SUGISAKAMASANORI

Journal of Robotics, Networking and Artificial Life
Vol. 10(4); March (2024), pp. 294–298
ISSN (Online): 2352-6386; ISSN (Print): 2405-9021
https://alife-robotics.org/jrnal.html

Research Article

Effect of Interlayer Anions with NiZn Hydroxy Double Salts on
Adsorption of Selenite, Selenate and Arsenate
Kaoru Ohe, Ryosuke Tabuchi, Tatsuya Oshima

Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-Nishi, Miyazaki, 889-2192, Japan

ARTICLE INFO
Article History
Received 24 November 2023
Accepted 11 April 2024
Keywords
NiZn hydroxy double salts
Langmuir adsorption modelSe(IV)
Se(VI)
As(V)ABSTRACT

Development of adsorbents for selenium and arsenic, which are particularly toxic, is urgently
needed. arsenic was prepared for adsorption and removal. The experimental data of adsorption
isotherms of As and Se oxyanions by NiZn adsorbents were well fitted to the Langmuir adsorption
model, which is characteristic of monolayer adsorption, with a coefficient of determination of
R2>0.94. The maximum adsorption (qmax) of Se(IV) by NiZn-Cl and NiZn-NO3 was similar tothat of NiZn-AcO, and no difference in adsorption due to interlayer ions was indicated. On theother hand, NiZn-Cl had the highest qmax for Se(VI) and As(V). qmax for As(V) by NiZn-Cl was
about twice that of NiZn-AcO, As(V) and Se(VI) adsorption performance was greatly improved.
© 2022 The Author. Published by Sugisaka Masanori at ALife Robotics Corporation Ltd.
This is an open access article distributed under the CC BY-NC 4.0 license(http://creativecommons.org/licenses/by-nc/4.0/).

Anion exchangeable layered compounds are mainly twotype layered double hydroxides (LDHs) and hydroxyl
double salts (HDSs). General formula of LDHs is [MII(1IIIx+ zII
IIIare cationsx)M x(OH)2] Y x/z nH2O, where M and M
zand Y is anion. The most investigated anion
exchangeable layered compounds are LDHs. On the otherhand, hydroxyl double salts, HDSs are inorganic anion
exchangers
withgeneralformula[MAII(1zIIx)MB 2x(OH)2(Y )]2x/z.nH2O. In detail, NiZn double basic
salt with acetate anion Ni1-xZn2x(OH)2(OCOCH3)2x.nH2O(NiZn-AcO) is an inorganic anion exchanger that has astructure in which 1/4 of Ni2+ in a brucite-like layer ofNi(OH)2 is removed from the brucite-like layer, and two
Zn2+ are located outside the layers, just above and below
the Ni2+ vacancy [5], [6]. The layers have positive
charges in excess, balanced by intercalation of acetateanion. The acetate anions bind directly to the tetrahedral
sites along with three OH- groups from the layer to satisfy
the coordination number of Zn2+. The acetate anions areexchanged with guest ions in aqueous solution. Most ofresearch on HDS is in the field of catalysis [7], and to myknowledge, there are few applications in the aqueous
environment. The NiZn-AcO is a more effective arsenic
removal adsorbent than MgAl Layered double hydroxide(LDH) with carbonate ion [8]. Using selectivity
coefficients, Kozai et al. showed that NiZn hydroxyl
double salts are more effective than LDH for selenium

1. Introduction
Arsenic and selenium are used as superior materials forsemiconductor lasers ((Ga, In) As ) and solar batteries(Cu(In, Ga)(Se, S)2), but are known to be damaging to thehuman body even in tiny amounts. In WHO guidelines,
the standard value of arsenic [1] and selenium [2] is lessthan 0.01 mg/dm3 The International Agency for Researchclassifies arsenic and selenium compounds on Cancer(IARC) as Group 1 and 3, respectively, and cause cancer
and other health damage. The main oxidation states ofarsenic in aqueous solution are +3 and +5, and they exist
as oxyanions arsenite, As(III) and arsenate, As(V).
As(III) exists as HnAsO3-(3-n) (n = 0-3), and their aciddissociation constants are 9.23 (pKa1), 12.13 (pKa2) and13.4 (pKa3) [3]. As(V) exists as HnAsO4-(3-n) (n = 0-3),
and their acid dissociation constants are 2.24 (pKa1), 6.96
(pKa2) and 11.5 (pKa3) [3]. The main oxidation states ofselenium in aqueous solution are +4 and +6, and they
exist as oxyanions selenite, Se(IV), and selenate, Se(VI).
The acid dissociation constants of Se(IV) are pKa1 = 2.62
and pKa2 = 8.23 and the chemical species of Se(IV),
HnSeO3-(2-n) (n = 0-2). The acid dissociation constant ofSe(VI) is pKa = 1.7 [4], and chemical species are HnSeO4(1-n)(n = 0, 1).
Corresponding author E-mail: okaoru@cc.miyazaki-u.ac.jp

