- Email: [email protected]
Removal of Cu(II), Zn(II), Cd(III) and Hg(II) from waste water by poly(acrylaminophosphonic)-type chelating fiber
Chemosphere, Vol. 38, No. 13, pp. 3169-3179,1999
Pergamon
© 1999ElsevierScienceLtd. All rightsreserved 0045-6535/99/$ - see frontmatter
PII: S0045-6535(98)00506-2 R E M O V A L Of Cu(II), Zn(I1), Cd(ll) AND Hg(ll) F R O M WASTE W A T E R BY P O L Y ( A C R Y L A M I N O P H O S P H O N I C ) - T Y P E C H E L A T I N G FIBER
Ruixia Liu ' , Hongxiao Tang, Baowen Zhang
(State Key Lab of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O.Box 2871, Beijing 100085) (Receivedin USA 27 August1998;accepted6 October 1998) Abstract: The distribution coefficients (D) for Cu(II), Cd(II), Zn(II) and Hg(lI) ions and adsorption isotherms of Cd(II) and Hg(II) ions on the poly(acrylaminophosphonic)-type chelating fiber were investigated using the batch reactor system. It was found that D values for the tested metal ions were above the magnitude of 103 at pH 5.0, and the order of metal ion affinities was: Hg(lI) > Cu(lI) > Zn(ll) > Cd(II). At low pH value (2.0), D value for Hg(lI) ion was higher than that of the other ions, above 103. The adsorption of Hg(II) and Cd(ll) ions on the new chelating fiber followed a Langmuirtype adsorption isotherm. The elution of the metal ions from the chelating fiber column using dilute nitric and hydrochloric acid as eluent were examined. The results show that the elution for Cu(ll), Cd(II) and Zn(II) ion was complete using appropriate concentration of hydrochloric acid, while the high concentration of dilute nitric acid was necessary for the quantitative desorption of Hg(Il) ion. The breakthrough curves for the metal ions were determined, and the efficient removal of the listed metal ions from model or waste water by the newly developed fibrous sorbent was achieved. © 1999 Elsevier ScienceLtd. All rights reserved Keywords: Poly(acrylaminophosphonic)-Type Chelating Fiber, Metal ion, Removal, Desorption
INTRODUCTION
The possibility of ion exchange or chelating process to removal heavy metal ions from solution has been explored by a number of workers fl-31. However, since those ion exchangers are of granular form, lower adsorption capacities, inferior kinetic properties and cost considerations have prohibited the widespread application of ion exchange or chelating technique on an industrial scale, and their applications in large-scale processes is hardly possible because of the high resistance of filtering layers. The stricter limitations on the concentration of toxic heavy metal ions in the discharged industrial effluents have rendered new research necessary on such a water treatment method. Therefore, the viability of ion exchange or chelating technique depends on the development of modified adsorbents. • Aulhor to whom all correspondence should be addressed. E-mail: [email protected] 3169
3170 Fibrous ion exchangers or chelating adsorbents exhibit some features associated with their structure. The main advantages are (1) the large specific surface, which is larger by about two orders of magnitude than the one of a gel-structure granular ion-exchanger or 5-6 times higher than the surface of a porous copolymer, assuring good kinetic characteristics; (2) the high swelling capacity, which is attributed to the presence of linear or branched macromolecules; (3) the excellent mechanical strength; (4) the convenient use. The fibrous sorbents might be produced in the forms of filaments, staple, cloths and non-woven materials, opening up many possibilities for new technological processes. As a result of these properties, the intensive research has been carried out to develop the preparation methods for different types of fibrous adsorbents. Fibrous ion exchangers with PAR, alizarin, tailor-made, amidoxime groups based on cellulose or its graft copolymers have been prepared through the transformation of hydroxyl-groups and further activation of cellulose derivatives~4'5j, Polyacrylonitrile fiber has been used in creating fibrous adsorbents containing amidoxime and hydroxam groups t6j, carboxyl- and tetrazine groups I7'81, amidrazone-hydrazide groups [91 and bisamide groups °°1. The method and technology of introducing thiocarbamide and amino-groups onto polyvinyl alcohol fiber have been developedtH'~21. In recent years ion exchange or chelating fiber as one type of adsorbents has been widely used to various research fields, such as the preconcentration and determination of trace elements t~31, air purification from acid gases and vaporst~41 and extraction of useful elements from aqueous mediat~Sl. Despite numerous publications, the applications of fibrous adsorbents in waste water treatment are not fully studied. The present paper mainly deals with the properties and applications of newly developed poly(acrylaminophosphonic)-type (PAAP-1I) ion exchange chelating fiber in the removal of Cu(II), Zn(II), Cd(II) and Hg(II) ions from model or industrial water.
EXPERIMENTAL
Chemicals and materials All chemicals in this study were of analytical-reagent grade. Adsorptive solution were prepared by dissolving CuC12. H20, Cd(NO3)2, ZnCI2 in distilled water with appropriate quantities of concentrated nitric acid and HgSO4 in distilled water with glacial acetic. The rinsing solution samples in electroplating zinc were collected from Mechanical Factory of Beijing Aeronautical University. The model waste waters separately containing Cu(II), Hg(II) and Cd(II) were prepared by dissolving appropriate salt in tap water. The characteristics of these waters were listed in Table 1. The PAAP-II chelating fiber used was prepared through the following steps: (1) The polyacrylonitrile fiber was cross-linked with hydrazine for 3 h at 95°C; (2) An amount of dry hydrazine-modified fiber and diethylenetriamine were mixed in a one-liter three-necked reaction vessel, heated for 5 -10 h at 95°C. Afterward the mixture was cooled, suction-filtered, washed with distilled water; (3) The final product,
3171 PAAP-II chelating fiber, was prepared by the reaction of the above fiber-aminated with phosphoric acid for 6h at 85 ~ 95°C, suction-filtered, washed with distilled water and dried at 60 ~65°C overnight. The introduction of aminophosphonic groups into the hydrazine-modified fiber could be briefly expressed as follows: I
hydrazine-modified fiber ( - - ]C
)
NH 2C2 H 4 I~-IC 2 H4 NH 2 ~ .
