New treatment methods for waste water containing chloride ion using magnesium-aluminum oxide

Article abstract of DOI:10.1246/cl.2000.1136

The removal of hydrochloric acid utilizing magnesium-aluminum oxide (Mg-Al oxide), as prepared by the thermal decomposition of hydrotalcite (HT), was investigated. Cl^- in hydrochloric acid can be removed almost 100% by adding 1.75 times the sto

Full text of DOI:10.1246/cl.2000.1136

1136
Chemistry Letters 2000
New Treatment Methods for Waste Water Containing Chloride Ion Using
Magnesium–Aluminum Oxide
Tomohito Kameda, Yoshinori Miyano, Toshiaki Yoshioka, Miho Uchida, and Akitsugu Okuwaki
Department of Applied Chemistry, Graduate School of Engineeing, Tohoku University, Aoba 07, Aoba-ku, Sendai 980-8579
(Received July 3, 2000; CL-000636)
The removal of hydrochloric acid utilizing magnesium-alu-
M HCl solution using Mg0.70Al0.20O or [Mg0.78Al0.22(OH)2]-
(CO3)0.11 of 1.75 times the stoichiometric quantity at 60 °C.
[Mg0.78Al0.22(OH)2](CO3)0.11 showed only negligible
hydrochloric acid removal. Mg0.70Al0.20O exhibited a much
higher degree of Cl– removal, almost 100% after 0.5–1 h. It
was confirmed by XRD that Mg0.70Al0.20O was restored to
Cl–HT after 10 min. In the case of adding CO3–HT, Cl– can
minum oxide (Mg–Al oxide), as prepared by the thermal
decomposition of hydrotalcite (HT), was investigated. Cl– in
hydrochloric acid can be removed almost 100% by adding 1.75
times the stoichiometric quantity of Mg0.70Al0.20O at 60 °C for
1 h. Mg2+ and Al3+ in solution after the reaction were not rec-
ognized, because the solution was weakly alkaline.
2–
hardly exchange with CO3 that has been intercalated in HT
since the charge density of CO32– is higher than that of Cl–. The
2–
Waste water containing chloride ion which is discharged
from such places as landfill is high concentrated saline solution,
and it has caused the corrosion of waste pipe, the scale block, or
the agricultural wreck of crops by damage from salt.1,2 The
desalting treatment of this waste water with electric dialysis
installation is carried out recently, but there are some problems
as the existence of K+ in produced drying salt and absence of
receiver of it.3 New treatment methods for waste water contain-
ing chloride ion are desired.
degree of anion intercalation in HT is ordered CO32– > SO4
>
OH– > Cl– .8 It is thought that with Mg–Al oxide, Cl– was easi-
ly intercalated into the reconstructed HT because CO3 and
2–
OH– was nonexistent in the initial reaction stage.
HT ([Mg2+1–xAl3+x(OH)2](An–)x/n·mH O : 0.2
x
0.33) is
<
<
=
=
2
a layered double hydroxide with anion exchange properties.
HT transforms into Mg–Al oxide when heated to 500–800 °C.
The Mg–Al oxide can intercalate anions in solution, and then
the original HT structure can be reconstructed as expressed by
It is expected that the Mg–Al oxide is applied to waste
water treatment as remover.4–6
In this study, the hydrochloric acid in waste water was tar-
geted as waste water containing chloride ion, and the optimum
condition of Mg–Al oxide quantity and time was examined for
the removal of Cl– at various HCl concentration. The differ-
ences between HT and Mg–Al oxide were also examined.
CO3–HT ([Mg0.78Al0.22(OH)2](CO3)0.11·mH2O), with an
Mg/Al molar ratio of 3.5, was synthesized by “LDH Synthesis
by the Variable-pH Method” of S.K.Yun and T.J.Pinnavaia.7
Mg0.70Al0.20O was prepared by the calcination of CO3–HT at
500 °C for 1 h. A 0.01–0.5 M HCl solution (10 mL) and
[Mg0.78Al0.22(OH)2](CO3)0.11·mH2O or Mg0.70Al0.20O of 0.5–2
times the stoichiometric quantity, according to eqs (2) and (3),
were placed in a 50-mL screw tube and shaken at 60 °C for 1–3 h.
The following study was carried out in order to determine
the Mg0.70Al0.20O quantity for the removal of Cl–. The reaction
was allowed to proceed for 3 h, and equilibrium was thought to
be completely attained within that time.
Figure 2 shows the relationship between Cl– removal from
0.5 M HCl solution and the Mg0.70Al0.20O quantity at 60 °C for