294

(4)
Ceq / q = Ceq / qmax + 1 / KL qmax
where qmax is the maximum adsorption capacity[mmol/g] and KL is the adsorption equilibrium constant[dm3/mmol]

removal [9]. However, adsorption isotherms andadsorbent evaluation after selenium adsorption have notbeen investigated in detail.
In this study, NiZn adsorbents were prepared by adding
chloride (NiZn-Cl), nitrate (NiZn-NO3), and sulfate(NiZn-SO4) to the acetate ion of NiZn-AcO to improve
the adsorption and removal performance of arsenic andselenium. The effect of interlayer anions of NiZnadsorbents on the adsorption of arsenic and selenium wasinvestigated.

3. Results and Discussion
3.1. Characterization of NiZn adsorbents
Four NiZn adsorbents prepared were identified by XRD
and FT-IR analysis. XRD diffraction pattern of NiZnAcO is shown in Fig. 1. In the XRD pattern of NiZn-AcO,diffraction peaks specific to the layer structure were2. Experimental
2.1. Preparation of NiZn adsorbents
NiZn-AcO, NiZn hydroxide double salt with acetateanion (AcO) was prepared by a modified hydrothermal
synthetic method reported by Rojas et al. [5], [8]. NiZnCl adsorbent was prepared using an ion exchange method
using NiZn-AcO. 50 cm3 of 1 M NaCl solution and 1 gof NiZn-AcO were placed in a glass vessel and stirred at
333 K for 24 h. The supernatant was then discarded andthe sample was stirred in a new 1 M NaCl solution, which
was repeated three times. NiZn-NO3 and NiZn-SO4 wereprepared in the same method as NiZn-Cl using aqueous
solutions of NaNO3 and Na2SO4, respectively. The NiZnadsorbents were washed several times using deionizedwater and dried in a vacuum oven. XRD, FT-IR, andCHN elemental analysis characterized the adsorbents.

Fig. 1 XRD patterns of NiZn-AcO, NiZn-Cl,NIZn-NO3 and NiZn-SO4..

2.2. Adsorption test of arsenic and selenium
The adsorption experiments of Se(IV), Se(VI) andAs(V) were carried out by batch method. 1.0 × 10-4 Maqueous metal solution was adjusted to a given pH using
HCl solution or an aqueous NaOH solution in the pHdependent adsorption test. In the adsorption isotherm
experiments, metal concentrations were prepared at 2.0 ×
10-4 - 4.0 × 10-3 M and adjusted to the prescribed pH withthe aqueous NaOH solution. Ten mg of NiZn adsorbent
and 15 cm3 of metal solution were added to a sample tube
and shaken at 303 K, 120 rpm for 24 h. pH of the filtrate
was measured. The metal concentrations of the solutions
before and after adsorption equilibrium were measured
using atomic absorption spectrophotometer and ICPemission spectrometer. The amount of adsorption(q) andthe adsorption percentage (A%) were calculated
according to the following equations, respectively:(1)q = (Cint – Ceq) v/w(2)
A = (Cint – Ceq) / Cint
where Cint and Ceq are initial and equilibrium
concentration, respectively [mM], v is the volume ofsolution, w is the weight of adsorbent [g], q is the amountof arsenic or selenium adsorbed, A is the adsorption
percentage [%]Langmuir equation and its variant equation are given
in Eq.(3) and (4), respectively.
(3)
q = KLqmax Ceq / (1 + KLCeq)

