodynamic
analysis).
As expected, regardless of the metal and the temperature,
the sorption capacity continuously increases with metal
concentration but tends to stabilize (saturation plateau) for
residual concentrations in the range 150-200 mg metal L-1.
The appearance of the saturation plateau suggests that the
sorption isotherm will be preferentially fitted by the
Langmuir equation (Eq. 5) than by the Freundlich equation
(Eq. 6) [71]:
Langmuir equation: q eq= (qm×b×C eq)/(1+b×C eq) (5)
Freundlich equation: q eq= kF ×Ceq1/n(6)
where q eq and q m are sorption capacities (mg metal g-1) at
residual concentration, C eq (mg metal L-1) and saturation of
the monolayer, respectively. The coefficient b is the
Langmuir constant (L mg-1), and the coefficients K F and n
(heterogeneity factor) are the constants of the Freundlich
equation. The parameters of the models are summarized in
Table 2: the determinations coefficients are systematically
higher for Langmuir (compared to Freundlich); in addition,
the maximum sorption capacity (both experimental and
calculated from the saturation of the monolayer; i.e., q m)
increases with temperature. Figure AM5 (see Additional
Material Section) reports the linearization of experimental
sorption isotherms with the Langmuir equation).
Two other models are frequently tested for modeling
sorption isotherms: (a) the Dubinin-Radushkevich (D-R)
model (Eq. 8), which can be used for calculating the mean
free sorption energy E DR (kJ mol-1), and (b) the Temkin
model (Eq. 9) [71]:

Cellulose for the sorption of rare-earth metal ions Current Applied Polymer Science, 2017, Vol. 0, No. 0 7
Figure 3: Sorption isotherms of La(III) , Nd(III) and Er(III)
ions at different temperatures using Cellulose (pH i: 5; t: 3 h;
SD: 0.2 g L-1).
Dubinin-Raduskevich equation:
ln qeq = ln qDR – KDRε2 (8a)
with: ε = RT ln(1 + 1/Ceq ),(8b)
qDR is the theoretical saturation capacity, while ε is the
Polanyi potential. KDR is the constant of the DR model
associated to the mean free sorption energy per molecule of
target sorbent (EDR=(2 KDR)-1/2).
Temkin equation:
qeq = BT ln Ceq + BT ln AT (9)
where AT is the equilibrium-binding constant (corresponding
to the maximum binding energy: this reflects the initial
sorption heat), BT is the constant related to heterogeneity of
the sorbent surface, T is the absolute temperature (K), and R
is the ideal gas constant (8.314 J mol-1 K-1). The constants
can be obtained from the slope and intercept of the straightline plot of qeq versus ln Ceq (Figure AM6, see Additional
Material Section).
Table 2: Sorption isotherms for La(III), Nd(III) and Er(II)
recovery using cellulose – Parameters for the Langmuir , and
Freundlich models (pHi: 5).
Metal ion Temp. (K)qm,exp.
(mg
g-1)Langmuir Freundlich
qm,calc
(mg g-1)b ×103
(L mg-1)R21/n KF R2
La(III)293 31.1 33.1 81.1 0.999 0.099 14.8 0.981
300 33.7 35.9 82.9 0.998 0.101 16.1 0.974
313 35.8 38.0 89.8 0.999 0.104 17.2 0.964
323 38.4 40.7 90.5 0.999 0.104 18.6 0.954
Nd(III)293 40.3 42.7 98.2 0.991 0.224 13.7 0.957
300 44.6 47.2 100.5 0.996 0.283 21.9 0.980
313 48.4 51.2 102.5 0.997 0.272 23.8 0.980
323 51.1 54.1 103.2 0.998 0.244 25.4 0.980
Er(III)293 41.5 44.0 96.4 0.999 0.143 20.3 0.984
300 45.4 48.0 99.4 0.999 0.142 22.3 0.983
313 49.2 52.0 101.1 0.999 0.141 24.3 0.984
323 52.4 55.3 105.2 0.999 0.141 26.0 0.981
The parameters of the DR and Temkin models are
reported in Table 3, while Figure AM3 (see Additional
Material Section) shows the linearization of DR model for
experimental data. As expected the maximum sorption
capacity for DR model increases with the temperature,
regardless of the REE; the mean free sorption energy (E DR)
also increases with temperature (from 6.2 to 7.4 kJ mol-1).