C=O I OCH3
fiber-aminated (
C
)
HPCO)(OH)2 + HCHO
C=O I NH C2 I-h NHC2l-h NH 2 I poly(acrylaminophosphonic)-type chelating fiber(- C - ) i
C=O I NH C2 I-h NHC2H4NH I CH 2 PCO)(OH)2 By infrared spectroscopy analysis, it was shown that PAAP-II chelating fiber contained carboxyl, aminophosphonic and hydrazide. The nitrogen, oxygen and phosphorus contents of the chelating fiber were respectively 16.17, 19.18 and 3.99% t16].
Table i. The characteristics of the waste water Type of waste
Concentration (mg/L)
pH
Medium
Hg(lI)
10
6.0~6.5
Cu(II)
51
6.0~6.5
CI, NIL +
Cd(II)
50
6.0~6.5
NO3-, NIL +
Zn(II)
26
6.0~7.0
KC1, ILBO3
water
Apparatus
5042 ,
Ac-, NIL+
and Instruments
Z-6100 Atomic Absorption Spectrometer (A.AS) and Coleman-50 Mercury Analyzer were used for the determination of Cu(II), Zn(II), Cd(II) and Hg(II) ions concentration. The pH value of solution was adjusted by pHS-3C pH-meter.
3172 Experimental procedure
The batch adsorption experiments were carried out to determine the distribution coefficients of Cu(II), Zn(II), Cd(II) and Hg(II) ions between the PAAP-II chelating fiber and liquid phase and the adsorption isotherm of Hg(II) and Cd(II) ions on the chelating fiber. Dried samples (0.10g each) of the PAAP-II fiber were equilibrated by shaking for 24 h in 10 mL of metal ion solutions at 25°C. The metal ion solutions were adjusted to the desired pH value with aqueous ammonia prior to equilibrium. The concentrations of Cu(II), Cd(II), Zn(II) and Hg(II) ions in filtrate were determined by AAS and Coleman-50 Mercury Analyzer respectively. Triplicate samples were run. The desorption of metal ions from the PAAP-II chelating fiber was carried out by dynamic experimental technique. The fiber columns (20cm long x lcm i.d) loaded with metal ions were eluted with diluted nitric or hydrochloric acid at a flow rate of 2 mL/min.
Removal of metal ions from waste water
500mL of model waste water containing Hg(II) ion was added to 0.Sg of the PAAP-II fiber sample, and mixing started immediately.
After time interval of 10rain, 1.0 mL aliquots were collected for the
determination of Hg(II) ion concentration.
The waste water samples containing Cu(II), Cd(il) and Zn(II)
ions passed through the PAAP-II chelating fiber column (50cm long x 3cm i.d) at a flow rate of 15 - 3m/h. The filtrates were collected at appropriate time interval for the determination of residual metal ion concentration.
RESULTS AND DISCUSSION
Distribution coefficieut
The affinity of ion exchange chelating sorbents for metal ions is usually expressed in terms of distribution coefficients (D) at appropriate pH value, which is concerned with the type and structure of functional groups in the sorbents, metal ion speciation and pH value of solution. The results of Fig. 1 showed that the D values of the tested ions between the PAAP-II chelating fiber and liquid phase, at pH 5.0, were above the magnitude of 103, and the following order of metal ion affinities was found: Hg(II) > Cu(ll) > Zn(II) > Cd(II). In addition, for Cu(II), Zn(II) and Cd(II) ions, D values were very low up to about pH 3.5, afterward increased and reached maximum value at about pH 5.0 for Cu(ll), 6.0 for Zn(II). For Hg(II) ion, even at pH 2.0, D value was also higher, above 103, and increased up to maximum value around pH 5.5. The effect of pH value on distribution coefficient may be explained from two points. One is that the pH value influences the surface structure, charge properties and adsorption site of sorbents.
In general, the protonation and
deprotonation properties of acidic- or basic-groups on ion exchange chelating sorbents is attributed to the pH value change. The other explanation is that the metal speciation depends on the pH value, and the different ion speciations express the different adsorption characteristics.
3173 250 200 150
....
Hg Cu
. . . . .
Zn
.....