detected. The lattice plane spacing (d) of the diffraction
peaks were 13.0 Å, 6.49 Å, and 4.33 Å for d001, d002, andd003, respectively, from the low angle side, which isconsistent with the literature values [5]. Diffraction
patterns of NiZn-Cl, NiZn-NO3, and NiZn-SO4 also
detected peaks originating from layered compounds,
similar to NiZn-AcO. As shown in Fig. 1, their d001 values
decreased to 8.09 Å (NiZn-Cl), 9.14 Å (NiZn-NO3), and9.14 Å (NiZn-SO4) After inorganic anions replaceorganic anions between the LDH layers, the space within
the LDH layers increases significantly [12]. The results
indicate that inorganic ions replace the acetate ions in theNiZn adsorbent. from the d001 of NiZn-AcO. FT-IR
spectrum of NiZn-AcO with the absorption bands at 1572
cm-1 for the carboxylate (COO-) and 1407 cm-1 for thesymmetric stretching, and an absorption peak at 1339 cm1for the C-H symmetric angular vibration. The interlayer
ions of absorption peaks of NO stretching vibration at1385 cm-1 for NiZn-NO3 and SO asymmetric stretchingvibration at 963 cm-1 and SO symmetric stretchingvibration at 1061 cm-1 for NiZn-SO4 were confirmed [10].
The chemical formula of NiZn adsorbents wasdetermined using atomic absorption analysis (Ni/Zn moleratio), CNH elemental analysis (amount of acetate) andTG/DTA (amount of adsorption water) [11], and isshown in Table 1. The ion exchange capacity of NiZn295

AcO is 2.45 meq/g ( = acetate anion content); the Cl-,
NO3- and SO42- amounts in NiZn-Cl, NiZn-NO3 andNiZn-SO4 are 2.22 meq/g, 1.57 meq/g and 2.09 meq/g
respectively.

Table 2. Parameters of the Langmuir adsorption
isotherms for Se(IV), Se(VI) and As(V)at 303 K.
Adsorbates Adsorbents

KLpHeqq max[mmol/g][dm3/mmol]

R2

Table 1. Chemical fomula of NiZn adsorbents

NiZn-AcO

8.54±0.33

1.48

7.10

0.94

NiZn adsorbents

NiZn-Cl

7.88±0.39

1.44

9.98

0.994

NiZn-NO3

7.67±0.59

1.54

7.47

0.971

NiZn-SO4

7.35±0.39

0.909

4.090.965

NiZn-AcO

6.85±0.15

0.979

14.20.989

NiZn-Cl6.72±0.54

1.19

4.310.988

NiZn-NO3

6.60±0.42

0.983

12.80.997

NiZn-SO4

6.77±0.21

0.718

0.531

0.99

NiZn-AcO

10.3±0.32

0.446

287

0.998

Chemical formula

AcO

Ni0.67Zn0.34(OH)2(CH3COO)0.34 0.65H2O

Cl

Ni0.67Zn0.34(OH)2(CH3COO)0.03(Cl)0.31 nH2O

NO3

Ni0.67Zn0.34(OH)2(CH3COO)0.12 (NO3)0.22 nH2O

SO4

Ni0.67Zn0.34(OH)2(CH3COO)0.05 (SO4)0.15 nH2O

Se(IV)

Se(VI)

As(V)

3.2. Adsorption isotherms of arsenic and selenium
Adsorption isotherms of Se(IV), Se(VI), and As(V) at303 K were conducted. The adsorption isotherms for
Se(IV), Se(VI), and As(V) increased with increasing
metal ion concentration and approached a constant value
at high concentrations, which the Langmuir adsorption
model characteristic of monolayer adsorption is applied.
The experimental data for Se(VI) adsorption fitted theLangmuir plot well (Fig. 2), with coefficient ofdetermination R2 >0.988. Se(IV) and As(V) adsorption
also fit the Langmuir plot well (R2 >0.94). The maximum
adsorption capacity (qmax) for Se(IV), Se(VI) and As(V)and adsorption equilibrium constants (KL) were
calculated using Langmuir's equations (equations (3) and(4)) and are listed in Table 2.