Regardless of the metal and the temperature, the value of E DR
is systematically below the value of 8 kJ mol-1, which is
generally considered as the limit value for making the
difference between physical adsorption (< 8 kJ mol-1) and
chemical adsorption (> 8 kJ mol-1). Regarding the impact of
temperature on EDR, it is noteworthy that Er(III) is the REE
that was less influenced by temperature (∆E DR/T = 0.2),
contrary to La(III) (∆E DR/T = 0.7) and Nd(III) (∆E DR/T = 0.9).
Table 3: Sorption isotherms for La(III), Nd(III) and Er(II)
recovery using cellulose – Parameters for the Dubinin-
Raduskevich , and Temkin models ( pHi: 5).
Metal ionTemp.
(K)D-R Temkin
qDR
(mg g-1)EDR
(kJ mol-1)R2AT
(L mg-1)BT
(J mol-1)R2
La(III)293 31.0 6.16 0.898 16.0 3.91 0.975
300 33.7 6.35 0.888 16.4 4.24 0.963
313 36.1 6.59 0.939 17.9 4.48 0.982
323 37.5 6.84 0.948 19.1 4.76 0.988

8 Current Applied Polymer Science, 2017, Vol. 0, No. 0 A.A. Galhoum et al.
Nd(III)293 40.7 6.46 0.956 20.8 5.01 0.984
300 45.1 6.65 0.990 21.5 5.52 0.985
313 48.9 7.00 0.962 22.2 5.97 0.985
323 51.5 7.37 0.946 24.7 6.22 0.983
Er(III)293 42.0 6.87 0.956 20.6 5.14 0.987
300 45.9 6.93 0.962 22.7 5.56 0.988
313 49.7 7.00 0.957 23.7 6.00 0.987
323 53.0 7.04 0.962 25.1 6.36 0.986
In the Temkin model, the value of A T is associated to the
initial sorption heat of the sorbent for target metal (correlated
to the affinity of the sorbent for the metal). The sorption heat
increases with temperature, as well as the BT (representative
of the heterogeneity of sorbent surface). However, these
differences are relatively small. The A T values for Nd(III)
and Er(III) are of the same order of magnitude (in the range
20-25 L mg-1) and higher than the values obtained for La(III)
(in the range 16-19 L mg-1): microcrystalline cellulose has
higher affinity for Er(III) and Nd(III) (almost equivalent)
than for La(III).
The experimental data obtained at different temperatures
were used for calculating the thermodynamics parameters:
standard Gibbs free energy change (ΔG°), enthalpy change
(ΔH°) and entropy change (ΔS°) were derived from Van't
Hoff equation (Eq. (10) and (11) .
ln b = (-ΔH°/R) 1/T + ΔS°/R (10)
ΔG° = ΔH° − TΔS° (11)
The values of enthalpy change (ΔH°) and entropy change
(ΔS°) were obtained by plotting ln b against 1/T (Figure 4).
The values of ΔH°, ΔS° and ΔG° are reported on Table 4.
The positive value of enthalpy change confirms that the
sorption of the three REEs on microcrystalline cellulose is
endothermic. This enthalpy change is associated to the
combination of two enthalpy changes for (a) the dehydration
(breaking of ion-water and water-water bonds) of hydrated
metal ions, and (b) the proper complexation reaction
between the reactive groups of the sorbent and metal ions
[72]. The negative value of free energy and the decrease in
the value of ∆Go with increase in temperature shows that the
reaction is enhanced at high temperature. The positive value
of ∆So may be related to the liberation of water of hydration
during the sorption process causing the increase in the
randomness of the system. Also the data showed that
│ΔH°│<│TΔS°│ in the studied temperature range. This
means that the sorption process is dominated by entropic
rather than enthalpic changes [43].