Cd
~
100
i
/
,,'"
..¢"" \
///.j./
50 0
i{ .2/,~
t
~ --'~ 7 ~-"
I
I
i
1
2
4
5
6
3
7
pH Fig. 1. Effect ofpH value on distribution coefficient (D)
At low pH, the differences of D value for Hg(II) and Cu(II), Cd(II), Zn(II) can be described by the selectivity which is expressed in terms of separation factor (KNM)E17,lsl,defined as KNM= DM / DN where DM and DN is respectively the distribution coefficient of M and N ion. When KNM value is much higher than l, it is obvious that the selectivity of chelating sorbent for M ion is higher. The separation factors of Hg(II) ion for the other metal ions on the PAAP-II chelating fiber were listed in Table 2. The results further revealed that the selectivity for Hg(II) was remarkably high, and KNM value was above 8.0 at pH 2.0. Therefore, the effective separation of Hg(II) ion from the mixture of Cu(II), Cd(II) and Zn(II) ions is possible by use of the PAAP-II chelating fiber at lower pH value. Table 2. The separation factors (KNM) of Hg(II) ion for the other metal ions (N) on the PAAP-II chelating fiber Metal ion
pH
(N)
2.0
3.0
4.0
Cu(II)
8.01
2.53
1.2
Cd(II)
173
48
Zn(II)
256
64
6.0 1.26
3.2
1.5
Initial concentration of metal ion: 0.001 mol/L
Adsorption isotherm
The Langmuir isotherm (L-type) has been expressed as follows: 1/Q = 1/Q° + (A/Q°)(1/C,) where Co is the equilibrium concentration in retool/L, Q the amount of adsorption in retool/g, Q0 the adsorption capacity at the monolayer coverage, and A the adsorption constant. The adsorption experimental data for Hg(II) and Cd(II) ions on the PAAP-II chelating fiber were adjusted according to Langmuir
3174 isotherm model and the isotherm parameters were calculated using a method o f least squares. The results were shown in Fig.2 and Table 3
1.6 1.4
#_
•
o
• •
•
9~ '
0.8 O' 0.6 0.4
•
O-i----k------
1.2
/A
0.2 0
L-type regression curve for Hg(II) experimental data for Hg(II) experimental data for Cd(II) L-type regression curve for Cd(lI)
• • .... t 0.5
I 1.5
1
I 2
I 2.5
I 3
3,5
C° (mmol/L) Fig.2. Adsorption isotherms for Hg(II) and Cd(II) ions on PAAP-II chelating fiber
Table 3. Langmuir adsorption parameters for Hg(II) and Cd(II) ions on PAAP-II chelating fiber at 25°C Metal ions
pH
Adsorption parameters
L-type equation
Q0
A
r
Hg(II)
6.00+0.25
1.14
0.112
0.9922
Q = 1.14 x C~/(0.112 +C~)
Cd(II)
5.20_+0.25
1.28
0.00192
0.9815
Q = 1.28 × C~ / (0.00192 + C,)
The examination revealed that, in low and intermediate concentration range, the experimental data were better fitted to Langmuir isotherm, while with metal ion concentration increase, the experimental data slightly deviated from Langmuir equation. This deviation is mainly contributed to the differences of real adsorption behavior and Langmuir theoretical hypothesis as well as the structural complexity of the PAAP-1I chelating fiber. The existence of multi-functional groups results in the interactions of groups, adsorbed metal ions as well as groups and fiber skeleton, which makes the adsorption mechanism of the fibrous sorbent with Hg(II) and Cd(II) ions complicated.
Further investigation on this respect seems to be necessary for a better
understanding of adsorption properties for metal ions on the PAAP-II chelating fiber.
Elution curve The elution curves for Cu(II), Cd(II), Zn(II) and Hg(II) ions at a flow rate of 2 mL/min, using diluted hydrochloric or nitric acid as eluent, were shown in Fig.3.
The elution of Zn(II) ion was relatively easy
compared to the other ions. The adsorbed Zn(II) ion could be quantitatively recovered only with 0.5 mol/L hydrochloric acid, and the remarkable delay-action did not exist in its elution curve, which showed a fast
3175 elution velocity for Zn(II) from the PAAP-II chelating fiber column. Tile adsorbed Cu(II) ion could not be eluted with 20 mL of 0.5 mol/L hydrochloric acid, and a higher concentration (2 mol/L) of hydrochloric acid was required to improve the recovery efficiency. With respect to Cd(II) ion, the elution velocity using 6 mol/L hydrochloric acid as eluent was higher than that of 2 mol/L hydrochloric acid as eluent, and the larger volume of hydrochloric acid was favorable to the recovery of Cd(II) ion. However, the elution o f t t g ( l l ) ion was different from the other ions.
The preexperiment showed that diluted hydrochloric acid was not as
effective as diluted nitric acid for the recovery of ttg(ll) ion.
In Fig.3, it is indicated that the high
concentration of dilute nitric acid was necessary for reaching a quantitative recovery of ttg(lI) ion. This property further revealed the high affinity of the PAAP-II chelating fiber for Hg(ll) ion.
05...o.,L.c. 8 g
sr,
2 mol/L ttCI
6
4
4
~ 2
~ 0
l0
20
30
2
40
10
Elution volume (mL) Cu(ll)
30
40
Cd(ll)
~4
~1.5
.~
m
20
Elution volume (mL)
t
2 0 0
10
I
I
20
30
Elution volume (mL) Zn(ll)
~ ~ 40
0.5 0
I
'
.',
tO
20
30
40
Elution volume (mL) 1lg(ll)
Fig.3. Tile elution curves of metal ions front PAAP-I1 chelating fiber colunm
Renloval of metal ions fi'om solution To evaluate the applicability of the PAAP-I1 chelating fiber, the removal efficiency of Hg(I1) ion from tile model water was examined The result of Fig.4 showed that the removal of Hg(II) ion by the PAAP-II chelating fiber was complete, reached a percentage of 99% at a treatment time of 4 rain, and afterward remained constant, which showed that the PAAP-II chelating fiber exhibited a fast removal velocity for Hg(II) ion from solution. This provided a possibility for tile PAAP-II chelating fiber to treat the real waste water containing tlg(ll) ion.
3176 120
80 e~
°° 8.
60
~
20
40
0
I 10
] 20
I 30
I 40
I 50
60
Time (rain) Fig.4. Removal of Hg(ll) ion from model waste water
Fig5, 6, 7 showed the breakthrough curves of Cu(ll), Cd(II) and Zn(lI) at different column bed height (H) and linear flow rate (V).
The breakthrough capacities were calculated according to the following
equation: breakthrough capacity (Q) = volume at the breakthrough point x mass concentration/amount of fiber The breakthrough point (TO was attained when the concentrations of Cu(II), Cd(II) and Zn(ll) ions in the solution came up to 1, 0.1 and 5 mg/L respectively. The point where the concentration of metal ions in the outflowing solution reached a 90% percentage of initial concentration was considered as the exhausting point
I:T2).