NiZn-Cl9.67±0.43

0.947

14.3

0.997

NiZn-NO3

10.0±0.36

0.524

77.6

0.999

NiZn-SO4

9.59±0.49

0.564

11.10.988

AcO and NiZn-Cl The Se(VI) exchange percentage wasestimated to be 80.0% and 107% by comparing theamount of acetate anion and Cl- (meq/g) in NiZn-AcO
and NiZn-Cl, respectively, as shown in section 3.1.
When Se(IV) was examined similarly, the exchange rateof Se(IV) by NiZn-Cl (82.7%) was slightly lower thanthat of NiZn-AcO (96.7%) From the pH given in Table
2, the qmax of NiZn-AcO and NiZn-Cl were calculated tobe 0.918 meq/g and 1.91 meq/g, respectively, considering
the mole fraction of As(V) chemical species, and theexchange percentage of As(V) was estimated to be 37.5%
and 85.9%. These results indicate that NiZn-Cl canadsorb Se(VI) and As(V) more effectively than NiZnAcO.
3.3. Effect of contact time of Se(VI) adsorption
Fig. 3 shows the effect of contact time on the Se(VI)adsorption by NiZn-AcO and NiZn-Cl. The time for theadsorption of Se(VI) by NiZn-AcO and NiZn-Cl to reachequilibrium was 5 min, which was extremely rapid. The
result is the same as the ion exchange reaction with LDH[12], indicating that the Se(VI ) adsorption is considered
to be due to the ion exchange reaction.

Fig. 2 Langmuir plots of Se(VI) on NiZn-AcO, Cl, -NO3 and -SO4....
The maximum adsorption capacities (qmax) of Se(IV),Se(VI), and As(V) by NiZn-Cl and NiZn-NO3 werealmost the same or increased compared to that of NiZnAcO, except for NiZn-SO4. Since the dissolved speciesof Se(VI) or As(V) have a significant effect on qmax, thesaturated adsorbed amount of Se(VI) or As(V) wasconverted to an equivalent unit by considering the mole
fractions of the main dissolved species at each pH, whichwere obtained from the acid dissociation constants. As
shown in Table 2, Se(VI) species are SeO42- from pH, theqmax of NiZn-AcO and NiZn-Cl are calculated to be 1.96
meq/g and 2.38 meq/g, respectively. Acetate in NiZn-Fig. 3 Time course of Se(VI) adsorption on NiZnAcO and NiZn-Cl..

296

3.4. XRD results of NiZn adsorbent after Se(IV)and Se(VI) adsorption

References
1.

The d001 values of NiZn-AcO and NiZn-Cl changed
before and after the adsorption of Se(IV) or Se(VI) (Fig.
1 and 4). The thickness of the basic brookite layers does
not change much during the anion exchange process, but
the interlayer distance varies with the configuration andsize of the intercalated anions. After selenium adsorption,these interlayer distances were nearly equal, suggestingthat the interlayer acetate anions and Cl- are exchanged
for anions by Se(IV) and Se(VI).

2.

3.

4.

d001= 9.13 Å5.

(a) NiZn-Cl adsorbend Se(VI)d001= 9.13 Å (b) NiZn-Cl adsorbend Se(IV)d001= 9.12 Å

10

R. Rojas, M. A. Ulibarri, C. Barriga and V. Rives,
Chromate intercalation in Ni-Zn layered hydroxidesalts, Appl. Clay Sci., 49(3), 2010, pp.176-181.
R. Rojas, M. A. Ulibarri, C. Barriga and V. Rives,
Intercalation of metal-edta complexes in Ni-Zn
layered hydroxy salts and study of their thermalstability, Microporous and Mesoporous Mater., 112,
2008, pp. 262-272.

6.

(c) NiZn-AcO adsorbend Se(VI)d001= 9.23 Å (d) NiZn-AcO adsorbend Se(IV)5

B. K. Mandal and K. T. Suzuki, Arsenic round the world:
A review, Talanta, 58(1), 2002, pp.201-235.
S. O. Okonji, G. Achari and D. Pernitsky, Environmentalimpacts of selenium contamination: A review on current
issues and remediation strategies in an aqueous system,Water, 13(11), 2021, 1473
D. Mohan and C. U. Pittman Jr., Arsenic removal fromwater/wastewater using adsorbents-A critical review, J.
Hazardous Metals, 142(1-2), 2007, pp. 1-53.
S. Santos, G. Ungureanu, R. Boaventura and C. Botelho,
Selenium contaminated waters: An overview of analyticalmethods, treatment options and recent advances insorption methods, Sci. Total Environ., 512-522, 2015,
pp.246-260.