Figure 4: Van't Hoff plots of ln K L against 1/T, (K-1) for
RE(III) sorption using cellulose .
Table 4 Thermodynamic parameters of La(III), Nd(III) and
Er(III) ions sorption using Cellulose.
Metal ionTemp.,
K∆H⁰
kJ mol-1∆S⁰
J mol-1 K-1∆G⁰
kJ mol-1T∆S⁰
kJ mol-1R2
La(III)293
32.3 88.6-22.7 26.0
0.944300 -23.3 26.6
313 -24.5 27.7
323 -25.4 28.6
Nd(III)293
12.5 83.8-23.3 24.6
0.932300 -23.9 25.1
313 -25.0 26.2
323 -25.8 27.1
Er(III)293
21.7 88.0-23.6 24.6
0.950300 -24.2 25.8
313 -25.4 27.5
323 -26.2 28.4
3.5. Sorption isotherms and thermodynamic
characteristics
The sorption properties for selected REEs by
microcrystalline cellulose are compared to relevant values
reported in the literature (Table 5). This material is supposed
to constitute the reference material for on-going studies on
the grafting of specific reactive groups (such as thiourea,
poly(carboxyl)/pol(amine) groups). Obviously the maximum
sorption capacities of this simple material are relatively low
compared to the most efficient sorbents such as activated
carbon derived from rice husk for La(III) (175 mg La g-1 vs.
38 mg La g-1), phosphorus-functionalized adsorbent for
Nd(III) (160 mg Nd g-1 vs. 51 mg Nd g-1), or D1113-III resin
for Er(III) (250 mg Er g-1 vs. 53 mg Er g-1). However; the
values of the maximum sorption capacities are roughly of the
same order of magnitude than most of the conventional
materials found in the literature. These sorption
performances will be considered as base values for the
chemical modification of the raw material (on-going
research).
Table 5 Comparison of sorption capacity for La(III) , Nd(III)
and Er(III) ions with various sorbents
Metal
ionSorbent pHi T
(K)qmax
(mg
g-1)Reference
La(III) Magnetic aminated-chitosan
nanobased particles5 320 50.2 [43]

Cellulose for the sorption of rare-earth metal ions Current Applied Polymer Science, 2017, Vol. 0, No. 0 9
Activated carbon derived
from rice husk3.5 293 175.4 [73]
Tannic acid/multi-walled
carbon nanotubes4 293 9.8 [74]
SiO2-TiO 2-NCs
nanocomposite5 298 65.6 [75]
Polydopamine/nanofibrous
mats4.5 298 59.4 [76]
Cysteine-chitosan magnetic
nanobased particles5 320 21.3 [44]
Cellulose 5 323 38.4 This
work
Nd(III)Magnetic aminated-chitosan
nanobased particles5 320 51.5 [43]
EDTA and DTPA/chitosan 3-6 298 77.0 [46]
Ion-imprinted particles 7.5 (a) 33.0 [77]
Phosphorus-functionalized
sorbent6 (a) 160.0 [78]
Phosphonic acid/silica
microspheres2-8 (a) 45.0 [79]
Cysteine-functionalized
chitosan magnetic nanobased
particles5 325 35.0 [44]
Cellulose 5 323 51.1 This
work
Er(III)D113-III resin 6 298 250.0 [23]
Activated carbon derived
from rice husk3.5-
5303 250.0 [73]
Activated charcoal 4 323 225.6 [80]
Cellulose 5 323 52.4 This
work
3.5. Metal desorption and sorbent recycling
The evaluation of the efficiency of a sorbent and its
ability to be applied at large scale should take into account
its capacity to be desorbed and re-used. Indeed, metal
desorption may contribute to improve the competitiveness of
the sorbent, its selective separation properties or its
enrichment factor. In order to evaluate these properties, 4
successive sorption/desorption cycles were operated and the
sorption and desorption efficiencies were compared under
identical experimental conditions (Table 6).