1
H 15cm, V 3111/1/ - - ~ - H 20era, V 3m/h ~ H 2 5 c m , V3m/h
0.8
0
5
~
.f/x~6
10
/~"
I
,..-
y
15
20
Time (h) Fig.5. The breakthrough curves of Cu(ll) ion
25
30
3177 0.2
l
/
0.8
i, H 25cm, V 3m/h ~
0.6
~'~o.4
0.15
i
0.2 0
-~ -~i ~- .% ~ . 0 5 10
. . 15
. . 20
. 25
b
j
o.1
0.05 0
30
• "-i . . . . 0 5 10
Time (h)
- - l - H 20ClU,V 3m/h I H 30cm, V 3mih
• .~ ~ ' . ~ 15 20 25
I,
30
35
Time (h)
Fig.6. The breakthrough curves of Cd(II) ion
Fig.7. The breakthrough curves of Zn(ll) ion
For Cu(II) ion, at a bed height of 20 cm, the breakthrough point corresponded to 16.8 and 8.25 h respectively at linear flow rate of 1.5 and 3 m/h, and the chelating fiber was exhausted after 26 and 18 h. Similarly, the breakthrough points of Cd(II) ion at a bed height of 15, 20, 30 cm were obtained from Fig.6. The results were shown in Table 4. The treatment efficiency of real waste water with Zn(II) ion by the PAAP-II chelating fiber was evaluated (see Fig.7) at a linear flow rate of 3 rn/h. When the bed height was 20 and 25cm, the breakthrough point and breakthrough capacities were respectively 14.6 h, 0.738 mmol/g and 17.8 h, 0.720 mmol/g
Table 4. The breakthrough point T~ (h), exhausting point T2 (h) and breakthrough capacity Q (lmnol/g) of metal ions on PAAP-II chelating fiber column Metal
V
ion
(n~h)
H (cm) 15 TI
Cu(ll)
Q
20 T2
1.5 3
7.0
0.930
Cd(ll)
3
10.7
0.796
Zn(II)
3
-14
25
TI
Q
T2
TI
Q
'1"2
16.8
0.837
26
8.25
0.822
18
11.5
0.916
19
16.0
0.893
25.5
0.949
14.6
0.738
17.8
0.720
Due to good kinetic properties of fibrous sorbents, the removal of metal ions by the PAAP-1I chelating fiber at a fast linear flow rate would require further investigation.
Acknowledgements This work was supported by Key Project of Resource and Eco-Environmental Research in Chinese Academy of Sciences (No: KZ 952-S 1-231) and SKLEAC.
3178
References 1. A. B. Osteen and J. P. Bibler, Treatment of radioactive laboratory waste for mercury removal, Water, Air and Soil Polluttion 56, 63-74 (1991). 2. F. M. Husband and A. G. Rowley, Polystyrene-bound poly(maleic anhydride): a new type of leadadsorbing polymer for water clean-up, Chem. Ind. (5), 164-165 (1982). 3. T. B. Qian and W. L. Liu, Application of chelating resins, Technology o f Water Treatment 12, 300-304 (1986). 4. H J. Fischer and K. H. Lieser, Cellulose exchangers with tailormade chelating groups for selective separation of uranium, Fresenius J. Anal. Chem, 346, 934-942 (1993). 5. V. V. Tolmachev and L. V. Miroshnik, Chromatographic separation of metal ions by means of a graft cellulose copolymer containing hydroxamic and amidoxime complex forming groups (complexit TsG), Zh. Anal. Khim., 30, 754-761 (1975). 6. N. Takagi, Y. Hirotsu, J. Sakakibara and S. Katoh, Spherically-formed fibers with amidoxime groups for the recovery of uranium from seawater. In New Dev. Ion Exch. Proc. btt. Conf. Ion Exch. Part. Hydrometallurgy, (Edited by A. Mistuo, K. Takashi and S. Takashi), pp.105. Tokyo (1991). 7. V. M. Zarechenskii, Yu. M. Khoroshevshkii, M. P. Zverev and Yu. N. Surov, Nature of functional groups and chemical stability ofhydrazided polyacrylonitrile fibers, Zh. Prkl. Khim., 64, 849-855 (1991). 8. B. W. Zhang, K. Fischer, D. Bieniek and A. Kettrup, Synthesis of carboxyl groups containing hydrazinemodified polyacrylonitrile fibers and application for the removal of heavy metals, React. Polym, 24, 49-58 (1994). 9. X. J Chang, Z. X. Su, X. Y. Luo and G Y. Zhan, Synthesis of poly(acrylamidrazone-hydrzide) chelating fiber and application of enrichment-separation for traces of indium, tin, chromium, vanadium and titanium from solution samples, Talanta 40, 527-532 (1993). 10. T. V. Nemilova, L. N. Smirnova, V. E. Nemilov and L. V. Emets, Preparation of poly(bis-amide) chelating ion exchange fiber and study of its properties. In Khim. Telo~ol. Svoistva Primen. Plastmass, (Edited by A. F. Nikolaev), pp.120. Tenknol. Inst. Leningrad, Leningrad (1990). 11. S. Q. Tang, Y. Lu and H. M. Zeng, Preparation of chelating fiber containing thioureido groups and its redox adsorption properties for Au 3÷, Ion exchange Adsorption 11, 34-38 (1995). 12. S. Q. Tang, Y. Lu and H M. Zeng, Study on functional redox fiber: V. Synthesis of functional fibers containing amine or ethylenediamine groups and their adsorption properties towards Au3÷, Ion exchange Adsorption 12, 202-207 (1996). 13. X. J. Chang, Z. X. Su, G. Y. Zhan, X. Y. Luo and W. Y. Gao, Synthesis and efficiency of a polyacrylacylisothioureachelating fiber for the preconcentration and separation of trace amounts of gold, palladium and ruthenium from solution samples, Analyst 119, 1445-1449 (1994). 14. M. P. Zverev, Chemosorptive Fibres (in Russian), p. 191. Khimiya, Moscow (1981),
3179 15. F. Vernon and T. Shah, The extraction of uranium from seawater by poly(amidoxime) / poly(hydroxamic acid) resins and fiber, React. Polym. 1,301-308 (1983). 16. R. X. Liu, Synthesis, properties and applications of ion exchange / chelating fiber with multi-functional groups, Ph.D. Thesis, Chinese Academy of Sciences, China (1998). 17. G. V. Myasoedova and S. B. Savvin, Chelating Sorbents, Nauka, Moscow (1984). 18. K. H. Lieser, New ion exchange, preparation, properties and application, Pure ,4ppl. Chem. 51, 15031517(1979).