15202θ [degree]

257.

30
8.

Fig. 4 XRD patterns of NiZn-AcO adsorbed (a)Se(IV) and (b) Se(VI)..and NiZn-Cl adsorbed (c)Se(IV) and (d) Se(VI)..

9.

4. Conclusions
10.

After hydrothermal synthesis preparation of NiZn-AcO, NiZnCl, NiZn-NO3, and NiZn-SO4 were prepared from NiZn-AcO

by ion exchange method to obtain NiZn layered basic salt
adsorbents. These four NiZn adsorbents were found to beable to adsorb and remove Se(IV), Se(VI), and As(V)from the aqueous solution. NiZn-Cl was able to adsorb
Se(IV), Se(VI), and As(V) according to Langmuiradsorption model. NiZn-NO3 and NiZn-SO4 adsorbed thesame amount of Se(IV) as NiZn-Cl and NiZn-NO3. In
contrast, the maximum amount of Se(VI) adsorbed by
NiZn-Cl was slightly increased compared to NiZn- The
adsorption performance of As(V) and Se(VI) wasimproved by ion exchange of the interlayer anions ofNiZn adsorbent from acetate to chloride ions.

11.

12.

T. Hara, M. Ishikawa, J. Sawada, N. Ichikuni and S.
Shimazu, Creation of Highly Stable Monomeric Pd(II)Species in an Anion-Exchangeable Hydroxyl Double Salt
Interlayer: Application to Aerobic Alcohol Oxidation
Under an Air Atmosphere, Green Chem., 11, 2009,
pp.2034-2040.
K. Ohe, R. Tabuchi, T. Oshima, T. Hara and S. Shimazu,
Adsorptive removal of arsenic (III) and arsenic (V) fromaqueous solution using nickel-zinc hydroxyl double salts,Kagaku Kogaku Rombunshu, 45(2), 2019, pp.80-85.
N. Kozai, T. Ohnuki and S. Komarneni, Selenium
Oxyanions: Highly Selective Uptake by a Novel Anion
Exchanger, J. Mater. Res., 17, 2002, pp.2993-2996.
R. Rojas, C. Barriga, M. A. Ulibarri, P. Maletb and V.
Rive, Layered Ni(II)-Zn(II) hydroxyacetates. Anion
exchange and thermal decomposition of the hydroxy salts
obtained, J. Mater. Chem, 12, 2002, pp.1071-1078.
N. Kozai, H. Mitamura, H. Fukuyama, F. Esaka and S.
Komarneni, Synthesis and characterization of nickelcopper hydroxide acetate, NiCu(OH)3.1(OCOCH3)0.9･0.9
H2O, Microporous and Mesoporous Mater., 89, 2006,
pp.123-131.
T. You, G. F. Bance and H. Zhao, Selenium adsorption on
Mg-Al and Zn-Al layered double hydroxides, App. Clay
Sci.20, 2001, pp.13-25.

Authors Introduction
Dr. Kaoru Ohe

Acknowledgments
The authors thank Prof. S. Shimazu and Dr. T. Hara ofChiba University for their advice on preparing NiZn-AcO
adsorbent.

297

She received her Ph.D. degree from
University of Miyazaki, Japan, in 2014.
Currently, she is an Associate
Professor of Center for Science andEngineering Education, Faculty ofEngineering. Her
research isseparation engineering, especiallyadsorption hazardous heavy metals andoxyanions.

Mr. Ryosuke Tabuchi
He received his Master’s degree inEngineering in 2019 from Faculty ofEngineering, University of Miyazaki inJapan.

Prof. Dr. Tatsuya Oshima
He received his Ph.D. degree fromKyushu University, Japan, in 2001.
Currently he is a Professor of theDepartment of Applied Chemistry,Faculty of Engineering. His researches
are separation engineering (especiallysolvent extraction for precious metalions) and formulation techniques forpoorly water-soluble drugs andnutrients.

298