REE desorption from metal-loaded cellulose is efficiently
operated using 0.5 M HCl solutions: the desorption
efficiency slightly decreases with the number of cycles but
even after 4 cycles the desorption yield exceeds 92 % (a loss
limited to 2 % between the first and last cycle). In addition,
the comparison of the sorption levels (under selected
experimental conditions) remained higher than 91 %: the
decrease in sorption efficiency does not exceed 2-3 %.
The sorption and desorption properties are remarkably
stable and confirm that microcrystalline cellulose can be re-
used for the sorption of La(III), Nd(III) and Er(III) for a
minimum of 4 sorption/desorption cycles.
Table 6: Sorption performance (sorption and desorption
efficiencies, %) for 4 successive sorption/desorption cyclesfor the recovery of La(III) , Nd(III) and Er(III) ions using
cellulose.
4. CONCLUSIONS AND PERSPECTIVES
This study shows that microcrystalline cellulose has the
potential to bind rare-earth metal ions such as La(III),
Nd(III) (Cerium group of REEs, i.e., light rare-earth
elements) and Er(III) (Yttrium group of REEs, i.e., heavy
rare-earth elements) at pH close to 5. Sorption levels are
relatively low (in the range 40-55 mg REE g-1) compared to
some values collected in literature; however, this renewable
resource is relatively cheap making the material interesting
for further investigations. In addition, these values are
considered as reference level for an on-going research on
chemical modification of cellulose-based sorbents (obtained
by grafting amino groups, carboxylic groups or sulfur
groups) for enhanced sorption of rare-earth metal ions. The
readily desorption of bound metal ions with 0.5 M HCl
solution (and successful re-use of the sorbent) is also an
important advantage of this simple material. Sorption
capacities increase with temperature: the sorption process is
endothermic (with enthalpy changes in the range 12.5-32.3
kJ mol-1, depending on the metal) and is controlled by
enthalpic rather than entropic change (entropy varies
between 84 and 89 J mol-1, while free Gibbs energy varies
between 22 and 27 kJ mol-1). The kinetic profiles are
controlled by the resistance to intraparticle diffusion
(mechanisms of resistance to intraparticle diffusion through
pores of different sizes); however, the pseudo-second order
rate equation fits well uptake kinetics.
It is noteworthy that the sorption performances (both in
terms of equilibrium and kinetics) are hardly affected by the
type of metal (light and/or heavy REEs). Though sorption
was not investigated in multi-component solutions the results
suggest that the separation of the REEs cannot be
successfully achieved with microcrystalline cellulose.
However the availability of this cheap re-usable renewable
resource may be interesting for the broad recovery of REEs.
Acknowledgements
This work was supported by the International Atomic
Energy Agency for financial support (IAEA for TC project
number (Oracle Project No.: 1060242) and Fellowship Code
Number: C6/EGY/15019). Authors acknowledge Mr.
Thierry Vincent (Ecole des mines d’Alès, France) forCycle numberLa(III) Nd(III) Er(III)
S
(%)D (%)S
(%)D (%)S
(%)D (%)
Cycle I 93.0 93.3 94.0 94.1 94.4 94.9
Cycle II 92.1 92.6 93.2 93.8 94.0 94.3
Cycle III 91.5 92.3 93.0 93.4 93.0 93.5
Cycle IV 91.3 91.8 918 92.1 92.2 93.0

10 Current Applied Polymer Science, 2017, Vol. 0, No. 0 A.A. Galhoum et al.
technical support. Special dedication to the memory of Prof.
Dr. Ahmed Donia.
ADDITIONAL MATERIAL
Additional material available.
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