Pergamon
© 1999ElsevierScienceLtd. All rightsreserved 0045-6535/99/$ - see frontmatter
PII: S0045-6535(98)00506-2 R E M O V A L Of Cu(II), Zn(I1), Cd(ll) AND Hg(ll) F R O M WASTE W A T E R BY P O L Y ( A C R Y L A M I N O P H O S P H O N I C ) - T Y P E C H E L A T I N G FIBER
Ruixia Liu ' , Hongxiao Tang, Baowen Zhang
(State Key Lab of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O.Box 2871, Beijing 100085) (Receivedin USA 27 August1998;accepted6 October 1998) Abstract: The distribution coefficients (D) for Cu(II), Cd(II), Zn(II) and Hg(lI) ions and adsorption isotherms of Cd(II) and Hg(II) ions on the poly(acrylaminophosphonic)-type chelating fiber were investigated using the batch reactor system. It was found that D values for the tested metal ions were above the magnitude of 103 at pH 5.0, and the order of metal ion affinities was: Hg(lI) > Cu(lI) > Zn(ll) > Cd(II). At low pH value (2.0), D value for Hg(lI) ion was higher than that of the other ions, above 103. The adsorption of Hg(II) and Cd(ll) ions on the new chelating fiber followed a Langmuirtype adsorption isotherm. The elution of the metal ions from the chelating fiber column using dilute nitric and hydrochloric acid as eluent were examined. The results show that the elution for Cu(ll), Cd(II) and Zn(II) ion was complete using appropriate concentration of hydrochloric acid, while the high concentration of dilute nitric acid was necessary for the quantitative desorption of Hg(Il) ion. The breakthrough curves for the metal ions were determined, and the efficient removal of the listed metal ions from model or waste water by the newly developed fibrous sorbent was achieved. © 1999 Elsevier ScienceLtd. All rights reserved Keywords: Poly(acrylaminophosphonic)-Type Chelating Fiber, Metal ion, Removal, Desorption
INTRODUCTION
The possibility of ion exchange or chelating process to removal heavy metal ions from solution has been explored by a number of workers fl-31. However, since those ion exchangers are of granular form, lower adsorption capacities, inferior kinetic properties and cost considerations have prohibited the widespread application of ion exchange or chelating technique on an industrial scale, and their applications in large-scale processes is hardly possible because of the high resistance of filtering layers. The stricter limitations on the concentration of toxic heavy metal ions in the discharged industrial effluents have rendered new research necessary on such a water treatment method. Therefore, the viability of ion exchange or chelating technique depends on the development of modified adsorbents. • Aulhor to whom all correspondence should be addressed. E-mail: [email protected] 3169
3170 Fibrous ion exchangers or chelating adsorbents exhibit some features associated with their structure. The main advantages are (1) the large specific surface, which is larger by about two orders of magnitude than the one of a gel-structure granular ion-exchanger or 5-6 times higher than the surface of a porous copolymer, assuring good kinetic characteristics; (2) the high swelling capacity, which is attributed to the presence of linear or branched macromolecules; (3) the excellent mechanical strength; (4) the convenient use. The fibrous sorbents might be produced in the forms of filaments, staple, cloths and non-woven materials, opening up many possibilities for new technological processes. As a result of these properties, the intensive research has been carried out to develop the preparation methods for different types of fibrous adsorbents. Fibrous ion exchangers with PAR, alizarin, tailor-made, amidoxime groups based on cellulose or its graft copolymers have been prepared through the transformation of hydroxyl-groups and further activation of cellulose derivatives~4'5j, Polyacrylonitrile fiber has been used in creating fibrous adsorbents containing amidoxime and hydroxam groups t6j, carboxyl- and tetrazine groups I7'81, amidrazone-hydrazide groups [91 and bisamide groups °°1. The method and technology of introducing thiocarbamide and amino-groups onto polyvinyl alcohol fiber have been developedtH'~21. In recent years ion exchange or chelating fiber as one type of adsorbents has been widely used to various research fields, such as the preconcentration and determination of trace elements t~31, air purification from acid gases and vaporst~41 and extraction of useful elements from aqueous mediat~Sl. Despite numerous publications, the applications of fibrous adsorbents in waste water treatment are not fully studied. The present paper mainly deals with the properties and applications of newly developed poly(acrylaminophosphonic)-type (PAAP-1I) ion exchange chelating fiber in the removal of Cu(II), Zn(II), Cd(II) and Hg(II) ions from model or industrial water.
EXPERIMENTAL
Chemicals and materials All chemicals in this study were of analytical-reagent grade. Adsorptive solution were prepared by dissolving CuC12. H20, Cd(NO3)2, ZnCI2 in distilled water with appropriate quantities of concentrated nitric acid and HgSO4 in distilled water with glacial acetic. The rinsing solution samples in electroplating zinc were collected from Mechanical Factory of Beijing Aeronautical University. The model waste waters separately containing Cu(II), Hg(II) and Cd(II) were prepared by dissolving appropriate salt in tap water. The characteristics of these waters were listed in Table 1. The PAAP-II chelating fiber used was prepared through the following steps: (1) The polyacrylonitrile fiber was cross-linked with hydrazine for 3 h at 95°C; (2) An amount of dry hydrazine-modified fiber and diethylenetriamine were mixed in a one-liter three-necked reaction vessel, heated for 5 -10 h at 95°C. Afterward the mixture was cooled, suction-filtered, washed with distilled water; (3) The final product,
3171 PAAP-II chelating fiber, was prepared by the reaction of the above fiber-aminated with phosphoric acid for 6h at 85 ~ 95°C, suction-filtered, washed with distilled water and dried at 60 ~65°C overnight. The introduction of aminophosphonic groups into the hydrazine-modified fiber could be briefly expressed as follows: I
hydrazine-modified fiber ( - - ]C
)
NH 2C2 H 4 I~-IC 2 H4 NH 2 ~ .