3 h. Almost 100% Cl– removal was achieved by adding
Mg0.70Al0.20O of 1.75 times the stoichiometric quantity.
Excessive amounts of Mg0.70Al0.20O were required to remove
Cl–. This is because OH– is produced by the reconstruction
reaction, as expressed by eq (3), and there is competition
between the reactions of OH– and Cl–, as expressed by
The pH of the solution was measured after the reaction, and
Cl– concentration was determined by ion chromatography. The
degree of Mg2+ and Al3+ leaching were determined by ICP–AES.
The precipitates were identified by X-ray diffraction (XRD).
Figure 1 shows the time dependence of Cl– removal from 0.5
Figure 3 shows the relationship of dissolved Mg2+ and pH
to the Mg0.70Al0.20O quantity at 60 °C for 3 h. The pH after the
reaction increased with increasing the Mg0.70Al0.20O quantity,
and reached pH 8.6 at the stoichiometric quantity. The amount
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1137
The intercalation capacity of Cl– in NaCl solution with
Mg–Al oxide is investigated.9,10 The degree of Cl– removal
was 50% by adding Mg–Al oxide of 2.5 times the stoichiomet-
ric quantity at 80 °C for 1 h, and it was known that the degree
of Cl– removal was low because OH– was easily intercalated
with increasing pH as expressed by eq (3).9 However, in this
study, it was clear that Cl– was removed above 90% by using
Mg–Al oxide of 1.75 times the stoichiometric quantity in the
strong hydrochloric acid below initial pH 1.
The advantage of this treatment method is that Mg–Al
oxide can be used efficiently as increasing initial HCl concen-
trations. The treatment method for waste water containing
chloride ion (CaCl2) which is discharged from landfill is
thought that HCl and CaSO4·2H2O are produced by adding
H2SO4 to this waste water, and Mg–Al oxide is applied for the
removal of the produced HCl. It is also thought that Mg–Al
oxide is applied for the removal of HCl which is discharged
from garbage incinerator or flon decomposition plants. It is
expected that the produced Cl–HT can be used as ion exchanger
for removing phosphorus to prevent eutrophication of surface
water by algae bloom.11 Kawamoto et al. have reported that
residual concentrations of the phosphate ion from rural sewages
treated with Cl–HT were less than 1 mg/L.12
of dissolved Mg2+ decreased with increasing the Mg0.70Al0.20
O
quantity. It is thought that the once dissolved Mg2+ was repre-
cipitated as hydroxide with increasing pH, since the solubility
product of Mg(OH)2 is small. This was confirmed by XRD
analysis of the precipitates. Dissolved Al3+ was not recognized.
Since Al is amphoteric, it initially dissolves, but it precipitates
as a hydroxide as the reaction progresses.
References and Notes
The following study was carried out in order to know the
degree of Cl– removal for various concentrations of HCl. The
reaction was finished within 1 h in consideration for the indus-
trialization of this waste water treatment.
1
2
3
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Figure 4 shows the effect of HCl concentration on the
removal of Cl– using Mg0.70Al0.20O of 1.75 times the stoichiomet-
ric quantity at 60 °C for 1 h. The degree of Cl– removal decreased
with decreasing HCl concentration. The degree of Cl– removal
was almost constant at 0.1–0.5 M HCl, but the removal decreased
significantly below 0.1 M HCl. It is suspected that the rate of
intercalation by Cl– was faster than the rate of acid neutralization
with the reconstruction reaction of Mg0.70Al0.20O as increasing
HCl concentration, and Cl– was intercalated into the reconstructed
HT promptly without the competition reactions as expressed by eq
(4). The residual concentrations of Cl– was 0.009 M at 0.5 M
HCl. It has satisfied the desirable concentration range, since the
concentrations of Cl– should be below 0.014M to prevent the agri-
cultural wreck of crops by damage from salt.2
4
5
6
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8
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