C=O I OCH3
fiber-aminated (
C
)
HPCO)(OH)2 + HCHO
C=O I NH C2 I-h NHC2l-h NH 2 I poly(acrylaminophosphonic)-type chelating fiber(- C - ) i
C=O I NH C2 I-h NHC2H4NH I CH 2 PCO)(OH)2 By infrared spectroscopy analysis, it was shown that PAAP-II chelating fiber contained carboxyl, aminophosphonic and hydrazide. The nitrogen, oxygen and phosphorus contents of the chelating fiber were respectively 16.17, 19.18 and 3.99% t16].
Table i. The characteristics of the waste water Type of waste
Concentration (mg/L)
pH
Medium
Hg(lI)
10
6.0~6.5
Cu(II)
51
6.0~6.5
CI, NIL +
Cd(II)
50
6.0~6.5
NO3-, NIL +
Zn(II)
26
6.0~7.0
KC1, ILBO3
water
Apparatus
5042 ,
Ac-, NIL+
and Instruments
Z-6100 Atomic Absorption Spectrometer (A.AS) and Coleman-50 Mercury Analyzer were used for the determination of Cu(II), Zn(II), Cd(II) and Hg(II) ions concentration. The pH value of solution was adjusted by pHS-3C pH-meter.
3172 Experimental procedure
The batch adsorption experiments were carried out to determine the distribution coefficients of Cu(II), Zn(II), Cd(II) and Hg(II) ions between the PAAP-II chelating fiber and liquid phase and the adsorption isotherm of Hg(II) and Cd(II) ions on the chelating fiber. Dried samples (0.10g each) of the PAAP-II fiber were equilibrated by shaking for 24 h in 10 mL of metal ion solutions at 25°C. The metal ion solutions were adjusted to the desired pH value with aqueous ammonia prior to equilibrium. The concentrations of Cu(II), Cd(II), Zn(II) and Hg(II) ions in filtrate were determined by AAS and Coleman-50 Mercury Analyzer respectively. Triplicate samples were run. The desorption of metal ions from the PAAP-II chelating fiber was carried out by dynamic experimental technique. The fiber columns (20cm long x lcm i.d) loaded with metal ions were eluted with diluted nitric or hydrochloric acid at a flow rate of 2 mL/min.
Removal of metal ions from waste water
500mL of model waste water containing Hg(II) ion was added to 0.Sg of the PAAP-II fiber sample, and mixing started immediately.
After time interval of 10rain, 1.0 mL aliquots were collected for the
determination of Hg(II) ion concentration.
The waste water samples containing Cu(II), Cd(il) and Zn(II)
ions passed through the PAAP-II chelating fiber column (50cm long x 3cm i.d) at a flow rate of 15 - 3m/h. The filtrates were collected at appropriate time interval for the determination of residual metal ion concentration.
RESULTS AND DISCUSSION
Distribution coefficieut
The affinity of ion exchange chelating sorbents for metal ions is usually expressed in terms of distribution coefficients (D) at appropriate pH value, which is concerned with the type and structure of functional groups in the sorbents, metal ion speciation and pH value of solution. The results of Fig. 1 showed that the D values of the tested ions between the PAAP-II chelating fiber and liquid phase, at pH 5.0, were above the magnitude of 103, and the following order of metal ion affinities was found: Hg(II) > Cu(ll) > Zn(II) > Cd(II). In addition, for Cu(II), Zn(II) and Cd(II) ions, D values were very low up to about pH 3.5, afterward increased and reached maximum value at about pH 5.0 for Cu(ll), 6.0 for Zn(II). For Hg(II) ion, even at pH 2.0, D value was also higher, above 103, and increased up to maximum value around pH 5.5. The effect of pH value on distribution coefficient may be explained from two points. One is that the pH value influences the surface structure, charge properties and adsorption site of sorbents.
In general, the protonation and
deprotonation properties of acidic- or basic-groups on ion exchange chelating sorbents is attributed to the pH value change. The other explanation is that the metal speciation depends on the pH value, and the different ion speciations express the different adsorption characteristics.
3173 250 200 150
....
Hg Cu
. . . . .
Zn
.....
Cd
~
100
i
/
,,'"
..¢"" \
///.j./
50 0
i{ .2/,~
t
~ --'~ 7 ~-"
I
I
i
1
2
4
5
6
3
7
pH Fig. 1. Effect ofpH value on distribution coefficient (D)
At low pH, the differences of D value for Hg(II) and Cu(II), Cd(II), Zn(II) can be described by the selectivity which is expressed in terms of separation factor (KNM)E17,lsl,defined as KNM= DM / DN where DM and DN is respectively the distribution coefficient of M and N ion. When KNM value is much higher than l, it is obvious that the selectivity of chelating sorbent for M ion is higher. The separation factors of Hg(II) ion for the other metal ions on the PAAP-II chelating fiber were listed in Table 2. The results further revealed that the selectivity for Hg(II) was remarkably high, and KNM value was above 8.0 at pH 2.0. Therefore, the effective separation of Hg(II) ion from the mixture of Cu(II), Cd(II) and Zn(II) ions is possible by use of the PAAP-II chelating fiber at lower pH value. Table 2. The separation factors (KNM) of Hg(II) ion for the other metal ions (N) on the PAAP-II chelating fiber Metal ion
pH
(N)
2.0
3.0
4.0
Cu(II)
8.01
2.53
1.2
Cd(II)
173
48
Zn(II)
256
64
6.0 1.26
3.2
1.5
Initial concentration of metal ion: 0.001 mol/L
Adsorption isotherm
The Langmuir isotherm (L-type) has been expressed as follows: 1/Q = 1/Q° + (A/Q°)(1/C,) where Co is the equilibrium concentration in retool/L, Q the amount of adsorption in retool/g, Q0 the adsorption capacity at the monolayer coverage, and A the adsorption constant. The adsorption experimental data for Hg(II) and Cd(II) ions on the PAAP-II chelating fiber were adjusted according to Langmuir
3174 isotherm model and the isotherm parameters were calculated using a method o f least squares. The results were shown in Fig.2 and Table 3
1.6 1.4
#_
•
o
• •
•
9~ '
0.8 O' 0.6 0.4
•
O-i----k------
1.2
/A
0.2 0
L-type regression curve for Hg(II) experimental data for Hg(II) experimental data for Cd(II) L-type regression curve for Cd(lI)
• • .... t 0.5
I 1.5
1
I 2
I 2.5
I 3
3,5
C° (mmol/L) Fig.2. Adsorption isotherms for Hg(II) and Cd(II) ions on PAAP-II chelating fiber
Table 3. Langmuir adsorption parameters for Hg(II) and Cd(II) ions on PAAP-II chelating fiber at 25°C Metal ions
pH
Adsorption parameters
L-type equation
Q0
A
r
Hg(II)
6.00+0.25
1.14
0.112
0.9922
Q = 1.14 x C~/(0.112 +C~)
Cd(II)
5.20_+0.25
1.28
0.00192
0.9815
Q = 1.28 × C~ / (0.00192 + C,)
The examination revealed that, in low and intermediate concentration range, the experimental data were better fitted to Langmuir isotherm, while with metal ion concentration increase, the experimental data slightly deviated from Langmuir equation. This deviation is mainly contributed to the differences of real adsorption behavior and Langmuir theoretical hypothesis as well as the structural complexity of the PAAP-1I chelating fiber. The existence of multi-functional groups results in the interactions of groups, adsorbed metal ions as well as groups and fiber skeleton, which makes the adsorption mechanism of the fibrous sorbent with Hg(II) and Cd(II) ions complicated.
Further investigation on this respect seems to be necessary for a better
understanding of adsorption properties for metal ions on the PAAP-II chelating fiber.
Elution curve The elution curves for Cu(II), Cd(II), Zn(II) and Hg(II) ions at a flow rate of 2 mL/min, using diluted hydrochloric or nitric acid as eluent, were shown in Fig.3.
The elution of Zn(II) ion was relatively easy
compared to the other ions. The adsorbed Zn(II) ion could be quantitatively recovered only with 0.5 mol/L hydrochloric acid, and the remarkable delay-action did not exist in its elution curve, which showed a fast
3175 elution velocity for Zn(II) from the PAAP-II chelating fiber column. Tile adsorbed Cu(II) ion could not be eluted with 20 mL of 0.5 mol/L hydrochloric acid, and a higher concentration (2 mol/L) of hydrochloric acid was required to improve the recovery efficiency. With respect to Cd(II) ion, the elution velocity using 6 mol/L hydrochloric acid as eluent was higher than that of 2 mol/L hydrochloric acid as eluent, and the larger volume of hydrochloric acid was favorable to the recovery of Cd(II) ion. However, the elution o f t t g ( l l ) ion was different from the other ions.
The preexperiment showed that diluted hydrochloric acid was not as
effective as diluted nitric acid for the recovery of ttg(ll) ion.
In Fig.3, it is indicated that the high
concentration of dilute nitric acid was necessary for reaching a quantitative recovery of ttg(lI) ion. This property further revealed the high affinity of the PAAP-II chelating fiber for Hg(ll) ion.
05...o.,L.c. 8 g
sr,
2 mol/L ttCI
6
4
4
~ 2
~ 0
l0
20
30
2
40
10
Elution volume (mL) Cu(ll)
30
40
Cd(ll)
~4
~1.5
.~
m
20
Elution volume (mL)
t
2 0 0
10
I
I
20
30
Elution volume (mL) Zn(ll)
~ ~ 40
0.5 0
I
'
.',
tO
20
30
40
Elution volume (mL) 1lg(ll)
Fig.3. Tile elution curves of metal ions front PAAP-I1 chelating fiber colunm
Renloval of metal ions fi'om solution To evaluate the applicability of the PAAP-I1 chelating fiber, the removal efficiency of Hg(I1) ion from tile model water was examined The result of Fig.4 showed that the removal of Hg(II) ion by the PAAP-II chelating fiber was complete, reached a percentage of 99% at a treatment time of 4 rain, and afterward remained constant, which showed that the PAAP-II chelating fiber exhibited a fast removal velocity for Hg(II) ion from solution. This provided a possibility for tile PAAP-II chelating fiber to treat the real waste water containing tlg(ll) ion.
3176 120
80 e~
°° 8.
60
~
20
40
0
I 10
] 20
I 30
I 40
I 50
60
Time (rain) Fig.4. Removal of Hg(ll) ion from model waste water
Fig5, 6, 7 showed the breakthrough curves of Cu(ll), Cd(II) and Zn(lI) at different column bed height (H) and linear flow rate (V).
The breakthrough capacities were calculated according to the following
equation: breakthrough capacity (Q) = volume at the breakthrough point x mass concentration/amount of fiber The breakthrough point (TO was attained when the concentrations of Cu(II), Cd(II) and Zn(ll) ions in the solution came up to 1, 0.1 and 5 mg/L respectively. The point where the concentration of metal ions in the outflowing solution reached a 90% percentage of initial concentration was considered as the exhausting point
I:T2).
1
H 15cm, V 3111/1/ - - ~ - H 20era, V 3m/h ~ H 2 5 c m , V3m/h
0.8
0
5
~
.f/x~6
10
/~"
I
,..-
y
15
20
Time (h) Fig.5. The breakthrough curves of Cu(ll) ion
25
30
3177 0.2
l
/
0.8
i, H 25cm, V 3m/h ~
0.6
~'~o.4
0.15
i
0.2 0
-~ -~i ~- .% ~ . 0 5 10
. . 15
. . 20
. 25
b
j
o.1
0.05 0
30
• "-i . . . . 0 5 10
Time (h)
- - l - H 20ClU,V 3m/h I H 30cm, V 3mih
• .~ ~ ' . ~ 15 20 25
I,
30
35
Time (h)
Fig.6. The breakthrough curves of Cd(II) ion
Fig.7. The breakthrough curves of Zn(ll) ion
For Cu(II) ion, at a bed height of 20 cm, the breakthrough point corresponded to 16.8 and 8.25 h respectively at linear flow rate of 1.5 and 3 m/h, and the chelating fiber was exhausted after 26 and 18 h. Similarly, the breakthrough points of Cd(II) ion at a bed height of 15, 20, 30 cm were obtained from Fig.6. The results were shown in Table 4. The treatment efficiency of real waste water with Zn(II) ion by the PAAP-II chelating fiber was evaluated (see Fig.7) at a linear flow rate of 3 rn/h. When the bed height was 20 and 25cm, the breakthrough point and breakthrough capacities were respectively 14.6 h, 0.738 mmol/g and 17.8 h, 0.720 mmol/g
Table 4. The breakthrough point T~ (h), exhausting point T2 (h) and breakthrough capacity Q (lmnol/g) of metal ions on PAAP-II chelating fiber column Metal
V
ion
(n~h)
H (cm) 15 TI
Cu(ll)
Q
20 T2
1.5 3
7.0
0.930
Cd(ll)
3
10.7
0.796
Zn(II)
3
-14
25
TI
Q
T2
TI
Q
'1"2
16.8
0.837
26
8.25
0.822
18
11.5
0.916
19
16.0
0.893
25.5
0.949
14.6
0.738
17.8
0.720
Due to good kinetic properties of fibrous sorbents, the removal of metal ions by the PAAP-1I chelating fiber at a fast linear flow rate would require further investigation.
Acknowledgements This work was supported by Key Project of Resource and Eco-Environmental Research in Chinese Academy of Sciences (No: KZ 952-S 1-231) and SKLEAC.
3178
References 1. A. B. Osteen and J. P. Bibler, Treatment of radioactive laboratory waste for mercury removal, Water, Air and Soil Polluttion 56, 63-74 (1991). 2. F. M. Husband and A. G. Rowley, Polystyrene-bound poly(maleic anhydride): a new type of leadadsorbing polymer for water clean-up, Chem. Ind. (5), 164-165 (1982). 3. T. B. Qian and W. L. Liu, Application of chelating resins, Technology o f Water Treatment 12, 300-304 (1986). 4. H J. Fischer and K. H. Lieser, Cellulose exchangers with tailormade chelating groups for selective separation of uranium, Fresenius J. Anal. Chem, 346, 934-942 (1993). 5. V. V. Tolmachev and L. V. Miroshnik, Chromatographic separation of metal ions by means of a graft cellulose copolymer containing hydroxamic and amidoxime complex forming groups (complexit TsG), Zh. Anal. Khim., 30, 754-761 (1975). 6. N. Takagi, Y. Hirotsu, J. Sakakibara and S. Katoh, Spherically-formed fibers with amidoxime groups for the recovery of uranium from seawater. In New Dev. Ion Exch. Proc. btt. Conf. Ion Exch. Part. Hydrometallurgy, (Edited by A. Mistuo, K. Takashi and S. Takashi), pp.105. Tokyo (1991). 7. V. M. Zarechenskii, Yu. M. Khoroshevshkii, M. P. Zverev and Yu. N. Surov, Nature of functional groups and chemical stability ofhydrazided polyacrylonitrile fibers, Zh. Prkl. Khim., 64, 849-855 (1991). 8. B. W. Zhang, K. Fischer, D. Bieniek and A. Kettrup, Synthesis of carboxyl groups containing hydrazinemodified polyacrylonitrile fibers and application for the removal of heavy metals, React. Polym, 24, 49-58 (1994). 9. X. J Chang, Z. X. Su, X. Y. Luo and G Y. Zhan, Synthesis of poly(acrylamidrazone-hydrzide) chelating fiber and application of enrichment-separation for traces of indium, tin, chromium, vanadium and titanium from solution samples, Talanta 40, 527-532 (1993). 10. T. V. Nemilova, L. N. Smirnova, V. E. Nemilov and L. V. Emets, Preparation of poly(bis-amide) chelating ion exchange fiber and study of its properties. In Khim. Telo~ol. Svoistva Primen. Plastmass, (Edited by A. F. Nikolaev), pp.120. Tenknol. Inst. Leningrad, Leningrad (1990). 11. S. Q. Tang, Y. Lu and H. M. Zeng, Preparation of chelating fiber containing thioureido groups and its redox adsorption properties for Au 3÷, Ion exchange Adsorption 11, 34-38 (1995). 12. S. Q. Tang, Y. Lu and H M. Zeng, Study on functional redox fiber: V. Synthesis of functional fibers containing amine or ethylenediamine groups and their adsorption properties towards Au3÷, Ion exchange Adsorption 12, 202-207 (1996). 13. X. J. Chang, Z. X. Su, G. Y. Zhan, X. Y. Luo and W. Y. Gao, Synthesis and efficiency of a polyacrylacylisothioureachelating fiber for the preconcentration and separation of trace amounts of gold, palladium and ruthenium from solution samples, Analyst 119, 1445-1449 (1994). 14. M. P. Zverev, Chemosorptive Fibres (in Russian), p. 191. Khimiya, Moscow (1981),
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